Tektronix Z Instruction Manual

IV l/X IN I U A L

Tektronix, Inc.

S.W. Millikan Way • P. O. Box 500 • Beaverton, Oregon • Phone Ml 4-0161 • Cables: Tektronix

Tektronix International A. G.

Terrassenweg 1A • Zug, Switzerland • PH.042-49192 • Cable: Tekintag, Zug Switzerland • Telex 53.574

070-251

WARRANTY

All Tektronix instruments are warranted
against defective materials and workman
ship for one year. Tektronix transformers,
manufactured in our own plant, are w ar

ranted for the life of the instrument.

Any questions w ith respect to the w a r
ranty mentioned above should be taken up
with your Tektronix Field Engineer.

Tektronix repair and replacement-part
service is geared directly to the field, there
fore all requests for repairs and replace
ment parts should be directed to the Tek
tronix Field Office or Representative in your

area. This procedure w ill assure you the
fastest possible service. Please include the

instrument Type and Serial number with all
requests for parts or service.

Specifications and price change priv
ileges reserved.

Copyright © 1960 by Tektronix, Inc.,
Beaverton, Oregon. Printed in the United

States of America. All rights reserved. Con
tents of this publication may not be repro
duced in any form w ithout permission of
the copyright owner.

CONTENTS

W arranty

Section 1

Specifications

Section 2

Operating Instructions

Section 3

Circuit Description

Section 4

Maintenance

Section 5

Calibration

Section 6

Accessories

Section 7

Parts List and Diagrams

® Type z

m

TYPE Z PLUG-IN UNIT

CALIBRATED DIFFERENTIAL CO MPACTO R

.1 0 0 0 CM. DYNAMIC SCALE LENGTH

/UUU V.f'l- " ■ ■ ’ — _

COMPARISON VOLTAGE -x

VOLTS/CM

(ATTE NUATION !

VAR. ATTEN

I PUSH TO j

0 I 5 C O N N E C T

SIGNAL j

ptSCO N N E d

signal

u n i a eh

ATTEN.

GAIN

ADJUST

b a ia n c e

'position

VOLTS/CM

{ A T T I N U A T I O N )

onto on.

PORTIA I

rlATEONIX,

Type Z

http://manoman.sqhill.com

O INI 1

SPECI F I CATION

General Information

The Type Z Plug-In Unit is a calibrated differential com

parator preamplifier designed for use in all Tektronix

Type 530-, 540-, 550-, or 580-Series Oscilloscopes. The

unit may be used for three different modes of operation:

(1) as a conventional plug-in preamplifier, (2) as a differential

input preamplifier, or (3) as a calibrated differential com-
pa rator.

As a conventional preamplifier, the Z Unit alone has a

risetime of 24 nanoseconds and a maximum sensitivity of

0.05 volt per centimeter of deflection. Table 1-1 summar
izes the risetimes and bandwidths available when the Z
Unit is used in combination with various types of Tektronix

oscilloscopes.

TABLE 1-1

Z Unit and

Type.-

Risetime in

Nanoseconds*

Bandwidth, —3 db,

Megacycles/Seconcl*

532

70 5

531 or 535

39 9

536

40

9

531 A, 533, or 535A

35

10

541, 543, 545,
541 A, 545A,
551, or 555

27 13

581 or 585**

27 13

*For signals which do not overscan the graticule.

**Type 81 Adapter must be used.

In differential input mode of operation, the dynamic
range of r'zlOO volts allows the application of common
mode signals up to 100 volts to be applied to the unit with
out attenuation. The common-mode rejection ratio of
40,000 to 1 at dc or low frequencies allows measurement

of differential signals less than 50 mv in amplitude on

7+c 100-volt common-mode signals.

As a calibrated differential comparator, the Z Unit has

an effective screen height of ih2000 cm at maximum sensi

tivity. Within the dynamic range of :J:100 volts, calibra'ed

±DC comparison voltages can be added differentially to
the input waveform to permit a maximum of 0.005% or
5 mv per mm to be accurately resolved.

Vertical Deflection Factors

0.05 to 25 volts per centimeter in nine calibrated steps;
also continuously variable (uncalibrated) between steps and
up to 60 volts per centimeter.

