Fluke 8040A Service manual

maintenance manual

John Fluke Mfg.

Co.,

Inc.

P.O.

Box

43210 Mountlake Terrace, Washington 98043

/

/

Table

of

Contents

SECTION

1

INTRODUCTION AND SPECIFICATIONS

1.1

.

INTRODUCTION

.

1.6

OPERATING INSTRUCTIONS

2.1

2.3

2.6

2.8

2.10
2- 12
2- 14

2.16

2.18

2.22

THEORY OF OPERATION

3.1

3.3

3.4

3.6

3.8

3.10
3-1 1

3.13

3.15

3.17

3.19

3.26

3.28

3.33

3.35

3.38

SPECIFICATIONS

.

INTRODUCTION

.

SHIPPING INFORMATION

.

INPUTPOWER

.

OPERATING FEATURES

.

OPERATING NOTES

.

.

.
.
.

.
.
.
.
.

.
.
.
.

.

.
.
.
.

.

.

Fuse Replacement
Overrange Indication

Input Overload ~rotectlbiA
ASSEMBLY AND INITIAL OPERATION
FUNCTION SELECTION EXAMPLES

INTRODUCTION
OVERALL FUNCTIONAL DESCRIPTION

Introduction 3-1

Analog Circuits

Digital Circuits
CIRCUIT DESCRIPTION

Introduction

Input Divider

Current Shunts

Buffer

A/ D Reference

Ohms Voltage Source 3-5

RMSConverter 3-5

A/DConverter 3-5

Timing and Control 3-6
Display 3-6

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TITLE PAGE

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;

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1-1

1-1
1-2

2-1

2-1
2-1
2-1
2-1
2-1
2-1
2-1
2-1
2-3
2-5

3-1

3-1
3-1

3-2

3-2
3-2
3-2

3-2

3-2

3-2

3-2

(Continued on next page)

SECTION

TITLE

PAGE

4 MAINTENANCE

4-1

.

INTRODUCTION

4-4

.

GENERAL MAINTENANCE

4-5

.

4-7

.

4-9

.

4-1

1 . PERFORMANCE CHECK

.

4-13
4-15

.

4-17

.

4-19

.

1

.

4-2
4-23 . CALIBRATION 4-5
4-26

.

4-29 . TROUBLESHOOTING

5 LISTOFREPLACEABLEPARTS

5.1

.

INTRODUCTION

5.4

.

HOW TO OBTAIN PARTS

.

5.7

6 OPTIONS & ACCESSORY INFORMATION

6.1

6.3

6.4

6.6

6.8

6.10

6.12

6.14

6.16
6- 17

6.20

6.25

6.27

6.29

6.30

6.32

6.34

6.35

6.39
6-4 1

6.44

6.45

6.49
6-5

6.54

6.55

6.58

6.59

6.61

6.62

USE CODE EFFECTIVITY LIST

.

INTRODUCTION

.

RECHARGEABLE BATTERY PACK, 8040A.7005

.

.

.

BATTERY COVER KIT, 8040A-7004

.

BATTERY COVER, 8040A-7007

.

CARRYING CASE (C88)

.

BATTERY CHARGER/ ELIMINATOR

.

TEMPERATURE PROBE (80T-150)

.
.

.
.

DELUXE TEST LEAD KIT (A80)

.

CURRENT TRANSFORMER, CLAMP-ON (801-600)

.

.

.

HIGH VOLTAGE PROBE (80F-5)

.
.

.

.

HIGH VOLTAGE PROBE (80F-15)

.
.

1

.
.

HIGH VOLTAGE PROBE (80K-40)

.
.

HIGH FREQUENCY PROBE (81 RF)

.
.

HIGH FREQUENCY PROBE (82RF)

.

.................................................................

......................................................

............................................

Access Information
Cleaning
Fuse Replacement

.............................................................

....................................................

.....................................................

..............................................

DCVolts
ACVolts 4-3
Resistance Measurements 4-3
Directcurrent 4-3
Alternating Current

.............................................................

.............................................................

...............................................

........................................................

....................................................

........................................................

Required Method for Votlage Source Connection 4-5

.................................................

..................................................

......................................................

..............................................

......................................................

Introduction
Operation

...........................................................

............................................................

................................................

Introduction
OperatingNotes
Operating Instructions

Introduction

Operation

Introduction

Cleaning

Calibration

Introduction

Cleaning

Calibration

Introduction

Introduction

Introduction

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4-1

4-1
4-2
4-2
4-2
4-2
4-2
4-3

4-3

4-8

5-1

5-1
5-1
5-1

6-1

6-1
6-1
6-1
6-1
6-1
6-1
6-1
6-3
6-3
6-3
6-3
6-3
6-4
6-4
6-4
6-5
6-5
6-5
6-5
6-5
6-6
6-6
6-6
6-6
6-7
6-7
6-7
6-7
6-7
6-7

.

'

7

SCHEMATIC DIAGRAM

.........................................................

7-1

List

of

.

