Princeton 124A Operating And Service Manual

,

.

"

Jan-29-02

ll:43A

MODEL

124A

LOCI<-IN AMPLIFIER

OPERATING

AND

SERVICE

MANUAL

-e-n~EGc.G

PRINCETON

APPLIED

RESEARCH

P.Ol

MDl12<11A.;

3/n·QQ

Copyrlc

[e-mail]&.QPRiNCETONAPPt..IlDRESEARCH

Prtlt'lIJd In U.S.....

Jan-29-02

11'43A

P.02

SHOULD YOUR EQUIPMENT REQUIRE SERVICE

WARRANTY

A.

Contact

the

factory

(6091452·2111) or your

local

factory

-aprasantativetodiscuss

the

problem.Inmany

cases

It

willbepossibletoexpedite

servicingbylocalizing

the

problemtoa

particular

plug-in

circuit

board.

B. II it is

necessarytosend

any

equipment

backtothe

fac-

lory,weneed

the

following

information.

(1)

Model

number

and

serial

number.

(2)

Your

name

(instrument

user).

(3)

Your

ecoress.

(4)

Addresstowhich

instrument

shouldbereturned.

(5)

Your

telephone

number

and

extension,

(6)

Symptoms

(in

detail,

including

control

settings).

(7)

""01,,11'

purchase

order

number

tor

repair

t.ha,rges

(does

not

applytorepairsinwarranty).

EG&G

PRINCEtON

APPLIED

RESEARCH

warrants

each

tn-

strumentofits

manufacture

to be

free

'rom

detect

s in

material

and

wcrkrnanshlp.

Obligations

under

this

Warranty

shall

be

limitedtoreplacing,

repairingorgiving

credit

for

the

purchase

prtce,

at

our

option,

of

any

instrument

returned.

freight

pr'£"paid,toour

factory

wtthtn

ONE

yearofdeliverytothe

original

purchaser.

provided

prior

authorization

for

such

return

has

been

givenbyour

authorized

rapraaantauve.

This

Warranty

shall

not

applytoany

Instrument

which

Our

in-

spection

shall

disclose

10 Our saustecucn.

has

become

detec-

liveOrunworkable

duetoabuse,

mishandling,

misuse.

acct-

dent,

alteration.

f1egliger'ce,

improper

installation

or

other

causes.

beyond

Our

control.

Instruments

manufactured

by

cthera,

and

tnctuded

in or

supplied

with

OUf

equipment,

are

not

coveredbythis

Warranty

but

(:~HrY

tne

odginal

rnanu

tactur

era

warranty

whichisextendedtoour

customers

and

maybemore

restrictive,

Certain

subassemblies,

accessories

or Com-

ponents

maybospecifically

exctuded

from

tnts

Warranty,

ill

which

case

such

exclusions

are

listedinthe

Inetructton

Manual

supplied

with

each

Instrument.

C, U,S,

CUSTOMERS-Ship

the

equipment

being

returned

to:

(8)

Shipping

instructions

(i1

you

wig

h 10

authorize

ship-

men.

by

any

method

other

than

normal

surtaca

transportation),

we

reserve

the

righttomake

changesindesignatany

nme

without

incurring

any

ohlig(:llion10install

same on

units

previously

purchased.

THERE

ARENOWARRANTIES

WHICH

EXTEND

BEYOND

THE

DeSCRIPTION

HEREIN.

THIS

WARRANTY

IS IN

LIEU

OF.

AND

eXCLUDES

ANY

AND

ALL

OTHER

WARRANTIES

OR

RePRE-

SeNTATIONS,

EXPReSSED,

IMPLIeD

OR

STATUTORY.

IN·

CLUDtNG

MERCHANTABILITY

AND

FITNESS,

AS

WELL

AS

ANY

AND

ALL

OTHER

OBLIGATIONS

OR

LIABILITIES

OF

EG&G

PRINCETON

APPLIED

RESEARCH.

INCLUOING.

BUT

NOT

LIMITED

TO.

SPECIALORCONSEQUENTIAL

DAMAGES.

NO

PERSON.

FIRM

OR

CORPORATIONISAUfHORllED

TO

ASSUME

FOR

EG&G

PRINCETON

APPLIED

RESEARCH

ANY

ADDITIONAL

OBLIGATION

OR L1ABII,.ITY

NOT

EXPRESSLY

PROVIDED

FOR

HEREIN

EXCEPT IN

WRITING

DULY

EXE·

CUTED

BY AN

OFFICER

OF EG&G

PRINCETON

APPLIED

RESEARCH.

FG&G

PRINCETON

APPLIED

nESEARCH

P 0

Bo'

2565

Princeton,

NJ

085~.J

phone:

609/452-2111

TELEX:843409

Address

correspondence

10:

EG&G

PRINCETON

APPLIED

RESEARCH

7 R(lSzel

Road

(Off

Alexander

ROCld,

EastofRoute

1)

Princeton,

New

Jersey

D.

CUSTOMERS

OUTSIDE

OF

U.S.A.-·To

avoid

delay

in

customs

clearanceofequipment

being

returned,

please

contact

tile

rectoryorthe

nearest

factorv

dtstnbutor

for

complete

shipping

information,

E.

Jan-Z9-0Z

11:44A

TABLE

OF CONTENTS

•

oection

Page

CHARACTERISTICS

1·1

'_1

Introduction

1-

1

1.2

Specifications:

1-3

1.2A

Signal

Channel

Specifications.

1-3

1.2B

Reference

Channel

Specifications

1-3

1.2C

Dumodul

ator

Characteristics

1·3

1.20

Outputs

1·4

1.2E

Dvnernic

Rcmge

Specifications

1-5

1.2F

Other Characteristics

1-5

II

INITIAL

CHECKS

11·1

2.1

Introduction

11-1

2.2

Equipment Needed

11-1

2.3

Procedure

11-1

III

OPERATING INSTRUCTIONS

111-1

3,1

Block

Diagram

Discussion

111-1

3.1A

Introduction

111-1

3_1B

Signal

CharH"H:~1

111-1

3_'C

Reference

Channel

111-1

3_10

Synchronous

Detector

111-1

3.2

Signal Channel

Operation

111-3

3_2A Introduction

...

111-3

3.2B

Preamplifier Choice

111-3

3.2C

Grounding

111·3

»

3.20

Remote

Preamplifier

Adapter

111-4

,,'3_2E

Sinqle-Endsd, Differential. and Transformer Inputs

111-4

:l2F

Common-Mode

Rejection

111-5

3_2G

Noise

and

Source

Resistance

111-5

3.2H

Selectiv@

Amplifier

111-6

3_21

Dvnarnic Range

111-13

3_2J

Dvnamic:

Over-ride

111·15

3_2K

Overload

111,15

3_2L Offset Due to Noise

111-17

3.2M

Overload Racnverv

111-17

3.2N

Signal

Monitor

111-18

3.3

Reference

Channel Operation

111-18

3,3A

Sync

Input/Output

111-'8

'.3.3B

Phase

Control'

111-19

3A

Outpu

t Channel OPeration

111-21

4AA

Filter Time

Constant

111-21

3AB

Offset Controls

111·21

3_5

Harmonic

Response

111-21

3_6

Sensitivity and Notch Calibration

111-22

3_7

AC Voltmeter Operation

111-23

3_8

Digit(ll Panel Meter

Modification

111-24

3_9 "./

Phase

Me

aauremerrts

111-27

3_10 Rear Panel Connectors

111-28

3,lOA

Interlace Connector (J9)

III-n

3,1011

Ext. Time Constant

111-29

3,11

Flattery Operation

111-29

3.12

Phase

Modification

111-29

)

P.03

Jan-29-02

11,44A

P.04

3.13

Mixer Monitor Mo<lifiCiil(ion

111-29

3.14

Remote Programming Option Modification

111-30

3.15

Selective

External

Reference

Modification

11I·31

(

IV

ALIGNMENT

PROCEDURE

IV-'

4.'

Introduction

IV-'

4_2

Equipment

Needed

IV-'

4.3

Procedure

IV-'

4.3A

Preliminary

Steps

IV-'

4.3B

±24 V

Adjustments IR6028 and R60101- Power Supply Board

IV-'

4.3C

Initial

Reference

O~cillator

Board Adiusrmanrs IV·3

4.3D

Auxiliary

Reference

Board

Adjustments

IV-3

4.5E

Mixer Board

Adjus

tmenrs

IV-4

4.5F

lntermediate

Amplifier Board Adjustments

IV-5

4.5G

Final Reference Oscillator Board

Adjustments

IV-5

4.5H

Signal Board Adjustm@llts IV-5

4.31

Final

Adjustments

IV-6

4.3J

Phase

Meter

Option

Alignment

IV-6

4.4

Model 116,

"7,

or 119 Preamplifier Alignment

IV-7

4.4A

Preliminary Steps

IV-7

4.4B

Procedure IV·7

4.5

Model

118

Preamplifier

Alignment

IV-8

4.5A

Preliminary

Steps

IV-B

4_5B

Procedure

IV-8

V

TROuBLESHOOTING

_v.t

5_1

I

ntrod

ucnon

_

V·l

5.2

Equipment

Required

.

V-'

5.3

Initial

Steps

V-'

5,4

Power

Supply

_

V·l

5.5

Reference Checks

v-t

(

5_6

Signal Channel

V·3

5.6A

Preamplifier

V-3

5.66

Signal

Arnplifier

V-3

5.6C

Intermediate

Amplifier

V·S

5.6D

Mixer Board AC Gain

V·S

5.6E

Mixer

Schmitt

Triggers

V·5

5.6F

Mixer

Circuit

V-S

5.6G

DC Ampl

tflers V·6

5.7

Noise Checks

V·6

VI

SCHEMATICS, TABLE OF

VI-l

c

»

Jan-Z9-DZ

11:44A

FIGURES

'.Imber

1-1

Model 124A Lack-In Amplifier

1·2 SYnc. Signal Slewing Rate

1·3 Typical Calibrator

Accuracy

111-1

Functional

Block Di.gram, Model 124A

111-2

Optimum Performance Regionsofthe Prearnpfifiers

111·3

Distortionv,Frequency,

Model

118

.

lirA

Ground-Loop

Voltage

Heiection

Using Di

tferenttal

Inputs

111-5

Model 183 Remote Preamplifier

Adaoter

111·6

Typical

Common-Mode

Rejection

....

__

....

III· 7

Tvolca!

Noise Figure Contours for Model t 17, Model 116 (Direct! and Model 119 (Direct)

11I·8A

Typical Noise Figure

Contours

for

MOdel

116

Operatinq

in the Transformer Mode . .

111·86

Typical Amplitude Transfer Curve, for Model 116 Operating in the Transformer Mode

III-SA

Tvpicat

Noisl! Figure Contours for Model 119 Operating in the Transtorrner Mode , .

111-98

Typical

Amplitude

Transfer

Curves for Model

119

Operating in the

Transformer

Mode

111·10

Typical

Norse Figure Contour's for

Model

118

, ,

__,..

111·11

A Tvpical

NoiSe

Figure Contours for Model 190 Transforrner-Plus-Preamptitier

111-118

Model 190Wiring Diaqrarn

If

l-t

l C

Tvpical

Amptirude

Transfer Curves for

Model

190

111-11DPhotoofModel

190

Transformer

111-12

S-H

Curves and Waveforms

111-13 Degaussing

Wetveforr'J)s

111·14

Model

124A

BandpassCharac taristics

111-15

Model 124A Notch Characteristic'

111-16

Model

124A

Low

Pass

Characteristics

111-17

Model 124A High Pass Characteristics

111·18

Dynamic Range Cnaracteristics of the Model 124A

1-19 Typical

Output

Offset as a Function of Input Noi,e

111-20

Typical

Reference Oscillator Slewinq Rate

111-21

Net

Phase

Difference

Between Signal and Reference Channels as a

Function

of Frequeucv

111-22

Output

Filter Transfer

Function,

_ .

111-23

Tvpical

Calibraticn

Accuracy _ _

111·24

Mixer

Output

for In-Phase and

Quadrature

Signals

IV·l

Model

124A

Adjustments. ijlnrj Testpoinrs

TABLES

Number

P.DS

Page

1·2

1-4

1-5
111-2
111-3
111-3
111-4
111-4
111-5
111-7
111-8
111-8
111·9
111-9

111-10

111·11
111-11

111-11

111-11

111-11

111-11
111-12
111·12
111·12
111·12
111-

14
111-17
111-18

II1·19

111-20
111·24

111-29

IV-2

Page

,

1-1
1·2

I"

-1

111·2

111-3
111-4
111-5
11I6A
111·68
111-7

II1·8

111·9
V-I

Praarnpfifiar Specifications

.,

,

...

__

, .

Model

124A

Dynamic: Range Specifications

Stability and

Output

Noise as a FunctionofOperating

Dynamic

Tradeoff

Maximum RMS

Input

Levels for

Mixer

and

Tuned

Amplifier

Overload as a

Function

of

Sensitivity and Operating Dynamic Range _

Maximum

Frequency

Acquisition

iime$

of

Oscufator

.

Typical Harmonic

Response

Operating in the

Flat

M<'H.:I~

Typical

Harmonic

Res~onse

Oper

atinq in Bandpass

Mode

with

0 - 10

Digital

Output

Pin Assignments

Digital

Output

Truth Tables _ .

Interface

Connector

Signals and Pins .

External

Time

Constent

Connector

Signals and Pins

Remote

Programming

Connector

Pin Assignments

Gain and Relay Switching for tho Model 124A

.

1-1

_ 1-5

111-

15

111-16

111-19
111-22
111-22
111-25
111-26
111·28

II 1·29

111-30

. V·4

Jan-Z9-0Z

11:45A

SECTION I

CHARACTERISTICS

P.06

1.1 INTRODUCTION

The

Model

124A

Lock-In

Amplifier

accurately

me asures

the

rms

amplitude

and

phase

of

weak

signal~

huried

in

noise.

Signalsinthe

rangeofpicovoltsupto500

millivolts

at

freouencies

from

0.2 Hz to

210

kHz Can be

measured

quickly

and

precisely.

Meter

and

voltagp.

outputs

are

provided

for

the

amplitude,

arid

t1H~'

phaseofthe signal

m<1Y

be

read

fromadial.

These

measurements

are

with

reference

to~wnchronjzjqg

signal

supplied

to.orsupplied

by,

the

Model

124A.Ineither

the

ExternalorExternal

f/2

mode

of

op~ratiorl,

the

instrument

will

accept

any

rl?ferel~~

wave-

form

that

crosses its.

mean

twice

each

cycle,

and will lock

to

and

track

that

signal

OVC(

a

100:1frequency

range.Inthe

Internal

mode,

the

frequencyisdetermined

by

front-panel

dials

orbyan

externallv

derived

voltage,

A

selection

of

ptuq.in

preamplifiers

is available

for

pro-

vidinq

optimum

low-noise

performance

Over a

wide

range

of

input

frequencies

and

source

resistances:,

After

preampll·

ficatton.

noise

and

harmonics

acccmpenvinq

the

signal are

attenuated

in

the

Signal

Channel

by

filtering

out

all

frequencies

except

the

bandinwhich

the

signal lies.

Flat,

band

Pass.

band

reject,

high

pass,

and

low

PHSS

filtering

modes

maybeselected.

The

remaining

bandoffrequencies

is

converted

to

an

equivalent

bandwidth

about

de

by a

-vncbrrinous

detector.

which

is

lockedtothe

svnchronlztnq

qnat.Alow-pass

filter

elirnirlatEi!s

frequency

components

above de,

,0

that

the

detector

output

is a de voltage

propor'tional

to

th~

in-phase

componentofthe

fundamental

signal. Propi:!r

selection

of

signal

channel

and

output

channel

filtering

parameters

can

render

the

final

noise

bandwidth

extremely

narrow

_

The

rrns

valueofthe

[unda-

mQrHal signal is

indicated

on

the

pal'l~1

mater

when

the

synchronous

detection

phaseisadjusted

for

maximum

detector

output.

A SWitch is

provided

that

allows

drift

to

be

traded

tor

dynamic

reserve. In

addition.anoutputdeoffset

ff;!atul"I~;

is

provided

to

allow

higher

sensitivity

settir1gS for

relatively

steady

signals, These

fe<1ture~

permit

selection

of

the

optimum

opcr

atinq

mode

for

each

experimental

situation.

Other

de:;igr"l

fcaturas

include

selectionofoutput

filter

lime

constants.

to

300

seconds,

optional

digital

panel

meter

with

BCD

output,

ij

built-jrl

calibrator.

and

independent

use

of

the

phase-lockable

oscillator

and

tuned

amplifier

for

general-purpose

laboratory

work,

The

Model

124A

","y

also

be

used

as a

conventional

wideband

laboratory

voltmeter.

Accessories

include

an ac

zero

offset,

several

light

choppers.

a

computer

interface

system.

and a

wide

assortment

Of

low-noise

preamplifiers.

Specification

Model

116

Model

117

Model 118 Model

119

Input

Z

Selectedbyfront

panel

switch:

100

meqohrns

SEIDE

Direct;

100

rneq,

SEIDE

Transforrnere:

LowZSEIDE

10 kilohm'S

SEIDE

Selectedbyfront

panel

switch:

Direct;

100

rneq,

SEIDE

Transformer:

Low Z

SEIDE

Bandwidth

Direct; 0_2 Hz -

210kHz

0.2

Hz ..-

210

kHz

0.2

Hz -

210

kHz Direct;

0.2

Hz -

210

kl-lz

Transfcrmerb: 1.5 H.z:-l0 kHz

Transtormerv.1kHl-210

kHz

Common

Mode

Direct:

120dBat60Hz

120

dB at60Hz 110 dB at 60

H,

Direct;

120

dB at60Hz

Rejection

Ratio

Transformar:

140

dB at60Hz

Transformer:

120

dB at 60 Hz

Full

Scale

Direct:

100

nV

100

nV 10 nV Direct;

100

nV

Sensi tivi tv

Tr anstor

mer:1nV

a

Tr ansforrner: 1

riV

MaximLlm

Input

Direct:

i200

V de

±200

V de

±5 V

Direct:

±200

V de

Voltage

Transformer:

tn

mv

rrns

Transformer;

10

mV

rrns

sine wave

sine

wave

ayb.wired for

1:50to1:350

turn,

ratio.

Stand,,,dis1:100.

"varies

with

source

Impedance.

NOTE:

A cur

ten

t-sensi

tive

preamplifier,

Medel

184,

is also

available.

See

ACCESSOR

IES listatendofspecs,

.

"

Table

I.'.

PREAMPLIfIER

SPECIFICATIONS

1-1

FREQUENCY RANGE

fig.,"

1-1.

MODEL

124.0,

LOCK·IN

AMPUflER

il

>

o

'-J

-1>

U1

:t>

'"

'"

t,

III
:l

I

N

Ul

I

o

N

SELECTS

INSTRUMENT

FUNCTION. IN AC

FOSlnON~

..

CTS

"5

W'QEB"NO R

MS

VOLTIWETER. IN PSO

POSITIONS,

ACTS AS

l..OCI<·lN

A~PlIFIER

-

LECTS CA.L.

VOLTA.GE

CAL.

IN BAN0 PASS

S WIT ... HIGH

(l

AVE~

AGE-AEADJ

NG

METER

CA.L.lB;ftATEO

~N

RMS

FOR

SlNE-

WAVE.

If!lPUT

LI GHTS IF REf. OSC. 'S NOT

FREQ.

LOC~ED

TO REf. 'NPUT.

OQES

NOTmoICATE PH

A.SE

UNl.OCK

/OVERLOAO

INDICA.TOR

"'

...

_-~

/----

-.-

CRANII(S IN de OFFSET IN

f'RONi

OF

O'JTPLT AMPLIFIER. I

TURN'

I FULL SCA.LE,

FOR A

Tcrr"L

OF'0FULL SCALES.

TOGGLE SELECT POL..RI

TY.

SELECTS TIME

CONSTANT

OF OUTPUT

L

P FILTER. S ORIIdB/ OCT"VE

ROUOFF

SELECT PHASE OF SYNa-lRONOUS

DETECTlON

wml

RESPECT TO REI'

,,-

SELECT

E~"CT

FREe<UENCY

OF

esc:

LLA

TOR IF OPERAnNG IN

INTERNAL

MOOE.

NOT FUNCll ONAL

WH

oN OPERATI~GIN

o~1lERN"L

o.IOOE

AOJUST FOR ZERO

TR"NSFER or CENTER
FREQUENCY

IN NOTCH

MOOE

SELECTSsHA.RPN

ESS OF

SELECTIVE

A.M

PLIFI ER

e<'

lIto

1

3dB

OSC.

RANGE.

OECIMA.L

IN Ex:TERNAl POINT

MaOE SET TO
EXPEhEO

RANG.~i

OS(;.

PHA.SE

-LOCI<>

AU

TOMA

TIC

ALLY,

NULTI PLIEiR IN tNT.

SELECT EXACT CENTER
FREQUENCY

OF SELECTIVE

..

MPLIFIER

..t.

REFERENCE

INPUT

TO

WHICH OSCILLATOR

LOCKS.

osc.

LOC

KS TO

POSITIVo-GOIPlG ZERO

CROSSING

e

SELECTS 'OPERATI"G
MOOEOF OSCILLATOR.
IN

"Z

PQSITIO!',

osci

LLATQFl'

LUt,;:KS

TO

SECOND

IIAR"'ONJC

.1',)\,

'W._.~

.

@-

'"

~

•

USEO 'WHEN

CALIBRATING

SiENSITlVITV

SELECTS

OPERATING

MOOE

OF SIGI>IAL

CHANNEL

~

~\'=:-"

I'Q'r"-"O"'_oUOO'

PLUG-liN

PRt:AMP'.

-..,

..

MODEL 116,I~7,

lie

.-,__-...-.

OR

119.

SELECT

ACCORDINGTOFREe<.

RANGE

ANO

SOU~CE

'''PEOANCE. SEE
SPECS.

MOOEL II S

INCREA5ES

OVERA.LL

5ENS. BY

l(

10.

N

Jan-29-02

11'45A

1.2

SPECIFICATIONS

1.2A

SIGNAL

CHANNEL

SPECIFICATIONS

-"

Frequency

Aange

Model 124A; 2 Hz -

210

kHz

Model

124AL:

0.2

Hz -

210

kHz"

Sensitivity:

21 full-scale

ranges

in 1-2-5

sequence.

Full-scale

vol taqcs

are

determined

by

the

choice

of

pre

amplifier

,

Ser~$it.ivity

and all

other

preamplifier-determined

specifi-

cations are given in

Table

1.1.u

Sign,,1

Channel

ModesofOperation

(1)

FLAT:

Flat

response

within

±1%

from

10 Hzto110

kHz. ±2% from

110

kHzto210

kHz. and ±10% below

10 Hz.

P.OB

0.01%.

The

frequency

stabilityistypically

0.05%

of

the

set

freq\Jency.

121

EXTE

RNAL'

The

internal reference oscillator will

lock in

both

trequencv

end phasetovirtually any

extemaltv generated signal crossinq its mean onlv

twice

each

cycle.

Maximum

input

voltageis±20Vde.

Minimum

time

requiredoneither

sideofthe

mean

is

100

ns.

Amplitude

excursion must be

at

lean 50 mV

abovo and

below

the me

en.

rnou t irnpedanee is 1

r'r'n~

go hrn.

When

locked

on,

the

raferunce

oscillator

will

track

the

external

signal

overafrequency

range

of

l00~

1

within

the range of

the

set band of

frequeneie~.

Ma.imum

frequency

acquisition

(lock-on)

times

for

each

fre-

quency

band

are

giveninthe

following

table.

FREQUENCY

RANGE MAXIMUM

TIME'

•

121

BANDPASS;

Provide'atunable

bandpass response

with

the

center

frequency

set by

front-panel

digital

dials

o,v"

a ranqe

of

2 Hz to

110

kHz. Setting

accuracy

-is

within

12%

Or

0.05

Hz,

whichever

IS

greater.

Bandwidth

is adiustable over a

rang~

of 1% to

100% (at

3 dB

points).

correspondingtoa range of Q

between

100

and 1. by means of

the

front-panel

Q

control.

(31

NOTCH, Essentially

the

same as

the

Flat

mode,

but

with

the

addition

of a

tunable

notch

that

provide,

up

to

80 dB

of

attenuationatany

specific

frequency.

The

notch

is

tuned

with

the

same

controls

as

set

the

bandpass frequency.

BAND

Xl .

Xl0

.

Xl00

.

Xl K .

XlO

K .

0.2Hzto

21 Hz .

2 Hzto210

Hz .

20Hzto2.1

k Hz

..

200

Hzto21

kHl

.

2.1 kHz to

210

kHz .

15

minute,

2

minutes

10 seconds

2 seconds

2

seconds

(4) LOW PASS, Essentiellv

the

same as

the

Flat

mode,

but

with

the

addition

of

a low pass. filter

that

provides

a 12 dB

per

octave

rctlott

a~)ove

the

set freqv(!'lCY.

(51 HIGH PASS, Essentiallv the samea'the

Low Pass

mode,

but

with

the

substitution

of

a

high

pass filter in

place

of

the

low

pass filter.

1.2B

REFERENCE

CHANNEL

SPECIFICATIONS

Modes

(1)

INTERNAL:

Frequency

of

the

internal reference

oscillator

is

set

by

means

of

fr

ont-panat

digital

dials

and/or

rsar- panel VCO

control

voltage,

Setting

accu-

racv is

within

±2% Or

0.05

Hz,

whicheverISgreater.

veo

control

vcttege

of 0

to

±10 V

correspondstothe

full

frequency

range

on

all bands. VCO

input

irnped-

ance is 10 kilohrns.

The

amplitude

stability

is typically

°

Modtill

124AL

h;]5

5igrlifi!:::;!IlltIV

lunasl'

severe-over

toad

reCO\lllrv

nme

(80

s n

305with

~OOO

limes

1ull

$clIle

OV8,IoOid

for

onljl

""'11'l1J~el

.

••

Two

additionOiI

prel

...

rnplifier5.

t h e

Modal

lB4

;lind

thll

Modilll

186,

£Ira

evauetne.

r-or

informatIon,

cootac

r (118

hlctOrV

or

the

eecro-v

re~r65ti1rHlItivl!!r

invour

IIrl!rll.

1·3

Once

the

frequency

hJS

locked,

the

phase

will

trackatthe

rate

showninthe

diagram

on

the

following

page.

Phase

Adjustment:

Calibrated

10

turn

potentiometer

pro-

vides

0·100<)

phase

shift.

Linearity of phase

setting

is

within

±2Qfrom

2 Hzto21

kHz,

and

within

±5°

from21kHz

to

210

kl-lz.

Resolution

is D.1

Q

•

A

four-position

quadrant

switch

provides

901'

phase

shift

increments.

1.2C

DEMODULATOR

CHARACTERISTICS

ACVM;

An

ACVM

positiononthe

function

switch

permits

the

Model

124Atobe used as a convenrional or

Irsquencv-

selective ac

voltmeter.

Accuracyiswithin

±1%

from

2.

H2

to

20 kHz, increasingto±10% at

210

kHz.

Dc

Output

Stability

and

Noise'

Dependentonthe

oper.ting

mode

selected

by

the

front-panel

Function

switch,

as

shown in

the

Stability

& Noise Tobie

(next

pagel.

"Timl!l

cOIn

bll

$hQrtanl;td

.!I~p(ecillbIVbyr~lUmelHlIl'ily

switehino

(0

lntl!lrnollli

Modll

IjInd

rnal'llJll!llIy

1-ettir"lQ thE!

csc

Hta

ror

to

ene

pr

eper

're~uencY.

Jan-29-02

11'46A

P.09

(

"o~

o

"

,.

00'

l'.5

~

o·

..

-,

!il

..

"'

w

-O<f.

..

..

~

..

•

"

-180

XI

-0,004

-0,003

-O·QO~

~O.OOI

0

0.001

0.002

0.003

0.00"

..

"'0

-0.'

-0,3

-O·~

- 0.1 0 0,1

O.~

0.3

0.'

..

~

..

z

..

.".

XIOO

-.0

-30

-'0 -'0

0

'0

~o

z'"'

30

'0

"II:

""

""

X"

-

..

-30

-h

-"

0

,.

~.

..

••

.".

....

""

....

XIOII

..

11S'

""32.

"IU

-44t

~

..

0

•••

."

l!Jh

1711!i1l:

..

"

,,~

SY~c.

$IGiU.L

SLEWINt:i

,u.Tf:

I

Hi:I SE;CO-'O

Figurl!ll-2.

SYNC,

SIGNAL

SLEWING

RATE

Function

LOW

DRIFT

NO~MAL

HIGH DYN

RANGE

Output

Stability

<150

IN

I "c

<1

rnV/"C

<10

mv / "c

<100J.lV

rms

<1

mV rms

<10

mV rrns

EqutvutentNoise

Bandwidth:

416

,u:Hz

minimum

(300

s

time

constant

with12dB/octave

rolloff).

Zero

Suppress:

Calibrated

control

permits

off-setting

zero

by ".1000% 01 lull scale on

Normal

and High

Dynamic

Rang.

only.

•

Demodulator

Overload

Limits:

Dependent

on

Function

switch

settingasfollows

(see

Subsection

3.21

for

over-ride

conaiderations).

LOW

DRIFT

,.., . . 10 x lull

,cal.

NORMAL

,.

. 100 x lull scale

HIGH DYN

RANGE

, 1000 x lull scale

System

Gain

Stability;

100

ppm/

aC; 100

ppm/24

Hr in the

Flat

mode

and

with

Function

switch

set

to

NORMAL.

1-20

OUTPUTS

ME!ter Redding: Choiceofeither

center-zero or

lcf

thand-

JP.ro

panel

meter

of

taut-band

construction.

providing

0.5%

linearity.

This

limit

is

defined

CIS

the

ratio,

at

1I~(!

input.

of the

maximum

pkpk

voltage

of a

non-coherent

signal,

before

overload,

to

the

pk-pk

voltage

of a full-scale

coherent

slnewave.

Note

that,intermsofpk-pk

noisetorms Signal.

the

instrument

will

accept.

without

overload,

interfering

Signals

having

E1n

amplitude

up

to

3000

times

the

sensitivity

sc

ttinq,

(See

discussion

in

Subsection

3,21.)

OPtional

Digital

Readout:

file

Mo,I.1

124/\

mayb.ordered

withanoptiunal

diqit

al

readoutinplaceofthe

standard

panel

meter.

TIle

readout

is a 3% digit

display

with

a

linearityof0.05%ofthe

reading,±1count.Inaddition,

a

BCD

outputisprovidedatthe

rear

panel.

The

output

levels

are

DTLlTTL

compatible:

Logic 0 = +0.2 V ±0.2 V, 5 mA

maximum

sinking

current;

Logic 1 =

4-3.5V±l.O

V, 100

flA

maximum

sour

cinq

current.

Filter

Time

Comt;jlnb:

1 ms

to

300

s in

1-3-10

sequence.

and

a mi

nlmum

time

constant

posltlon

havingatime

constant

of

less

than

1 rns

[daterrruned

by

internal

stray

capacitnnce}.

n1E~

External

position

allows

capacitance

to

be

added

via a

rear-panel

connector"

to

obtain

special values

of

time

constant.

Either

6

or

12

dB/octave

r

ollotf

as

selectedbymeans

of

front-panel

switch

is pr

ovtded.