Input Impedance

1 megohm :Ul % paralleled by 24 pf.

Maximum Allow able Combined DC and Peak AC
Input

600 volts, ac-coupled.

Maximum Common-Mode Signal

r'rlOO volts at 0.05 volt per centimeter. Higher voltages

are permissible with larger vertical deflection factors.

Common-Mode Rejection Ratio

40,000 to 1 at 0.05 volt per centimeter with a 1-kc sine

wave, lower at other sensitivities and higher frequencies.

At 0.05 volt per centimeter, a 200-volt (p-p) 1-kc common

mode signal produces less than 1 mm of vertical deflection.

Comparison Voltages Available

Three voltage ranges are provided: 0 to r‘-l volt, 0 to

~10 volts, and 0 to : 100 volts. An accurate 10-turn
potentiometer is used to select the comparison voltages
over these ranges.

Comparison Voltage Regulator

A regulator circuit maintains comparison voltages es
sentially constant and independent of normal power supply
voltages supplied by the oscilloscope.

1-1

Specifications — Type Z

Comparison Voltage Accuracy

Within 5 millivolts (0.5%) on the ±l-v o lt range.
Within 20 millivolts (0.2%) on the ± 10-volt range.
Within 150 millivolts (0.15%) on the ±100-volt range.

Maximum Trace Shift

2 mm due to input grid or gas current.

Comparison Voltage Drift

Less than 0.1 % per 100 hours operation.

Temperature compensated over normally expected tem
perature range. Air filter in oscilloscope should be main
tained clean, particularly when using the Z Unit.

10-Turn Potentiometer Linearity

0.05%

Measurement Resolution

Resolution accuracy, at 100-volts comparison voltage—

0.005%
Maximum resolution—5 millivolts per millimeter.

Transient Response and Permissible Signal Volt
age Rate of Change

Rate of rise—1 volt per 6 nsec, maximum. If this rate

is exceeded, grid current will flow in the input stages.

Rate of fall—1 volt in 5 nsec, maximum. If this rate is

exceeded, the amplifier will momentarily cut off. If over

driven by a sufficiently fast pulse, the amplifier will ‘‘run
down" linearly at the above rate.

Because of the wide dynamic amplitude capabilities of the

Z Unit, transient response is a function of signal amplitude.

Mechanical Specifications

Construction—Aluminum-alloy chassis.
Front panel—Photo-etched.
Net weight—6 pounds.

Accessories

2—Instruction Manuals

1-2

®I

A front-panel view of the Type Z Unit is shown in Fig. 2-1.

In addition, a brief functional description is given of the
front-panel controls, input connectors, Securing Rod, and
Mechanical Lock.

Connecting the Z Unit to the Oscilloscope

Connect the Z Unit to the associated oscilloscope by

inserting the unit into the plug-in compartment and tighten

ing the Securing Rod. With the Intensity control of the
oscilloscope turned fully counterclockwise, switch on the
oscilloscope power. Normally it is necessary to wait a few

minutes for the oscilloscope and plug-in to warm up and
stabilize. Then turn up the intensity and set the oscilloscope
triggering controls to produce a free-running sweep. Posi
tion the trace on the screen using the POSITION control
and the oscilloscope beam-position indicators.

Preliminary Operational Adjustments

After the Z Unit has warmed up and stabilized, check

its operation to see if adjustment of one or more of the
following controls is necessary. Be sure that the oscilloscope

used in conjunction with the Z Unit is correctly calibrated in
the vertical-deflection circuit, and that the calibrator output
voltage is correct.

1. Amplifier DC Balance

If the trace cannot be centered on the screen when -he

POSITION control is set near midrange, the AMP DC BAL
adjustment (see Fig. 2-2) must be checked. Need for this
adjustment arises mostly when the Z Unit is transferred
from one oscilloscope to another. To make the adjustment,
set the POSITION control to midrange, remove the left
side panel from the oscilloscope, and adjust the AMP DC

BAL control to position the trace behind the horizontal
centerline of the graticule.

2. Differential Balance

Differential balance may be quickly checked by applying
100 volts of calibrator signal to both input connectors. Set
both VOLTS/CM switches to .05, the AC-DC switches to
DC, and the Mode switch to A-B DIFF. Ignoring the posit ve
and negative spikes, adjust the DIFF. BAL. control to elimin-

SECTION 2

O PERAT I N G

I NSTRUCTI ONS

ate any square-wave response (that is, to obtain a straight-

line appearance of the trace).

3. Variable Attenuator Balance

Any vertical shift of the oscilloscope trace when the VAR.
ATTEN. control is rotated, with no input signal applied,
indicates need for adjustment of the variable attenuator

balance. This adjustment must be made in conjunction
with the differential balance adjustment (step 2) due to
interaction between the circuits. Repeat the two adjust
ments until both are correct.

Set the Mode switch to A ONLY and remove any input
signals. Adjust the VAR. ATTEN. BALANCE control to
eliminate any vertical shift of the crt trace as the VAR.
ATTEN. control is rotated. Check to see if the trace can
be centered as described in step 1 (Amplifier DC Balance).
If not, repeat step 1.

4. Gain

The gain adjustment should be checked periodically to
assure correct vertical deflection factors. It should also be
checked when the Z Unit is transferred from one oscilloscope

to another. The adjustment is made using the calibrator

signal from the oscilloscope.

Set the Mode switch to A ONLY and apply 200 milli
volts of calibrator signal to the A input connector. Make
sure the VAR. ATTEN. control is set fully clockwise. Set
the A VOLTS/CM switch to .05 and rotate the GAIN AD
JUST control for exactly 4 centimeters of vertical deflection.

Input Signal Connections

It is often possible to make signal connections to the
Z Unit with short-length, unshielded test leads. This is par
ticularly true for high-level, low-frequency signals. When
such test leads are used, you must also use a ground con
nection between the oscilloscope and the chassis of the
signal source. (Note: Excessively long test leads may cause
parasitic oscillations.)

In many applications, however, unshielded leads are
unsatisfactory for making signal connections because of
pickup resulting from magnetic fields. In such cases, shielded
cables should be used. You must be sure that the ground
conductors of the cables are connected to the chassis of
both the oscilloscope and the signal source.

In high-frequency work it is usually necessary to terminate

signal sources and connecting cables in their characteristic

2-1

Operating Instructions — Type Z

VAR, ATTEN.— Varies the verti
cal d e fle ction factors betwee n
ranges o f the V OLTS/C M co n 
trols.

Po larity— Selects the co mpa r
ison voltag e p o la rity.

VOLTS/C M— Selects the
ca l d e fle ction factors.

verti-

A INPUT— Connecto r fo r coupl
ing input dc or ac vo lta g e s to
pream plifier.

AC-DC— Determines wheth e r
Inpu t signals are dc couple d or
ac coupled.

PUSH TO DISCONNECT
NAL— D isconnects signal

pream p lifier input.

DIF F. BAL.— A d justs the
am p lifier fo r maximum

fe re ntia l re jection ratio.

PUSH TO DISCONNECT SIG
NAL— Disconnects signal from
pream p lifier input.

AC-DC— Determ ines wheth er

inp u t signals are dc couple d or

ac coupled.

B INPUT— Connector fo r coupl
ing Inp u t dc or ac voltages to
pream plifie r.

Range— Selects the ap p rop ri
ate co m pariso n volta g e ra nge.

Mechanic al lock— Locks H eli-

dial when pressed dow n ward.

H e iid ial— Adju s ts the com 
parison voltag e ov er the range
selected by the Range switch.

VAR. ATTEN, BALANCE— A d
justed to preve n t v e rtical trace
shift as the VAR. ATTEN con
tro l Is ro tated.

POSITIO N— Sets the vertical
positio n of the trace on the
oscilloscope screen..

VOLTS/CM — Selects the ve rti
ca l deflec tio n factors.

GA IN ADJUST— Sets the de
flection factors o f the p re
am p lifie r to ag ree w ith the

fro nt panel m arkings.

Fig. 2 -1 . Functions of fro n t-p a ne l c o ntro ls, inp ut connectors. Securing Rod, and Mechanical Lock.