-

MI!.".uured

with

li''''''1iiI

(,QI"Ist.mt

of

1 S

Itnd12dl3!OCTilv\llulloff,

Function

Out;

A de signal corresponding to

the

panel-meter

rcadinq,

An

output

of 10 V

corresponds

to full-scale

deflection.

'The

output

impedance

is 1

1<>11.

Signal

Monitor:

Enables

continuous

monitoring

of

the

signal

channel

output

ahead

of

the

demodulator.

In LO

DRIFT

operation,

a full scale rrns

inputsfnewave

gives a

100

mV

rrns

sinewave

at

the

Signal

Monitor

jack.

In

NORMAL

operation,

the

signal

monitor

output

with

a

full-scale

input

is 10

mV.

and

in H I, it is 1

mv.

Dvnernic

(

1-4

Jan-29-02

11:46A

Operating

Dynamic

Range

Tradeoff

LO

DRIFT

NORMAL

HI DYN RNG

[Reserve]

Output

DYna(r'li~

Range

6_6 X 10"

10'
10

3

PSD

Dynamic

Reserv'!!

10

10

'

10'

PSD

Dynamic Range

6_6

x

10'

10'
10'

Total

Dynamic

R.iUig~

6_6 x

10'

10'
10'

P.I0

Table

1-2.

MODEL

12.11A

OYNAMIC

RANGE

SPECIFICATIONS

Over-ride considerations

applyasexplainedinSubsection

3.21.

Output

impedance

is 600 n.

Internal line

frequency

pickup

is less

than

20 nV rrns

(referredtothe

Direct

inputs

of a

Type

116

Preamplifier)

in

any

Signal Channel

mode

except

Bandpass

and

Notch,

where

the

level

may

rise to

500

nV at

highest0settings.

Hefarance

Channel: A sinewave

output

at the

reference

oscillator

frequerlC.~V.

Amplitude

is.

contmuouslv

adjustable

by

meansofthe

front-panel

Level

com-o!

over a range of

oV

to

10 V

rms

with less

than

2%

distortion.

Output

impedance

is 600 ohms.

.'"

;!

e10

·

C

·

1.01

'±10

•

?

~

i

!O,l

0'

.'

,,'

~.

)

1.2E

DYNAMIC

RANGE SPECIFICATIONS

Vary

as a

function

of

the

operating

Dynamic

Range

Tr

edeoffasindicated

in the

table

above.

..LF OTHER CHARACTERISTICS

Overload:

Front-panel

light

indicates

overloadatcritical

circuits.

Reference

Unlock;

Front-panel

light

indicates

that

the

reference

oscillator

has

not

completed

Irequeucv

lock.

Internal Calibr.ator: Square-wave calibrator signal supplied.

Rm5

amplitude

of

fundamental

frequency

component

sdjust

atuc

from

20 nV to

100

mV in 1-2-5

sequence.

Tvpical

accuracy

indicated

in

Figl.Jr~

1-3.

Ambient

Temperature

Range:

Unit

can

be

operated

at

ambient

temperatures

ranging

from

15°Cto45°C.

Auxiliary

Power

Output:

Regulated

t24

Vatuoto

100

mA

is available at rear-panel

connector,

Power

Requirements:

105-215 or

210-250

V; 50-60

HI;

unit can also be powered from batteries. by supplvinq

t31

V

to rear pdnel

connector.

Bi:ltterie~

must

be able to

supplv

at

least

400

mA at +31 V and

360

,~A

at

-31

V.

"NOT!::::

ThA'l;II ./:If'1

maxrrnumvalues

anu

do

nut

eootv

ro

r

~II

POSI~Il)nfj.

01

the

SenSITivity

swttcn.

for8g",n",ral

(hii(:~Jjj.~lon

of

yhll

rTHHllningatthese

termsIlI"IIJ

Hllllllr

Ilgnifil:;<lnce,

~ee

Appendix

A

A1t

thl!

,IISf

Of

thl~

manual,

,A I

so.

Gee

Subsllllcticrl

3.21.

1-5

fi9ur'J 1-3.

TYPICAL

CALIBRATOR

ACCURACy

Size: 17-1/8"

W,

7"

H x 18-114" 0

(43.6em

W,

17.8 cm

H x 46,5 em DI.

Weight: 34 lbs 115.5 kg!.

Accessories: Model

173

AC

Zero

Offset

provides

square

wave at

the

reference

frequency

which

can

be

used

to

suppress siqnals at the

input

of

the

Model 124A_

Other

accassoriss include a

computer

interface

system,

fixed

and

variable:

speed

I

ight

choppers,

and

a broad

selection

of

special purpose pre

ampfttlers.

The

AM-1.

AM-2.

and

190

input

transformers

allow

better

noise

performance

to

be

achieved

when

~Jsing

a

hiqh-input

impedance

preamplifier

to

process a signal arising in a low

source

impedance.

The

Model

184

Current-Sensitfve

Preamplifier

is also

available.

This

prear'r1~)lifier.

which

plugsi"like

the

Models

116. 117.

118.

and

119

Preamplifiers.

provides 1 V

out

for

input

currants

ranging

from

1 nAto10

J.1A

<IS

selected

by a

tront-pancl

Range

switch,

Frequency

range varies

with

sansitivitv,

bC!ing:;'>Hzto:3

kHl

on

the

1 nA ranqe

and

2 HT

to

200kl-laonthe

10

IlA

ranqe.

Jan-Z9-0Z

11:46A

•

SECTION

II

INITIAL

CHECKS

P.II

2.1

INTRODUCTION

The

followir19 procedure is

provided

to

facilitate

initial

per

tormance

chocking of H,e Model

124A.

In general,

the

procedure should be

performed

after

Inspecting the in-

Ur'I.JI"l)frH

for

shippinq damage

(any

notedtobe reported to

the carrier and to Princeton

Applied

Research Cor'pnra-

tlonl.

but

before

using it e

xpenmentallv.

IN

THE

CASE

OF

UNITS HAVING A

DIGITAL

PANEL

METER,

IT IS

IMPORTANT

THAT

THE

PHRASE

"meter

lull

scale"

BE

PRDPERLY

INTERPRETED.

READ

THE

PARAGRAPH

BEGINNING

WITH

"In

reading

tho

display

---" ON PAGE

111-24

BEFORE

PROCEEDING

WITH

THE

INITIAL

CHECKS.

Should

anv difficultv be

encountered

in carrying

out

these checks.

contact

the

factory

or

one

of

its

authorized

representatives.

2.2

EQUIPMENT

NEEDED

(1)

General-purpose

oscutcscope.

(2)

Oscillator, having

any1kHz

repetitive

waveshaps

that

crosses its mean

cxactlv

twice each

CYcle

and havinga

pk-pk

voltage

anywhere

between

100

mV

and 3 V.

(31

Assorted

BNC cables.

2.3 PROCEDURE

(for

digital

units,

see

page

111-24

before proceeding)

NOTE: This procedure

must

be

performedinsequence.

(1) Install a

preamplifierifnot

already

installed.

(21 Check

the

rear-panel

115/230

switch.

Make sure the

number

showing in

the

window

corresponds to the

line

voltag~

to be used.

(j)

Turn the front-panel

Power

switch

OFF.

(4) Plug

the

line

cord

into

the

rear

panel

and wall

racsptacles.

(5)

Set

the

front

panel

controlsasfollows.

M!tf!r:

Check mechanical zero. Adjust if necessary.

Preerrtplifier

Input:

DIRECT

(if

applicable)

Sensitivity

switch:1mV

{if

uainq a Model

118

Preamplifier, set the

Sensitivity

switch to 10

mVI

Signal Channel Mode:

FLAT

Signal

Frequency

dials:

4.05

Signal

Frequency

range: X

100

a

switch:

100

'r.me

Constant:

300

rns

Zero

Offset

potentiometer:

fully

coun

terclockwisa

10 X Full Scale

switch:

OFF

(center

pcsttionl

PreamplifJer Mode: A

Reference

Frequency

dials: Red,

NORMAL,

Digits,

4.05

fl·,

Reference Frequency range:

X100

Reference Mode:

INTERNAL

Referonce

level:

10 (cal.)

Phase

potentiometer:

90

(9 full turns)

Phase switch:

180

Q

Function

switch:

ACVM

Calibrator

switch;

1

mV

(6)

Connect

a cable

between

the

Calibrator

BNC iack and

the preamplifier's A input.

(7)

Turn

the Power on and

wait

five

minutes

for

warmup.

NOTE~

In an actual measurement

application,

allow

one

110ur

warmup

for

optimum

performance.

18) The Meter

should

readtotho right.

(91

Set

the

Signal Mode switchtoBANDPASS.

(101

Adjust

the

rtqht-most

Signal

Channel

Irequency

dial

for a

peakonthe

meter

[approximately lull scale].

(11)

Switch

the°switch

back

and

forth

between

100

and

10%

ENBW

positions,

end

adjust

the

Notch

(front-

panel screW(:Iriver

adjustment)

for

minimum

change

betwear

the

two

positions

(less

than

1%

of

F.S.

change).

After

adjusting,

leave the Q at

100.

(12)

set

the

Sensitivity

ADJ.

potentiometer

[fr on t-pane!

screwdriver

adjustment)

for

exactly

full

scale

meter

indication.

(13) Sot

the

Signal Mode

switch

to

NOTCH.

The

meter

should

now

indicate

40% ±1S% of positive full scale.

114)

Set

the

Signal

Mode

switchtoLOW PASS_

The

meter

should

now

Indicate

90%

±10%

of

positive

full

scale.

(151

Set

the

Signal Modo

switchtoHIGH PASS.

The

mete,

should

continuetoindicate

90"A.

tlO%

at positive lull

scale.

(16) Sot

the

Signal Mode

switchtoBANDPASS.

This

completes

the

Signal

Channel

checks.

The

Phase

and

Function checks.

follow.

(17)

Set tho f

unction

switch

to LO

DRIFT.

(181

Set

theaSelectorto10% ENBW.

Then

adjust

the

Phase

pctenriomc

rar for

zeroonthe

meter.

Lock

the

potentiometer.

.

(191

Set

the

Phase

switchto270

0

•

Adjust.ifneeded.

the

Sensitivitv screwdriver

control

for

plus full-scale

meter

indication.

1201

Set

the

Phase

switchto90

0

•

The

meter

should

indicate

minus

full-scale 12%.

Jan-29-02

11,47A

(211

Set

the

Phase

switchto0·.

The

motor

should

indicate

ZCfO

12% of full scale.

(22)

Set

the

Phase

switch

backto270

0

•

(The

meter

should

indicate

positive full scale ±1%).

(231

set

the

Function

switch

to NORMAL. The meter

should

remain at

positive

full scale

(t.l%).

(24)

Set

the

Function

switch

to

HI DYN RANGE. The

meter

should

continue

to indicate positive full scale

(±1%)_

This

completes

the

Phase and

Function

checks. The

Reference

Channel

checks

follow.

(251

Connect

the

Signal

Generatortothe

Referenet! Chen-

nel's

In

jack.

The

pk-pk

voltage

"an

be

anywhere

between

100

mV

and 3 V.

Set

the

signal generator's

frequencytoapproximately1kHz.

126)

Monitor

the

Reference

Channel's

Out

jack

with

the

oscilloscope.

The

waveform

should

be a 28 V

(i2

VI

pk-pk

slnewave.

(27)

Set

the

Frequency

Mode

switch

to

EXT. The Ref.

Unlock

light

should

come

on.

Observe the

frequency

of

the oscilloscope

waveform.

It should have bcqun

increasing as

soon

as the

Mode

switch

was set to EXT.

After

several seconds. it should

stop

increasing.

When

it

stops.

the

Ref.

Unlock

light

should

go

out,

(The

me

ter

will go to Zero also.I

IZ81

NQ~l:!:

01C

trequcncv

of the o$cillO$cope waveform,

Then

place tho

Reference

Mode

switchtof/2;

the

freql,.l~r'CY

should

double.

This

completes

the

Reference

Channel

checks.

The Sensi-

tivity Range

checks

foliow.

(291

Set

the

Reference

Mode

switch

back to INT,

(301

Set

both

the

Signal

Channel

Sensitivity and the

11-2

P.12

Calibrator

output

to

100

mV_ The

meter

should

remain at full

scale

±1%.

NOTE:

Calibratorto10 mV

with

Model

118

Pr

camphfier.

(31) Pr

oqressivefv

rotate the Sensitivity and Calibrator

switches

one

position

at a

time,

in a

count~rl:;Ic.>r.kwiS'.e

direction.

The

meter

should

remain al full

scal.

±2% if

the

two

switches

are in

Cor(e~ponding

positions.Ifthe.

meter

wavers

too

much

in the

low

nV

aettinqs,

increase the Time Constant to 10 seconds, (If using

the Model

118

Preamplifier,

remember

that

the

instrument

is.

10 X

more

sensitive than is marked on

the

Sensitivity

switch,

and set the

switches

accord-

ingly, Just he sure to

check

all sensitivities for

which

Calibrator

volt.gcs

are

available.l

This

completes

the

Sensitivity

Range

checks.

The

Output

Offset

end

Overload checks

follow.

(321 Remove

the

Input

signaltothe

Preamplifier.

(33)

Set

the

Time

Constant

switchto300

ms.

134)

Set

the

Sensitivity

switchto1 mY.

135) Place

the10X Full Scale <witchto"-".

(36)

Adjust

the

Offset

potentiometer

for

exactly

one

turn

clockwise.

The

meter

should

indicate

positive

full

scale

!2%.

(371 Place

the

10

X Full Scale

switchin".".

The

meter

should

nnw

indicate negative full scale ±2%.

(381 Increase

the

Offset

potentiometer

setting

to 1_6 turns.

The

Overload light

should

come

on.

1391 Bctur n

the

10 X Full Scale switch to its

neutral

off

position,

Ths

Overload light will go

out.

This

completes

the

Initial Checks. If the instrument

performedasindicated,

one

can be reasonably sure th at it IS

operating

properly.

Jan-Z9-0Z

11:47A

•

SECTION

III

OPERATING

INSTRUCTIONS

P.13

,

3.1

BLOCK

DIAGRAM

DISCUSSION

3_lA

INTRODUCTION

Bef()r~

discussing

the

actual

operation

of

the

Model 17.4A,

let

us e'l;amirll:! a

functional

block

diagram

to

bette

r

understand

what

each

adjustment

does,

and

how

the

various

adjustments

relate

to or

influence

one

another.

The

functional

block

diagram

i$

IQc.:';H~d

on

the

following

page.

Schematics

andachassis

wiring

diagram

ere

includedatthe

back. of

this

manual.

The

Synchronous

Detectoristhe

heartofthe

instrument.

around

which

are

situated

the

Signal

Channel,

the

Refer-

ence

Channel.

and

the

Output

Amplifier.

The

Signal

Ch

annal

amplifies

and

filters

the

siqnal,

clnaningituo

as

much

as possible

before

passing it

along'0the

Synchronous

Detector.

The

Referel1ce Ch(i"r'Iel

controls

svnchronization.

3.16

SIGNAL

CHANNEL

Preampljfle

r

Four

models

of

plug-in

preamplifier'

arc available:

the

Model

116,

the

Model

117,

the

Model

118,

and

the

Model

119~_

Together

they

cover

the

whole

frequency

spectrum

from

neardeto

210

k Hz,

each

model

having

the

best kind

of

input

circuit

for

optimum

tow-noise

performance

in its

frequency

range_

The

Mndel

116

may

be

considerec

the

qeneral-purpose

choice,

performing

well in

most

situations.

Specific

data

for

the

four

preamplifier

models

Is given in

the

specifications

in

SectionIand

in

the

discussions

in

Subsection

3_1.

Selective

Amplifier

The

Selective

Amplifier

functions

as a variable 0 filter,

which

l"Iiaybeoperated

in

the

high-pass. low-pass,

notch,

bandpass,

or

flat

mode.

Because

rrns

noise

amplitude

is.

a

direct

function

of

bandwidth.

much

of

thl!:

noise

can

be

rejected

in this.

stage

by

filtering

out

all

but

the

band

cont

aininq

the

wanted

signal. In

addition,

odd

harmonics,

to

which

the

Synchronous

Detector

is sensitive, clin be

eliminated.

Intermediate

Amplifjer

The

Intermediate

Amplifier

provides

additional

gain so

that

the

siqnat-p lus-ncise

applied

to lhe'

Synchronous

Detector

is

as.

large as possible

without

overload.

Presenting~Jlarqe

signal

to

the

Synchronous

Dete

cror

minimi

....

es.

for

a given

everett

senstrivitv.

the

noise

anddedrjft

contributedbythe

OutputChannel.

"AI!;!;)

avaIlable

cr e

the

Mod~1

184

Photorn~trjc

Preampldler

Il

....d

the

Morlel

1135

Sirlgle·Erldec1

Low

Nctee

PreamplIfier.

The:~e

two

preampl,f,e(!

ware

devlllioped

laul:(man

the

prU;:IrnlJllflers

dj!lt:U5S~d

in

thl!>

manual.

FOr

infcrm,UIOn

I!Ij~d

slJtlcific",tionl;',

contact

the

factory.

Seoarare

instruc:tion

m811UI!IIIs

lire

prQvidet;l

for

the

Models

184

and

185.

111·1

The

Intermediate

Amplifier

is ac

coupled,

thereby

eliminat-

ingdedrift

problemsinthe

Signal

Channel.

3.1C REFERENCE

CHANNEL

Voltage-ContrOlled

Osclllator

The

VCO

either

locks

onto

a

svnchronizinq

signal

from

the

e)(periment,

Or

provides

iii:

$Vf'lchroniling signal

to

the

experfrnent.

The

Vee

drives

the

Syr,dlfonOllS

Detector

so

that

theexpertment

an(1

the

Model

124A

are

properly

synchronized.

The

VCO

automatically

phase-locks

to any

kindofrefer-

ence

waveform

hoving a

frequency

within

approximately

two

decades

of

the Hcfe rcnce

Channel

band

setting.

the

only

requirements

heing

that

the

waveform

cross

the

mean

twice

{onlyI

each

cycle,

thatithave

a pk-pk

amplitudeofat

least

100

mV,

and

that

it be

svnchroriized

with

the

signal

of

interest.

The

vee

can also

lock

to

the

secono

harmonic

of

the

reference

~ign,al,

if

desired.

I~

is

important

to

realize

that,

even

though

the

VCO

will

phase

lock

over

a

two

decade

frequency

range, the

boundaries

of

the

lwu

dur.ades

an~

determined

by

the

settingofthe

O~r:iIlMnr

Ranqc

switch.

The

tracking

range

correspondtoqtoeach

po si

tionofthe

switch

is as follows.

Xl

,.""".""

_. _..__ .

0.2H,to

21 Hr

XlO

,.",.""".,,_,

.

2Hlto21OHI

X100

, , , ,

.'

__ . _.

.._20Hzto

2_1 kHz

X1K

"",,

.

._.

200Hz!o21

kHz

XlOK

,.., , 2

kHzto210

kHz

In the

Internal

mode.

a sinewavc OLltPut

from

th~

Oscillator

is

provided

for

synchronizing

the

experiment.

The

Oscil-

lator

can

free

run

accuratelyatany

selecled

frcqvency

from

200

mj-izto210

kHz,

Also,

the

Oscillator's

frequency

may

be

controlled

by a

voltage

applied

to a rear-pane!

jack.

Phase

Controls

The

Phase

Controls

combine

quadrature

outputs

from

the

VCO

such

that

the

resultant

sinewavs

presented

to the

Svnchronous

Detector' has

the

desired

phase

relationtothe

reference

(sync

input

and/or

output).

3.10

SYNCHRONOUS DETECTOR

The

Svnchronous

Detector

inverts

the

polarityofthe

part

of

II"Ie

input

signal

ccr

respondinqtothe naqativc

excursion

of

the

phosc.stutted

sinewave

from

the

VCO.

and

passes

the

remaining

waveform

uninverted.

Therefore,

the

de

corn-

ponent

of

the

resultant

waveform

is

proportional

to

the

value

of

signal at

the

same

frequencv

and

phaseasthe

phase-shifted

veo

sinewave.

Because

the

detected

signal

still has

noise

on

it. RC

low-pass

filters

that

follow

the

svnchrooous

detector

are

usedtoeliminate

ull

but

the

de

component

rspresentinq

the

wanted

signal. Adeampllfier

SIGNAL

CHANNEL.

./

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FUNCTJONAL

BLOCK

OIAGRAM.

MODEL

t24A

-

~

,I.'I

,

,.;

il

>

o

'"

Jan-30-02

05:24P

P.02

following

the

Detector

provides

the

finesl

gain.

This

ampli-

fier drives

the

output

connector

and

panel

meter.

To

daterminu

the

amplitudeofa signal.

the

operator

simply

adjusts

the

phase

controls

for

maximum

meter

indication.

The

meter

directly

indicates

the

signal

amplitude.

In

addition,

after

making

thil

adjustment.

the

phaseofthe

input signal relative to the reference may be accur etelv

r~ao

from

the

Phase

dial.

3.2

SIGNAL

CHANNEL

OPERATION

3.2A

INTROOUCTION

The

function

of

each

controlisindicated

in

Figure

1-1.

Instead

of

repeating

the

intormatlcn

qiven

there,

this

subsection

provides

additional

background

information

for

setting

the

controlstotheir

optimum

positions.

To

set

I,JP

the

Signal

Channel

controls,

the

operator

rnusr

know the

frequencyorfrequency

rangeofthe

signal. It also

halps if he

knows

the

expected

amplitude,

the

amount

and

tvpe

of

noise

obscuring

the

signal. and

the

signal-source

impedance.

The

stimulustotheexpsrirne

nt is

often

chopped,

Detecting

at

this

chopping

freqi

...

encv

eliminates

all

but

the

signal

relatedtothe

stimu

Ius.

Princeton

Applied

Research

Corpo-

ration

manufactures

several

modelsoflight

chopper

which

are ideallv

suitedtophoto-detection

applications.

Chopping

the

source

light

finds

its

analog

for

other

kinds

Of

experiments

in

chopping

the

stimulus

de.

ri, ac,

sound,

heat,

etc.

The

chopninq

frequency

range

must

be fairly well

known,

and

sync

sigr\als

must

be aViJilable. Of

course,

the

frequencyofinterest

may

not

be a resultofchopping

at all.

The:

chopping

technique

discussed

here

merely

serves as an

exampl

•.

3.28

PREAMPLIFIER

CHOICE

Four

modelsofplug-in

ureampltflers

are available.

each

one

providing

optimum

low-noise

performance

over

a given

input-resistancev,frequency

ranqe, as

shown

graphically

in

Figure

111-2.

Twoofthese

preamolifiars

can be

operated

bothindirect

and

transformer-coupled

modes,

and

all

four

of

them

can be

operated

single.ended

or

differentf

allv, A

Model

190

transformer

canbeused

with

anyofthe

plug·ins

to

improve

low-frequency

performance when working

from

low

source

impedances.

Useofthe

Noise

Figure

contours

is

discussed in

Subsection

3_2G.

Another

consideration

in selecting a

preamplifier

is its

ability

to

amplify

without

distortion.

If an

experiment

requires

measurement

of

low

level

harmonics

in

the

presence of a high level Iundarnentat, it is

important

that

tho

preamplifier

not

add

significant

harmonic

signals by

non-linearly

amplifying

the

fundamental.

Exceptinthe

case

of

the

Model 118

Preamplifier,

the

distortion

generated

by

preamplifiers

operatinginthe

direct

mode

is so small as

to

be

unmeasurable

using

conventional

methods.

The

Model

11B

tan,

however,

distort

more

und~r

certain

conditions,

as

indicatedinFigure

111-3. In

the

transformer

Mode,

both

phase

shif~

and

distortion

must

be

measured

for

each

individual

operating

condition.

Figure

111-3.

DISTORTION

v.

FREQUENCY.

MooEL

118

zo "'v

10'

10.11

10"

,R!QuENCV.

Hz

I;URY!$

1111142:

APPLY' FQR

ALL

MODEL

1Z~

$~SITlVITY-p$(J

SETTING

COJolelNATIONS EX"CEPT:

p:Sc_LODR,

SEN

~

10~VUHl,i

-'00

",Vi

f1'S D &

NO~MAl,

SEN~1 roY

Ihrll

W

'00

e v ; j!I!iD _I'll DYNRNIJ, $£N ..

l00pY",,"

"'00

1ft 1/. :;.

"OR

il'1ESf

COM~INATION:S,

CURlifS

~o1l1;!4

APPL....

II

100

roY

":.;

10 "'v

~~

~

..

'::~

J~

e

ev

i!a.

~ I

~1

~~

;;:i

tnt;;

~t.

10

3.2C

GROUNDING

In any

system

processing

low-level signals,

proper

grounding

to

minimize

the

effectsofground-loop

currents,

usually

at

the

power

frequency.

is an

important

consideration.

With

the

exceptionofthe

Models

184

and

185,

allofthe

Model

124A

preamplifiers

allow

both

differential

ar\d

single-ended

opaearion.

Two

properties

of

these

nraamofitiers

allow

them

to achieve a

high

degreeofimmunity

to qround-f

onp

currents.

In

differential

operation,

their

extremely

high

ccrnmon-rncde

rejection

(:l.SSUI'es

an

almosttotal

rejection

of

'.0

;!.

~.

Q

;:

"

-I

Q

10

t;

Ci

110

..

10

10

JQJ

'lOt

I'''EQUI!NCY. HI

11$,II",..119---"

tllll'Eer

IIIQfI[

101.0

Fig!,.....

111.2'.

OPTIMUM

PERFORMANCE

REGIONS

OF THE PREAMPLIFIERS

10

'0

10'

'0'

10'

~

~

10'

10'

111-3

Jan-30-02

05:25P

P.03

Impedance

matchingofthe

source

and

loading

considera-

tions

often

require

that

the

input

impedance

of

the

preamplifier

be

known,

HOMVer.

do

nat

confuse

imped-

ance

matching

with

optimum

input

impedance

for

low-

noise

operanon.

The

latter

is discussed in

detail

in

Subsection 3.2G.

The

input

impedanceateach

preamplifier

(direCt

model

is:.

Mo<:fel

116,100

rneqohrrs20pF;

Model

117,

100

msqohms

20

pF;

Model 118, 10

kilohm'

170

pF;

Model 119. 100

megohms

7.0

pF.

These

impedances

are

for

each

input

to

ground.

In

the

differential

mode.

for

all

models

except

the

118,

the

impedance

from

inputtoinput

is

twice

that

stated

(;.e., R

double,

C

heltl.

For

the

Mod.1 118, the

input

impedance

for

the

differential

modeisabout

the

Same as

the

jrnpeuance

for

single-ended

operation.Inaddition,

the

ditt.

input

impedance

at

tile Model

118

varies

with

sensitivity

and

the

setting

of

the

PSD

switch

Icomrnon-

mode

input

impedanceis25

kO

for

all

combtnattcns

l. In

the

Lo

Dr;ft

mode, on

the

10

mV

through

500

mV

sensirlvltv

ranges,

the

input

impedanceisabout

threa

times

that

specified.IntIH!'

Normal

mode.

the

higher

impedance

applies

to

the

1 (nV th rouqh

500

mV ranges,

and

in the Hi

Dynamic

Range

mude,

it

applies

to

the

100

IlV

through

500

mV ranges,

•

.,

Figu,01ll·4, GROUND-LOOP VOLTAGE REJECTION

USING

DIFFERENTIAL

INPUTS

GI'OUIUI LDOI'"

I;UIIlIII'![fIIT

unwanted

signals

which

appearatboth

inputs. at

the

sama

phase

and

amplitude,

the

usual

Case

for

ground·

loop

inter

tnranee.Insinqte-endert

operation,

their

unique

input

gro~.lr'Idin9

system, in

which

signal

yround

"tloats"

off

chassis

ground

by

ten

ohms,

assures a high degree

of

rejection.

As a

resultofthis

ten

ohm

grourld.

ground

loop

signals

<.JrIJ

efFectivelv

attenuated

by

the

ratiooften

ohms

to

the

braid

rosisteoce

(typically

20

mill

of

the

cable

carrying

the sign(:ll

from

the

source to the

input.

IIllP.lI;"~

...

(lIl."lhhllll

"",_III

110"110

I

Despite

the

immunity

granted

by

the

ten-ohm

ground,

far

better

rejection

can he

achievedinprocessinga$iglliiill

from

a

single-ended

sourceifone

operates

differentially

as

shown

in Figure

111-4.

In single··ended

opcr

ation,

the

preamplifier

"sees"

the

potential

difference

between

the

center

con-

ductor

of

the

cable

and

the

braid,

and

~rlY

ground

loop

sign~1onth~

braid

can be

attenuated

but

not

rejected

altogether.Indifferential

operation.

the

preamplifier

"sees"

the

potential

difkrence

between

the

"A"

Input

and

the

"B"

Input.

Ground-loop

signal

current

flowing

in

the

braid

isofno

consequence.

HOWC!V!J'r.

whan

operating

differentially,

it is

important

to

assure

that

cornrnon-rnode

interference

arising in

ground

loopsisjust

that,

i.e.,

without

a sigllifiC.i;lnt

differential

component.

This

should

not

proveOJproblem

as long as

both

sigr1al

cables

are

the

same

ler)g1l1

and

follow

the

Same

path.

3.20

REMOTE

PREAMPLIFIER

ADAPTER

In

situations

where

very

low

signal levels are

encounrsred,

it

may

be

desirabletooperate

the

preamplifier

very

close

to

the

signal

sourcetoreduce

noise

and

strcv

pickup,

while

leaving

the

main

Lock-In

unit~ta

convenient

opcr

atinq

location.

This

rnav be

accomplished

with

the

accessorv

Rarnote

Preamp

Adapter,

Model

183

(see

F;gu,e

111-5).

3.2E

SINGLE-ENDED,

DIFFERENTIAL,

AND

TRANSFORMER

INPUTS

All

of

the

preamplifiers

have

switch

setnctable

single·

ended/differential

lnpurs.

The

differeMial

inputs

can be

usedtocombine

siqnals

(A

- B) as well as

10

provide

common

mode

rejection.

For

the

preamplifiers

haviog

internet

transformers,

the

Input

switch

operates

the

same

for

the

transformer

as it

does

for

direct,

The

Input

impedance

is very

lowinthe

transformer

mode.

-:

Figure

111-5_

MODEL

183

Rf:MOTE

PREAMPLIFIER

ADAPTER

111-4

Jan-30-02

OS:2SP

P.04

If an

external

transformer,

SI,H;h

~$

the

Model

HJO, is

used.

it is

connected

to

the

preamplifier

single

ended.

The

ansf'orrncr

alone

provides

sufficient

common-mode

r@jec-

lion

l~igure

III-Eil.

The

total

output

noise

rnavbeconvertedtoan

equivalent

input

noise

by

dividing

by

the

amplifier

gain_

The

noise

figure,

expressedinthese

terms,

becomes:

(2) Noise Figure =

2010

total

rms

nois_~."'O!,;)gC'

referred

.~~.an1p.

input

dB

IJ10

source

thermal

noise

voHaqe frrl'ld

source

(3)

Total

equivalent

rrns input noise

voltage

thermal

noise"

antilog

NF/20

volts

rms.

Using

the

applicable

set

of

contours,

the

total

equivalent

rms

input

noise can bedeterrnined:

E=

V4KTBR

Each

amplifier

has its

own

characteristic

noise

figure.

which

varies as a

function

of

frequency

and

source

resistance.