2-2

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Operating Instructions — Type Z

Fig. 2 -2 . Left rear side view of the Z U n it showin g location of the
AMP DC BAL adjustment.

impedances. Unterminated connections result in reflections
in the cables and cause distortion of the displayed wave

forms.

When input signal connections are made, consider the
effect of loading upon the signal source due to the input
circuit of the Z Unit. The input resistance of the Z Unit is 1
megohm which is generally adequate to limit low-frequency
loading to a negligible value. At high frequencies, however,
the input capacitance of the Z Unit and the distributed
capacitance of cables become important. Capacitive load
ing at high frequencies may be sufficient to adversely

affect both the displayed waveform and the operation of

the signal source. Both capacitive and resistive loading
can usually be limited to negligible values through use
of attenuator probes.

Use of Probes

Attenuator probes reduce loading of the signal source.
However, in addition to providing isolation of the oscillo
scope from the signal source, an attenuator probe also de

creases the amplitude of the displayed waveform by the
attenuation factor of the probe. When making amplitude

measurements with an attenuator probe, be sure to multi
ply the observed amplitude by the attenuation of the probe.
(Additional information concerning probe attenuation will
be found under Differential Preamplifier Operation and At
tenuator Test Point portions of this section of the manual.)

An adjustable capacitor in the probe body compensates

for variations in input capacitance from one instrument to

another. To assure the accuracy of pulse and transient meas
urements, this adjustment should be checked frequently.

To make this adjustment, set the oscilloscope calibrator
controls for a calibrator output signal of suitable amplitude.

Touch the probe tip to the calibrator-output connector and
adjust the oscilloscope controls to display several cycles

of the waveform. If the probe cable is connected to the
A input connector on the Z Unit, adjust the probe capacitor
for flat tops on the calibrator square wave. If it is connected
to the B input connector, adjust for a flat bottom on the
square wave.

Conventional Preamplifier Operation

When the Z Unit is used for conventional preamplifier
operation, the Mode switch should be placed in either
the A ONLY or the —B ONLY position. Input signals should
then be connected to the corresponding input connector.
Operation of the unit in the two positions is essentially the
same except that signals applied to the B input connector
are inverted on the display. Positive voltages produce an
upward deflection when applied to the A input connector

and a downward deflection when applied to the B input
connector (see Fig. 2-3).

Fig. 2 -3 . W ave form s a pplie d to the A Inpu t connector p roduce an
up righ t d isp lay , wh ile w aveform s ap p lied to the B Inpu t are in 
verted.

The amount of vertical deflection produced by a signal

is determined by the settings of the VAR. ATTEN. control

and the VOLTS/CM switch. Calibrated deflection factors

indicated by the settings of the VOLTS/CM switch apply
only when the VAR. ATTEN. control is set fully clockwise.
Serious errors in display measurements may result if the
setting of this control is inadvertently moved away from

the fully clockwise position.

The range of the VAR. ATTEN. control is approximately

2.5 to 1 to provide continuously variable (uncalibrated)
vertical-deflection factors between calibrated settings of
the VOLTS/CM switches.

Voltage measurements may be made directly from the

oscilloscope screen by noting the deflection factor on the

appropriate VOLTS/CM switch dial, and the amount of

deflection on the screen. Then multiply the deflection on
the screen by the setting of the VOLTS/CM switch and the
attenuation factor, if any, of the probe.

Placing the AC-DC switch in the AC position inserts a dc
blocking capacitor in series with the input circuit. In the
AC position, the input time constant is 0.1 second and the
low-frequency response is —3 db at 2 cps. Thus some

attenuation exists even at 60 cps. Because the input dc
signal may be suppressed by means of the calibrated com

parison voltage feature, there are few occasions where the

ac-coupling mode will be needed. Two principle occasions

are: (1) When it is desired to get a quick look at the ac
component of a signal which has a large dc component

and (2) where there is a difference in dc levels of the two
signals to be observed during differential mode of operation.

The tolerances of the input circuit time constants (at

—3 db frequency) are nominally =h2%. When tighter

®T

2-3

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Operating Instructions — Type Z

matching between A and B input circuits is necessary, one
input dc blocking capacitor may be “ padded" with a small
additional capacitance, generally less than 0.001 /ifd.

The PUSH TO DISCONNECT SIGNAL buttons allow the
signal to be momentarily removed from the input without
the bother of disconnecting the probe or coaxial input con
nector. This provides an easy method for finding the base

line of zero voltage level on the crt. (When utmost ac
curacy in measurement is required, trace deviation from
exact zero due to gas or grid current must be considered.)
The POSITION control may then be adjusted to make the
zero level lie at any graticule mark desired.

Differential Preamplifier Operation

The primary purpose of differential operation is to elim
inate undesirable common-mode signals. The term “common-
mode signal" is defined as that signal which is common
to both inputs of a differential amplifier. It most commonly,
but not necessarily, represents unwanted hum or noise.

This feature can be used, for example, to observe the
signal across one circuit element while effectively eliminat
ing the remainder of the circuit from the observations. Tnis
is accomplished by connecting the signal at one end of
the element to one input of the Z Unit and the signal at
the other end of the element to the other input of the unit

Differential operation between the two inputs is obtained

when the Mode switch is in the A-B DIFF. position. Maximum

common-mode rejection is obtained when both input at
tenuators are set to XI. Common-mode rejection is a func
tion of frequency in practical amplifiers. It is 40,000 to 1
for dc common-mode signals in the Z Unit and remains
near that value through audio frequencies, decreasing as
the frequency increases.

The differential or common-mode rejection ratio of the
Z Unit describes the ability of the unit to reject common
mode signals. Common-mode rejection ratio is best defined

as the ratio of amplifier response to that part of the input

signal not common to both, with respect to the response

of the amplifier to any input signal which is common to

both inputs. It is defined numerically in the following ex

ample.

If an input signal consists of 100 volts (p-p) of 60-cps hum

and 0.1 volt of desired signal, the 100-volt hum would cause

-nr

----

;—7

-------

times 100 volts or 2000 cm of deflection, and

.05 volts/cm
the signal would cause an additional 2 cm of deflection.

If conventional preamplifier operation were used, the de

sired signal would be deflected off the screen and could
not be observed. However, if differential operation is

used and common-mode rejection were 2000 to 2 or
1000 to 1, then the hum and desired signal would each
produce 2 cm of deflection. The resulting combined wave-

i

r s r

i

/

/

la ) 100-volt, 6 0 ~ hum plus 0.1-volt, 1-kc square

wave. Vertical Sensitivity: 25 v/cm. Mode: A ONIY.
Sweep Rate: 5 miliisec/cm.

7

r

7

, V

L

j

\

/

V

/

\

u.

V /

(c) 100-volt 60 — hum only. Control settings similar

to (a) except Mode is — B ONLY.

(b) Top 4-cm of waveform (a ) at vertical sensitivity

of 0.05 v/cm. Mode: A-Vc, decoupled.

V c S i + S O v .

Sweep Rate: 0.5 millisec/cm.

++++

4+B ++++ t+H

W+

H + +

+-H4 ++++

m+

++++

id ) 60— hum is differentially suppressed and only the

1-kc square wave is displayed. Vertical Sensitivity:

0.05 v/cm. Mode: A-B DIFF., dc-coupled. Sweep Rate:

0.5 millisec/cm.

2-4

Fig. 2 -4. Com m on-mode rejection b y the Z U nit.

Operating Instructions — Type Z

form could be seen but not easily measured. With a
common-mode rejection of 40,000 to 1, the hum would be
reduced to 0.5 mm and the desired signal alone could be
accurately observed and measured.

The preceding example is shown pictorially in the series
of waveform photographs shown in Figs. 2-4(a), (c), and (d).
A combined 100-volt hum and 0.1-volt square-wave signal
is shown in Fig. 2-4(a). Although the square wave does
not seem to be present, it can be made visible by increasing
the sensitivity of the Z Unit to 0.05 volts/cm, which increases
the effective height of the waveform to 2000 cm. A dc com
parison voltage (using differential comparator operation
explained later in this section) of approximately 50 volts
is used to bring the top 4-cm portion of the combined
signals into view, shown by the waveform photograph in
Fig. 2-4(b). The 2-cm high square-wave signal, riding on
top of the hum but not synchronized with it, causes the
separated appearance of the hum signal. Fig. 2-4(c) shows
the 100-volt (p-p) hum signal which, by itself, is applied to
the B input connector. The resulting display using common
mode rejection is shown in Fig. 2-4(d).