These figures

are

obtainedexperimentatlv

and

plotted

graphically.

Figure,

111-7

through

111-11

include

typical

sets

of

noise figure

contours

for

the

Models

116,

117.

118.

and

119

operatingindirect

and

transformer

modes.

Althnuqh

the discussion

of

noise

considerations

is

not

eomplcte,asimple

exampleatthis

point

illustrates

the

use

of

the

Ioreqoing

equations

and

illustrates

howatransformer

can,onoccasion,

improve

the

siqnal-to-notse

ratio:

Notice

from

these

equations

that

the

bandwidth

must

be

specified:

usually

determined

by

the

external

circuitry

and/or

the

amp

lifisr

bandwidth.

Figure,

111-7

through

111·11

include

response

curvesofthe

preamplifiers

from

which

the

bandwidth

may

be

obtained

(in

the

direct

modes,

the

bandwidthiswider

than

the

widest

Tuned

Amplifier

Bandwidth).

However,amore

interesting

place

to

deter-

mine

noise level is at the

outputofthe

Tuned

Amplifier.

Because

there

is gain

ahead

of

the

Tuned

Amplifier.

its

noise

contribution

referred

to

the

input

is negligible

compared

to

that

of

the

preamplifier.

In

computing

the

total

equivalent

input

noise

of

the

signal

channel,

the

operator

only

need

use a Af as

determined

by

the

Selective

Amplifier

sattinq

(with

preamplifier

limitations

considered).

Suppose

that

one

intendedtooperate

the

Model

124A

in

an

experiment

havirig a

source

impedance

of

10

ohms.

Further

suppose

tho

signal

frequencytobe 5 k l-lz, A Model

116 Prp.arnplifip.r is

chosen,

In

order

to

see

how

a

transformer

car"!

improve

low-noise

performance,

the

noise

for

the

Direct

mode

is first

calculated.

Then

the

noise for

trans-former

operation

is

calculated

and

the

results

com-

pared. Since

the

source

thermal

noise

contributing

to

the

total

noise is

dependent

on

bandwidth.

the

Signal

Channel

bandwidthisminimizedbysetting

the

Mode

switchinthe

Bandpass

position

and

the0switch

to

the

10% ENBW

(equivalent

noise

bandwidth!

posf

non,

The

Freque-ncy

controls

are

set

to 5

kHz.

In

addition.

other

control

settings

are

made

ac:con.fingtoinstructions

in

other

parts

of

this

section.

The

source

thermal

noiseinthis

case

is:

where:

k is

Boltzmann's

constant=1.38

x Hr

iJ

ioules/K

~.

~

,

!

n.

I

Ii •

~oo'

,

<i"'IQ

-,

I".

Go,n

'"

f.~I.

) '<,

I

ll !!

eoecr.

117,

II

'I!II

(ll1iI'(cr

,

i

.0

~----L.-----

.L.------.L------"..L-...LL

'0

!l}~

10

1

F~fOU[NCY,

HI

ee

I---------.j---

z

o

"

U

Ita

~

•

z

-

c

c

•

,

is

100

f--,L---+-

•

z

c

"

3.2G

NOISE

AND

SOURCE

RESISTANCE

Best preamplifier performance is realized under

thost;!

conditions

where

the

overall

signal-to-noise

ratio

is least

oeq-aoeo.Inmany

instances.

the

thermal

noise

generat~d

by

the

signal

source

resistanceisthe

dominant

factor

in

determining

the

input

signal-to-noise

ratio.

In this.

respect.

amplifier

noise

performance

can be

specifiedbythe

amount

of

noise

the

amplifier

adds

to

the

amplified

source

thermal

noise;

expreS5~O

ira

decibels this is

called

the

"Noise

Figure";

20

10

9 10

tO~()t

rn)~

nUI$e

"'~~~~_e.":I.~I,hE::

'~,~T,l,P~.fi~,L.~.L.:!~

dB

gain x

source

thermal

noise

voltage

(mlsl

where

the

Source

Thermal

Noise =-J4K

lR~f

volrs

rms

~

E,

and

(1) Noise Figure =

Figur.III·6. TYPICAl COMMON·MOOe REJECTION

K =

Boltzmann's

constant,

l.J8x10-

2

J

joules/K

T""

absolute

temperatureinkelvins

.1.f

l1'li

equivalent

noise

bandwidth

in Hz

R

=

source

resistanceinohms

3.2F

COMMON·MOOE

REJECTION

Figure

111-6

illustrates

the

common-mode

rejection

charac-

teristics

of

the

preamplifiers. in

both

{differential)

direct

and

transformer

mode

operation.

Note

that

the

CMR Is

much

higher

for

the

transformer

mode

than

for

the

direct

mode.

•

,

111-5

Jan-30-02

05:25P

T is

the

absolute

temperatureofthe

source

in kelvins,

presumedtobe

290Kfor

the

example

B is

the

noise

bandwidth.

'""

500Hzwithaswitch

set

to

10%

ENBW

and

Frequency

Controls

set

to

!;i

kHz

R is

the

source

resistanceinohms,

given as 10

ohms,

ThuS'

E

=y'4

x 1.38 x

iiJ-

B

X

2.9

x

1'0'

xTOx

5~

10"

-;

8.9 X TO-? V

rms

From

Figure

111-7.

the

noise figure

for

the

Model 116 at a

center

frequency

of5kHz

andasource

impedance

of 10

ohmsis20

dB.

Substituting

E

and

this

NF

into

equation

131.

we

get:

total

equivalent

rrns

input

noise

=

8.9x10-'

x 10

'0,'0

=89nVrms

With a

transformer

inserted

between

the

signal

source

and

the

amptificr

input

we

can

increase

the

effective

source

impedance

toavalue

that

reduces

the

noise

figure to less

than

0.1

dB.

From

Figure

111-7,

the

source

resistance

should

be

about

200

kilohms.

The

transformer

turns

ratio

required

for

this

ilTlpt.:!dance

tncrease

is

yR~IR~

= 141. TIle

thermal

source

noiseatthe

amplifierinputisequaltothe

noise

generated

by

the10ohm

SOL;rcC

multiplied

by

the

turns

ratio.

Withanoise

figure

near

zero,

thl~

total

equivalent rms

input

noiseisalso

equal

to

the

noise

generated

by

th!1

10

ohm

source

multiplied

by

the

turns

ratio.

z.

1.25

J1V

rrns.

I\lthough

the

numerical

value

of

equivalent

input

noise

is

much

larger

than

before,

the

signal-to-noise

ratio

is sub-

stentiullv

increased.

This

canbeseen

by

coruiderinq

all

of

the

transformed

source

!iignal

voltageasappearingatthe

amplifier'

input

terminals,

p05sibla

because

the

Model

116'5

input

resistanceismuch

larger

than

200

kilohms

presented

by

the

transformer;

the

siqnal-to-noise

ratioisequaltothe

maximum

possible

value;

esig/(Exantilog

NF/20)

=?.

esig/E,

the

norse

contributed

by

the

amplj Her

being

negligible

under

the

"near

r

ere"

noise

fiqure

conditions.

In

this

example

the

transformer

ifl(rr.aSf~S

the

slqnal-to-noise

ratio

by a

factorofTO.

Signal·to,Noise

Improvement

Ratio

TOINF

unmatched-NF

matchedl/20

TO

(20---

11/20

~

10

'

= 10

However,

because

of

the

noise

contributed

hy

the

trans-

former,

and

because

a

transformer

influences.

bandwidth,

the

results

obt

ained

using

3 real

trensformer

are

never

as

good

<:15

the

ideal

theoretical

resultspredicted

in

the

example,

Also,

it

is

seldom

convenient

to

obtain

a

tr

ansfor

me r

having

cxectlv

the

ideal

hHn5

ratio.

It is

best,

therefore,

to use

noise

figure

contours

and

amplitude

tr

ansfer

curves

obtained

ernpiricallv

for

th~

individual

transformer.

Figure

1l1·8A is~set

of NF

contour's

for

the

111·6

P.05

Model

116's

built-in

transformer.

and

Figure 11I·8B i. its

amplitude

transfer

curves.

The

10·ohm

amplitude

tran$fet

[.:urve

indicates

thatinthis

example

thll!:

transformer

does

not

t;:"han9fi!'

the

10%

equivalent

noise

bandwidth

as

set

with

theQswitch.'0thatEremains

8.9 x

llr'

V rrns. The noise

fjgure

fora10

ohm

sourceata center

frequency

of5kHz

is

about

1.5 dB, a Vast

improvement

over

the

20 dB NF

obtained

without

the

transformer.

NOTE:

For

optimum

noise

performance

with

a trans-

former,

it is

important

that

the

transformer

not

be

magnetized.

See

rRANSFORMER

MAGNETIZATION

ANO

DEGAUSSING,

page

111-'

r.

3.2H

SELECTIVE

AMPLIFIER

Noise

other

than

Source

thermal

noise

is

usuallv

not

wideband,

andisoften

difficulttocompute.

Some

kinds of

noise

canbedealt

with

very

effectively

u$ir~9

the

Selective

Amplifier.

Examples

include

flicker

(or

1If)

noise.

non-

synchronous

signals

arising

from

the

experiment,

non~

svnchronous

$igrlals.

from

external

pickup

suchasfrom

the

sc

power

lin~.

fast

transients,

and

harmonics

of the

reference

frequency_

Reducing

the

noise

level

aheadofthe

mixer

reduces the

dynamic

range

demand,

on

the

mixer.

tllereby

allowi~9

signals

to

00

measured

which

could

not

be

measured

otherwise.

The

Selective

Amplifier

canbeoperated

in five

dillerent

modes:

Flat.

flandpass,

Notch.

Low Pass,

and

High Pass.

Figures:

111·14

through

111-17

lltustrata

typical

transfer

characte

nsrtcsofthe

Selective

Amplifj@r for

the

last

four

of

these

modes,

Ultimate

attenuationofthe

four

frequency-

dependent

curves

exceed80dB.

In

selecting

filtering

per

ame

ters,

the

operator

must

be

careful

to

keep

the

signal

frequency

well

within

(he

passband selected, or

to

make

the

passband

such as to

accommodate

the

sigrlal

over

th~

range

that

it will

occupv.

If

chasei$important,

actual

measurementsofphase

error

over

the

frequency

rangeofquestionable

phasu

accuracv

wouldbebest.

These

regionsofquestionable

C1ccuracY

can

be

determined

from

the

individual

transfer

characteristics

of

the

preamplifier,

transformer,

and

Selective

Amplifier

settings.

The

bes

tthinqtodoisto

keep

the

bandwidth

wide

enough

so

that

phase

and

amplitude

errors

ars

not

a

problem.

Phase

control

errors

are discussed in Subsection

3.38.

Special

procedures

for

making

accurate

phase mea-

surements

are given in

Subsection

3_9. In

particular,

before

oper

atin

q in

LOW

PASSorHIGH

PASS,

the

operator

is

advised

to

check

Figures

111-16

and

111-17todetermine

the

amp!

itude

responses

in

these

modes

as a

function

of

Q_

"Equivalent

noise

bandwidth"

is a

concept

applied

to

widebano

noise.

Although

most

bothersome

noiseisnot

wideband,

but

rather.

coherent

non-synchronous

signal,

equivalent

noise

bandwidth

considaratfons

are usefu! in

helPing

to

choose

operating

parameters.

The

concept

of

«quivalentnoise

bandwldtharises

from

the

fact

that

Noise

Bandwidth

is an

unartenueted

rectangular'

bandwidth,

while

(cont.nuedonpage

111-131

Jan-30-02

05:26P

P.06

5.10'

10'

!OdB

101.0

10"

1.0
10-'

10'0

20dB

15dB

lOt

10 dB

6dB

10'

3dB

IdB

10'

0.5dB

o.ras

If)

10'

:=!

::r:

0

w

V

10'

Z

~

en
en

I.lJ

10·

0::

I.lJ

IdB

U

0::

::l

0

10~

3dB

(f)

BdS

lOde

10'

15de

20d

10

CENTER

FREQUENCY

I Hz

Fit.rolll-?

TYPICAL NOISE

FIGUIIE

CONTOURS

FOil

MOOEL

111.

MODEL

11G

IDIIIECTI

AND MODEL

119

(D1I1ECTI

111·7

Jan-30-02

OS:27P

P.07

EO,"

IE

I~

(TURNS

RATIO

I:

100)

>-

u

Z

on'"

::>

o

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LL

N

a

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o

..

o

-

o

o 0 0 0 0 0 0 0 0 0

0-

I"'1N

...

am

co

p....

to

III

'"

""

_,

-

-

--

~

<,

x

-,

,

"

~

--

""

,,'

I

,

.

I

·

·•

,

•

,

I

\

\

·

•

·

\

•

.

.

II

·

\

\

·•

,

II

·

·

·

·

Wwwl.LJ

\

(,)uuu

\

0:0::0::0:::

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0000

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(I)

(1)(1)

c:c:c:c:

,

-000

-00

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-on

I~

10·

10

1

10'

({)

:::;;

:r

0

w

10

2

0

Z

~

IdB

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10

W

a:::

~dB

W
U

6dB

a:::

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1.0

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10dB

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I

15dB:

10-'

zo

aa

I

1

I

i

10-

2

3~--

-:=--T

I
i

10-'

I I

1.0 10 10

2

10'

10

4

CENTER FREOUENCY,

Hz

Figure

1l1-8A.

1VPICAL

NOiSE

FlGURE

CONTOURS

~OR

MODEL

116

OPERATINGINTHe

TRANSFORMER

MODE

Figur~

111-8B. TYPICAL

AMPllrUDE

TRANSFEA

CURVES

FOR

MODEL

1'6

OPERA

riNG

11\1

THE

TRANSfORMER

MODE

111-8

Jan-30-0Z

OS,ZBP

P.OB

o

V>

~

10

o

5

w

u

Z

<l

f-

o»

V>

w

a::

w

u

a::

:::)

o

<n

FREQUENCY

(Hz)

FiglJrlillll·9A.

TYPICAL

NOISE

FIGURf

CONTOURS

FOR

MODEL 119 OPERATING IN THE TRANSFORMER MODE

22 5

FREQUENCY

5

2

In

SOURCE

--

2n

SOURCE:

a

iII.III

•••••

sn

SOURCE - • - •

/

"'\.

wn

SOURCE - - - -

._."

won

SOURCE

.-'-

.

~

......

Yo

• \:

• iii

•••

'"

l--

--::.

t-;y

..

1""

...........

/

-

"""""

--::.

'.

,

•

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/~

.

I

•

•

\

..

/

/

~

.

/

.'

I \

----

..

.,

\

..

"

~

.

"

... -.

-_.'~--_.

---

!

0130

o

~

120

':?

"0

I-

:

100

~

90

~

ao

I-

ro

w

60

"'-

~

~

o

'"

10'

,

Figu,""

111-9B.

TVPICAl

AMPLlTuOe

TRANSFER

CURVES

J=OR

MODEL

119

OPERATING

IN

TH~

TRANSFO,.MER

MODE

Jan-30-0Z

OS,ZBP

P.09

10'

10

3

10~

CENTER FREQUENCY, HZ

10

5

i

/

3OdS/

ZO dB

//

.:

15dB

ioea

:~

Y:

6dS

-:

3dB

Vi;

0j

V;

IdB

I

l

(

,,,-

IdB

,~

~

I"---

3dB

I--

6dB

'~

-----

io

as

1\

~

r---.

15dB

\

I---

ZOdB

I

-.

-.

----

30

dB

•

--

.....

r--

40dB

3

-

10·

10~

1.0

10"

(f)

~

I 103

a

"

UJ
U

Z

<l

t-

10'

(f)
(f)

UJ

0::

w 10

u

a::

::>

a

r.n

Figurlll

III-10.

TYPICAL

NOISE

FIGURe

CONTOURS

FOR

MODEL

118

111·10

Jan-30-02

OS:2BP

P.10

""

'00

,0

10

05

1.0

QIOOQOO

Q" 0.1

DZ

0

"

.....

Q';o\

rlQ=tO-

,

\

I{

,

Q~t

0-'

'lIOftH OUTPUT

,

_.

&IIFl.1 f

lD:

--"

f--

VS_

FRE:OUEI<'1

, r---

~

..

,-

_.

_.

,

._-

1-

,-

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".

-

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f-

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.0>

o

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o

00

.0'

o.

o

o

00

.0

00'

RlI'll;Ifl'l'l!

VOli091f

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'"0

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to ac

0.5 to

O~

0.1 o.a

0

V

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,

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r-,

21--

1---

.•

0='

1111\

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1\

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.,

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--

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'~-i-

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t;

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.0

°

O.

02

00'

c.

o

.00

.0;

OZ

.

oo~

FhtlQfl"lr

VOlfl;lI~.

Gou'!

~

to 20

0.:) I.Q

0.'

_0'

02

.

-,

"

.0"

-.

Q<IOO

~'O

<,

-.

--..

<,

O.?\

Q:IQQ

.

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"'-

--

-

.-

f-

NOfmd~J'Rd

~r~il'leY

=

fD

.0'

0.'

_90of!

-'0

"0

>0

'00

10 20

Q.~

10

O~

0,;

0..2

.

0"

'"-.j>"

\h.

0"0

\

--_.

-

--

_.

".....,..

\

"-

_ f

-,

<,

NorTOliled

rre~1'rlq-1

fll

.00"

-00"

••

0

~igurc

111·,4.

MODEL

124A

BANDPASS

CHARACTERISTICS

Fi~urtllll-15.

MODEL

124A

NOTCH

CHARACTERISHes

'"

100

5

10 lO

o.s 1.0 Z

O~

0.1 o.z

l\

-"'

."

.'

.

.lIPtII••GEI

.

~-~lJ'IO

.

!

1\

0_

;0,

.

.

.

I

.

--

..

I

•

. \

.

i

\

I---

.

•

I

I

•

I

•

•

,-

I

.

/

FR(lNoP·

.;-

.

I'(}R

IoI.lUU

.

'0

.,00'

.O! .oa

'0

0_'

o.z

c. ,

~(LJ,T1VE

0'

VOLTAGE

GAIN

02

0'

00'

00'

~Q

00

.0

ao

0.5

1.0

.05

0.'

o.e

.01.02

....

,,~_

..

-

_.-

--

..

.

I I

I

.

.

•

••+•••

.

Q

~

1

I

~--

O"tO

I

.

--~

Q::

tOO

,

1\

..-

f--

-

,

\

.

-

--

,

I

I--

,

-

--

----

\

.

_

..

,

-\

\

,

_.

",

-

,

.__.

I--

,

2

,

..

_-

..

I--

Nor1molizltd

Ff""'<lVIll~t;;y

=

\

.

to

,

,

,

to

2_0

0.

0.

0.

j::hloti

....

VQltO~1I!

.0

Gain

.0

.0

.00

00

.

00

Flgurl!l 111-16.

MOOEll~4A

LOW

PASS

CHAf-lACTERISTICS

•

Q<loo

>.'fj

"~V

~-,

I

-

..•

~

/

-

I

/

,...-/

/

~ORM"'L1~EO

FR[OUf"tCY~

i;

0"

.01

02

.M

0.1 o.z

O.!lo

I.O:!

~

10

lO

so

IfJO

Figurtlll-17.

MODE L

124AIiIGH PASS

CHARACTERISTICS(

::;Q

tQO

5

'0

20

D~

0.1

0.7

Q~

to

0"

-z»:

11'

'00

-

_.

\}-

-_

..

--_

...

_.-

••

0-

---

....

.-.

_.

--

_.-

"-

--

....

-

-

\

N[Jr~CIi.ll:!dl

Fre~Ulenl;Y

=.

,

-,

'---.J

f.

-

o'

01

.02

+~O"

+'1Z0

1ll

+1~DD

111-12

Jan-30-0Z

OS:Z9P

P.ll

•

•

signal

bandwidths

are

specified

as

the

number

of

HZ"

be

rween

two

pointsofgiVf:;!n

attenuation

on

the

response

ch

aracte

ristic.

Suppose

one

had

a filter

with

a given

signal

bandwidth.

and

some

amountof

wideband

noise.

measured

in

volts/He%,were

applied

to

it.

At

the

outputofthe

filter

one

would

measure

some

amountofnus

noise

voltage.

The

equivalent

noise

bandwidth

of

the

filter is

definedasthe

unattsnuated

bandwidth

ofanequivalent

theoretical

(but

physically

impossible)

perfectlysharp

filter

that.

with

the

same

wide

band

input

noise.

yields

the

same

rms

output

noise

amplitudeasthe

filterofinterest.

On

the

Model 124A, notice from Figures

111-16

and

111-17

that

the

frequency

dial

setting

correspondstothe

last

point

for

which

the

responseisunity.

However,

signal

bandwidth

is ordinarily taken between 3 dB (half-power) points on

the

rollolf characteristic. For the Bandpass mode, 3 dB

bandwidthisobtained

from

the

standard

tonrn

..

ila

forQ(0

• f

o

/M 3dBL

Calculating ENBW (equivalent noise bandwidthI from the 3

dB

bandwidth

is

fr~ql.Jer'ltly

complicated.

However,anexact

conversionisseldom

required.

The

3 dB

bandwidth

and

ENBW

are

of

the

same

order

of

magnitude

with

thn

generally

applicable

(and

sufficiently

accurate)

conversion

factor bei"9 "17.

The

FLAT mode ENBW is simply

the

3

dB

upper

limit

multiplied

by

rr/2.

The

same

appliestoa

close

approximation

for

oper

arioninthe

NOTCH

moue.

In

lOW

PASS operation, the

ENBW

is the

product

of the 3 dB

down

frequency

as detl:1rmined

from

Figure

111-16

times

"1':1-

In HI PASS operation, the ENBW is ,,/2 times

the

squareofthe

upper

limit

dividedbythe

sumofthe

upper

limit frequency and the 3 dB down frequenCY as deter­mined from Figure

111·17_

In BANDPASS

operation,

the

ENBW is

"/2

times flO,

where

f is the selected

tuned

frequency

and

Q is

that

selectedbytheQswitch.

For

all

modes,

bearinmind

thatifthe

sigr'lal

bandwidthislimited

ahead

of the lock-in amplifier, the limited

bandwidth

applies.

In

(;on~iderin9

equivalent

noise

bandwidth.

remember

th(;lt

the

output

meter

is an average reSpOII(ling

meter

calibrated

CO

indicate the rms amplitudeofa sinowzve.

Gaussian

noise,

""'ieh

has0'hos

not

been band-limited by filterin9 in tho

~gnal

and

Output

Channels,

makes

the

rnEWH

indicate

n(2

times

the

actua!

rrns

value.

When

the0,wi'ch

is set to 10% oNBW (bandpass

model.

the

0ofthe

tuned

amplifierisnot

15.7,asindicated

above

but

is

Instead

12_34_

This

lower

a is

necessary

to

compensate

the

noise

response

of

theacvoltmeter

cir-

cuitry_ If

the

voltmeter

were

a

true

rrns

responding

vohrnerar, (her) a Q of

15.7

would

indeed

be

proper,

With

.;In

Jlier(:lge

respondinq

voftrnute r

circuit

such

as is

employed

in

the

Model

124A,

exactly

the

same

ovc rafl

response

is

ob,a;ned with a 0 of 12.34. I"

a"y

case, 10% EN

BW

oPeration

should

prove

suitable

in mOst

applications.

3.21 DYNAMIC RANGE
The TOTAL DYNAMIC RANGE of

a lock-in

amplifier

is

dl:!finecj as

the

quotiem

of

the

maximum

Input

that

can

bl:!

111·13

applied

to

the

input

without

overload

divided

by

the

mtnlmum

disc

crruble

signal

(MDSl.

Total

Dynamic

Ri;lnge

in

turnisdivided

into

two

pans,

each

referenced

to

the

input

signal

required

to

give full-scale

output-

The

quotient

of

the

amount

of

s.ignal

required

for

full-scale

output

divided

by

the

minimum

discemlble

signaliscalled

the

OUTPUT DYNAMIC RANGE. The

quotient

of the maxi-

mum

inpu

t

without

overload

(OVll

dividedbythe

amount

of signal

required

for

full-scale

output

is

called

the

DYNAMIC RESERVE of the lock-in

arnpljfier,

Thus,

TOTAL DYNAMIC RANGE i, ,;mply

the

sum

(logarith-

mic) of the OUTPUT DYNAMIC RANGE and

the

DYNAMIC RESERVE. All three are

important

in

specifv-

ing

the

dynamic

range

characteristicsofa

tock-in

amplifier.

because,

depending

on

where

the

division is

made,

the

.suitabilitv

Of

the

lock-in

amplifier

to

makingaparticular

typeofmeasurement

can vary greatlv_ A

lock-in

amplifier

withaTotal

Dynamic

Fhulge

of

104could

have

that

Total

Dynamic

Ranqe

divided

in seve-at

differ

ant

ways_

For

example,itcould

have

a Dynamic Reserveof10

3

and

an

Output

Dynamic

Range

of 10

1

•

in

which

caseitwould

be

well

suited

to

processing

Vl;!ry noisY s.ignals

but

ill suited

to

processing

small-amplitude

noise-free signals. It

could

have

a

Dynamic

Heserveof10:2

andanOutput

Dynamic

Range

of

10

2

•

in

which

case

it

could

still

process

moderately

noisy

siqnals

and

also

be suitable

for

processing

reasonabtv

small

noise-free

Signals.

Finally,itcould

have a

Dynamic

Reserve

of

10

1

andanOutput

Dynamic

Range

of

10

J

•

in

which

case

its

capability

of

Processinganoisy

signal

would

be

severely

restricted

while

its

ability

to

process

a

small

noise-free

signal

would

be

\/r..ry

good_

Thus,

thl;!'

manner

in

which

Dynamic

Reserve is

traded

for

Output

Dynamic

Range

in a

lock-in

amplifierisone

of thp.

major

factors

involved in

determining

the

suitabilitv of

the

iflHrument

for

making a given measurement.

In.

the

case Of

the

Mod!:!1

124A,

the

operator

has

controlofthe

dyr)arniC

tradeoff

so

that

the

dynamicranqe

char

acteristicsofthe

inst

rumen

t

can

be QPtimizl:!d for

the

type

of

measurementathand.

The-

front-panel

Function

switch

gives

the

operator

the

choice

of

lOW

DRIFT, NORMAL, and HIGH DYNAMIC RANGE

[Reserve)

upcrution.

Each

position

of

the

switch

corre-

spondstoa

different

divisionofthe

Total

Dvrramic

R.ange

into

its

Dynamic

Reserve

and

Output

Dynamic

R~nge

components.

The

Dynamic

Range

characteristics

of

the

Model

124A

are

illustrated

in

Figure

111-18. R(!ferring

to

the

figure,

note

that

two

different

OVL

levels are

indicated.

The

first

of

these,

the

PSD

OVL

level.

defines

where

the

Phase

Sensitive

Detector

overloads

relative to a full-scale

input

signal. It is

this

overload

l~vel

that

de te rrnincs

the

maximum

tolerable

input

signal

when

the

InstrumentisoperatedInthe

FLAT

mode.

Whlm

the

instrurnanrisnot

being

operated

in

the

Flat

mode,

then

the

maximum

tolerable

inputisextended

to the PRE-PSD OVL for

';9nal,

not

in the passband of

the
eharacteri,tic selected (BANDPASS, NOTCH. HI PASS, LO
PASSI. Note

that

the

PSD DYNAMIC RANGE of the

instrument

is

10

6

r~gardl~ss

of

the

selected

dynamic

tradeoff. Depending on

th.

tradeoff selected, the PSD

DYNAMIC RESERVE

varies from 10' to 10] and the

OUTPUT DYNAMIC RANGE vartes from

10]

to

10'.

The

TOTAL DYNAMIC RANGE

is

10'

for

LO

DRIFT

and

NORMAL

operation and

10'

for HIGH DYNAMIC

Jan-30-02

05:30P

P.12

0"

-I

10

10-.4

10

'

-$

'0

PRE F$O OVL

Ove

LD

DRIFT

"

PRf~

PSD

-

-----

--

,

4

pAE~

PSO OVl

I

'"

u'"

...

:>

...

~:>

"SD

DVe

.

",

3

1--

..

z",

-----

--~

~-

0(::1(1;:

1-,.",

1-"'"

0"",

~ZW

"z'"

I-

"'

>-,..'"

'"

,..",

c",

e°ll:t:

:<:

?I------

PSD

DVl

a::

~

;i

ozll'i

,..

..,;

",,..,,,

<:>

z

..

,,'"

--'

I

PSD

OVL

a::

~

J~

C1Z~

g

",,..,,,

Z

d

"cO:

,..

...

'"

'"

0

..

.,,"'

z

rou,

0::

--'

I

SCALE

Z

<{

5

...

a

--'

t-

.~

<{

>-

t-

iC",,.;

0

>-,..",

...

..

=>c",

iC",,,

0

..

>-,.z

=>,,",

..

0

ii'",,,

>-,.z

.;;),,"'

;~

~---

1-

~--

I-

"OS

----

~~--

HIGH

DYN.

RESERVE

~-

---

"OS

---------

---

-

NORMAL

$

MOS

-----

-~-~--

~---

,0"

'0

'0

10

10

10

10

10

10

10

Figut8111-,8.

OYNAMIC

RANGE

CHARACTERISTICS

OF

THE:

MODEL

124A

RANGE

(Reserve)

operation.

In

applications

where the

PSD

OVL

level is

exceeded,

the

appropriate

pre-1

3SD

passband

limiting is usedtoreduce

the

noise

below

the

P~D

OVL level 50

that

the

measurement

can be

made,

Use of the

Bandpass,

Notch,

Lo-Pass and Hi-Pass characturisrics in this

manner

does.

not

improve

the

overall

achievable

improve-

ment

in

sfqnal-to-noisc

ratio.

butitdoes

achieve

a real

improvement

in

Dynamic

Reserve,

and

hence

in

Total

DYnamic

!lange.

In

FLAT

mode

operation,

the

PSD

DYNAMIC

RANGE

""d

tho

TOTAL

OYNAMIC

RANGE

are

the

same.

It

shouldbenoted

that

the

Dynamic

R<lnye

characteristics

showninFigure

111-18

are

maximums,

not

applicable

for all

positions

of

the

Sensitivirv

switch.InLO

DRIFT

operation,

maximum

Total

Dynamic

Range

IS

attained

with

the

Sensitivity

switch

setto1

!,J,V"

Below1IlV

the

Model

124A

au

romaticnllv

transferstoNORMAL

operationasdescribed

on

paqe

111·15.

In

NORMAL

and HIGH

DYNAMIC

HANGE

(Reserve)

operation.

maximum

Total

Dv narruc

Range

is

attained

with

the

Sensitivity

switch

setto100

nV.

For

all

three

Dynamic

Trcdecft

poss·ibilities, as

the

Se nsi-

tivitv

switch

is

set

"to succnssivelv "lower

sensitivities,

the

Iota!

Dynamic

Range

available is

proportionally

reduced.

Situations

could

arise

where

the

signaltobe

measured

was

of

relatively

high

ampfi

tude,

and

accompanied

by

enough

noise

and

interferencetorequire

that

the

lock-in

amplitiar

have

a 'very

wide

Total

Dynamic

RClI)ge_

Where

thisisthe

case.

attenuato.s

canbeused

aheadofthe

lock-in

amplifier

to

reduce

the

signal

plus

Interference

~uffiCiently

to

take

advantage

of

th(!

inherently

wide

Total

Dynamic

Rrlng(!o

of

the Model 124A. It is almost ;nconceiv"[)le that a r..I

measurement

problem

could

exist

that

would

require

all

of

the

Total

Dynamic

Range

available wi th

this

iostrurncrn.

for

a

more

detailed

oucussioo

of

Dynarnrc

Hilllgt:!,

the

readerisrufarred

to

the

Appendix

at

the

rear

of

the

manuat.

111·14

Jan-30-02

OS:31P

3.2J DYNAMIC OVER·RIDE

Although

thi:!

trent-pane!

FUNCTION

switch

allow') {he

'era

tor[0select LO

DRIFT,

NORMAL, or HI DYNAMIC

\NGE

{Heservc)

operatum.it15

impor

ran ttounders

tand

that

the

instrument

does

not

necess

arilv

operate

with

the

dynamic

tradeoff

selscted.For

certain

positions

of

the

Sensitivity

switch,

there

i~

an

"over-ride"

CIt-lion

that

determines

the

dynamic: rrude

off

independent

of

the

settinq

of

the

Function

switch.

and

it

;50

the

true

or

operating

dvnarnic tradeoff that determines the overload and stability

characteristics.ofthe

instrument.

Thus.

in

u~ing

the

tables.

that

define

the

Overload

and

Output

Stability

character-

istics of

the

Model

124A,

the

ooeratcr

must

always

take

care to read

the

data

from

the

column

correspondingtothe

true

dynamic

tradeoff.

which

may

differ

from

that

selected

with

the

Function

switch.

The:

dynamic

tradeoff

obtained

as a

function

(If

the

settingofthe

Function

and

Sensitivity

switches

is as follows.

3.2K OVERLOAD

DependingOnthe

natureofthe

inout

signal

plus

noise,

and

on

the

controlsettlnqs.

overload

call

occur

at

several

different

p()irHs in

the

ins

trurne

nt.

All

of

(he

critical

points

are

monitored

so

that

an

overfeed

anywhere

in

the

instrument will

operate

the OVERLOAD light, From an

operator's

point

of

v;t1:W,

the

problem

with

regard

to

overloadisnot

one

of

determining

whether

overload

is

taking

place

(the

Overload

indicator

light

performs

this

function

automatically).

but

rather

of

determining

the

proper

action

to

take

to

eliminate

the

overload.

The

appropriate

remedial

action

in

turn

dr:::peI1ds.

on

wherp.

the

instrument

is

overload

ir~9.

Each

overload

"type"

IS

con-

sideredinthe

fcllowinq

paragraphs,

III

DC Amplifier Overload

P.13

LO

DRIFT

AND ACVM: The unit operates in LQ DRIFT

except

when

the

Sensi tivirv

switch

is

s.~t

to

100

nv,

200

nV,

or

500

nV.

For

those

positions.

the

unit

opera-tes in

the

NORMAL

mode

and

the

NORMAL

mode

drift

and

no ise toter

ance

specifications

apply.

If

the FUNCTION

switch

is

set

to;

Then:

Overload

of

the

de

amplifiers

is.

the

easiest

type

of

overload

to

identify

and

detect.

Such

ov@rload is

usually

the

resultofthe

signal

amplitude

(independent

of noise)

b~1in9

too

large for

the

selected

sensitivity.

When

th is is the

case,

the

panel

meter

indication

exceeds

full scale and

the

Overload

light

turns

on.

The

solution

is simply to

select

a sensitivttv

setting

which

yieldsanon-scale

lndjcafion.

NORMAL:

The

unit

operates io NORMAL with Sensitivity

switchsettinqs

of

100

nV

through

50

mV.

With

settings

of

100

rnV

through

500

mVittransferstoLO

DRIFT.

HI:

Thj-!

unit

operates

in HI

with

Sensitivltv

switch

settings.

of

100

nV through 5 mV. With settiogs of 10 mV

throuqh

50

rnv,

it

~ramfNS

to

NORMAL,

and

with

setting,

of 100 nlV through

500

mV, it transfers to

LO

DRIFT.

Generallv

speaking,

one

should

operate

with

the

switch

set

to

LO DR IFT

to

take

advantage of

the

excellent

output

stability

obtained

with this setting (see Table 111.1).

However. if

the

noise level of

the

signal

is.

high

er'lQugh

to

overload

the

demodulator

0)

explained

in

the

following

paraqraphs ,

one

can oper

ats

in

either

NORMAL or' HI, in

which the- noise toler-ance is incraasad

hy

LI factor

of

10 or

100

respectively

tl:t

the

expense of

degraded

output

stability.

DYNAMIC

OUTPUT

RMS OUTPUT

TRADEOFF

STABILITY NOISE VOL TAGE

LOW

DRIFT

15

p~m/'C

10 ppm/Hz%-

,

NORMAL

100

,om/'C

100

ppm/H/h

HI

1000.=/·C

1000 ppm/Hz'!,

lable

111-'_

STABllI-ry

A."O

OUTPUT

NOISEASA

FUNCTIONofOPERAT'''G

DYNAMIC

TRAOEOFF

DC Amplifier overload can also be produced by a
high·amplitude

quadrature

,ignal

component,

or by

high

amplitude

spikes

and

other

noise

which

may

be

reaching

the

Output

Amplifier

(the

latterispar

ticu

tartv

true

when

operatinginthe

Flat

model.

The

jest

and

solution

is

sim~)lv

to

increase

the

Time

Constan

t

settinq.

Except

when

operating

with

extremely

nolsv

signals.<1time

cons

t

ant

of

one

second

should

suffice

to

eliminate

quadr

arure

arid transi crtt

overload

of

the

de

ampli

tiers.

12)

Demodulator Overloar1

Overload

at

the

demodulator

is also

easily

detected;

one

has

only

to

monitor

thp. signal

at

the

Signal

Monitor

connector

withanoscilloscope.Ifthe

siqnal

exceeds 1.5 V pk.

the

demodulatorisoverloading.

If

the

signi;11

is less

than

1.!;i

V pk , it is

not.

There

are several

possible

courses

of

action

when

faced

with

Mixer

tdemoduletor]

overload.

First,

one

iSI]wiSlys

has

the

option

of

operating

the

instrument

with

less

sensirivirv

Second,

operating

withanarrower

band-

width

ahead

of

the

Mixer

may

prOVE:!

helpful.Ifthe

instrumanrisbeing

operated

in

the

Flat

mode.

and

operationinthe

LOW-PASS,

HIGH-PASS.

or,

better

yet,

the

BANDPASS

modeispossible.aconsiderable

reductioninnoiseatthe

inputtothe

Mixer

may

b~

achieved

by

lY'I~king

the

transfer.Ifthe

instrument

is

operatinginbandpasstobegin

with,

lncrea$'.ing

the

a

will

further

decrease

the

bendwidth.

If

the

inter-

ference is

at

a sirlgle

frequency

removed

from

the

signal

trequencv,

operatinginthe

Notch

mode

with

the

signal

channel

tunedtothe

inrcrterence

frequency

may

provetobe

the

beat

solution.

111-15

Jan-30-02

05:32P

This third choice is to make a

different

tradeoff

of

dynamic reserve for output dynamic range, If the

instrument is already operating

with

the Function

switch

set to

HI,

no

Improvement

by this means is

possible. If, however, it is operating with the switch

set

to

NORMAL.

a factor of ten reduction in the

Mixer input signal amplitude can be obtained simply

by

setting

the

Function

switchtoHI. If the

Function

switch ls set to 1.0 0

RIFT,afactor

of

100

reduction

in

Mixer

inpu

t $ignal amplitude is possible, the first

factoroften by setting the switchtoNORMAl

•• the

second by settinq it to

HI.

In other words, in choosinq

the position for this switch. be

sure

to take

th~

Mixer

overload considerations

into

account

as

W(!11asoutput

drift

requirements.

Also, one

should

be aware

of

the

dynamic

over-r ids transfers that

take

place

for certain

positions

of

th~

Scnsjtivitv

switchasexplained

earlier.

Note

that

the

Function

switch

gives a simple

"test"

for Mixer

overloadaswell,

which,

though

not

as

definitive

as monitori

ng

the

signal at

the

Signal

Monitor

jack, may still prove

useful.Ifthe

Function

switchisset

to

LO

DRIFT,

and

the

Overload light is

on, and setting

the

Function

switchtoNO

RMAL

or

HI

causes

the

Overload

light

to go

out.

the problem is

obviousfv

one

of

Mixer overload. Similar lv, if

the

switch

is sc t 10

NORMAL

(Overload Indicator

onl.

and

sl;;!tting

it to HI

causes

it togoout,

the

same

is

true.Itdoes

nut

necessarilv

follow

that

failureofthe

P.14

lighttoextinguish

whan

making

this

test

means

the

Mixer is not

overloading.

It

may

prove usefultoknow

the

maximum

rmS input

sinewave signal

that

can be applied to

the

inputofthe

instrument without

overloading

the

Mixer

as a tunc-

tionofthe

Sensitivity

and

Operating

Dynamic

Trada-

off.

The

input overload limits for

both

the

mixer

and

the

tuned

amplifier are

shown

in

Table

111-2.

By

referring to this

table,

the

operator

can qUickly

determine

the best way

to

process

a given signal

with

the Model 124A. Fur exampta. suppose one had a

signal

of

nominally1J1V

amplitude.

Consider

the

possibilities for

measuring

this Signal

given

different

noise levels. From

Tablu

111-2.

the

mixer

limit

with

a

Sensitivity

settingofone

microvolt

is 1.10

mV,

110

JiV. or 11 iJ,V,

according

to

the

dynamic

tr ade off.

What

this

means

practically

is

that

for

noise

levels

below

11

J1.V.

the

signal

could

be measured' in

the

FLAT

mode

with

the

Function

switch set to LO

DRIFT

(Normal and Hi operation is,ofcourse, also

possible].

If

the

noise

level is greater than 11 /-lV,

but

less

than 110

!'V.

LO

DRIFT

operation in tho

Fl.AT

modeisnot

possible

and

the

operator

will have to

uithar operate in

NORMAl.

(or

Hil

or

narrow

the

noise

bandwidth

ahead

of

"the

Mixer by

meansofthe

tuned

ampli

lier

. This is usually

best

accornpttshcd

by

operannq

in BANDPASS. By

sufficient

narrowing

of

the pro demodulator

bandwidth.LODRIFT

operation

MAXIMUM

RMS

SIGNAL

INPUT

MIXER

LIMITS

TUNE;D AMP.

LIMITS

SENS.

H.D.R. N

L.D.

H.D.R.

N

L.D.

100

nV

110/lV

11

!'V

e-

19.6mV

19.6

-e-

200

nV

254

!'V

25!'V

....

....

!i00

nV

635

!'V

63!'V

•

"

....

l/lV

1.10

mV

110/lV

11

/lV

19.6

r"V

2!'V

2.54

mV

254/lV

25J.1V

5/lV

6.35

mV

635!'V

63/lV

10/lV

11.0

mV

1.1OmV

110

/lV

20

!'V

19.3

mV

2.54

mV

254/lV

50/lV

6.35

mV

635/lV

100

!'V

110mV

11.0

mV

1.10

r"V

196mV

"

200/lV

193mV

19.3

mV

2.54

mV

500/lV

6.35

mV

1

mV

720mV

110

mV

11.0

mV

720mV

196

mV

2mV

193

mV

19.3mV

5mV

10

mV

.,

720mV

110

mV

~

720mV

196

mV

20mV

-+

193mV

-+

196

mV

50mV

• 196

mV

100mV

-+ -+

720mV

-+

120mV

700mV

-+ -+

....

720mV

500

mV

...

...

-+

720mV

I

l'<'Ible

111·2.

MAXIMUM

RMS

INPUT

lEVELS

FOR

MiXeR

AND

TIJNEDAlVlpl.lfll'R

OVI::RU)Ao

AS A

FUNCTION

OFSENSITIVJTV

ANO

OPERATING

DYNAMIC

RANGE

111-16

Jan-30-0Z

OS:34P

P.1S

•

mev

$till

be

possible

evan

with

the

higher

Input

noise

level, If

the

noise

exceeds

110

J.1V,

but

is less

than

1.10

mV.

FLAT

mode

operationisonly

possible

with

the

Function

switch

set

to

HI.

although

NORMAL,

or,

coneaivaulv,

even

LO

DRIFT

operation

may

still be

Possible

by

sufflcientlv

narrowinq

the

bandwidth

ahead

of

the

Mixer.Ifthe

Norse

level

exceeds

1.10

mV,

then

FLAT

mode

oper

aticn

becomes

impossible

and

the

operator

must

narrow

Ihe

bandwidth

ahead

of

the

Mixer.

Flnallv,ifthe

input

noise

exceeds

19,6

rnv

rms,

the

Selective-

Amplifier

overloads

and

the

signal

cannot

be

measured

with

the

Model

124A.

The

onlv

possibilitiesinthat

case

aretonarrow

the

bandwidth

aheadofthe

lock-in

amplifier,

ortoattenuate

ahead

of

the

lock-in

arnplifiar,

whichever

ranhnique

most

conveniently

reduces:

the

input

noise

below

the

1

!l6

mV

limit,

far

from

suchapoint.

the

likelihoodofimproving

the

situation

in

this

matter

becomes

remote.

For

example.

suppose

one

had

a 1 pV signal

accompanied

bv40mV

of

noise.

The

nearest

ser~sitivity

position

that

could

be

used

without

overloadina

tho

Tvned

Amplifieris100

/lV,

where

the

signal

wouldbeonly

1%offull scale.

Given

the

high

noise

level,itwouldbevery

difficult

to

detect

a 1%offuusca!e

signal,

even

jf a

very

lonq

time

constant

were used,

At no

time

can

the

input

exceed

720

mV

rms

without

overloading

the

instrument.

With

larg~

input

signals,

thi$

fimit

pre

....

cn ts

one

from

processlnq

very

noisy

signals.

However,

by

inserting

an

attenuator

ahead

of

the

lock-In

amplifier,

large

amplitude

signals

having

poor

signal-to-noise

ratios

can

be

measured.

AS a

general

rule,

it is

most

desirable

to

oper

ate

in LO

DR 1FT

and

with

the

bandwidth

.h~.d

of

the

Mixer

at

maximum

(FLAT).

If

the

noise

levels are

such

as

to

force

tradeof

ts,

the

operator

must

decide

which

is

better

to

giveupfifst,

output

drihora

flat

pre.mixer

response,

according

to

his

individual

requirements.

Where

the

noise

level is

extremely

high,

thereisno

choice

buttogiveupboth.

One

waytoapproach

the

problemisto:

3.2L

OFFSET

DUE

TO

NOISE

Becauseofimperfections

in

the

Phase

Sensitive

Dli!t/;1!ctor,

large

input

noise

levels

can

cause

offsetstoappearatthe

output.

Ar:.

shown

in Figure 111,'9, these

offsets

are

g12r"1erally

so small as

to

be

ncqliqible.

Even

with

the

extremely

high

1000

times

full scare

noise

levels

which

can

be

processedinhigh

dynamic

reserve

operation,

the

offset

is

typically

only

1

%_

I

,

,

,

,

/

I J

,

f--f-I

p/

i)-

"

~P"

~l~-

...

~\"

\}"~

[pY

,

;V~

~

,

o

o

.0

0-

~

0-

:::>

o

'"

--'

...

u

'"

j

--'

:>

"­"-

o

~

~

00

...

~

.00

"-

u,

o _00

(0)

Set

the

controls

as

determined

in

"b"

and

attempt

the

measurement.

Some

exp!!'r'ir'rleM~tjon

may

be

required

to

achieve

the

optimum

control

settings.

(3) Set

the

Function

switch

to ACVMtogetanide.

of

the

signal

plus

noise

rms

amplitude.

(b)

Based

on

an

estimate

of

tt1"!!

$ig'\~l

ampfitude,

determine

the

best

combination

of

operating

dynamic

range

and

pre-detector

bar"ldwidth

con-

trol

from

table

111-2_

Be

sure

the

Sensitivity

sening

COr"l~it;lered

is

that

appropriate

to

the

expected

signal level.

ForanOiSY

signal,

the

Sensitivity

setting

will be

very

much

different

from

that

usedinthe

preceding

step.

where

one

was

measuring

the

signal

plus

noise,

•

('II

Pre-Mixer

Overload

10

10

~J.4S

NONCOHERENT

,~pu'r

SIGNAL

RELATIVE

TO

FULL SCALE

,

Circuits

aheadofthe

Mixer

only

overload

when

the

input

level

exceeds

the

Tuned

I\mplifi~r

Limi ts

ind!

catedinTable

111-2. In

any

case,

thereisrelatively

little

on"

car

doatthe

Modal

124Ainthe

case

of

pte-mixer

overtoad.

The

only

action

th at

might

help

is

to

reduce

the

sensitivity,

for

example,

suppose

one

wished

to

measure

a

500

j.J.V

sign<ll

accompanied

tN

400

mVofnoise.

From

Table

111-2

it is

clear

that

the

Tuned

Amplifier

would

overloadifthe

ma asur

ament

were

attempted

on

the

500

J.1.V

sensitivity

range.

However,

by

setting

the

Ser1sitivity

switch

to 1

mV,

the

overload

tolerance

is increasedto720

mY,

and

the

me

asuremant

can

be

made,

This

techniqueismost

useful

when

oneisnearanoverload

tolerance

cross-

over

point.

as in

the

example

just

given_

Should

one

be

._~-

_.

- ..

_._

...

_----------'

Fi~urlJ

111-19,

TYPICAL

OUTPUT

OFFSt:l

AS A

fUNCTION

OF

INPUT

NOISE

3_2M

OVERLOAD

RECOVERY

The

frequency

r

anqe

of

the

Signal

Channel.

axcf

udinq

the

Preamplifier

rarlg~.

is 2 Hz to

210

kHl

011

the

standard

models.

Dr

200

mHz

to

210

kHz

if

requested

upon

ordering.

Unless

very

low

frequcncv

response

is really

needed.

we

advise

that

units

notbeordered

With

200

ml-lz

response

because

larger

coupling

capacitors

make

recovery

time

from

overload

much

longer

than

for

units

with

2 Hz

response.

Typical

maximum

overload

recovery

time

for

units.

having

2H2LF

responseis30

sl:"!(:(Jnd:!:,

for

200

mHz

units,80seconds.

111-17

Jan-30-02

OS:34P

P.16

1'0

0

\

e

u

~

"".

:;

..

..

.

~

0

....

"

..

..

~

..

-od!

..

...

"

..

...

•

"

-leo

XI

-0.004

-0.003

"0.002:

-O.(()I

0 0.001

0._

O.OO!

0.004

~

"0

-0

.•

-0.:11

-0.2

- OJ

0

0.1

0.'

O.!

0.'

...

"'

...

"'''

0

'0

!O

'0

..

'"

XIOO

-00

-'0

-'0

-10

Z<>

%

..

U"

.....

XI.

-0'

...

-20

-"

0

"

20

!.

o.

uu

.".

.....

""

.....

)1;1011

-17'11

~1:5Z11.

-t

...

-

...

0

00'

1Ia.

1!20

17ill:

.....

...

'"

SYNC.

$IGNA.l,.

SLEWI""

'UTE.

H~

/

S[COND

"

..

Fiijuu!lIII·20.

rVPICAll'lEFERENCE

OSCILLATOR

SLEWING

RATE

,

3.2N

SIGNAL

MONITOR

fhe

output

of

the

Signal

Channel

goestothe

Synchronous

Detector

and

to

the

Signal

Monitor

jack.

The

Signal

Monitor

output

is useful

for

monitoring

the signal

after

Signal Channel

filtering;

the

operator

can thereby

improve

his

ideaofhow

much

noi5lJ' is

present

aheadofthe

Mixer.

In

addition.

this

output

makes

the

Model

124A

usable

as a

straightforward

Low

Notse

Tuned

Amplifier,

which

can

find

many

applications.

Notice

from

the

Functional

Block

Diagram

(Figure

111-')

that

the

signal

from

the

Signal

Channel

is

attenuated

bl:!fore

being

appliedtothe

Signal

Monitor

[ack,

This

is

because

the

amplification

in

the

Signal

Channel

is SUd1 as

to

make

the

overcqe-r

espondinq

meter

at

th~

[)~tet.tM

output

indicate

the

rms

valuecfthe

detected

signal.

Theatrenuatoratthe

Signal

Moniter

jack

sets

the

signal

toamore

convenient

level.

The

Signal

Monitor

output

impedance

is fiOa

ohms.

Ihe

output

siqnal

ampfit

ude

corresponding

to

a

full

scale

input

depends

on

the

dynamic

range.InLO

DRIFT,afull·scale

input

vields

100

mV

rrns

out

(sinewava

in;

ainewave

out).

In

NORMAL.

a full-scale

input

yields 10

mV

out,

and in HI

DYNAM

Ie

RANGEafuflacale

input

yields

1

mV

rrns

out.

These

figures

depend

on

the

"true"

operating

dynamic

ranqe,

which.asexplained

earlier.

eccordlnqtothe

selected

sensitivity.

carl

differ

from

the

dynamic

range

SI.,deCt!:d

with

the

Function

switch.

3.3 REFERENCE

CHANNEL

OPERATION

3.3A

SYNC

INPUT/OUTPUT

In

the

Fxte

rnal

Sync

mode.

,1""Ie

Heference-Cn

anne!

veo

au

tornn

ticallv

pIHI$C·lochtoany

kindofreference

wave-

form

at a freqlJl}rH;y

within

the

two

decades

listedinTable

111-3.

the

only

requirements

being

that

the

waveform

cross

its

mean

exactly

twice

each

cycle,

thatithave

a pe ak-

to-peak

amplitude

of

at

least

100

mV,

and

that

it be

synchronized

with

the

signalofinterest.

The

positive-going

zero

crossing

of

the

zero

reference

phase

of

the

VCO

sinewave is

coincident

with

the

positive-going

zero

crossing

of

the

sync

input

waveform.

The

VCO

canbemadetolock

to

the

second

harmonic

of

the

reference

signalbyplacins

the

Mode

switchinthe

Gxt.

f/2

posjtion,

Maximum

svnc

input

frequency

in 1/2 is 105 k Hz,

Sync

input

R = 1

meqobrn.

A

Reference

Unlock

panel

indicator

lightS

when

the

veo

is

outofsync

with

the

reference

signaL

Often,

the

Ir

cquancv

of

the

signal

being

detected

is

changing.

As

long

as

the

reference

maintains

a

fixed

freq~Jency

and

phase

relationship

to

the signal,

detection

is

no

different

than

for

tixed-Iraquencv

signals.

HOWI;!Vf!r,

it is

necessary

that

the

frequency

does

not

changesofast

that

the

oscillator

cannot

st<lY

locked

in.

Figure

111-20 provides.

slewinq

rate

information

for

the

oscillator,

Becausecfthe

rapidityofthe

External

Reference

circuitry

response

time,

some

care

mustbetakentoassure

rhu t

there

are

no

"extra"

mean

Crc,lssings in

the

applied

reference

signal.Ifextra

crossings

should

occur,

the

Model

174A

will

see

them

as

!JLJr~ls

of

some

higher

reference

fl'equerlcy,

which

the

Reference

Channel

will

attempt

to

follow.

c:au!5ing

phase-lock

loss

and

improper

drivetothe

dcmodu-

latcr,There

are

three

common

Wi:lYsinwhich

problems.

of

this

nature

occur.first,

any

noise

accornpanvinq

the

signal

can

cause

multiple

mean-crossingstooccur

in the!

rj~gion

of

the

rise

and

fallofthe

reference

signal.

Thus

the

reference

signal

appfied

must

tit' retativcfv

clean.

Frcquentl

v,

moder

atetv

noisy

signals

can

be c:1f!J,neo

up

';1,Jfficientlv

fur

satisf

actorv

operation

by

lJ~ing

a

simple

ainqlc.section

111-18

Jan-30-02

OS,3SP

P.17

.

err.

n;~.....

n

~",:

j I ;.

.c;T~.~._

;.

r----~.~.

~

••.

I) -4

t-.~'.':·'J

t , ..

f-----....:---

,-+

t~lJ

..-

o 2

,===:;::::

-;~

........

,

..

" ,

..

..----

c

"

fTI·

_":

II·

~

._~

." .

·..,.HI

..

,-,

..

..

~

.o o

-t=

.

--'-----.-

--,

~

,

..

~

• -.-+-•..

~

'00

D._

'0

.-'--

!

r;dl!l

'00

:::t

..-

.:

.:..::

."

"1

...

'DO

6

dB/Oct.

An'lPlilLlde

Transfer

12 dB/Oc{,

Amplitude

Transfer

..

0'"

.-

'-

-

f

[\

-

'--

f-.-

r--.

..

'0

-,-

I

...

,

D.'

-

_.

-

f-

-

.

\

0

0

.•

1-

•.

0

01--

-

''''
"
"

0,01

'"

'"

.0

so

.0

'0

o

.0

;

'0

...

100

.

~

IIQ

~"

"

'

..

""

reo

'0

'.0

,

'".

0_'

o

'0

'0

"

6

dB/Oct.

Phase

rr~lIu,h:(

12'

dB/Oct.

Phil$1II:

Transfer

I.=.

20

.n

s.o

,.~

(~

...

~b

Trl,&£,

IN Tlt.t[

~~IAtH:S

IN x

HI

1.0

..

_~.

--

·1-

1....-

.-

.-

J.-'-

0

1/,_(

I"T

'/

Telt-

In c

-

/'

--_..

0

_.

'-

--".-

-/

f----

.... --

0

:/

Q

.-

.0'_'".,.

./

--

.-

• •

, 0

"

reo

..

.,

!

I

..

1 '

~

40

'"

'.0

..

,

"

I,~

20

l"

~(1

[lJ.II''H1;I

rllll{

."1

TIIII(

CON!iT.I.IoI~

(N.

TC)

0.0.so

...'.'.'

...

-

J

4

0

--:;;

I_.-'/rt

'--

1-

..

"/

0

...

II

.

I--

0

--

--

,.-

-.-

0

I

0

17

_.".,_

..

1--

0

-_

..

..

_-

..

--=:J

~

L,--

100

..

".

•

< ,

~

6

dti/Oct.

Smp-Funcrion

Response

Figure

111-22.

OUTPUT

Fil

TER

TRANSFER

FUNCTIONS

111·20

•

•

,

Jan-30-02

OS,36P

NOTF.:

When

operating

the

Siqnal

Ch~r1nel

in

the

Bandpass

mode.

particularly

with

high

0,

the tre

quencv

dials

must

also be

finc.udjus

ted

for

pe ak

meter

readinq.

Otherwise.

the

filter

rotloff

will

attenuate

the

signal

and

also

causeaphase

error.

In

al!

circurns

tances.attenuation

and

phase

shift

in

the Siqnal

Channel

mustbeminimized

or

aC::i;(~unted

for.

3.4

OUTPUT

CHANNEL

OPERATION

3.4A

FILTER

TIME

CONSTANT

The

amplified

and

filter~d

sign.al is

synchronously

d~;t€!c:ted

with

respect

to

the

phase-shifted

Reference-Channet

siqnal,

and

the

detected

signal is

appliedtothe

RC low'pass filter,

Eitheraone

section

or a

two

section

filter

maybeselected

with

the

center

knob

of

ttl!:!

Time

Constant

switch.

The

one

section

filter

has

a 6

dB/octav~

roll

off

character.

istic

and

an

equivalent

noise

bandwidth

of

1/4TC.

The

3

dB-down

point

011 the trequeocv axis is 1/2rrlC. In the

time

domain.

it has a

step-function

response

of

l_e-

t/l C

,

The rise

time

from

10% of full

amplitude

to

90%

of full

amplitude

is

2,2TC

seconds, and

from

0to95% is

3TC

seconds. With

the

TC switch

setto300

s, the equivalent

noise

bandwidth

is;::

800

pH2.

The

two

section

filter

hJS a 17nazoctave

rulloffcbarecter-

istic and equivalent

noise

bandwidth

of I/B'I'C.

Th~

6

dB·down

point

on

the

frequencv

axis is

1I2";'1"TC.

In

the

time

domain,

it has. a

step-function

response

of

1 - \ 1 + t{TCI"

-tITC

The rise

time

From 10% of full

amplitude

to 90% of full

amplitudeis3.3TC

seconds,

and

from0to

95% is

4.8TC

seconds.

If

the

operator

requiresalime

constant

gn~atc(

than

300

seconds.h~carl

place

the

Time

Constant

switchinthe

Ext.

pos.uoo

end

connect

a

pair

of

caoacitorsofequal

value

between

pins

8-9

and

1011

of

the

rear-pane!

octal

SOCkIH,

To

determine

the

time

con

stan

t

for

this

external

mode,

mul

tiplv

the

sinqle

capacitor

varus

(in

Far'ads) by

30

megohms.

The

external

cap

acitorsshould

be low-Ieakaqe

film

r

vpcs

[mvlar,polv

car

bonate

,

polvstv

renc,

teflon)

rated

at 25 Vorhiqher.

The

Time

Const

ant

shouldbesetsothat

the-

output

noise.

either

as

read

on

the

panel

meter

or on

the

external

rnonitor

, is

reduced

to

an

accep

rab!e level.Ifthe

signal

arnphtude

is

steadv

(ind~)pj~!1dellt

of

noise),

a fairly

long

time

constant

carl be

used

bec:;)u~i7!

th~

lag

timeinsetting

the

chase

c.:ontrl.lh can

usuallybetolerated.

However.ifthe

signal

vurics

OVe(

n

periodoftimu,

and

the

operator

wants

to

ohserve

the

variations,ashor

te r

time

constant

must

be

used at

the

expense

of

qrcater

noise.

Sometimes.

for

the

latter

case.

the

Signal

Channel

fil

ter

can

be readjllSted for

less

noise

<:ihcr

operating

pi:lrarnCtefS

<ire

better

I-!stablished.

WhE;Orl

operating

the

instrument

<:IS

a widl?bar)(J ae

voltmeter

(by

PJacing

the

functIon

switch

ir!

the

ACVM

position),

the

Time

Constant

switch

shouldu~'$oettodi1mpen

the

meter.

111-21

P.18

3.4B OFFSET CONTROLS

The

ten-turn

dial

and

its

associated

puluritv

switch

alto'

v

calibrated

ottsetsofuptoten

ttme

s

f~JII

scale to be

applied.

Two

applications

for

this

fe

ature

arc mar it

allows

small

amplitude

variations

in a signal to be

expanded

and

examined

in

detail.

and

thatitallows

a $ignal

amplitude

to

be

read

with

greater

resofution

than

is

possible

with

the

panel

meter

alone.

Forexampte,

suppose

one

had

a

I1HHN

indication

to

the

right.

To

read

the

amplitude

with

the

qreatest possible

rcsotution.

the

polnritv

switch

would

be

set

to

If,,"

and

the

dial

adjusted

for

"null"atwhich

tirne

the

sigrl{ll

amplitu

de

couldberead

directly

hom

the

dial.

The

followinq e-xi1mple

illustrates

me

of

the

Zero

Suppress

feature

to"cxpand

' signal

amplitude

variations.

SUPIlOSC

one

had

a 70 JiV signal.