The following five operational notes provide helpful in
formation to obtain optimum performance from the Z Unit
using this mode of operation.

1. Large signal response of the Z Unit as a differential am
plifier is shown in Table 2-1.

TABLE 2-1

Signal Handling Capabilities of the Z Unit

Attenua

tion

Maximum

Calibrated

Sensitivity

(volts/cm)

Minimum

Uncalibrated

Sensitivity

(volts/cm)

Maximum

Signal or

Common

Mode
(volts)

Magni ■
fication
Factor

XI

.05 .12

100

2000X

X2

.1

.24

200

1000X

X5

.25 .6

500 400X

X10

.5

1.2 1000*

200X

X20

1

2.4 1000*

100X

X50

2.5

6

1000*

40X

XI00

5

12

1000*

20X

fox

X200

10

24

1000*

X500 25

60

1000*

5X

^Maximum continuous dc input level with AC-DC switch set to DC: 800

volts; momentary maximum dc level should not exceed 1000 volts.

2. Any difference in attenuation factors of the two attenua
tors (VOLTS/CM switches) will decrease the differential
capabilities of the Z Unit to the extent shown in Table 2-2.

3. Both AC-DC switches should be in the DC position if
possible as explained under Conventional Preamplifier
Operation.

4. Differential balance may decrease slightly as the VAR.
ATTEN. control is adjusted away from the calibrated
(clockwise) position.

5. Either input signal alone may be viewed without switch
ing back to the A ONLY or —B ONLY positions of the
Mode switch by depressing the PUSH TO DISCONNECT
SIGNAL button of the other input channel.

TABLE 2-2

Attenuator Performance

Attenuation

Attenuator

Accuracy, ± %

Input Resistance

Tolerance, ± %

XI 0

1

X2

1

1

X5

1.5 1

X10 and up 2

1

If conventional probe is used, the probe resistor tolerance of 1 % de
creases the Z Unit attenuator accuracy. These inaccuracies can be ac
curately measured as explained later under Attenuator Test Point.

Calibrated Differential Comparator Operation

When the Mode switch is in the A-Vc or Vc-B position,
the Z Unit is a calibrated differential comparator or slide-
back voltmeter. The calibrated comparison voltage, which
has a range of 0 to 100 volts, may be added (differentially)
to either input signal.

In this mode a calibrated dc voltage is internally applied
to cancel out any unwanted dc component in the applied
signal, thereby allowing accurate measurements of relative
ly small ac signals riding on top of relatively large dc
signals.

When the Mode switch is in the A-Vc position, the com
parison voltage is applied internally to the amplifier input
where the B signal is ordinarily applied during differential
mode of operation. The switches and input connector in
the —B ONLY section of the front panel are not used.
Signals applied to the B input connector will not be ob
served.

In Vc-B position of the Mode switch, the comparison
voltage is applied to the amplifier input where the A input
signal is normally applied during differential mode of op
eration. All switches and the input connector in the A ONLY
section of the front panel are not used.

The dc comparison voltage is set by 3 controls: the COM
PARISON VOLTAGE Polarity, Range, and Helidial. The
Range control has ranges of 0 to 1, 0 to 10, and 0 to 100
volts. The Helidial varies the comparison voltages over
this range and indicates the precise comparison voltage at
any particular setting.

NOTE
The regulator circuit in the Z Unit maintains con
stant, accurate, comparison voltages as long as

the oscilloscope — 150- and + 225-volt power
supplies are in regulation and within their output
voltage tolerance ratings. Be sure these and other
regulated power supplies in the oscilloscope are

operating properly.

Differential comparator mode of operation may be used
to make the following voltage measurements: (1) dc volt
age measurements, (2) ac signal measurements superimposed
on dc, and (3) high-amplitude ac signal measurements.