Assunnnq

this

signal

were

me asur ed

on

the

100

/J.V

'sensitivityranqe,

the

resulting

rncte r

indication

would

be

70%

of full scale.

To

examine

5111

a

ll

variatinns

in

this

signal.

one

would

first

s~t

the

pclantv

switch

to

".j."'

(assume

initial

meter

indication

was to

the

right),

followed

by adjusting the dial for

moll.

Tho dial

setting

requirud

would

be 0.70

and

the

meter

sensitivity

would

be ±

100

fJV

wirh

respecttothe

70

J..1V

ambient

level.

A

recorder

cormcc

tcd

to

the

output

would

allow

the

amplitude

vanations

(I~

a

function

of

some

experlrnentsl

nararnetertobe

recorded.

Because

theranqeofthe

Offset

dial

extendstoten

timc s

full

scate.

the

me

asurementcan

be mo

dified

slightly

so

that

the

amplitude

Variations

are

greatly

expanded.

In

the

exampleatband,

the

Sensitivity

switch

could be

set

to 10

IJ.V_

Because

the

siqnal

amplitude,

70

J..1V,

is less

than

ten

times

the

selected

senstttvttv

(10

x 10

IlV

= 100 /-lVI. it

is.

within

rangeofthe

offset

dial.Ifthe

diu!

werE:!

adjus

ted

for

null

(s~Hting

of

7_00),

the

me re r ranqe

would

then

be

±10

j.1V

full scale

with

respect

to the 70 I1V

ambiant

siqnal

levfo!l,

3.5

HARMONIC

RESPONSE

The

Synchronous

Dctcctnr

responds

to signals

which

are

harrnonicattv

related

to,

and

svncbroniaed

with,

the

fun-

damental.

Thl:!

harmUrli[;

response

is less

than

Ihe

funda-

mental

response.

but

Still

may

be large

enoughtocause

signifil;';lI"'lt

errorsinthe

functerne

ntat

measurement.

Rernembcrinq

that

svnohr

onous

detection

has

features

similar

to

full.wave

rectiHeation,

one

would

see

imme-

diately

from

symmetry

considerations

that

the

response

to

even

harmonics

is.

different

from

the

response

to

odd

harmonics.

For

MId

harmonics,

the

detsctorresoonse

relativetothe

tundnmental

rusponseissimply

lin,

whe-e n

is

the

num

ber

of

the

harmonic.

For

example,

the

third

harmonic

responseis1/3

ihe

tundarncnta!

response.

the

fifth

harmonic

ri:!SPOrlSH

i:;.

1/5

the

fundLimental

rcsponse,

etc.

Theoretically,

the

SyndH

nnous

Detector

should

havp. nn

responsca,alltoeven

harmonics.

However,

the

reference

wavefor-m is

not

perfectly

sYmmetrical.

c.ausing a 5rnall

n

Jan-30-02

05:37P

fe:!:pCI1Si!'.

The

even

hatmo

nic

response

dLJ~~

to

disavmme

trv

can be

expressed

as;

sin

M(

1 i

el/2

Respom~e

Relative to

Fundamental

=

where

n is

the

number

of

the

fundarnenrnt

end

e is

the

fractional

departureofthe

half

period

from

the

actual

half

periodofthe

reference

waveform.Ifn is even and nc is

vcrv

much smatter than unity, the expression simulifies

to.

JPproximately.

trel2. In

other

words.

the

response

to cdl

even

harmonicsisabout

the

same

andisdetermined

by

the

symmetry

of

the

reference

siqnal

at

the

Phase

Se nsrtive

Detector.

lr"l

gCrhi:ral. a giver'!

half-cvcleofthe

reference

signal

will

be

within

0.3%ofhalf

the

period,

giving

0.003

as

l/1C

V;:IIUf:!

of

e.

Inserting

this

into

the

tnrmula,

one

ohtains

0,5%, a

good

working

value

for

the

rQspor,se

to

even

harmonics.

Actual

symmetry

error

V.(iries

with

the phase

sening,

so

that

the

resp

onse

to

even

h.i:umonics

can

be less

than

0.5%.

The

harmonic

sensitivitv

of

the

Synchronous

Detector

is.

one

mason

for

minimizing

the

passband

of

the

Siqnal

Channel.

The

portionofoverall

output

duetoharmonics

will be

reduced

by

the

attenuation

factor

the

Signal

Channel

providesatthose

frequencies,

Transfer

curves in

Figure,

111·14

through

111·17

should be ,eferred to. Tobie

111·4 lists

typical

measured

synchronous

detector

responses

to

harmonics.

Table

111·5

lists

overall

responses

to

lIH~SI:!'

same

harmonics

if oper

atinginthe

Bandpass

mode

with

a 0

of 10.

....

armonic

0°

90

0

180

0

270°

2nd

0.15%

0.5%

0.2%

0.5%

3ro

35% 35%

35% 35%

4th

0.13% 0.55% 0.25% 0.7%

Bth 15% 15%

15%

15%

Table

111-4.

TYPICAL

HARMONIC

RESPONSE

OPEAAllNG

IN THE

FLAT

MODE

Harmonic

0°

90·

160

0

270

0

2nd

0.017% 0-017%

0.008%

0.04%

3rd

1.2%

1.2%

1.2% 1.2%

4th

0.0035%

0.014%

0006%

0.017%

5th

0.35%

0.35%

0.35%

0.35%

table

111.5.

TYPICAL

HARMONIC

RESPONSE

OPERATING

IN

BAN

DPA:siS

MOOE

WITH

a....,

10

These

constderar.ons

and

examples

assume

the

worst

possible

phase

relationship

hetwaan

the

harmonic:

and

the

re Ier

ence

signal.Practlcally

ancnurucrcdphase

-elettonstucs

are

not

LJsu,llly

the

worst

case.

Lind

the

tr'uc errorwill

be

smaller

than

the

computed

error.

P.19

A

related

probtem

i$

that

of

errors

resulting

from

sub.

harmonic

components

of

the

input

signal.

Sub-harmonic

Sitlrlalsdonot

directly

conttibu

tctothe

output

indication

that

is,

the

Detector

does

not

respond

to

them.

However,

if

a

sub-harmonic

ls

distorted

in

the

Signal

Chi;lr"lr'lel.

OUtput

errors

canbeintroduced.

TIllS is

because

distortion

results

in

higher

hnrrncnica

bcing

generated,towhich

the

Detactor

is scnaitive,

especially

the

harmo nic

at

the

primary

fre-

quencyofdetection.

Sub-harmonics

Lire

net

qcucr

allvasignificant

component

(,:If

the

Input

signal,

("X(~CPt.

p!~rhaps,

when

the

Reference

Channel

ij;

operated

in the

Ext.

fl2

mode.Inthis

situation.

and ones simifar to it.

th~

second

harmonic

is

regarded

as

the

fundamental

fur

the

Signal

Channel,

and

the

original

svnc

inp~Jt

Iund

ame

ntn! is

regarded

{is

a

large-amplitude

sub.harmonic.

Cart"!

must

be

exercised

to

not

distort

the

Iundarnantal.

althoughitcon

be a

ttcnueted

by

filtering

in

the

Signal

Channel.

Distor

tioninthe

Signal

Channel,other

than

duetoOVLD

cnpptoq,

r..x~C:\HS

mostlyinthe

Preampli-

fier,

3.6

S~NSITlVITY

AND

NOTCH

CALIBRATiON

The

accuracvofthe

sensitivity

calibr

afion

in thi!

Oandpass

mode

requires

that

the

notch

be

properly

adjusted. There-

fore,

each

time

thl1'

sensitivityiscalibrated,

it is

wisetofirst

make

the

tine

notch

adjustment.

In HIGH PASS

and

lOW

PAS~.

thp.

notch

adjus.tment

has.

ve..-y

little

effect

because

a

Q

of

one is nurrnatlv

used

in these

modes.

In FLAT, (he

adjustment

hasnoeffant

at all.

The

procedures

given

hcre

are

ccmbined

nr

ocedures,

first

for

adjusting

the

notch

and

then

for

calibr

atinq

thesensitivitv.

The

fine

Notch

adjustment should he made for

exactly

zero

cente r-fr

cqucncv

siqnal tr',1r1sfcr

throuqh

the

Signal

Channel

when

in {he

Notch

mode.

However,

because

the

Cattbr

aror

output

is a

square

wave,

corHaininH

harmonics,itwould

be

difficult

to

lise

this

~ignal

lor

making

the

fine

notch

adjustment in

the

NotCh

mods:

the

harmonics

would

disall nw an

output

zero,

and

adjusting

foradefinite

value

would

be

difficult.

The

Reference

Channel's

sinewave

nU(pUI would be

better,

but

~.=.eml~g~.~9_~!!.OW

foranaccurate

selting.

One

good

way

to

adjust

the

notch

in

the

Notch

mode

is

by

using

a

separate

high-purity

sioewave

source.

An

alternative

wavton1<lke

the

fine

notch

adjustmentisto

adjust tilt!

Notch

Adj.

control

for

proper

center-frequency

siqnal

transfer

through

the

Signal

Channel

when

in the

Bandpass

mode.Ifthe

adjustment

is

off.

changing

the

0

will

c:hangp,

the

!]<1in

at

the

center

ft"f~quency.

Making

the

fine

notch

adjustment

is

C;,]!iY

if

this

last

factismade

tJ~e

of;

r.e..

the

tine

notch

;J(JjLJ~lrJ)C!tll

should

be

made

such

(hat

a

change

of Q

does

not

change

the

gain

at

theccnter

traquencv.

The

latter

method

has

Ihe

rnnri t

of

allowinqaIf'S!).

pure

waveformtobe

used

because

the

harmonics

are

elimfna

tcd

in

the

Bandpass

mode.

If

Q'~

of

100

iH1U

50

arc

usad,

the

Calibrator

waveform

can

be

usee

tor

an

adjustment

uccur

acv

withinafew

ten

ths

of(Ipercent.Ifthe

RefCl'en(~e

)

Jan-30-02

OS,3BP

Char'mel"s sinewave is used, all accuracv of better than a

tenth

of a

percent

canbeachieved.

The

following

proce-

re I,.I$CS

the

Calibrator

output

becauseitis.

more

conve-

...

enttocontinue

on

into

the

sensitivitv

adjustment.

The

operator

ought

10 be abletoadapt

this

proceduretousing

the

reference sincwave if he requires

more

accuracy.

Make

the

following

pteliminarv

control

settings.

(1) Reference Channel

The

Frequency

switches

shouldbesettoor

near

the

frequency

whichisto

be

used

or

expected

when

cperatinq

with

the

experiment.

and

the

mode

switch

shouldbesettoInternal.

The

Phase

quadrant

selector

should

he

setto270

c

,

and

th@

fine phase

control

setto90°.

Note

th~t

this

adds

up

to Oa; 'Setting

this

way

allows

the

fine

control's

overlaptoadjust

the

phase

through

0°.

when

adjusting

for

maximum

meter

tndlcation

in

the

steps

that

follow_

(2)

Preamplifier

Operate

ainqle-ended

direct,

Connect

the

Calibrator

output

to

the

Preamp

input.

(Use a

short

cable,

RG·58/UorRG-59/U

havinq

BNC

connectorsatboth

enos_)

:31

Output

Channel

The

Time

Constant

switch

should

be sat

such

that

the

signal

driving

the

meter

is well

filtered.

However.

too

longatime

constant

will

make

the

adju

stmen

t ttma

too

long.

Tvpicatlv. if

the

operating

frequency

werf!

400

Hz a

good

time

constant

setting

is 100 rns.

The

Zero

Offset

toggle

shouldbesettothe

neutral

off

position,

and

the

Function

switch

set

to

the

PSD

positiontohe

usedinthe

experiment.

(The

gain

error

introduced

when

switching

from

one

PSD

position

to

anotherisvery

small.

about

0.5%

maxlmum.)

(4) Signal Channel

The

Sensttlvitv

switch

should

be

settothe

intended

cper

atinq

position.

However,

jf

one

of

the

nV r

anqcsi:-o

used,

internal

noise

can

cause

the

meter

reading

to

waver

too

much

for

making

an accur

atc

adjustment.

It

is

better',

therefore.

to

use

one

of

the

/-1VOrrnV

positions.

The

gain

error

when

switching

back

down

l<)

the

nV

range

for

operation

will be less

than

the

adjustment

error

if

adjus

tcd

in a nV

ranqe.

lhe

Calibrator

switch

should

b~~

'Settothe

same

level as

the

Sensttivitv

switch,

The

Frequency

switches

sboutdbesettoexac

tlv

the

same

settings

as thp.

Reference

Channel

frequency

switches.

The

Mode

switch

should

he

set

to

the

Bandpeas

posiucn.

111-23

The0switch

shouldbeset

to

50.

Proceed

to makp.

the

Notch

adjustmentasfollows.

(1)

Adjust

the

Signal Ch anne!

trequencv

control

and

fine

Phase

control

for

maximum

meter

indication.

(2) Changp.

the

0

switch

setting

It)

100; if

the

meter

indication

change'S,

adjust

the

Notch

Adj.

screwdriver

control

to

minimize

the

change.

Continue

switching

the Q back and

forth

between

50 and

100

and

adjusting

th~

Notch

Adj.

potentiometer

fornochange

in

the

meter

reading,

Now

that

the

Notchisadjusted.

before

adjustinq

the

fine

sensitivity

cor"ltr'ol,

make

the

following

changes

in

the

control

settings:

The

Calibrator

output

is a square

wavP.

haVing its

fundamental

rms

component

as

indicated

for

each

switch

posttlon.

Therefore.

whCr1

calibr

atinq

tne

se nsi.

tivitv,

the

Mode

switch

should

he

set

to

the

Bandpass

position

and

ttlo a

switch

setat10 or

higher

(if

the

Q

tobeused

when

operating

is higher

than

10, calibrate

with

thatQ,etting).

All

other

control,

shouldbe1>'11

as

set

for

the:

notch

adjustment.

An

attenuaror,

packaged

in a

small

box

having

male

anti

female

BNC connectors. is provided

with

each

Mod.1116

and 119_ This

attenuator

attenuates

100:1

so

that

the

Model

124A

can

be

calibrated

in

the

transformer

mode.

The

attenuator

output

Z is 1

ohm,

If

the

transformer

mode

is to be used,

connect

the

male

BNC

connectoroftha

attenuator

directlytothe

input

BNC.

end

connect

the

calibrator

output

to

the

attcnuetor's

female

jack

withashort

cable.

It is

important

that.ifanother

sourceisused

for

callbr

a.

tion,

the

source

presentsanlrnped..neeofexactly

50

ohmstothe

attenuator,

After

these

settings

are

rflade, Itte

actual

procedure

is

simple:

Adjust

the

fine

Phase

control

for

maxirnum

meter

indication.

Then

adjust

the

Sensitivity

screwdriver

control

foranaccurate

full-scale

meter

indication.

3.7 AC

VOLTMETER

OPERATION

With

the

Function

switchinthe

ACVM

position,

the

Signal

Channel

output

is used

to

operate

the

Svnch

ron ous

Detector.

This

makes

the

Model

124

oper

ate

as an ac rrns

voltmeter.

If

the

siqoel

driving

the

synchronous.

detef:tor

is ;;I

clean

slnewave.

the

rms

voltage

Indication

will be

very

accura

te .

The

filterinthe

Signal

Channel

canbeusedtodean

liP a

waveform

if

necessary.

If

the

waveform

is

not

clean,

however,the

meter

reading

will still he

within

10

or 12

percent

of

the

widaband

rms

arrmlitodeofthe

input

aiqnal

plus noise.

This

wide

band

capability

is

very

useful

for

widsbend

noise

and

corruilax

waveform

measurements.

A~

in

toek.in

operation,

the

Time

Constant

is

usee

to

smooth

the

meter

indication.

However,

bearinmind

that

P.20

FQb-07-0Z

OZ:ZOP

P.Ol

both

the

signal

and

tht1 noise

contribute

to the de

output

of

the

detectorinACVM

opar

ation.

The

sigl''1al-to-noise

ratio

is

not

improved.

lnstaad,

the

signal

phl$

noise is

measured.

with

the

time

constant

sf!rVing

solelytosmooth

the"

output

indication.

It

should

boo

noted

that,inACVM

operation,

the Model

124Aiseffectivelyinthe

LO

DRIFT

mode.

except

for

the

100 nV, 200 nV. Or

500

nV

sensitivitv

setting" where the

unit

operates

in

the

NORMAL mode. Consequently, for all

but

the

three

"NORMAL

mode"

renqes,

the

drift

<:l"d

overload

charactertsttcs

of

theLODRIFT

mode

apptv.

3.8

DIGITAL

PANEL

METER

MODIFICATION

(1241/98)

If

requested

upon

purchasing,

a 3\1;

digit

Nixie"

display

maybeinstalled

insteadofthe

panel

meter.

This

display

provides

direct

numerical

readout

of the

output,

and

the

corresponding

digital

logic is

available

at

a rear-panel

connector.

This

logic is well

suited

for

sending

Lock-In

output

information

to

a

computer

via a Model 131

Instrument/Computer

lntsrface

System.

lower

logic level

and

sourcing

0,'

mAatthe

upper

logic

level,

Dllring

normal

operation,

the

diqital

meter

is triggerod

internally

at a

rate

of

approxirn

atelv10times

per

second.

Other

internal

trigger

rates

canbeobtainedbychanging

the

value

of

the

resistor

(nominally

300

kn)

conf1ecte~

betWf:!p.n

pins1and15of

OJ-2

(upper

connector

on Digital

Panel

meted.

With

this

resistor

removed,

the

rateisreduced

to

twiceasecond.

There

may

be

occasions

where

it is

advantageous

to

trigger

externally,

suchasto

facilitate

operation

of

the

Model

124Ainconjunction

with

other

sigr'al

P(ocessing

equipment

which

maybemonitoring

the

digital

output.

Considerations

that

govern

external

trig·

gering

Lire

that

the

intarnal

trigl;ler

must

be

inhibited

and

that

the

proper

external tril:lger

mustbeapplied.

lnl,emal

triggering is inhibited by

grou~ding

pin 23 (BUSY) of the

digital

output

connector,

The

external

trigQ@"isapplied

to

pin

20;

it

must

be a

loqic

one

that

goestologic

zero

for

at

least

one

and

a halt

microseconds

{but

for less

than

two

milliseconds).

This

unit

resetsonthe

neqative-qoinq transi-

tion;

conversion commences

on

the

positive-going

rransl-

non.

The

maximum

allowable

external

trigger

rate

is 60 Hz,

When

the

Model

124A

is

being

operated

internally

triggered

(the

usual

easel,itis

important

that

signals be

provided

to

indicate

whenaconversion

is in prcqrsss

(or

nat

in proqress

as

the

case

may

be)

if the-

Model

124A istob€!

successfullv

incorporated

intoalarger

diqital

system.

Three

different

signals

are

provided

for

this

purpose.

The

firstisthe

E'ND

OF

C"ONVE"RSION

level at pin 14 of the Digital

Output

connector. Thi$

outputisup

(ncmrnallv

+3.5 V)

while

a

conversion

is in

progress,

Lind

down

for

the

full

duration

of

the

display

plus

reset

time.

The

second

stqnat.

provided

at

pin

19

of

tile

Digital

Output

connector,

is a 75~slogic VIle

pulse, CONVERSION COMPLETE, generated at the end ot

the

convcrslon

period.

The

third

signal,

provided

at pin 18.

is the inverse, CONVERSiON COMPLETE,

.1'0

751'5

but

at logic 0"

,,'

D'

.'

0'

o

~

"

"'

~IJ"'"

,oo~

~OO·~

~LKI"Y

=====::::::::::=::::::~~~~~~

~~~~:"\1

Figure

111-23.

TypICAL

CALIBRATION

ACCURACV

".,.

~

! lQ

·

0

·

•

·

+1,0

•

o

•

i :!:O.I

In

r~ading

the

display,

the

numerals

cor

respond

directly

to

the

signal

voltage.

However,

some

care

mus

t be

exercised

in

interpreting

the

decimal

indication.

On

any"'"

range; 1

I'V, 10 I'V, 100 I'V, 1

mV,

10 rnV, 100

rnv,

etc., at full

scale

output

the

mc ter

will

read

1,000.

Above

full scale the

meter

will

follow

until

ove

rloed

occurs.

On

"2"

ranges,

however.attull scale

the

meter

will

"try"toread 7..000,

but

will Instead read 1 BLANK, i.e.. the decimal and three

riqht-hand

nUrl1crals will

not

illuminate

at

hJ11

scale. On "5"

ranges,

at

full

scale

the

meter

will

read

,500, and above full

scale

the

meter

will

follow

until

overload

occurs.

The

voltage

output

at full scale is

-:1:10

V on all ranqes. No

uolarltv

symbol

is

dlsrilavsd

for

pos itivs rHadin9S. A

"-"

sign is

displayed

foranegative

reading.

The

information

displayed

on

the

digital

meter

is

provided

in

binary

coded

decimal

form

at

connector

J7

at

the

rear.

Table

111·6

identifie-s

the

pinsatwhich

this

information

is

provided

and

gives

the

output

levels.

PO$i

tive logic is

employed;

a "1" is

01-3.5

V ±1 V

anda"0"is0.2

V ±O,2 V.

All

digital

ourpu

t s.ignals

are

capab!c

of

sinking

5

mA

at

the

In

the

case

of an

instrument

equipped

with

both

the

Remote

Programming

Option

and

Digital Panel

Meter

option,

there

are

some

special

considerations

that

must

be

observed

for

proper

operation.Inunits

equipped

with

the

Digital Panel

Meter

option

alone,

switching

controlled

by

the

front-panel

Sensitivity

switch

sets

the

digital display

sensitivity.Inthe

caseofunits

equipped

with

the

Remote

Programmingoption.

the

Sensitivity

switch

is

rendered

ineffective

when

the

sensitivity

is.

being

controlled

re-

motely,

and

control

over

the

digital

display

sensitivity

is

lost.

To solve this

problem.

an

additional

toggle

switch

has been

added

to

the

rear

panal

of

instruments

equipped

with

both

options.

This

switch

has

two

positions,

NORM,

~nd

O.P.M.

'.000.

For

operation

with

the

(emote-programming

option

(nactiVf: (this

option

i'i

controlled

by a

raar-panc!

push-

button),

the

switch

should

be

set

to

NORM,

in

which

position

the

display

functions

exactly

as

described

in

Subsection

3.8.

In

rerno

tc-or

oqrammed

operation,

the

switch

should

bu

set

to

a.r,M,

1.000.inwhich

poaition

the

digital

panel

meter

indicates

the

input

sii]nal

IPo",el

as a

fraction

of

full

scale,

independent

of

the

selected

sensitiv-

111·24

Feb-07-0Z

OZ'ZOP

irv.

A full-scalp.

input

gives a

displ~y

Indicationof1.000,

Indapendentof

whether

the

proqrarnmed

sansitivitv

is 1

mV, 2

mV,

5 mV, or

some

other

value. Similarly,

with

a

full-scale

input

applied

the

I1CD

output

will

be

1,000

and

the

recorder

output

will

be 10V.The

display

indicnttcn

P.OZ

anr"l

output

levels

are

proportionally

Ie-~~

with

less

than

full-scale

inputs,

For

example,ifthe

programmed

seasitiv

ity

is

700

mV, and a 100 rnV siqnal is

applied,

the

d.qital

display

will

indicate

0,500

(half

SC(:ilel.

the

BCD

output

will

he

0.500.

and

the

recorder

output

will be 6 V.

•

Model

174A

J7 Pin #

1

2

~

4

5

6

1

8

9

10

11

12

13
14
15
16

17

18

19

20
21

n

2J

24
25
26
77

;18

29

~O

31

32

33

~4

35
36

Function

Polarity (Logic 1 = +)

+4

volt.

de

Overload

Output

(Loqic

1 = OverloadI

Overload

Output

(Logic 1 =Overload)

DVM

Most

Significant

Digit,

A

Digital

Ground

DVM

2nd Most Slqnificant

Digit,

A

DVM

2nd Most Significant

Digit,

C

DVM

3rd

Most

Significant

Digit,

A

DVM

~rd

Moot Significont

Digit,

C

DVM

Loa<t Significan!

Digit,

A

DVM

Least

Significant

Digit,

C

Spare

ENIYOFCONVERSION

Spare

Spare

DVM

Least

Significant

Digit,

0

CONVERSION

COMP"LETE

CONVERSION

COMPLETE

Ext.

Trigger

Input

Spare

Spare

NOT

BUSY

input

(Output

data

will remain

fixed

when

this

line is at

logicO.Must

be 1

or

open

for

conversions. to

continue)

Sensi

tivitv

Switch

Position

A

(see

TruthTable]

Sensitivity

Switch

Position

C (see

Truth

Table)

Sensitivity

Switch

Position

B {see

Truth

Table)

Digital

Ground

DVM

Overload

Output

(Logic 1 = Overload 1

DVM

Overload

Output

(Logic 1 =

Overload)

Digital

Ground

Digital

Ground

DVM

2nd

Most

Signific:ant

Digit,

B

DVM

Znd Mos.t

Significant

Digit,

0

DVM

3rd Mast

Significant

Digit,

B

DVM

3rd Moot Siqnificant

Digit.

0

DVM

Lease

Significant

Digit.

B

Function

When

AppliedtoMoool 131
Sy.tem

Model 267

1 =

Polarity

+

Not

used

Digit

1,A

Digit

1, C

Digit

2, A

Ground

Digit

3, A

Digit

3, C

Digit

4, A

Digit

~.

C

Digit

5, A

Digit

5, C

Digit

5, D
EXECUTE
Not

used

Not

used

BUSY

Iftcrn

Model 2621

Digit

6. A

Digit

6, C

Digit

6. B

Digit

6, 0
Oigitl,8
Digit

1,0
Digit2,B

Digi[2,D
Digit

3, B
Digit

3. 0

Digit~.B

Diqit

vl, D

Digit

5, B

NOTE:

Log:c 1 = +3.5 V ±1 V, Loqic 0

10.2

V ±0,2 V.

The

DVM

u::.;-j in

the

Model

124A

has a

"3VJ"

(4

digits)

Nixie

tube

dispf

av.

Each

digit

ls repr-esented at

the

rear

panel

connector in S

1Jry

Coded Decima! (BCD)

format.

The

Mast

Significant

Digit

is the

leftmost

of

the

four

digits

disolaved.

The

Tetetvce

d.q:

.:.:1(?for

OVI-!rloadl is 1

digittothalettof

the

Mos.t

Siqnificant

Digit,

The

notationA.8.

C. &. 0

after

the

digit

notation

abi.".:!

-etet

s

to

COllJITHl

hearlinqsofthe

truth

rablc.

The

value of

Poachofthese

outputs

when

at i:I

logic

1 is 1. 2. 4, &

R,

respect

IV';; •

ror

each

digit,

the

A. B. C, & 0

outputs,

taken

together.

representanumber(0to

9l in

BCD

format.

Fii~ure

11I-6A.

DIGITAL

OUTPUT

PIN

ASSIGNMENTS

111-25

Feb-07-0Z

OZ,ZlP

T~I~tvp~

Digit

No.

'2 ) " 5

•

P.03

Always

O. fIlr:Clipt~mark

"'h,nm"",n",'n'd'~

~

I

~~~l:~~l:

r3~7"111

!) X

Xl

xl xl xl

' X

IL

_

...

- E:I\IJUI1E.'11t; 0

10"

iI~

front

r.mel

Display

, X X X )( j)E'(

TI\llh

Tatlle

for

I I I I

Sr"'~i1i'oliW

~wi,,:h

......

12~

o

01""'1

0

!~

each

Priotovt is in microvolts

Digital

QlJWut

for

Ear.:h

Obplay

Fi'iiilur.:

Binary

Coded

DecilOlIl

Digitllt

Output

Display

Shew!

8101

, lei

2161

1IAI

0

Q

0

Q

Q

,'"",

-

------

1

Q

0

Q

1

--

f----

""

2 0

Q

1

0

J

Q

0

,

1

-,,-

4 0

,

Q

Q

,---,

..

"-

5 0

1 0

1

...

__

...

---

S 0

I

,

Q

,

0

,

,

1

----

---

--

8

1

0

0

0

--

s

1

0 0

1

NOTE:

Princeton

Applied

Research

Corporation

manu-

Iscturesacable

suitable

for

interconnecting

a Model

124A

and

3 Model

262

Teteprinter/Svstem

lnter tace

Module

(par

t

of

the

Model 131

lnstrumcru/Computer

lnterf

ace Svstern}.

The

part

number

of

this

cableis6020-0023·06.

A sche-

matic

dr~wing

of

this

cableisincludedinSection

VII on

page

VII·31.

Diyill:ll

Output

for

Ead1

Swi1d1

S<!t1ll'itJ:

..

--_.

Switch

nco

Digital

Output

'-1'~

Exp.

SeItifl9

41C1

2 (81

--

I

5QOmV

1 1

1

200

mv

1 1

Q

S

100 mv

1 1

0

50mV

1 1

a

20mV

1 0

,

5

10niV

1

Q

,

5mV

1

Q

,

..-

2 mV

1 0

Q

4

, mV

1 0

0

!iOO

I1V

,

0

0

200#1V

0

1

1

3

lOO"N

0

1

1

50/AV

0

1

1

20~V

0

1

0

2

10j.lV

0

1

0

5/lV

0

1

0

------

2 "v

0

0

I

I

1

"v

0 0

,

~OO

nV

0

0

1

.~~~~~-

---

200

nV

0

0

0

0

'00

nV

0

0

0

Table

111·68_

OIGITAL

OUTPUT

TRUTH

TABl.~S

111-26

)

•

Feb-07-02

02:21P

3.9 PHASE

MEASUREMENTS

To

measure

pha'5!~

with

a Model

174A,

the

Phase

controts

-re

adju

atadtoobtain

a positive

peak

indication,

the

S31l1€

s

for

[In

amputude

me

asurernent.

When

positive

peak

is

achieved.

the

Phase

controls

will

indicate

the

number

of

degrees

by

which

the

input

signal teeds the

applied

rafercuce.Ifthe

angle is

gfeater

than

180". it may be

more

convenient

to

subtract

the

indicated

anqle frorn

360')

and

state

the

difference

as

the

anglebvwhich

thf!

input

signal

lags

the

reference.

NOTE:

Any

internal

phase

shifts,

51Jch

as

mightbeintroducedbythe

signal amplifier's"

must

be taken

into

account

for

accurate

measurements.

Sometimes,

after

the

lock-in

amplifier

has been peaked up,

a

change

in an

experimental

parameter

will

causeaphase

shift

and

a

resultant

loss in

peak

indication.

If

this

happens.

it mav be

of

Interesttoknow

whether

the

shift

wasalead

or

a lag.Todetermine

the

direction

of

a

phase

shift.

simply

re-adjust

the

M174A

Phase

controlsasrequired

to

restore

the

peak

indication.

and

whill! so

doing.

r~otc

whether

the

new

phase

settingishigherOflower

than

the

old

one.Ifthe

new

phase

settingishigher.

the

phase

shiftofthe

signal

relativetothe

reference

was in

the

leading

direction.Ifthe

new

phase

settinq

is.

lower.

then

the

shif t

was

in

the

laggin9

direction.

As

mentioned

previously.

whan

the

phase

controls

are

adjusted

for

peak

meter

reading,

they

indicate

the

phase

of

the

signal

with

respecttothe

reference

signal.