2-5

Operating Instructions — Type Z

1. DC Voltage Measurements.

When the Z Unit is used to make any dc voltage measure
ments, it is first necessary to establish a reference line on
the screen of the oscilloscope. This line will usually be the
horizontal centerline of the graticule. To establish the
reference, set the COMPARISON VOLTAGE Polarity switch
to 0 and press the appropriate PUSH TO DISCONNECT
SIGNAL button to disconnect the input signal. (As noted

previously under Conventional Preamplifier Operation, slight
trace deviation from exact zero must be taken into account
to obtain best accuracy.) Use the POSITION control to
set the oscilloscope trace at the centerline of the graticule.

To measure a dc voltage component of ±100 volts or less,
apply the input signal to one of the connectors. For ex
ample, suppose the signal is applied to the A input
connector, then proceed as follows:

(a) Place the A VOLTS/CM switch to .05 and the Mode

switch to the A-Vc position.

(b) If the dc voltage component to be measured is posi
tive, place the COMPARISON VOLTAGE Polarity switch to
the + position. If it is between 10 and 100 volts, set the

COMPARISON VOLTAGE Range switch to 100 V.

(c) Rotate the COMPARISON VOLTAGE Helidial to bring
the desired portion of the trace onto the screen. Set the
trace exactly on the reference line with the Helidial.

(d) Recheck the reference as described in the first para
graph.

(e) When the zero reference line and signal trace appeiar
at the same place on the screen, the input voltage and
the comparison voltage are equal.

2. AC Signal Measurements Superimposed on DC

Small ac signals superimposed on a dc component can
be measured accurately by first using the comparison volt
age to effectively eliminate the dc component. The ac
signal can then be measured in the same manner as in con
ventional preamplifier operation. The VAR. ATTEN. control

must be kept clockwise to obtain correct results.

3. High-Amplitude AC Signal Measurements.

High-amplitude ac signals, subject to the rise rate and fall
rate limitations listed in the Specifications section, can also
be measured with the Z Unit at maximum sensitivity. This
type of measurement is very similar to dc measurements
except that it is not necessary to establish a zero voltage
reference line unless measurements of both ac and dc volt
age levels are to be made. To measure the voltage differ
ence between two points on the waveform, proceed as fol
lows:

(a) Set the Helidial to zero and position one point on the
waveform to the horizontal centerline of the graticule.

(b) Use the Helidial and Range controls to bring the other

desired point to the centerline.

(c) The voltage difference between the two points is

read from the Helidial and the setting of the Range switch.

AC-DC Voltage Measurements Exceeding ±1 0 0
Volts.

If ac, dc, or both ac and dc voltage components are
greater than ±100 volts, the .05 settings of the VOLTS/CM
switches cannot be used. It will be necessary to use a lower
sensitivity in order to prevent overdriving the preamplifier
and to prevent exceeding the comparison voltage available.
To obtain the correct voltage measurement, use the multi

plication factor which appears below the volts per centi
meter setting on the VOLTS/CM knob. The product of the
multiplication factor times the comparison voltage used

is the input signal voltage.

ATTENUATOR TEST POINT

Two applications included here show how the ATTEN
TEST PT connector, located on the left side of the Z Unit,
can be used to make attenuation factor or ratio checks on
probes used with the Z Unit and on the internal attenuators
of the unit. The test point, when connected to a voltage
divider network under test, forms a bridge circuit as shown
in Fig. 2-5. The crt is the null indicator and the Helidial
reading is used to determine the attenuation factor or ratio
of the divider resistors.

A third application describes how the unit may be used
to measure external resistors.

± 1 0 0 V

Fig. 2 -5 . S im plified diagra m o f the brid g e circuit fo rm ed durin g
use of the ATTEN TEST PT connector.

2-6

Operating Instructions — Type Z

Checking Attenuation Accuracy of VOLTS/CM
Switches

The attenuation accuracy of the X2, X5, XI0, and X20
positions of the VOLTS/CM switches can be determined by
utilizing the 100-volt comparison voltage available at the

ATTEN TEST PT connector. The following procedure ex

plains how to check the X2 position of the A VOLTS/CM
switch. The other positions are checked in the same manner,

1. Set the A VOLTS/CM switch to X2, the AC-DC switch to
DC, and the Mode switch to A-Vc.

2. Place the COMPARISON VOLTAGE Polarity switch to 0

and position a free-running trace to the center of the screen
for reference,

3. Remove the left side panel from the oscilloscope. Connect
a test lead from the A input connector to the ATTEN TEST
PT connector (see Fig. 2-6).

Fig. 2 -6. Left side vie w of the Z U nit sh o w ing the lo ca tion o f the
ATTEN TEST PT.

CAUTION

Use care in making the test lead connections to
prevent shorting the 100 volts at the ATTEN TEST
PT to ground. An accidental short circuit may
damage the CAL. 4 adjustment (R7684).

4. Set the COMPARISON VOLTAGE Polarity switch to +

and the Range switch to 100 V.

5. Rotate the Helidial to return the trace to the reference
level obtained in step 2. Use the vertical trace indicator
lights to aid in returning the trace. In this example the
Helidial should end up in the vicinity of 5.00 (or 50 volts).

6. Divide the Helidial reading into 10 to obtain the at

tenuation factor. (Assume the Helidial reading to be 5.02.

5.02 divided into 10 is 1,99 or an attenuation factor of XI.99.

The attenuation ratio is 1.99 to 1).

Checking Attenuation Accuracy of Probes

Passive attenuator probes can be checked for attenuation
accuracy by a method similar to that used for determining
the VOLTS/CM attenuation accuracy. Referring to Fig. 2-5,

divider resistor R1 is the 1-meg input resistor in the oscil

loscope, R2 is the resistor in the probe. The procedure which
follows describes a method for checking a 10X attenuator
probe.

1. Set the A VOLTS/CM switch to XI, the AC-DC switch to
DC, and the Mode switch to A-Vc.

2. Place the COMPARISON VOLTAGE Polarity switch to 0

and position a free-running trace to the center of the screen

for reference.

3. Remove the left side panel from the oscilloscope [if not
already removed). Connect the probe cable connector to

the A Input connector on the Z Unit and connect the probe

tip to the ATTEN TEST PT.

4. Set the COMPARISON VOLTAGE Polarity switch to -j-

and the Range switch to 100 V,

5. Rotate the Helidial to return the trace to the reference
level obtained in step 2. In this example the Helidial should
end up near a reading of 10 volts,

6. Divide the Helidial reading into 100 to obtain the at

tenuation factor of the probe.

Checking External Resistors

External resistors can be checked for value against the

1-megohm input resistance of the unit by using the bridge
circuit of Fig, 2-5. In this application, R2 is the resistance
to be measured and R1 is the internal 1-megohm resistor.

The following procedure can be used:

1. Set the A VOLTS/CM switch to XI, the AC-DC switch to

DC, and the Mode switch to A-Vc.

2. Place the COMPARISON VOLTAGE switches to 0 and

100 V. Position a free-running trace to the center of the
screen for reference.

3. Remove the left side panel of the oscilloscope. Connect
one end of R2 to the A input connector and the other end
to the ATTEN TEST PT (see Fig. 2-6) by using a jumper
wire.

4. Set the COMPARISON VOLTAGE Polarity switch to -f.

5. Adjust the Helidial to return the trace to the reference
level obtained in step 2. Use the vertical trace indicator

lights to aid you in returning the trace.

6. Let H be the Helidial reading. Then use the folowing
equation to find the value of R2.

R2 = R1 1 ^ - = — ^ Megohms.

If R2 is small compared to 1 megohm, the Helidial read
ing will be very close to 10,00 making it difficult to obtain
an accurate measurement. When this occurs, R1 can be
shunted by an accurate external resistor which will permit
Helidial readings around 5.00. The only restriction on the
shunting is that the total resistance to ground from the
ATTEN TEST PT should not be less than 20 k. This limits the
current drawn from the test point to a maximum of 5 ma. If
the 1-megohm resistor is shunted, R1 in the equation will
have to be changed to the new value of the 1-megohm
and shunt resistors in parallel.

@1

2-7

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