However.

a

more

accurate

determination

can

be

made

bv

takinq

advan

taqeofthe

gl'eater

quadrature

adjustment

sensitivity.

Also,

the

phaseshitt

differences

between

the

Reference

Channel

and

tho

Signal

Channel

mustbeaccounted

for if an

accurate

phase-

determination

is

required.

When

adjusting

for

the

peak,

the

meter

reading

varies

around

the

peak

as

the

sineOfthe

phase

angle

for

small

errors.Ifthe

phase

is

adjusted

for

quadrature

null

instead,

the

meter

reading

varies

around

nullasthe

cosineofthe

phase

angle

for

small

errors.

Therefore,

for

any

small

number

of

degrees

change

of

the

Phase

ver

nier

while

adjusting

foraquadrature

null.

the

meter

reading

changes

much

more

than

for'

the

same

vernier

change

while

adjusting

for an

in-phase

peak.

Two

high-sensitivity

procedures

follow.

Procedure

;lf1

This

procedure

;5

relatively

sirnplc,and

canbeused

with

signals

that

V('lrVinamplitude

(independentofnoise).

(1)

Mellsure

the

amplitude

of

the

signal in

the

normal

manner,

so

that

the

controls

are initially

optimized

for

time

constant.

dynamicranqe,

Sigrul

Channel

filter

set

tinqa,

etc.

Use

the

Bandpass

mode

and

high0,if

possible

[frequency

constant),toeliminate

the

effects

of

harmonic,

on

making

the

null.sellings

below.Ifthe

frequency

is

changing,

it

would

be

best

to

use a Wide

P.04

bandwidth

and

avoid

using

a tr

ansformcrinpo

t ,

because

internal

phase

variations

(I')

a

function

of

frequency

could

notbeaccounted

for.

(2)

Disconnect

the

si~nal

from

the

Preampfifier.

and

connect

the

sinewave

from

the

Hefe

ranceChannel

Out

jack

to

the

Pr

aamptif

iers

A input. If this. OI,HPLJt is

alr

csdv

hcinq

used

for

svnchr

onizinq

theexpcrimcnt

,

usc

a

"T"

connector.

The

amplitude

must

be

low

r,noughsothat

the

Signal

ChannelisnoI,overf

uadcd

.

The

phaseufthis smewave is

going

to he

used

for

zero

refercnce.

If a clean slnewave

having~phase

more

suitable

for

zero

referenceisavailable.

use

it.

If a

transformer

inputisused.

it is

important

th~t

the

Referl;!nCf!

output

impedance

be

made

to

look

the

Same-

as

that

of

the

signal

source.

Ar'

aoorocriatetv

designed

attenuator

can

generally

b~

used

to

achieve

this

goal.

Otherwise.

phase

measurement

errors. will

be

introduced.

(3)

Set

the

Prcarnplifier

Mode

switch

to

"A",

IThe

Transformer/Direct

switt;.h

should

be

set

as

appro-

priate

for

the

intended

input

coupling.)

(4)

Set

the

Zero

Offset

switch

to

OFF

(center

ccslrlonl.

(5)

Adjust

the

Phase

controls

for

an

exact

meter

null.

Increase

the

Signal

Channel

sensitivity

as

much

as

possible

without

overload

while

making

this

adjust

ment

.

(6)

Record

the

Phase dial

setting

(phase

zero).

(71

Disconnect

the

Reference

Channel

aincwavc

from

the

Preamplifier,

and

reconnect

the

Reference

Channel

slnewave

from

the

Preamplifier.

and

reconnect

the

signaltobe

measured.

(8)

Adjust

the

Phase

controls

for

exact

meter

null.

Increase

the

Signal

Channel

sensltlvitv as

rrHJcJ1

as

possible

without

overload

while

making

this

edlust-

ment.

(9)

The

difference

between

the

zero

reference

phase

recordedInstep

(6)

and

the

phase

setinstop

(8) is

the

accurate phase

of

the signal WIth

respect

to

the

reference

signal.

Procedure

=2

This

prQ~@d"'lre

is

more

comPlicatcr;:t,

but

it

has

the

advantageofprovidingavoltage

output

(& digital

output

if

the

optional

digital

meter

is installed]

proportionaltothe

cosineofthe

phase

angle.

which

canbesenttoa

Computer

or

used

for

other

purposes.

It is

important

that

the

amplitude

(independcntof

noise)ofthe

zero

reference

signal and tho signal

whose

phase

is to be

measured

be

111-27

FQb-07-0Z

OZ:ZlP

constant.

This procedure is

often

used to

monitor

the

relative phase change, as an

ongoing

functionoftime,

of a

signal

that

does

not

varyinamplitude.

(1) MeasLJre

the

amplitude

of

the

zero-phase

reference

signal

and

the

signal

whose

phase

istobe

measured

in

the

normal

manner,

and

record

the

amplitudes

mea-

sured.Ifthe

relative

phase

variations

of a signal

are

to

be

measured,

however,

the

amplttudo

need

not

be

known

but

it must be constant.

{2~

Apply

the

zero-phase

reference

signal

to

the

input.

(3)

Set

uo

the

Signal

Channel

filter

parameters.

If

the

frequencv

is

constant.

use

a Q

of

100

and

the

Bandpass

mode.Ifthe

frequencyischanging,itwould

be

beUtouseawide

bandwidth

andtoavoid

usin9 a

transformer

input,

because

internal

phase

and

ampli-

tude

....

arlations

as a

functionoftrcquencv

could

not

be

accounted

for.

(4}

Set

the

Zero

Offset

toggle

to

neutr-al.

Then

adjust

the

Phase

controls

forapositive

peak.

Also, if

the

Bandpass

mode

is

used,

tins-adiust

the

Irequencv

controls

forapositive

peak.

(5)

Adjust

the

fine

sensitivitv

[screwdriverI

control

for

an

exact

+ full scale ml:HEH

indication.

(This

throws

the

gain

calibration

off,soafter

the

phase

measurement

is

ccrnptcte,

the-

inst

rurnant

shouldberccalibr

atcd.]

The

Sensitivity

switch

setting

at

which

this full-scale

adjustment

is

made

is

referred

to

below

as

the

"reference

full-scale

range".

Becauseofthe

limited

range of

the

fine

sensirivitv

control.

forafixed

reference

amplitude

it is

not

always

possible

to

adjust

for

exact

full-scale

rueter

indication.

In

suchasituationadifferent

level of

reference

signal

shouldbeused.

If this is

not

possible,

an

intermediate

levelonthe

scale

canbereferredtoas

"tun-scale".

However,

the

following

procedure

and

readings

mustbemodified

accordinqlv.

P.05

110)

Change

the

Pha,e

quadrant

90',

and

return

the

Zero

Offset

toggletoneutral

(center

posinon),The

me rer

should

read

near

zero,

but

the

small

phase

error

will

probably

causeareading

slightly

off

null.

Adjust

tile

Phase

dial

control

for

ex ac t

meter

null.

Turn

the

Sensitivity

switch

counterclockwise

as far as

possible

without

overload

while

making

this

adjustment.

(11)

Return

the

Sensitivity

switch

to

the

reference

full-

scale range ae

ttlnq.

(12)

Apply

the

signal

whose

phaseistobemeasuredtothe

Preamplifier

input.

The

meter

indication

with

respect

to

the

unity

meter scale is

accurately

equal

to the-

cosine of

the

phase

angle if

the

reference

signal

and

measured signal

are

exactly

equalinamplitude.

Be-

cause

the

full-scala

output

is 1a V,

the

output

voltage

is.

10 x

the

cosineofthe

phase

angle.Ifthe

reference

signal and

the

signal

whose

phaseisbeing

measured

are

unequalinamplitude.

the

cosine

function

m~Js.t

also be

multiplied

by

the

ratioofthe

amplitude,ofthe

two

signals,

Vrf::t!V

x

.

The

amplitudes

were

measured

in

step

(t).

For small angles, much

higher

resolution

C13n t;e

obt

alnad

by

lncrcasinq

the

sensitivitv.

Rc-member,

however,toalways

refer

vormces

and

meter

readings

obtained

with

Increased

senaitivltv

backtothe

full-

'Scale

reference

r~nge

by a

multiplier

equaltothe

ratio

of

the

ranges.

(13)

Use a

cosine

table

oracomputer

to

convert

the

readings

and

voltages

obtainedtothe

phase

anqle.

3.10 REAR

PANEL

coNNECTORS

3.10A INTERFACE CONNECTOR (J9)

J9 is a

14·pin

connector

havinq

cutoutsasgiveninTable

111-7.

This

connector'

mates

with

Amphenol

i:'57-30140,

andiswired

for

compatibilltv

with

the

Model

127,

which

is

a

two-phase

accsssorv.

If it is

desiredtooperate

a Model

(6l

Set

the

Zero

Offset

control

to

"t-".

and

turn

the

Offset

vernier

exactly

ten

turns

clockwise

from

aero.

The

overload

lamp

will

light.

and

the

meter

will peg

downscale.

Pin Signal

(7)

Increase

the

sensltivitv

by a

factorof10

[scnsirivitv

control3positions

c.:cwl,50that

the

meter'

again

reads

on

scale.

(8)

Adjuat

the

Phase

dial fc rInup-scale

pc ak, If

occrutinq

in

the

Bandpass

mode,

atter

natelv

adjust

the

Vernier

and

Signal

Channel

Frequency

fine

controls

for an

up-scale

peak.

Alter

nate

between

the

two

adjustments

untilnofurther

increaseinthe

meter

indication

can

be

obtained.

(9)

Adjust

the

finc

scnsltlvitv

screwdr-iver

control

for tin

exact

meter

null

(which.

Inciden

tallv,

cor

responds

to a

more-

exact

futl-scale

setting

Ior

the

10)(

less

seosttive

range) _

111-26

1 _

__

_

__

_

Ground

2 "

__

_

__.., "

'24

V de

3 _

..

__ __ __ __

_. _

-24

V de

4 _.._

..•••

, , ,

..

, _. _ No

connection

5 . , _. __ , __ ,

0°

Refer

ertcc

6 . _

90°

Reference

7 '.."".

_. . . _.._ , ,.."..180"

Reference

8

""

, __ __

__

_

Signal

Out

9 . _ , _

Signal

Ground

10 __ . _ _ _ No

connection

11 "

__

__

_ _ _

VCO

Input

12 _" _. _ __ _..__ , _

Refer

ence

Input

13

'"_..

_. _

.•..,...•..•

__ _. _..No

connection

14 . _

....

..

, , __ '

•.....

210"

Re Ier

cnce

Table

111·1.

INTERfACE

CONNECTOR

SIGNALS

AND

PINS

Feb-07-02

02:22P

P.06

123

AC

Zero

Offset

Accessory

with

the Model

124A,

a

special

cableisavailable

which

interconnects

between

the

Model 173 and J9ofthe

Model

1241\.

Note

that

the

VCO

Input

(pin

1l l

is.

atso

accesstbte by

meansofa

rear-panel

BNC

jock.

3.101'

EXT.

TIME

CONSTANT

J8

is

the

External

Time

Constant

socket.

By

connecting

axternal

capacitorstothe

proper

pinsofthis;

socket,

time

constants

in excess of

300

So

can be

obtained.

Two

capacitors

are

required,

onetobe

connected

betw~f.!n

pi ns 8

and

9rand

the

other

between

pins10and

11.

The

resulting

time

constant

is.

3C x 10

7

seconds,

where

C is

the

capacitance

(s.ingle

capacitor)

in

farads.Atable

of

the

signals providedatthis

connector

follows.

1

Ground

2

-24V(maximumof100

mAl

3

-24

V

[maximum

of

100

mAl

4 . _ ,

.•.......

__..,

.•.•..••

, • , _ No

connection

5

-31

V in

(for

[lottery

oper

aticn)

6 . _

__

, _, __

__

No

con

nection

7 .

__

" _ _..+31 V in

(for

battery

operation)

8

__ __

• One lead of first

time

constant

capacitor

9.._

Other

lead

of

first

time

constant

capacitor

to ..

__

One

lesd

of

second

time

constant

capacitor

11 ,

..

"

Other

leadofsecond

time

constant

capacitor

)

Pin

Function

depending

on

the

position

of

the

rear-panel

NORMAL/

PHASE

switch.

When

the

instrument

is

operated

as a

phase

meier,

the

input

signal.

after

some

initial

ac gail), is

routed

through

an

amplifier

limiter

that

has

a

constant

amplitude

(clipped)

rectangular

output.

This

signal,

when

synchronously

de-

modulated,

yields

J de

output

that

is a

linear

function

of

the

phase

difference

between

the

reference

and

input

sigrlClIS.

The

phase

sensitivity

is

100

rnV

out

per

degree

with

the

Function

switch

set to

I..OWDRlfT.

Only

LOW

DRIFT

operation

can

be

used

and

the

SCnsitivity

switch

is

constrainedtosettingsinthe

range

of

1pVto500 rnv. In

the

case

of

units

equipped

with

the

Digital

Panel

Meter

option,

Phase

measurements

can

only

be

made

with

the

Sensitivity switch sCI to 1

I.IV,

10

~V,

100

~V.

1

mv.

10

mV.

or 100

mV.Inother

words

the

"2"

end

"5"

positions

should

notbeused

for

making

phase

measurementsifthe

unitisequipped

withadiqita!

panel

meter.

In

phase-meter

opar

ation

the

input

sigr1al

shouldbelimited

to less than ten times full

scale

(but

not

more

than

200

mVI for

Sensitivity

switch

se

ttinqs

from

1

J.1V

to

100

mV.

For

the

200

mV

and

500

mV

sensttivitv

positions,

the

maximum

input

signal is 500 rnV.

The

phase

indication

will

not

be in

error

by

more

than5°maximum

providing

the

signal

amplitude

is at

least

100

/lVor20% of full scale as

indicatedbythe

settingofthe

Sensitivity

SWitch,

whichever

is

greater.

Figure 111-24.

MIXER

OUTPUT

FOR

IN-PHASE AND

QUAORATURe

SIGNALS

3.13

MIXER

MONliOR

MODIFICATION

(1241/92)

Units

equipped

with

the

Mixer

Monitor

Option

have

an

additional

rear-panel

8NC

connector.

The

signal

available

at

this

outputistaken

directly

from

the

output

of

the

Mlxcr

and

before

any

filtering.

Figure

111-24

illustrates

the

Mixer

output

corresponding

to

in-phase

and

quadrature

signt':lls

respectively.Ifthe

signal

ar"l(J

reference

inputs

to the

Mixer

are

eitherinphaseor90"

out-of-phase.

the

siqrial at

the

output

of

the

Mixer

will be as

shown.

For

signals 1801)

out-of-chase.

the

Mixer

output

will be

the

inverse of

the

90\J

output.

Takinq

the

maximum

possible

area

that

can

bE:

enclosed

by

one

cycle

(one

polaritv]

as a

unit

output.

the

output

averaged

overacycle

for

any

Mixer

input

phase

relationshioissimply

the

unit

output

times

the

cosine

of

the

anqle

between

the

input

and

refer-ence signals_

o',P1'LlI:ABL.E

O"ll

y

BI!I..!;lW

!lO_

"'I

IIoNI,l

FOR

NOISEL.E.SS

INPUT

SICjN.AL..!I.

+----1-+_

-,

B - 51CjNiIlL .AND REF, 901;1

out

(IF PH,t,SE

~

I

Tillble 111-8.

EXTERNAL

TIME

CONSTANt

CONNECTOR

SIGNALS

AND

PINS

3.11

BATTERY

OPERATION

Bntte rv

operationofthe

Model

124A

Lock-In

Amplifier

may' be

necesserv

where

no ac

power

is

available,

or

as a

last

resort

where

power

line

interference

is a

problem,

Battery

operation

is

particularlystraiqhtforward

because

the

neces-

sary

internal

points

are available at

the

rear,

panel'lt-ptn

seeker.

Two

batteries

are

required,

one

to

supply

+31 V

(400

mAl

and the

other

to

supply

-31

V 1360

mAl.

The

+31 V

source

should

be

connectedtopin 7.

The

-31

V

sourr:e

shouldbeconnectedtopin 5.

Ground

for

both

is

at

pin1_It is

generallyagood

idea

to fuse

the

battery

lines

external

to

the

instrument.

and

to

provide

an

ON/OFF

switch

as well.

The

front-pans!

ON/OFF

switchisnot

functional

when

the

instrumentisoperated

from

batteries.

The

line

cord

should

be

disconnected.

Other

than

the

alreadv

mentioned

ON/OFF

switch

not

functioninq,

there

Is

onlv

one

other

pointofdifference

betweenabattery

oper

ate d

instrument

and

one

o per

ated

from

the

line,

and

that

is

that

the

pilotfarnns

which

illuminate

the

panel

meter

will

not

light.

Becauseofthe

ole

power

requirements

of

the

diqitel

panel mc ter,

UNITS

INCORPORATING

THE

DIGITAL

PANEL

METER

OPTION

CANNOT

BE OPteR·

ATED

FROM

BATTERIES.

3.12 PHASE

METER

MODIFICATION

(1241/85)

A

Model

124A

equipped

with

this

option

canbeoperated

either

as a

normal

lock-in

amplifier

or 3S a

Phase

Meter,

111-29

Feb-07-02

02:22P

P.07

There

are

two

operating

"restrictions"

that

th'l! operatOr

should

bearInmind

when

operatingaunit

equipped

with

this

modification.

First

of

all,

the

DynamicTradectt

Over-rides that

occur

as a

tuncuon

of

selected

(program-

med) Scnsitivitv apply in Re-mote

Programmed

operation

exactly

the

same as in

Local

operation.

(For

details, see

page

111-15.)

Second.

there

is a

reductioninthe

amount

of

±24 V

power

available

for

external

use.

From

Table lira

±100

rnA

lire

available.

In

the

caseofunits

equipped

with

the

Remote

Programming

Option.

these

levels are

reduced

to

±80

mAo

The

cosine

response

dependsonthe

sinusoidal

natureofthe

input

signal.Ifthe

signal

wereasquare

wave

and

the

tuned

amplifier

were

not

used;

the

Mixer

output

would

vary

linearly

with

the

angle

between

the signal and reference

inputs.

Never

theless.

maximum

output

would

stlt!

beatOQ

end

180

0

•

and

zero

output

wouldbeobtainedat90°

and

270°,

Note

that

when

the

Model

124A

is being

operated

in

the

Phase

Meter

mode

(assuming

the

instrumentinquestion

is

equipped

with

that

option).

internal

lirnitinq

circuitry

"conver

ts"

any

input

to a

rectangular

wave

of the- Same

period.

(ind it is

this

rectangular

wave

that

would

he

observed at the Mixer Monitor

connector.

Pin U,e

The

amplitude

of

the

Mixer

Monitor

output

is

555

mV

peak

with

a full-scale

input

signalat0°

and

operatinginthe

LO

DRIFT

mode.

Operated

in

NORMAL,

the

Mixer

Monitor

!iignal

decreases

to 55.5

mV

for a full

scale

input

andinHI,itdecreasesto5.55

mV.

The

output

resistance

is

1000

ohms.

It

might

bE!

mentioned

that

the

waveforms

illustrated

in

Figure

111-24

apply

onlyatfrequencies

below50kHz

and

with

a

noise-free

input

signal.

At

higt,er frequer"lcies,

switching

spikes

become

Visible

and

some

Mixer

filtering

effects

become

evident.

Even

relatively small

amounts

of

input

noise

can

completely

obscure

the

signal at

the

Mixer

Monitor

output,

especially

in

FLAT

mode

operation.

3.14 REMOTE

PROGRAMMING

OPTION

MODIFICATION

(1241/83)

In

units

uqulpped

with

this

option,

the

Sensitivity

and

Dynamic

Range

Tradeoff

(an

be

remotely

controlled

by

,pplying

logic 0

(groundIto

the

appropriate

pins of

the

rear-panel

Remote

lnterfece

connector,

J8001,

Associated

with

the

connector

is a

pushbutton

switch

that

transfers

the

instrument

from

localtoremote

operation

and

vice versa.

In

Local

operation.

the

Sensitivity

and

Dynamic

Range

Tradeoff

are

controlled

by

the

front-panel

controls

in the

usual

manner.

In

Remote

operation,

these

parame

ters are

inde-pendent

of

the

front-panel

control

settings

and

are

determined instead l)y

the

inputstothe

Remote

lnter

tece

connector'.

Table

111-9

indicates

the

pin

assignmentsofthis.

connector.

Note

that

there

are

thr'~e

"qroups"ofcontrol

input

lines. To

obtain

any

given

combinationofSensitivity

and

Dynamic

Tradeoff,

one

input

in

each

group

is

qrounded.

Usuallv,

[111

of

the

other

pins

Gem

he

left

"floating".

However,

in a

noisv

environment,

particularly

where

H1e

cable

leading

to

J8D01isrelatively

long, it may

be advisal)le to

apply

logic

1 (4-3.5 V ±1 Vl to the

other

active

input

pins

to

assurestable

operation.

Otherwise

tr'al1!:ient

pickup

could

cause

undesired

"switching"

of the

Sensitivity

and

Dynamic

RanqeTradeo

tf.

A

COI~r,et.lol'

(AMPHENOL

57,30360)

that

mates

with

JR001i~suppfied

with

the

modiflcatlon,

In

additiontothe

three

groupsofinput

lines,

two

outputs,

OVERLOAD

and

REF.

UNLOCK,

are

provided.

Each 01

theseoutputs

is

"up"

when

the

corresponding

tamp

is

illuminated,

and

"down"

when

the

correspondlnq

lamp

is

dark.

111·30

1

oVERLOAD

- logic

'"0"=lamp

off

2

REF.

UNl.OCK

-Iog;c

'"1" -

lamp

on

3-18 No

connection

19

100

nV Sensitivity

20

1

/lV

Sensitivity

21.,..............•.............

lOJ,LV

Sensitivity

22

,.,..,..,

100

/lV

Sensitivity

23 1mVSensitivity

24 10

mV

Sensitivity

25

100

mV

Sensitivity

26

'"

LODRIFTTradeoff

27

NORMAL

Tradeoff

28

_ HI

DYNAMIC

RANGE

IReserve)

Tradeoff

29·32 .

__

No connection

33 . _. . _

X1.0

sensitivity

Multiplier

34

.........•............

X5.0 Sensitivity Multiplier'

35

X2_0

Sensitivity

Multiplier

36

_.

Ground

iabl.III-9.

REMOTE

PROGRAMMING

CONNECTOR

PIN

ASSIGNMENTS

In

the

case

of

an

lnstrumentequipped

with

both

the

Remote

ProgrammingOption

and

the Digital PeineI Meter

option.

there

are

some

special

considerations

that

mus

t be

observed

for

proper

operation.

In units

equipped

with

the

Digital Panel

Meter

option

alone.

switching

controlled

by

the

front-panel

Sensitivity

switch

sets

the

digital

display

sensitivity.

In

the

case

of

units

aqutpped

with

the

Remote

PJ'ogramming

option,

the

Sensitivity

switchisrendered

ineffective

"",he", the

sensitivity

is

being

controlled

remote-

ly,

end

control

over

the

digital

display

sensitivity

is lost.

To

solve-

this

problem,

an

additionel

toggle

switch

has

been

add~d

to

the

rear

panelofinstruments

equipped

with

both

options.

This

switch

has

two

positions,

NORM,

and

D_P.M_

1.000.

For

operation

with

the

remote-programming

option

inactive

(this

optioniscon

trclle

d by a

rear-panel

push-

button).

the

switch

should

be

set

to

NORM. in

which

position

the

display

functions

I:1xactlv 3S described in

Subsection

3.8.

In

rerno

te-pr

oqramminqocererlon.

the

switch

should

be

set

to

D.P,M_ 1_000. in

which

position

the

digital

panel

meter

indicates

the

input

signal level as a

fraction

of

full

scale.

independent

of

the

selected

sensiuv-

ity_ A

full·scale

input

gives a

display

indicationof1.000,

indepanden

t

of

whether

the

proqrarnrned

sensitivi tv is 1

rnV. 2

mV,

5 n

...

V,

01'

some

other

value.

Similarly,

with

a

full-scale

input

applied.

the

BCD

output

will be

1.000

and

Feb-07-02

02:23P

P.os

•

the

recorder

output

will be 10 V.

The

displev

indication

and

output

levels are

propor

tionatlv

less

with

tess

than

full-scale

inputs.

For

examp!e.ifthe

programmed

scnsi

tiv-

ity is

200

mY,

anda100

mV

signal is

applied.

the

digital

display

will

Indicate

0.500

(half

scalcl,

tho

BCD

output

will

be

0.500,

and

the

recorder

output

will be 5 V.

3.15

Sl:::lECTIVE

I:::XTERNAl

REFERENCI:::

MODIFICATION

(1241/77)

In

some

applications.itmay

happen

that

the

reference

signal

produced

by

the

experimental

appar

atus

is of vp.ry

poor

quality.

that

is, It is

accompanied

by

much

noise

and

interference.

As

explained

earlierinthe

manual,

useofa

simple low-pass filter in series with the reference signal will

usuallv clean

up such a signal 'Sufficiently to make it

acceptable

to

the

Model

114A

reference

circuits.

Never-

theless,

there

could

arise

Situations

where

this

relative'[v

simple

technique

would

prOVE!

Inadequate.

If

thisisthe

case, the

best

one

can

doisto

pass

the

reference

signal

throughatuned

bandpass

filterofmoderate

G, perhaps 10.

Ever)

the

poorest

reference

waveform.

onceithas

been

passed

throuqh

suchafilter,

will beofsufficiently

good

quality

to

allow

normal

refercnce

channel

operation.

The

sacrifice

one

makes

in USing

suchafilter

is

that.

for

all

practical

purposes,

the

tracking

capabilityofthe

RefereTH":c

Oiannel

is given

lIP,

Any

change

in the

frequency

of

the

reference

signal

resultsinarnplitvde

loss

and

phase

shift

as

the

frequency

mOVE;!S

outofthe

centerofthe

passband.

Such

a

filter

can.

of

course,

be

connected

exte

rnallv

.

Howeve

r,

ir~

the

caseofModel

1211A's

equipped

with

thc

selective

External

R~ference

Modification,

a

Q-of-'0filter

is

provided

internally.

These

units

arc

equipped

with

a

rear-panel

switch

that

allows

the

Selective

External

(tuned)

Reference

mo de

to

be

selected.

With

the

switch

in

the

NORMAL

position,

the

instrument

workscxacttvasde-

scribed

previously.

With

tho

switch

in

the

SEL

EXT.

position,

the

instrument

ooe

ratesinthe

Sclcc ttve

External

Reference

mode

providing

the

front-panel

Reference

Mode

switch

is set

to

INT/VCO.Ifthe

fronf.panel

Reference

Mode

switch

is.

in

any

other

position

whe-n

the

rear-panel

switchis$C!t

to SEL.

EXT,

improper

Refercr~ce

Chann(![

Operation

results.

111·31

The

only

other

consider

atton

in using

the

Selective

External

Reference

modeisto

rune

the

R~fer~rl(..~

Channel

to

the

frequencyofthe

input

reference

signor.

Thisiseasily

done

by

applying

the

reference

signal, and

then

monitoring

the

amplitude

of

the

signalatthe

Reference

OUT

connector

with

the

Signal

Channel.Asuitable

procedure

follows.

(1)

Set

the

controlsasfollows.

Power:

ON

Selective

Exter-nal

Selector

switch

(rear

panel):

SEL

EXT.

Reference

Mode

switch:

INT/VCO

Reference

Lovel

switch:

10 (if

Preamp.

is Model 11B,

set

to

1)

Reference

Level

ve-nter:

CAL

Function

switch:

ACVM

sensitivity:

500

mV

Signal Mode:

FLAT

Signal

Input

switch:

A

l2)

Set

the

Heferencs Frequency

controlstothe

appr

oxi-

mate

frequencyofthe

Reference

signal.

(3)

Connect

the

Reference

signaltothe

~EF

IN

connec-

tor.

NOTE;

The:

amplitude

of

the

Reference

signal

should

be in

the

rangeof100

mV

pk-pkto3 V

pk-pk

,

(4)

Connectacable

frorn

the

REF

OUT

connectortothe

"A"

Input

connector

of

the

preamptlfier.

The

panel

meter

should

show

some

deflection,

If it

does

not,

adjust

the

Reference

Frequency

controls

as

required

to

obtain

some

deflection

and

then

further

arljust

them

fur

maximum

meter

indication.

If

the

meter

indication exceeds full scale. usa

theHeterence

Level

vernier'

to

reduce

the

indicationtoabout

50%offull

scale.

Then

readjust

the

Reference

Frequency

corHI'OIS

for

the

dcairerl

maximum

indication.

This completes the

tuning

procedure. The

internal

bandpass

filterisnow

tuned

to

the

refsrence

frequency.

The

cable

interconnecting

the

REF

OUT

connector

and

the

"A"

Input

of

the

Pre

ampfiflar

can

now

be

removed

and

the

instrument

operated

in

the

usual

manner,

het'!ring in

mind

that.ifthe

reference

frequencyischanqcd,

retuning

will

be

requirud.

•

Fsb-07-02

02:24P

SECTION IV

ALIGNMENT PROCEDURE

P.09

•

,

4.1

INTRODUCTION

The Model

124A

Lock-In

Amplifier"

i~

a reliable

conserve-

tivelv

designed instrument. High

q\J~li(y

stable components

have been

used

throughout

in its construction and one can

reasonably

expect

a long period of

troublefrae

operation

without

any

need for realignment. However, to be assured

of continued high

confidence

in the experimental data

obtained

with

the Model

124A.

it may be advisable to run

through the

followinq

alignment at one year intervals, and

af

ter

.

doing

a repair

on

the instrument. Due to

possible

lntsractton

between

someofthe adjustments, it is necessary

that they be carried

aut

in the indicated

sequence.

Any

decision

to make a

partial

allqnment

should

b~

reserved to

someone

having sufficient knowledge of the

Mod~1

124A

to

hJlly understand all possible interactions. Figure

IV-

t

identifies the adjustments

an(1

board-edge

tcsrpoln

ts

To

identify

the gold

prn-tvps

testpoints

by

their

"TP"

number

{these

tes

tpoints

(Ire

not

located at the board edge), it will

be necessary to refer to

the

appropriate individual-board

parts location diagra.m in section

VI.

Some of these

tostpotnts

are also identified by an

"E"or"B"

number

printed

on the

board.

This number also appears in the text

references.

allowing the

testpoints

to

be easily iderrtified.

Note that this alignment procedure is not intended to be

used in

trcubleshootlnq.

If the

unit

is suspected to be

malfunctioning, go

directly

to SectionV,which deals

with

troubleshoottnq.

The

instrument

must be working

normallv

before it can he aligned,

4.2

EQUIPMENT

NEEDED

(1)

DC

Voltmeter

with

"center

2~rO".

A de

coupled

scope

may be used Instead.

(21

Digital

Voltmeter.

(3) General

purposeoscilloscooe.

(4)

General purpose

sineweve

generator.

(6)

Freuucncv counter.

(51 AC

Voltmeter

such

as tile HP

Mode1400EL.

(7)

Two

BNC

shortinq

pluqs, CW·159/U

IAmph.nol

or

equivalent}.

(8)

Extender

Board, Princeton Applied Research

#1710·00·14035.

(9)

Nonmetallic

alignment tool

16

be used for high

frequency "screwdriver

ediustrneots".

IV-1

4.3 PROCEDURE

4.3A

~RELIMINARY

S1'EPS

(It

Plug in anv of the following preamplifiers: Model 116

operated

direct,

Model 117. Model 11B, or Model 119

operated

direct.

NOTE:

If a Model

118orModel

185

Preamplifier is used. it will be

necessarv

to take

into

account the

factor

of

ten

hiqher

gain of this prc

ampfi-

fier. This is dune by always seleeting a sensitivity

that

is a factor of ten lower than that called for in the

procedure.

(2)

Connect

the

BNC

shorting plugs tu

both

inputsofthe

Prearnpttfter ,

(3)

Remove the

top

and

bottom

covers.

The top

COVE:!r

sli(les

off

to the rear after removing the

two

screws

underneath

the

upper cover overhang at

the

rear of the

instrument.

The

bottom

cover slides

off

to

the

rear

attcr

rcmovtnq

thp.

two

screws

which

secure the two

ruar

humper

feet.

(4) 5et the Model

124A

control,

as

follows.

Sensitivity; 500/.l.V

Mode:

FLAT

Siqnal Frequency Digits:

4,00

Signal Frequency

MUltiplier:

X100

Signal Q: 1

Reference

Frequcncv

Controls:

NORM,

4.00.

X 100

Reference Mode:

INT

NCO

Reference Level: 10
Reference Level Vernier:

CAL

(fully

rtockwlse}

Ph

ase

dial:

0.00'

Phase

switch:

0°

Time Constant:

MIN.

6 (18/12 dB switch: 6 dB

Zero

Suppress

Toggle

switch:

OFF

(center

posttton)

Zero

Suppress dial:

0.00

Function:

HI

DYNAMIC:

RANGE

Calibrate:

100

mV

Power: ON

(5)

Anewafifteen

minute

warmup.

4.38

±24VADJUSTMENTS

(R5028

and

R6010)-

POWER

SUPPLY

BOARD

(1)

Monitor

the voltage at

TP6002

(yellow

testcointl

wi

til

the digital

voltmeter

(referred

to

harcatter

as.

DVM),

(2)

Adjust

R6028

1 24 V

ADJ)

for.

DVM

indication

of

-24.0

V.

(3)

T'an$fer

the

DVMtoTP6000

(rod

testpoint]

,

"

ID

tr

I

o

-..J

I

o

N

o

N

..

N

,f>

"'0

-=-~

'-

~

._.

J

....

~

.'

',T

P I

..•.

".'

,l.

,,/.000,

SIGNAL

__

."..=....:

L!:"'.-:~~,....;t'"~

AMP.

IN

' •.-

~-.:::--SIGNAL

AI.lP.

BOARD

.

''''.'<~'!'

-T

PoIOOI, SiGNAL.

AMP.

OIJT

CIOO?',

I-!IIIj,H

FREQUENCY
NOTCH

ADJ.

RlOIS, FREQ. AOJ,

.,..

-,~]:'

..

:.,.,""

-, ,"t.

~'7

,<....,...

'_

r »

..

---

,~~,

- ,.....

:L,$,~

~:,..~#,J;:.

,

__

l.,~-~

,.~.~,!-:.'l!:iiG;-:'

< 4 _

~"

"'0

BOARD

AUXILIARY
REFERENCE

BOARO

T P SOOO, EXT,

T

iF':

s002fE

f

MIXER

BOARD

~~

~

-

'j-

~"

R3101,ACBAt.

le

0 " "

- LL

"..

J

~'.--:'

R5020

• EXT,

ZE.RO

(SY

..

METRYI

j;i).

~~~~-:'

:-1U§:t~~~5J.7;f,

-:~~~

SUPPLY

.'

...,....

.X

li

!

RG028,

-2.4

V . • ,. .

.'

"

AOJ,

R3218~

OCA I

ZERO

R30~e,

ADJ.

R2.30~.

ZERO

SuP~

CAL,

R2305,

METER

CAL

C4002.

200IHI~

FREel.

ADJ.

<

;.,

'"

o

Figure

I

V·1,

MODEL

124A

ADJUSTMENTS

AND

TESiTPOINTS

•

•

,

Fsb-07-02

02:25P

(41

Adjust

R60lO

(+24 V

ADJI

for a

DVM

indication

of

+74.0

V.

4.3C

INITIAL

REFERENCE

OSCILLATOR

BOARD

ADJUSTMENTS

(1)

Turn

off

the

power.

Then remove the

Reh~rence

Oscillator

board

and

plug

the

Ext~rlder

board

into

the

unitinplaceofthe

Reference

Oscillator

board.

(2) Plug the Reference Oscillator board

into

the Extender

boa-d.

turn

or'!

the power', and

allow

a five-minute

warmup,

(31 E

ZERO3ADJUST

(R43051

(a)

Connect

the de

voltmeter

(not

the

OVMl

10

TP4004 (gray

rcstpomt}.

(bl

Connect a

jumper

between CR4007 and R4050

as indicated on the PMl')

Location

Diagram on

page V 1-16.

Under

no circumstances use chassis

ground as the circuit

may

oscillate.

lei

Adjust

R43Q5 (E

ZERO3ADJI

for 0 V ±1

Vat

the

testpoiru.

Note

that

this

is an

"open

loop"

high gain

adjustrne

nt.

and so

willbedifficult

to

set. and,

once

set. will

drift

quickly from the

ideal

"0"

rcudinq

(d) Remove the

jumper.

The de

voltage

at the gray

testpoint should stabutee at

-3.8

V ±0,5 V.

(4) I

ZERO1ADJUST

(R40401

(at

Connect

two

jumpers.

011(:

hom

TP4005

(B1)

to

ground and the

other

frnm

TP4006 (E11to

ground.

TP4005

and TP4006 are

both

gold·pin

testpoints

down

on

the

board.

Ib) Connect the

voltmetertoTP4DDI

(9,""n

test-

point].

(c)

Adjust

R40~O

(I

ZERO

1 ADJ) so

that

the

monitored

voltageisdrifting

equallv

about

zero.

(dl

Remove

the

[umper

which

extond,

from

TP4006

(Ell

and

ground.

but

Ie

avc

the

jumper

which

extends

from

TP4005

(£31) and

ground.

(5) E

ZERO1ADJUST

(R40301

(al

Adjust

R~030

(E ZE RO 1 ADJ)

for

equal

drift

about

zerointhe

mo

nirored

voltage

(voltmeter

still connectedtoTP400l).

(bl Remove the Jumper which

extends

frorn

TP4005

(B1I ana ground.

IV·:1

P.II

(61 I

ZERO2ADJUST

IR4044)

{al

Connect

two

jumpers,

one

fr

orn

TP4007

(B2)

and

ground.

and the

other

horn

TP4008

(E2)

and

qround,

These are

both

gold.pin

testpoints

down

on the

board.

(b)

Connect

the vcf

tmeter

{(J

TP4003

(violet

test-

point).

(c)

Adjust

R4044 (I

ZERO

21 such

that

the

moni·

toted

voltaqe drifts

equallv

plus

and

minus

about

zero.

(d) Remove the jumper

which

extends

from

TP400B

lE2'

and ground.

but

leave the jumper

which

extends

from

TP4007

(87)

and

ground.

(7) E

ZERO2ADJUST

(aJ

Adjust

R4033 (E ZERO 2

ADJ)

for

equal

drift

about

zero (:IS measured at

TP4003

(violet

test

point).

(b) Remove the jumper which extends

from

TP4D07

(B21 and

grou"d.

(8l Turn off

the

power,

Then

remove

the

Reference

Oscillator

board

from

the

extender,

remove

the

extender.

and return

the

Reference

Oscillator

board

to

its

proper

place in the

instrumenr.Turn

the

power

back on,

4.3D

AUXILIARY

REFERENCE

BOARD

ADJUSTMENTS

(11

INTfRNAL

ZERO

SYMMETRY

ADJUST

(f'15038!

(a)

Connect

the oscilloccupe to the

front-panel

CALIBRATE

OUT

connector.

The sweep

time

should

be

0.2

ms/cm

arid the

oscilloscope

should

be

adjusted

to trigger on the

positive

slope

of

a

222

mV

pk-ok square wave.

(b)

Carefully

note

the

duration

of

the

positive

half

cycle

of

the

square wave. Then trigger

Of]

the

neg,Hive

slopeofthe

square

W[3Ve and

carefully

f~Ot~

the

duration.ofthe

negative

half

cycle.

The

two

"half

cycles"

should

have

exactly

the

same

duratjon.

If

they

do

not,

adjust

RS038

{INT

ZERO

ADJl

as required

to

obt

ain

the

desired

svmmetry.

(3) DC

CALIBRATE

ADJUST

(RGD15)

(.1 Set tile

front-pane!

Calibrate

switch

to 222

mV

dc.

{hI

Remove

the

oscilloscope

from

the

Calibrate

jack

and connect the

DVM

there instead.

lei

Adjust

R5015

(DC

CAL

ADJ)

for.

DVM

indication

of

~.2220

V.

Remove

the

DVM.

Feb-07-02

02:25P

(4)

EXT,

ZERO

SYMMETRY

ADJUST

(R5020)

(al

SC't

the

front

panHI r-tefcr'cnce Level

switch

to

".2" _

{b)

Connect

the

oscilloscope

to TP5QOO (qroc n test-

point].

(d

Connectacable

frorn

the

REF.

OUT

ji:H~k

to

the

REF,INjack.

(d) While observing the square- wave at TP5000,

9r~(ju~lIy

rotate

the

frortt-panal

Reference

Ver-

nier

counterclockwise.

As

the

controlisadjus

ted ,

a

point

will

be

reached

where

the

svmmetrv

of

the square wave will begin to degrade.

Wh~fl

this

occurs.•djust

R5020

(EXT.

ZERO

SYMMETRY

ADJ)

as

required

to

maintain

as near

perfect

symmetry

as.

oossib!e.

Continue

until

the

wave-

form

"locks"toeither"~..orground.

indicatinq

that

the

vernieristoo

far

counterclockwise.

(e)

Set

the

Reference

Level

switch

W 1Q and

ret

ate

the vernier to

the

fully

clockwise

(CAL)

position.

0)

Remove

th~

cable

interconnectinq

the

REF

IN

and

REF

OUT

couneutors.

4.3E

MIXER

BOARD

ADJUSTMENTS

(1)

Turn

off

11~e

power,

Then

remove

the

Mixer

board And

pluginthe

Extenderboard

in its

place.

(2) PI'Jg

the

Mixer

board

into

the

Extender

hoard,

turn

the

power

back

on,

and

allow

a five

minute

warmup.

Set

the

Function

switchtoLO

DRIFT.

(3) DC

AMP2ZERD

ADJUST

IR33061

I.)

Connect

jumpers

from

TP3301toTP3302

and to

TP3303.

Note

that

these ore

not

bua,d'Nlge

toetpof

nts

but

rather

gold'pin

tesr

oointsdown

on

the

board.

(bl

AdjL"t

R3306

(DC

AMP2ZERO)

for

"0"

on Ihe

lr

ont-panel

me ter , This. is a

driftv

open-

loop

adjustment.

(cl Remove

the

jurnp~rs,

(d)

Turn

ulf

the

power.

separate

the

Mixer

board

and

the

Extender,

end

remove

the

Extender.

The

n

returnthe

Mixp.rboard

1()

the

instrument

and

t

urn

Ihe p

owur

back

011.

141

DC

AMP1,CRD

(1137181

fa)

Set

the

Function

switchtoHI

OYN

nANGE_

{b]

Connect

II,e

OvMtothe

FUNCTION

OUT

[ack.

lei

Adjust

R:l218

IDC

AMP

1

Z~R()I

for

0,00

V'I

the

DVM.

Remove the

DVM

..

lV-4

P.12

(~;I

AC

BAL

ADJ

(R31Ol)

(a)

Connect

the

oscilloscope

to

the

front

pane

I

fUNCTION

(JUT

connecter.

(bJ

Set

the

rime

Constant

switchtoMIN,

(01

Adjust

R3101

lAC

RAL

ADJI

for

minimum

riPple as observed at i he oscilloscope.

(d)

Increase

the

ttme

const

arnto300msand

remove

the

oscilloscope.

(61

SYMMETRY

ADJUST

(R30181

(a)

Change

tile

invu

ume

nt

control

sct

tinqs

as tot-

lows.

Signal

Frequency

Diqits:

8.00

Siqnal

Mode, 8ANDI' ASS

SignalQ;20

Function:

ACVM

Sensitivitv:

10

mV

Reference

Frequency

controls:

NORM,

3.( 10\ 1.

X

100

(net

freq.

=

101

Hz)

(b! Remove the

shc'u

ting

plug

from

the- A

Input

of

the

Preampfifjar.

Then

connect

the

External

Signal

Gener

ator

to

the

.,"'''

Input.Besure

the

Input

Selectorofthe

Preamplifierissetto"A",

The

frequency

of

the

signal

generator

output

shouldbe800

Hz.

(c)

Adjust

the

arnptitude

()f

the

~ignal

generator

output

for

an

"on

scale"

indication

on the Model

124A

panel metar .

Then

carefully

Vi;jrV

the

fr

equencv

of

the

siqnal

generator

output

for

maximum

deftecticnof

lhe

panel

rne

tar.

(d)

Readjust

th~

amplilude

of

the

signal

qcnerator

output

forexac

tlv

full scale

dMlection

of

the

Model

124A

panel

meter.

(_I

Sot the

function

switch

to

HI

DYNAMIC

RANGE

;1I~d

the

rime

Constant

switchto1

SEC,

(f)

SP.t

the

Scn~ilivily

switchto100

J1.V_

(g)

Adjust

{he

Reference

Fruquencv

controls

for

a

panel

mater

"be

at"ofabout

1 Hz.

(hi

Adjust

R3018

(SYMMETRY

ADJI

tor

minimum

uk.pk

amplitude

in

the

observed

beat.

I;) Set

the

Pb ase

switch

to

ao'.

Thenoote

cod

rC!':CJr(~

the

pk.pk

amplitudeofthe

beat.

iii

Adjust

R3018

(SYMMETRY

ADJ)asrequired

to

reduce

the

amptitude

of

the

"beat"

by

exacttv

one

h.;llf.

(k) Rp.set

the

Phase

switchto0::'

and

check

to

'wt!

•

•

Fsb-07-02

02:26P

thi;lt

thE;!

"beat" is the same amplitude on 0° as it

is

on

90°,

(l) Reset the

TifT1~

Constant to

300

rus. Rernove the

o;;ignal

from the input and reconnect the shorting

plug removed in step b.

4.3F

INTERM~DIATE

AMPLIFIER BOARD

ADJUSTMlONTS

(ll

ZERO SUPPRESS CAL (R23031

(a) Set the Function switch to LO DR1FT.

(b)

Set

the

Zero Suppress Polar! ty switch

to"

"

lei Set the Zero Suppress dial to 1.00

Ion.

turn from

the

fully

counte

rctockwise

position).

(dl Connect the DVM to the

front-panet

FUNCTION

OUT connector. Then

adjust R2303 IZE RO

SUPPRESS CAL) for a DVM indication of
+10.00

V.

(2) METER

CALIR2305)

(a)

Note

the

panel

meter

indication.Itshould

be

near full scale to the right.

(bl Adjust R2305 (METER CAL) far exactly full·

scale panel

meterdeflection.

(c) Set the Zero Suppress Polarity switch to the

center

(OFF)

position,

4.3G

FINAL

REFERENCE OSCILLATOR

BOARD ADJUSTMENTS

(11 AC BAL 1 and AC SAL 2 ADJUSTMENTS

(R4003

and R40171

(a) Connect the ec voltmeter to

TP4000

(white

testpointl.

Ibl Set

the

Model 124A Refo,ence Frequency

con-

trois to NORM.

4.00,

Xl00

(400 Hz).

(c) Set the Fleference Levol switch to

"1"

and

the

Reference

Vernier

fullv clockwise.

(d)

Connect

the

Frequancv

Counter to the RE.F.

OUT

connector.

(e) Carefully

nate

the .ignal level at TP4000. Then

transfer

the ac

voltrneter

to

TP4002

(blue

test-

point)

and

note

the

signal

level

there.

III Adjust R4003 (AC

SAL11so

that

the

amplitude

at TP4002 is

the

samea'it is at TP4000,

(g)

Note

the ditterence

between

the

frequency

indi-

cared

by

the

counter

(about

400

Hz) and tho

frequency set bv the Reference

Frequency

con-

tj-ols Iexacttv

400

Hz). Then readjust R4003 (AC

P.13

BAL , as

required

to reduce the difference

trequencv

by

exactly3factoroftwo

.

(h) Adjust R4017 (AC SAL21for a

counter

indica-

tion of exactlv

400

HI.

(2) HIGH FREQUENCY AMPLlTUDF ADJUST (C4010}

and

200

kHz FRFO. ADJ (C40021

(.a) Set the Reference FreqllCr"lcycontrols to

NORM,

2.00, and XlOK.

(b)

Note and record the frequency indicated on tho

counter.

(c)

Set

the

Reference

Frequency

controls.toADD

10, 10.00, and X10K.

(d)

Connect

the

ac

voltmeter

to

TP4002

(ulue

testpotnt]

.

(01

Adjust

C4010 (HIGH FREQ, AMP, ADJ) for an

ac volrrne rcr indication of exactly 1 V rrns, Be

sure to use the non-metallic

aliqnrnent

tool

for

this

adiustme

nt.

(fl Adjust C4002 (200 kHz FREQ. ADJ) for a

counter

indicafionexactlv

ten times

that

noted

in step

"b".

(g) Reset the Reference Frequency controls. to

NORM, 2.00, and

Xl0K.

The frequency should

be the same as

notedin"b".

If it has changed,

record the new

treque

ncv,

and

then

set the

Frsquencv controls bock to ADD

10,10.00.

and

Xl0K.

Readjust C4002 (200

kHl

FREQ, ADJI

to obtain a counter reading

exactly

ten times. the

new

frcquencv.

4.3H SIGNAL BOARD ADJUSTMENTS

(11 SIGNAL FREQUENCY ADJUST

(Rl015)

(.1 Set the controls as follows,

Sign.1

Frequency

control"

4.05

Xl00

(405 Hz)

Reference Frequency controls; NORM, 4.05

X100 (401)

Hz}

(Note: Do

not

change

Reference controls during this check]

Signal Mode: BANDPASS

Function:

ACVM

Sign.IO,

100

Calibrate: 2 mV

Sensitivity: 2 mV

Preamp

Input

Selector: A

(b)

Remove

the shorting plug from

the

"A"

Input

of

the preamplifier and connect a cable fr-om the

"AU [npu t to the Catlbrate

Output.

(c)

Adjust

the

third

dialcfSignal

Frequency

con

trot

for

peak

panel

meter

indication.

Feb-07-02

02:26P

(d) Change

the

settinq of tne Signal Q switch from

100 to 10% ENBW. The signal

amplitude should

not

change.

If

it does, change the setting of the

front-panel NOTCH ADJUST screwdriver ad-

justment as required sothat no amplitude change

takes place when the 0 is switched

from

100 to

10"";

ENBW. Leave the 0 set

to

100.

Ie) Now set the third Signal Frequency dial to

"5".

(Note:

Both Signal and Reference Frequency

controls

should

be set the

same.]

(I) Adjust

Rl015

(SIG. FREQ. ADJI

lor

maximum

panel meter

indication.

(2)

HIGH FREOUENCY NULL ADJUSTMENT (ClOOl)

(a)

Set

the

control,

as follows.

Signal

Freq"en<y

controls:

10.95.

Xl0K

1109,5

kHz)

Reference Frequency

controls; NORM, 10,95.

Xl0K

1109.5 kHz)

(b)

Adjust

the

third

dial of

the

Reference

Frequency

controls for peak panel

mater

indication. Care-

hilly

note

the

panel rnster

indication.

(e)

Set

the Q Selector to 10%

ENBW_

If the meter

indication

chanqes, adjust

Cl0D7

(HIGH

FREQ.

NULl)

so

that

there is no

meter

indication

change as the 0 is switched back and

torth

between

100

and 10%

E.N~W.

Leave the 0

set

to

10% ENBW.

(d)

Disconnect

the cable

which

extends

from

CAL

OUT to

the

A INPUT.

4,31 FINAL ADJUSTMENTS

The

following

adjustments. can be made

only

after

the

instrument

has been

thoroughly

warmed

up

with

the cover

in

place.

At

the

factory,

a special

top

cover is used, one

having hales drille(1 in it to give access to

R3101,

R3218.

and C1007.

TtH!:

first

twoofthese adjustments are located

(1I1

the

Mixer

board.

'TI1e

third

is located on the Signal

board.

It is

not

expected

that the per

son

doing

the

afiqnrne

nt

will

drill

holes in his cover. By

substituting

a

piece

of

cardboard

for

tha cover the

alignment

can be

successfully

completed.

Be sure the holes are accurately

located

and

no larger than

they

have to be.

With

the

"cover"

in place,

allow

a one

hour

warmup

before

proceeding.

(11 AC BAL. ADJ IR31011 . MIXER tlQARD

(a) Set

the

fr-ont-pane!

contrcls

as follows.

Reference Frequency controls: NORM.

1,00,

Xl0

Scnairivitv

switch; 5

mV

Time

Constant:

MIN.

Function

switch:

HIGH

{).YNAMIC

RANGE

P.14

(bl

Connect

a shorting plug to the

"A"

Input.

(c)

Connect

the oscilloscope to the FUNCTION

OUT

connector.

(d) Adjust R3101 lAC SAL ADJ) so

that

the

square

wave

ripple

observedisminimum.

It should

b~

p

osaible

to get it

below

400

mV

pk-pk,

(2)

Hilill

~REQUENCY

NUl.L ADJUSTMENT

ICI(07)·

SIGNAL BOARD

(a) Set the

controls

as

fouows.

S;gnal Frequency, 10.95. X 10K 1109.5 kl-lz)

Reference Frequency: 10.95.

Xl0K

(109.5

kHz)

F

unction:

ACVM

Calibrate

and Sensitivitv: ?

mV

(h)

Remove

the shorting plug

from

the

··A"

Input

of

the

Preamplifier

and

connect

a cable Irom the

"A"

Input

to

the

Calibrate

Output.

(c) Adjus.t the

third

dial of the

Reference

Fraquancv

controls

tor

peak panel

meter

indication.

Cere.

fully

note

the

meter

Indication.

(d) Set the Q Selectorto10% E

NBW.

If the meter

indicat

ion changes.

adju't

C1007 IHIGH FREO.

NULL)

so

that

there

is no

meter

indication

change as the Q is

switched

back

and

forth

between

100 and

10"";

ENBW,

(e)

Remove

the

cable

interconnecting

the

CAL

out-

put

and

"A"

Input.

Then

return

the

shorting

plug

to

the

"A"

Input.

(3)

OC AMP 1 ZERD ADJ IR32181 . MIXER BOARD

(a)

Set

the

controls as follows.

Sensitlvltv:

500pV

Signal

Prequencv

Digits; 4,00

Signal Frequancv

MUltiplier:X100

Reference Frequency controls: NORM, 4,00,

X100

Function,

HIGH DYNAMIC RANGE

{bl

Connect

the DVM 10 the FUNCTION OUT

connector.

(cl

Adjust 113218 (DC AMP 1 ZERO ADJI for

000

Vat

the DVM.

This

completes the aliqnrnent. All test aquiprnc m can be

removed

and the covers

secured

in

flla(;:~.

4.3J PHASE METER OPTION ALIGNMENT

The

Ioltowmq

aliqnmcnt is carried

out

only

on

untl~

equipped

with

rhc

Phase

Meter

Option.

This

procedure

is to

he pc r

formud

alter

the

requtar atiqnms nt is

compte

red.

•

•

,

Feb-07-02

02:27P

(1)

Remove

the

top

cover.

Then

turnonthe

power

and

all

owafifteen

minute

warmup.

(2!

Set

the Model

124A

controls

as rcltows.

Input

Selector

{Preemptificrl: A

Sensttlvitv:

50 rnV

Signal Mode; FLAT
Reference

Frequency

controls:

NORM.

4.00,

Xl00

Reference

Mode; INT

Re

terence

Level

switch:

.1 V

Reference

level

vernier: fully

clockwise

Phase dial:

g,OO

(90°)

Phase switch:

270

0

lime

Constant:

300

rna (6 dB)

Zero

Offset

dial:

0.00

(fully

counterclockwise)

Zero

Offset

switch:

OFF

(center

position)

Function

switch:

ACVM

NORM/PHASE

switch

(rear panel]: PHASE

(3}

Connect

a

cable

from

the

Reference

Channel

OUT

connector

to the

Preamplifier

"Iv"

Input,

(4)

Connect

the

oscilloscope,

de

coupled.

to pin 9 of the

Phase board.

NOTE:

This

board is

mounted

aqatnst

the

Signal Amplifier

board

,I'ield.

(51 The signal observed at the

oscilloscnpe

should

bu a

400

Hz square wave.

After

verifying

that

the signal is

as

indicated,

rotate

the

front-panel

Reference

Level

vernier

ccunterclockwiac

as

required

10

make

the

square wave

noisy.

(6)

Adjust

the

A2 DC

control

(located

on

the

Phose

board) for best

svmrnetrv

in

the

observed

square

wave_

Wherl best

svmrnatrvisobtained.

try

further

reducing

the

Reference

Output

amplitude

and

re~)~at

the

symmetry

adjustment.

Repeat

these

two

steps

until

no

further

improvementinthe

setting of (he svmrnetrv

adjustment

Can

be

made.

(7)

Before

proceeding,

check

at pin 5ofthe

Phase board

far

a sinewsve

output

with

an

amplitude

of

approxi-

mately

20·to·60

mV

pk-pk.

Then

set

the

rear-panel

NORM/PHASE

switch

to

NORM.

and

adjust

the

Reference Level Vernier for 1 V

pk-pk

at

the

cacltloscope.

(8)

Connect

tho

oscilloscopetoJ3·9

(Mix",

board}.

Then

set the

Sensitivity

switch

to

5 mV and

adjust

the

Reference

vernier

for

1 V pk-pk

amplitude

in the

observed

signal,

(9)

Set

the

Sensitivitv

switchto50

mV.

(10)

Adjust the A1

GAIN

trim.potentiometer

(located

on

the-

Pha5e board) for 1 V pk -pk

amplitude

il"'l

the

observed signal.

(11)

Set the

NORM/PHASE

switch

back

to PHASE.

Then

set

the

Model

124A

Function

switchtoLOW

DRIFT.

P.15

(12)

Obser

vinp

the

oscilloscope,

adjust

the

fron

t-pane

l

Reference

LHv~~1

vernier

until

the

amplitude

of

the

monitored

sineweve

is just high

enoughtocame

both

negative

and

positive

clipping,

(13)

Adjust

the

CLIPPING

SYMMETRY

trim-paten.

tiorneter

,

located

on

the

Phase

board, for symmetrical

clipping of

the

observed

signal.

Then

remove

the

osciltoscope.

(14)

Connect

the

DVM (digital

voltmeter!

to

the front-

panel

Function

OUT

connector.

Then

adjust the A2

AMPLITUDE

trim-potentiometer

(located

on the

PhaSE:!

board) for a

DVM

indication

fJf

9.00

V_

(15) Corefully se t

the

front-panel

Phase

dial

for

peak DVM

indication.

Then

readjust the A2 AMPL

lTUDE

trim-

pctentiorne

ter

for the

desired

9.00

V reading,

This

completes

the Phase hoard

alignment.

4.4

MODEL

116,l17,OR

119

PREAMPLIFIER

ALIGNMENT

To align the

pre

ampfifiar.

it will be necessary to use a

Model

183

Remote

Preamplifier

Adapter

with

extender

cable.

4.4A

PRELIMINARY

STEPS

(1) Plug

the

Mod£'1

183

Remote

Preamplifier

Adapter

into

the Model 124A_ Then

interconnect

the

Model

183

and

the

Preamplifier

with

the

Extender Cable.

(2)

Remove

the two

screws

at the rear of

the

prearnptifler

that

secure

the

cover. Theil slide the

cover

back

onto

the cable to get it

out

of

the

way.

(3)

Set

the

PreampIifie'

Input

Selector

to

"A-B",

In the

case of a Model

116

or " Model 119. set the Mode

,electortoDIRECT.

(41

set

tlte

Model

114A

controls

as

follows.

Sensitivity:

500

J1V

Mode:

F~AT

Signal

Channel

Frequency

dials:

settinq

immaterial

multiplier

switch:

setting

immaterial

oSelector;

setting

immaterial

Reference Channel Frequency

dials:

4,00.

NOAMA L

multiplier

switch:

Xl00

Mode:

INTNco

Phase swir

ch:

0°

Phase dial;

90.0°
Roference Level: 1.0 V rrns
Function:

NORMA~

Calibrator

Output

Levet:

setting

immaterial

power: ON

4.4B

PROCEDURE

(1) BIAS

AOJUST

(R101!

Feb-07-0Z

OZ,Z7P

(al Connect the

DVM

to

that

end of R130

which

is

ill

common

with

R127 and R133.

(b)

AdjuSl

Rl01

(BIAS

ADJUST)

for

a voltage

indicationof-5.1

V.

(21 DC

ZERO

(R119)

(a)

Transfer

the

DVMtoeither

endofR

132.

(bl

Adjust

Rl19

(DC

ZERD)

for

a voltage indication

of

0.00

V.

!31

COMMON

MODE

REJECTION

(R1361

(a) Connect the

M124A

Rafarance Channel output

to

bod)

the A and B

inputs

of

the preamplifier.

NOTE:

If an

overload

indication

occurs, ignore

it.

(b)

Monitor

the siqnal at R

132

with an ac voltmeter

or

sensitive

osciflcscooo.

Then

adjust

R

136

(COMMON.MOOE

RFJECTION)

for

a null in

the

ac

voltmeter

ind.catron.

(4)

HIGH·FREOUENCY

COMMON

MODE

REJECTION

tcros:

(a) Change the

setringofthe

Reference

Frt~qLJency

controls

to 10,00.

NORMAL.

,10k.

The tre-

quencv

of the JPplied siqnal will now be 100

kHz.

Set the M

124A

Reference

output

level to

0.5 V.

(b~

While

continuinq

to

monitor

the

~ignal

at R132

with

the

ac

voltmeter

[or

csclucsccce).

adjust

C109

for

3 pull in the ac

signe:1

level.

(51 DC

ZERO

CHECK

(3)

Disconnect

the

calibrator

output

fromthe

pre.

amplifler

inputs.

Also, remove the ac vof

tmc

ter

trorn

R 132 and

connect

the

DVM

to this point

instead.

(bt

Ttll;!

iurlicute d vo!

taqe

should he 0 V ±SO

mV.

If

IV-8

P.16

it is

not.

touchupthe

setting of R11 9 as required

to

obtain

on indicated voltage of

0.00

V.

This completes the

preamplifier

alignment. The pr

nampli-

fier

cover

can

now

be

ratumcd

to its normal

posttion,

4.5

MODEL

118PREAMPLIFIER

ALIGNMENT'

To align the

preamplifier,

it will be necessary to use a

Model

183

Remote

Pre

amplificr

Adapter

with

ex

tcuder

cable.

4.5A

PRELIMINARY

STEPS

pp.rform steps 1 through 4

inclusive

of the procedure

outbncdinSubsection

4.4A,

4.58

PROCEDURE

(1) DC

ZERO

(R105

and

R133)

I.)

Connectthe

DVM

to R125.

{bl

Adjust

R105

(DC

ZERO)

for

an

indicated

voltage

nf

0.0

V.

tel

Alternate

the

voltmeter

between resistors R 125

and 11144.and

adjust

R133

(DC

ZERO)

until

the

voltage at both points is the same.

(d) Readjust

R105

IDC

ZERO)

for

0.0

V at R125.

(21

COMMON·MODE

REJECTION

(R130)

AND

RC

SAL

(R1031

(a) Set the Sensitivity to 1

mV.

Then connect the

M124A

Reference

OlJlPUt

to

botn

tht"!

A and B

preamplifier

inputs.

Reduce

the frequency to

40

H~.

Ibl MOr,i10r the

~Ignal

at R125

wit

h the

ac

volnno

ter.

Then

»Itcmctetv

adjust

11

no (CMR

ADJ.I

and

R103

(He

BAll

for a null ill the rne

asured

si!:jrl;:l!

level.

Continue

un til no

Iur

ther

improvcmen

t in

the null can be

obtained.

This.

completes t he

prc

amplifier

nliqnrne

nt.

Apr-lS-02

03:06P

SECTION

V

TROUBLESHOOTING

P.Ol

5.1

INTRODUCTION

This section consists or a series of procedures to be

followed in

troubleshooting

the Model 124A_ The purpose

ot

the

procedureisto

narrow

the

trouble

downtoa specific

circuit

boardbymaking

voltage

and

waveform

chacksat

critical points. Once the faulty board has been identified,
the

operator

can

contact

the

factory Or

one

of its

autnorized

representatives

for

advice

on

howtoget

the

instrument

back

into

operation

in

the

shortest

possible

time, It

may

prove

expedienttosimply

exchange

the

board

for a new one. In the case of units still in Warranty, it is

partit.ularly

important

that

the

factorv

or

one

of its

authorized

representativesbecontacted

before

doing

any

repair

workonthe

board

itself.

because

any

damage

that

occurs as a result of

unauthorized

work

could

invalidate

the

Warranty.

Although

past

experience

indicates

that

most

instrument

failures

turn

out

tobethe

fault

of a

specific

component

failure on

one

of the boards, it is of course perfectly

possible

that

some

component

other

than

the

one

located

on a

circuit

board

couldgobad.

Where

thisisthe

case;

the

penon

troubleshooting

will have

to

appropr

lajelv

adapt

the

procedure

to

isolate

the

faulty

component.

In

g€r"HHal,

it is suggestod

that

the

person

who carries

out

the

troubleshooting

procedure

be well

grounded

in basic

transistor

electronics.

The

procedure

is

more

tobethought

of as a general

guide

foranexperienced

repairman

than

as a

minutely

detailed

treatise

to

educate

tho newcomer.

5,2 EQUIPMENT

REQUIRED

111

General purpose oscilloscope,

(2) DC Voltmeter.

(3) Signal

Generator

abletosupply a 1 V rms sinewave at

1 kHz,

(4)

Extender

Board, Princeton Applied Research

#1710,00,14035,

This item is

not

really required for

any 01 the

checks called for in

the

following pages.

However, it will

prove

indisoensible tor

the

trouble-

shooter

who

wantstogo a

little

beyond

the

checks

providedtoisolate

the

trouble

more

specifically

than

is possible

with

the

procedure.

Iii using

the

board,

be

sure

to

install

and

remove

circuit

boards

with

the

pOWP.r

off,

5.3

INITIAL

STEPS

(I)

Remove tne

top

cover. It slides

offtothe

rear

after

the

two

screws

which

secure it are

removed,

These

two

screws are

locatedonthe

undersideofthe

upper

cover

overhangatthe

rearofthe

instrument,

V-l

(2)

After

rernovinq

the

hold

down

strap,

lift I?ach

circuit

board and give cnch

1:1

brief

visual

damage

inspection.

If any

"charred"

or

otherwise

damaged

components

are

noticed,

there

is little pOint in going

further.

(3) Be sure to check the fuses, There are two on the

Power

Supply

hoard

and

oneatthe

rear

panel.

They

are

discussedinSubsection

5.4,

which

follows.

5,4

POWER SUPPLY

(1) On

the

Power

Supply

board.

check

the

voltage at

TP6000

Ired

testpcint)

lor

1:24

V and at

TP6002

(yellow

testpoint)

for

-24

V. If the voltages are

correct.

go on

to

Subsection

5.5. If

the

voltages are

incorrectormissing,

proper

power

supply

operation

must

be

established

before

anv fur

tber

checks

can be

made. Note from the

schematic

on page V1-23

that

the

-24

V regulator supplies the reference voltage for

the

+24 V

regulator.

Thus,

any

trouble

with

the

-24

V

supply

would

cause

lossofregulation

in the

+24 V

circuit

as well.

(21

Note

that

th~

unrequlatad

inputtoboth

regulators

is

fused.

If a

check

shows

one

of

these

fuses

to be

blown,

try

replacingitonce.

If it

blows

again/ it

will

be

necessarytolocate

and

repair

the

short.

One

way

to

narrow

thi]

short

down

IS to pull atl

boards

but

the

Power

Supply

board

{power

off

when

boards

are

removed

or

replaccdj

, and

thentoturn

the

power

back on.Ifthe fuse still blows, the trouble is most

likely on

the

Power Supply

board,

If it does

not

blow,

the

board

having

t1w·

short

Can be easily

determined

by

returning

them

one

at a

time

until

the

fuse blows,

(3)Ifthe regulator input tuses are

not

blown,

but

the

±:24

V levels

ar@

missing or

Incorrect,

check

the

unregu-

lated

supply

levels

(nominally

±31 V)

to

isolate

the

problem

to

the

Power

SllPply

board

or

to

the

Unregulated

Supply

cornpooents (line fuse. trans-

former.

rectifiers,orfilter

capacitors).

Note

that

the

high·puwer

transistors

are

not

located

on the

Power

Supply

board,

but

are

instead

mounted

on

the

same

plateasthe

transformer

ann filter

capacitors.

5.5 REFERENCE CHECKS

(1) Control Settings

Ml!!'ter:

Check

the

mechanical

zero

and

adjust

it if

necessary.

Preamplifier~

Plug in a Model 117 Preamnttner,

01'

a

Mode'

116

or 119 operated in the DIRECT

mode. A

Model 118 or Model 185 can also be

used,

but

certain

Signal

Channel

cheeks

will have

tobemodifiedasindicatedintha

text.

Apr-lS-02

03,07P

Sensitivity:1mV
Sign.1

Channel

Mode:

FLAT

Reference

Channel

Mode:

INT/vCO

Reference

FreQve"cy;

3.99.

Xl00

(399

Hz)

Reference

Level: 1 V rrns

(red

inner

knob

fully

elockwisel

Phase switch: 0°

Phasedial: 90u

Time

Constant:

300

rns, 6

de/octave

Zoro

Offset

dial:

0,00

(fully

counter

clockwise]

toggle switch; center

(OFF)

position

Function

switch:

NORMAL

Calibrator:

1 mV

(100

IlV if

preamplifier

is a Model

1181

Power switch: ON

(21

Reference

Oscillator

Board

(a)

Check

for

-3.8

V

±05

V at

TP4004

(gray

testpoint

on

Reference

Oscillator

boardl.

As

inrtiCilt@d

by

the

schematic

on page

VI-15.

TP4004

monitors

the

output

of

A3,

the

Butler

berwcan

the

front-

panel

Refel"~nce

Frequency

dials

and

the Voltage

Controlled

oscillator. If the

Voltage reading is

correct,

one can reasonably

assume that the dial-controlled voltage dividers

and Buffer A3 are

functioninq

norrnatlv.

(bl

Monitor

fP4002

(blue

testpctnr]

with

the

oscn.

Icscope

and

check

fora2.8

V ±,3 V

pk-pk

smewave

at

399

Hz,

NOTE:Afaulty

cucuit will

usuallv give indication of a "gross" error. For this

reasonitis

not generally advisabit! to spend

much

time

trying to

determine

wne

the

r the

trequencv

or amplitude are

"exactlv"

as specified. This

appliestoboth

this

step

andtothe

remainder

ot

the procedure,

[c]

Similarly

check

for.

2,8 V

±,3

V pk-pk at

399

Hz at

TP4003

(violet),atTP4000

{whitel,

and

at

fP4001

(green).

These

tastpoints.

together

with

TP4002.

give

access

to the four outputs of the

Reference Oscillator. If these signals are normal.
one can be reasonably

confident

that the Refer·

ence Oscillator

bourd

is rUrlctiollil1Q

uormntlv

Idl Transfer the

oscitloscope

to the Reference Out-

put

connector

(front

panel) and check for a 2.8

V ±.3 V pk-pk slnewave at

399

Hz. If this Signal

is as indicated, one can assume that the Refer-

ence

Output

Power Arnpl lfler.

located

on the

POWP,r

StIlJIJ/Y

nonr

d, is

functioning

normally.

(3) Auxiliary Reference

Bnard

(a)

ConnectCI1 V

ok-pk

sinewave at 1 kHz fr orn the

signal generator to the Reference Channel IN

connector

_

Ib)

Set

the

Reference

Channel

Mode switchtoEXT,

The

REF

UNLOCK

light

.should

glow for a few

V-2

P.02

seconds and then extinguish.

(c)

Monitor

the signal at the Reference Out con-

nector

with

the

oscilloscope.

One should observe

a 1 V rms

(2,8

V ±.3 V

pk-pk)

sinew.ve

at 1 kHz.

(dl

Set

the

toggle

switchtoEXT

f/2.

Again,

the

REF

UNLOCK

light

should

glow,

this

time

for

about

seven

seconds/ and then extinguish.

Ie)

Verify

that

the

signal at

the

Reference

QUI

connector is unchanqed in

amplitude

but

that

its

frequency has

doubled

(2 k

Hzl_

(I)

Reset

the

Referenne

Mode

switchtoINT/VCO

but leave the signal generator connected to ttw

Reference

Input

connector.

NOTE: If

normal

indications

were obtained in steps

"a

r

'

through

"f",

one can reasonably assume that the

Au>(iliary

Reference

boardisfunctioning

normally

and

go

on

to

Subsection

5.6. If abnormal indications were

noted, thereisa good Possibility

of

a malfunction on

this

board. The

remaining

steps in this

sequence

may

prove hp.lpfullnnarrowing the problem

down

to the

specific malfunctioning circuit.

(g) >5V

Regulator:

Check

the

voltageatthe

positive

erld of capacitor

C5004.

This voltage,

which

is

indicative of

the

current

flow

through

Q5OO1

(and

hence

the

+5 V

load),

should

be +11 V ±3

V.

C5004isthe

35IJF

capacitor

located

near

the

upper

edge

of the board.

Next

check. the +5 V

regulator

output,

which

should

be +5 V

10,5

V,

This is

most

easily

checkedatthe

positive

end

of

capacitor

C5005.

the

151lF

6 V

capacitor

located

near

the

upper edge at about the center of the

board.

{hi

Schmitt

Triggers:

Check

fora399

Hz

square

waveatTP5001

(blue

testpotntl.

The

upper

and

lower levels of the square wave should be

+4.5

V

±1

Vend

0.3V10.3Vrespectively.Ifthe

sign.

I

is as described, the

Schmitt

Trigger driven from

the

180C.

output

of the

R~flHence

O:!:cilIMQr is

functioning

normally.

Next

transfer the oscilloscope to

TP5000

(green

testpoint},

A 1 kHz square wave with the same

level

limitsasdescribed

in

the

preceding

para-

graph should be observed.Ifthe signal is

normal.

one can

conclude

that

the

Schmitt

Trigger driven

from the External Reference signal is functioning

normallv,

Ii)

Frequency

Comparator; A thorough checkout

procedure for this circuit is beyond the

scope

of

this

manual.

Neverrhaless.

failure to pass the

following two tests is a clear indication of

malfunction,

If these tests are passed, no clear

conclusions

concerning the

normalityofthese

circuits

can be made.

Apr-1S-02

03:07P

Test

1: Check for +4 V ±1 V at

pin

11

of
integrato<! circuit U500G. NOTE: IC packages
U5001

through

U5006

are labeled as

"I"

through

116"

with

labels

consisting

ot small

etched

foil digits on

the

,iet. of

the

board

opposite

the

components.

Pin 1 of

each14digit

package is simllartv

marked.

The

pins are

counted

clockwise (viewed from

the

label side).

Test

2: Check

fora399

Hz square wave at

TP5002

(grav

testpolnt).

The lower levei of

the

square wave

should

be 0 V.

There

should

be two

upper

levels.

both

between

+3 and +4 V.

The

,ignal

generator

shouldbedisconnected

from

the

Reference

Input

at this time.

NOTE: If

step,

"s"

through

"in

fail to identify the

fa(lllY circuit.

but

the

board

continuestomalfunction,

there

is a

,trong

possibility

that

the

trouble

is with

the

associated wiring or switches.

5.6 SIGNAL CHANNEL

All of

the

gain

,witchinginthe

Model

124Alsdone

bv

means

of relays. In

the

following checks.

the

various

amplifiers are

i,olatedbVappropriatelv

,electing

the

San-

sitivity and

Function.

Bv applVing a suitable ,ignal and

checking

at

critical

points

•.amalfunctioning

amplifier can

be

quicklv

identified. Table

V-I,

which lists

the

gain and

energized relays for all possible

combinationsofSensitivity

and

PSD

Function,

is provided as a

convenient

reference.

Note th

at overload lel/el

,igMls

are applied at various

points

throughout

the

following

procedure

to

assure

that

the

signal levelatthe

outputofthe

earlv amplifiers will be

above

the

noise floor.

Anvtime

the

applied signal is

greater

than

the

selected $8l1Sitivitv, overload is a possibility, and

the

operator

should

notbeconcernedifthe

Overload light

glows

during

suchameasurement.

However; if

the

Overload

light

should

glow with normal signal levels

applied,

a

malfunctionisindicated.

anditshould be

corrected

before

proceeding.

5.6A

PREAMPLIFIER

NOTE; It

the

preamplifiertobe used is a Model

118

or

Model

185,

set

the

Calibrator

Output

lovel to 100/J.V and

the

Sansitivity to 1

mY.

In the case of a

tvpe

117

Preamplifier, Or a Model

116or119

operated

direct,

both

the Sensitivitv

and

the

Calibrator

Output

level

shouldbeset

to 1 mY.

For

all preamplifier"

the

Function

switch

should

be

settoNORMAL.

(H

Connectacable

from

the

Calibrate

Outputtothe

'lA"

Preamplifier

Input.

121

Monitor

the

signal at

TP1000

Igreen

testpoint)onthe

Signal

board.

The observed signal

shouldb.an 11 mV

pk-pk

square

wave at

399

Hz, indicating

that

the

preamplifier gain is five (fifty

for

a Model 1181.

NOTE:

A square wave with an rms value

(fundamental

rrequencv

component

onlv) of 1 mV has • pk-pk

amplitude

of

2.22

mV.

Therefore,

the

total

,ignal

V·3

P.03

amplitudeatth@

outputofthe

Preamplifieris2.22

x 5

• 1t mY. This

"X2.n"

factor

mustbetaken

into

account

throughout

the

entire

procedure.

The opera-

tor

is again

cautioned

nottospend an

undue

amount

of

effort

convincinq

himself

that

the

observed

signals

comply

with

the

text

descriptions

downtothe

last

decimal

place. In

most

instancesofmalfunction,

the

signal discrepancy will be 'alarge as

to

leave no

doubt.

If the signal is as

indicated.

the

operator

can

conclude

that

the

Preamplifierisfunctioning

properly

in its

gain·of-five

mode

(gain-of·fifty

for

Model

118

or

Model 1851. If

the

signal is

incorrect

or missing,

the

trouble

probablv

is in

the

Preamplifier

and

the

operator

can

proceedtothe

schematic

for

his particu-

lar Preamplifier if he wishes to

troubleshoot

further.

As can be seen from the Signal

board

schematic

on

page V

1-9,

the

signal is

actually

being

monitored

after

relev KlOOSonthe

Signal

board.

Hence, if the signal

is missil1g. it

mightbeworth

cMecking for

the

signal on

coupling

capacitorC1004

to isolate

the

relav. Also,

take a

moment

to be sure

that

the

Calibrator

Output

Soigl1alisnormal.

that

is, a square Wave

with

a

pk-pk

amplitude

of

2.22

ttmes

the

selected

Calibrator

Out-

put

level.

(3) Change the Sensitivity

setting

to

500

/J.V,

thereby

energizing Preamplifier relay

K100

and

incr-easing

the

preamplifier gain to X50

(X500

for a Model

118

Ora

Model

185).

The

amplitudeofthe

signalatTP1000

should

increase

to

111 mV pk-pk, reflecting

the

increased gain. If thls

check

is

normal,

one

can

reesonablv assume

that

the

preamplifierisfunctioning

normauv,

at least

with

respecttoproviding

the

proper

gain, Noise and

common-mode

rejection checks are

bevond

the

scope

of this

procedure.

If this check

does

not

give a normal

indication,

but

step

2 does give a

normal

indication,

relav

Kl00

shouldbesuspected.

5.6B

SIGNAL

AMPLIFIER

The

Signal

Amplifier

gain,

measured

from

the

outputofthe

Preamplifiertothe

outputofthe

Signal Amplifier, is

either

XlO

(KlO08

energized] or Xl

(Kl009

energizedl. Note

thot

the

gain of

the

amplifier circuit is arwavs

Xl0.

The

factor

of ten gain

reduction

achieved

when

Kl009

is

energized

andK1008

is de-energized is accomplished by

reducing

the

amplitude

of

the

signal applied to

the

amplifier

input

with

a retav

controlled

attenuator.

(1) Transfer the oscilloscope

to

TPtOOI (violet

testpoint):

The

observed signal

should

be a 1.11 V

pk-pk

square

wave.

indicating

that

the

Signal Amplifier has a gain

of

ten.Ifthe

signal is

normal,

chances

arB'

the

amplifier

circuitisfunctioning

normally.

If

the

signal is absent,

the

problem

could

lie

with

the

amplifier

circuit

Or

with

K 1008jthe

energized

input

relay.

(2'

Set

the

Sensitivitv switch to

"10

mV".

The

signal

amplitude

should

decrease to 11 mV pk-pk. indicating

that

the

gain

of

both

the

Preamplifier and Signal

Amplifier

went

down

by a

factoroften.Ifthe

signal is

as

indicated.

chances

are

that

the

Signal Ampl

ifi€!r

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03,07P

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Apr-15-02

03,OBP

P.05

•

•

lnput

Attenuator

is.

functioning

norrnallv,

If

an

incorrect

reading is

obtained,

K1009, the

input

atten-

uatcr

relay energized

with

this Sensitivity switch

settinq,

should

btl

checked,

(31 Sot

the

Signal Mode

switch

to BANDPASS and the

Signal

Channel

Frequency

control,

to

3.99,

X100

(399

Hz).

Then

set

the

Signal Q

switch

to "10".

The

observed

'ignalatTP1001

mould

now be sinusoidal

with

an

amplitude

of 14 mV pk-pk. It may be

necessarytoslightly

adjust

the

third

Signal

Frequency

dialtoobtain

the

indicated

amplitude.

The

amplitude

drops

off

,harplyifthe

dial is set high or low. If

the

indicated

effects

are

observed,

the selective amplifier

circuitsofthe

Signal Amplifier are

functioning

nor-

mally.

5.6C

INTERMEDIATE

AMPLIFIER

There are

two

amplifiers

en

the

Intermediate

Amplifier

board,

each

with

a nominal gain of

ten.

The relay switching

on

the

board,

controlledbythe

Sensitivity $Witch,

actuates

various

attenuators

50

that

the

overall

board

gain varies

Irom X

100toXO.2, according to

the

Sensitillity switch

position,

Not

all possible gains are

checked.

Instead, each

decadeischecked,

and also

the

Xl,

XO.5. XO.2

sequence

within

one

decade.

This is

sufficienttocheck

all of the

relays

as wei! as

the

amplifiers.

Note

from

the

schernatic

on

page VI-13

that

the

front-panel Sensitivity

Adjustment

affects

the gain

of

the second amplifier

and

hence

the

overall gain of

the

Intermediate

Ampiifier, Hence, it may be

necessary

to

change

the

setting of this

adjustmenttoobtain

signals of

the

indicated

level. Howeller,

once

set.

the

control

setting

should

not

have to be changed again, at least

not

for

the

remainder

of

the

Intermediate

Amplifier checks,

(11

Set

the

Sensitivity

,witchto100nVand

the

Function

,witch

to NORMAL. Then set

the

Calibrator

output

to

"2

IlV"

(200nVwith

a Model

118

or 1651.

12)

Monitor

the

signal at

TP2oo0

fgreen

testpointl,

The

observed ,ignal

should

be a

399

Hz sinowave

with

a

pk-pk

amplitudeof0.28

V. It i,

oerfecnv

normal for

this signaltobe

obscured

by noise. If this signal is as

indicated,

one

can

assume

that

both

amplifiers on

the

Intermediate

Amplifier

board

are

functioning

nor-

mally. If

the

signal is

not

normal,

the

problem

could

be

with

oneofthe

two

amplifier

circuitsorwith

One

of

the

relays. With

this

combination of Sensitivity and

Function,

the

energized relays are

K2003,

K2005, and

K2007.

(3)

Set

the

Sonsitivity to

"IIlV"

and

the

Calibrate

Output

to

20

IlV

12

J,lV

with a Model

116

or

165).

The

observed signal

should

still have

the

same

amplitude

Ithe gain

reductionisexactly

compensated

by

the

increased

calibrator

output),

but

the noise

should

have

gone

down

by a

factoroften.

The

only

relay change

between

thi,

,tep

and

the

preceding

oneisthat

K2004

is

now

energized

and

K2oo3de..

nergized.

{41

Set

the

Sensitivity

switch

to 10

IlV

and

the

Calibrate

Outputto200

J,lV

(20

IlV with a Model

118

Or 1651.

As in

the

preceding

step,

the

decrease

in gain Is

compensatedbythe

increase in

calibrator

output

and

the

amplitudeofthe

obserlled signal

should

remain

constant

(0.28

V

pk-pkl.

A

further

factor

of ten

reductioninthe

observed noise will

take

place. The

reiav

state

cnanqas are

that

K2006

ls "Ow energized

and

K2005isd.·e"ergized.

15)

Set

the

Sensitivity switch to 2 mV

and

the

Calibrate

Output

to 2 mY. The

amplitudeofthe

observed

signal

should

decrease to

0.14

V pk-pk, indicating

the

gai"

reduction

which

occursasK2007

is de-energized

and

K2008

is energized.

16)

Set

the

Sensitivity switchto5 mY. The

amplitude

of

the observed signal

should

decrease to 57 mV

pk·pk,

reflecting

the

gain

reduction

which occurs as

K2008

drops

out

and

K2009

is energized_

Allofthe

Intermediate

Amplifier

board

relays have now

been

checked.

If

proper

operation

to

this

point

was

obtained,

the

lnterrredlate

Amplifier

board

can be pre-

sumed

to

be

functioning

normally.

5.60

MIXER BOARD AC GAIN

*_

The

Mixer

board

ac gain is

either

Xl1

or X1.1 as

determined

by

ettenuator

contrcttinq

relavs K3101 and

K3102_

The

gains are made 10%

"high"tocompensate

for

the

fact

that.

although

the

instrument

reads

out

in rms, the

Mixer is average responding.

(11 Set

the

Sensitivity

switchto50

/.IV

and

the Calibrate

Outputto500

/1V

(50

IlV with a Model 116or185).

Then

monitor

the

signal at the tront-panel

SIGNAL

MONITOA

connector.

The observed signal should

have a uk-pk

amplitudeof28.3

mV_This sig"al will be

noisy,

(2) Set

the

Sensitivity switchto100 /1V and Increase the

Calibrator

Output

to 1 mV

(100

J,lV

with

a Model

116

Or 185).

The

observed signal should remain

the

same

in

amplitude

(gain decrease

compensated

by increased

calibrator

output)

but

the

noise

should

decrease.

If

the

indicated

signal levels were observed.

one

can

assume

that

the

ac amplifier

portion

of

the

Mixer Circuitry is

functioning

normally.

5.6E

MIXER

SCHMITT

TRIGGERS

Connect

the

oscilloscope to

TP3002.

One

should

observe a

400Hzsqusre

wave

with

tho

lower

level at

-12Vand

the

upper

one

at 0 V. If this waveform is as indicated,

the

Mixer

Schmitt

Triggers are

probably

working

normally.

If

the

waveformisabsent,

eheck

for a

2.8Vpk-pk

sinewave

at

C3005

betors

concluding

there

is a

probleminthe

Schmitt

Trigger circuit.

Note

from

the

schematic

on page VI-19

that

the

blue

testpoint

gives accesstoonly

one

"half"

of

the

cornpternentarv

Schmitt

Trigger

output.

The

comple-

ment

(collectorof03003)

could be checked at

R3112orat

R3110_

V·5

Apr-15-02

03:0BP

5.6F

MIXER

CIRCUIT

(1)

Set

both

the

Sensitivity

and

Calibrate

switchestoS

mV (Calibrate

Outputto500

MV

with

a Model

118),

and

the

Function

switchtoLO

DRIFT.

(2)

Monitor

the

signal at the

junction

of

R3202

and

R3204.

Then

set

the

Phase switch to 270°.

The

observed

sign~1

should

be a full-wave

rectified

sine-

wave, althOugh a slight

adjustmentofthe

Phase dial

may be required

to

obtain this waveform. The

amplitudeofthe

half-waves

shouldbeabout80mV

relative to a 0 V baseline. If

the

slgnal is as indicated,

the

Mixer

circuitisprobably

functioning

normally.

S.6G DC

AMPLIFIERS

With Sensitivity switch

.etting,

from

1 /lV

through

S

mv,

th8 de gain is

determined

solelv by

the

posltion

of the

Function

switch. In LO

DRIFT

it is

X20.

in NORMAL it is

X200,

and

in HI DYNAMIC

RANGE

it is

X2000.

For

a

giver; sensltlvitv, changing

the

function

does

not

change the

output

de level because

the

ae gain varies as well astokeep

the

overall hnrument gain

constant.

Thus

the

de amplifiers

are

checked

simply by

monitoring

the

de

output

and

observing

that

it does

not

change as

the

Function

switch is

rotated

through

its

three

PSD

positions.

(1)

Adjust

the

Phase dial end

third

Sign.1

Frequency

dial

for

maximum

panel

meter

deflection.

Then

set

the

screwdriver

adjustable

Sensitivity Adj.

control

for

exactly

full·scale

panel

meter

deflection.Ifthis

cannot

be

done,

thereisprobably

B

matfunetion

in Oneof

the

de

amplifie"

Or in

the

meter.

The

meter can be

eliminated

by checking the de level at

the

front-panel

Function

Out

connector.

Ten volts

corresponds

to

full-scale panel

meter

deflection.

(21Atthis

point.

the

Function

switch

should

still be

set

to

LO

DRIFT.

Successively set it to NORMAL and

then

to

HI DYNAMIC RANGE. The panel

meter

should

continuetoindicate

full scale ±3%.Ifit

does,

one

Can reasonably assume

that

the

de ametlflers are

functioning

normallvv If necessary.

one

could

chock

the

output

of

the

first dc

amplifier

separatelv, This is

most

easily

done

at R.3228.

the

emitter

resistor of

03203

(schematic

on page V1-22).

The

voltage

there

shouldbe-1.5

V ±O.S V. The

outputofthe

second

amplifier

should.

of course, be +10 V.

(31 Check

the

ACVM

function

by

setting

the

Function

switch

to ACVM.

The

meter

indication

should

remain

unchanged.

Note

that

ac

voltmeter

operation

is

achieved

simply

by

taking

the

drive to the Mixer

Schmitt

Trigger

from

the Signal

Channel

instead of

from

the Reference Chennet. No

new

cirl';l,.Iits. are

activated.

If

the

instrument

has

passed

all

teststothis

point.

but

the

unit

is still

malfunctioninginsome

way

not

revealed

by

these tests.

then

the

problemisbevond

the

scope of this

V-6

P.06

troubleshooting

procedure

and

the

operator

should

contact

the

factory

or

oneofits

authorized

representatives for

advice on

howtoproceed.

5.7 NOISE CHECKS

These

checks

allow

the

operatortodetermine

whether

the

internally

generated

noise in his

instrumentisnormal,

NQt~

that

these

checks

vary

accordingtothe

tvpe

of preamplifier

used.

(1)

Set

the

front-penel

controls

as follows. NOTE:

If

pre.mplifier

is a Model

184.godirectlytostep

10.

Input

selector

IModels

116.117.

118.

& 1191: A

Transformer/Direct

switch (Models

1168<119):

DI-

RECT

Ground

tsolattcn

(Model lBS): IN

Sen.itivity

Models

116.

117.&

119:

lmV

Model,

118&

185:

10mV

Sign.1 Mode: BANDPASS

Sign.IFrequency

dials:

4.05

Sign.1 Range:

Xl00

Sign.I"0":

100

Reference

Frequency

dials;

4.05

Roference

Frequency

Range:

X100

Phase

switch:

270

0

Phase dial:

90·

Zero

Off,et

toggle

switch:

OF F

(center

position)

Function

swrtch: ACVM

Calibr.te

switch: 1 mV

(2)

COnnect a

cable

from

the

front-panel

CALI8RATE

connectortothe

preamplifier

input,

(3)

Adjust

the

right-most Signal

Frequancv

control

for

peak

panel-mater

indication.

(4)

set

the

Function

switchtoNORMAL.

Thsn

adjust tho

Phase

dial for

peak

meter

indication.

(5) Sot

the

front-panel

Sensitivity Calibrate

adjustment

for

exactly

full-scale meter indication.

(6)

set

the

Sign.1

"0"

switch

to 10.

(7) Remove

the

cable

that

interconnects

the

Calibrate

Output

and

the

Pre

smplitler

Input.

Then

short

the

preamplifier

input

using a shorting plug

such

as the

CW-159/U.

(B)

Set

the

Sensitivity switch to

100

nv.

Then

set

the

Time

Constant

switch

to

100 ITlS (Preamplifi@r is

Model

116,

117.or119)orto

300ms(Preamplifier;s

Model

l1Bor18S/.

(9)

Note

the

pk-pk

meter

fluctuates

l'lbout

zero

over

a ten

second

period.

If

the

preamplifier

is a Model

116,117.

Or 1

t9,

the

fluctuations

should

not

exceed

±25% of

meter

fuli scale. If

the

preamplifier

is • Model 118 or •

;

Apr-lS-02

03,09P

Model 185,

the

fluctuations should

not

e~ceed

±80%

of

meter full scale.

(101

Model 184 only. Set the controls as indicated in step 1

with the following exceptions. The SensitivitYofthe

Model 124A should be set 10 1 /lV, the Q to 10, the

Time

Constant to 1 SEC, and the Preemplifier Range

control to 10-7AN.

DO NOT ATTEMPT STEPS 2

V-7

P.07

THROUGH 9 WITH A MODEL 184 PREAMPLIFIER.

(11) Connect a

BNc

"cap"

(shielded open) to the Model

184 Input.

(12)

Note the

pk-pkfluctuations

of

the panel meter over a

ten second period. They should

not

exceed ±50% of

meter full scale.