Illustrations

FIGURE

TITLE

Control. Indicator and Connector Locations
Function Selection Examples
8040A Block Diagram
Simplified Buffer Circuit 3-3
Simplified
RMS Converter Representation 3-5
Simplified RMS Converter Circuit
Dual-Slope
Calibration Adjustment Controls 4-4
Required Method for Voltage Source Connection
Waveform at U26 Pin 8 for In Range and Overrange Inputs
Waveforms at TP1. Q10. C22 and U14 for In Range and Overrange Inputs
Oscilloscope Connections for Troubleshooting

A/ D Reference Circuit

A/ D Conversion Timing for VAC or VDC Inputs

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PAGE

2-2
2-5
3-1

3-4

3-6
3-7

4-5

4-9
4-10
4-11

MainPCBAssembly ............................................................... 5-4

Digital Conditioner PCB Assembly
Analog Converter PCB Assembly
8040AAccessories
Initial

CaseTemperature above Ambient versus Meter Reading above Ambient
Maximum RF Signal Limits (V RMS) at Probe Tip
DeluxeTestLeadKit
801-600 Current Transformer
80F-5VoltageDivider
80F-

15 Voltage Divider
80K-40VoltageDivider
81RFHighFrequencyProbe
82RF High Frequency Probe

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..................................... 6-4

iii

..............

5-8

5-10

6-2
6-4

6-4
6-5

6-5
6-6
6-7

6-7

6-7

List

TABLE TITLE PAGE

of

Tables

Accessories
Control. Indicator and Connector Description
8040A Maximum Allowable Input Overload Conditions
Buffer Gain Configuration.
Recommended Test Equipment
DCVoltage
AC Voltage Performance Check 4-3
Resistance Performance Check
Direct Current Performance Check
DC Voltage Calibration
Ohms Calibration
LowFrequencyACVCheck
HighFrequencyACVCheck
Direct Current Accuracy Check
Battery

......................................................................

.........................................

.................................

kR Function

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........................................................

......................................................

Charger/ Eliminator Input Power Configurations

................................

1 . 1
2-3
2-4
3-2
4-1
4-3

4-3
4-4
4-6

4-7

4-8
4-8
4-8
6-3

8040A Ranges for Current Transformer (801-600)

.......................................

6-5

Section

1

Introduction

1-1. INTRODUCTION

1-2. The Model 8040A Multimeter provides the control applications.
accuracy and portability required in today's field service
work.

A

display from glare when operating the 8040A in adverse
lighting conditions. The small size and battery power add

to the portability; yet the fold-away stand allows the
instrument to be positioned at a convenient angle for
bench top use.

1-3.

five functions which provides measurement resolution to

0.01 ohms on the 200 ohm rangeand I0 microvolts on the Insure that the correct form of the model number is used
200 millivolt range.

The 8040A offers 20,000 count resolution in all temperature probe and A81 battery chargerleliminator,

sunshade

AC

protects

voltage and current measure- when ordering either of these accessories.

the

41/2

digit

LED

ments are made using true rms conversion techniques for
improved accuracy in communications and industrial

1-4. Several
8040A to expand its' capabilities. A list of these
accessories is provided in Table 1-1 while more detail

about

1-5.

are configured at the factory for particular applications.

&

each

Note that two of the accessories, the 80T-150

Specifications

accessories

one

is

provided

are

available

in

Section

6.

for

use

with the

ACCESSORY

801 -600
80F-5
8OF-15
80K-40
81

RF

82R

F

~OT-I~OC

80T-150F
C88
A80
8040A-

7004K

Table

DESCRIPTION

Clamp-on current probe; 2 to 600 amps
High voltage probe; 5
High voltage probe; 15 kV
High voltage probe; 40 kV
High frequency probe; 20 kHz to

100 MHz
High frequency probe;

500 MHz
Temperature probe;

-58'

F

to

+302'
Carrying case
Deluxe test lead kit

A battery cover kit; includes 4
size alkaline batteries

kV

100 kHz to

-50'~ to

F

+I

50'~

"C"

1-1.

ACCESSORIES

ACCESSORY

8040A­7005K

8040A­7007

K

A81-115

A81 -1 00

~81-230-~

A81-230

DESCRIPTION

A rechargeable Ni-Cad battery pack

(batteries come secured in the battery

cover)
A battery cover intended for use with

alkaline batteries (batteries not included:
Battery

50
Battery

50 to 60 Hz line source
Battery chargerleliminator for 230V,

50 to 60 Hz line source
plug)

Battery chargerleliminator for 230V,

50 to 60 Hz line source (European
type plug)

chargerleliminator for 11 5V,

to

60 Hz line source

charger/eliminator for IOOV,

(U.S.

type

1-6.

DC Voltage

Ranges:
Accuracy:

Input Impedance:
Normal Mode Noise Rejection:
Common Mode Noise Rejection:

Maximum Input Voltage:

SPECIFICATIONS

(Autorangingor Manual)

(6 months, 18" to 28°C)

200 mV range:

1

2V thru

lOOV ranges:

..............

..............................

........................

............................

................

..............

.....................

A

AC Voltage (True rms)

Ratiges:
Accuracy:

Input Impedance:
Common Mode Noise Rejection:

Crest Factor:

Maximum Input Voltage: .....................

(Autoranging or Manual)

(6 months, 18' to 28OC, from 5% of
range to full range)
45 Hzto 10 kHz

10 Hz to 20 kHz

.............................

.............................

............................

................................

...............

..............

A

31200 mV, *2V, f20V, f 200V, f I

+(0.05% of reading f 3 digits)
f(0.05% of reading

10

MR,

all ranges
Greater than 60 dB at 50 Hz and 60 Hz
Greater than 120 dB at 50 Hz and 60 Hz

(1 kR in either lead)

200 mV and 2V ranges:
500V dc or rms ac (continuous)

1

IOOV dc or peak ac for less than 10 sec.

20V, 200V and 1 IOOV ranges:

1

IOOV dc or peak ac (continuous)

200 mV, 2V, 20V, 200V, 750V

+(0.5% of reading +I0 digits)

f

(1.0% of reading +I0 digits)

10 MR in parallel with less than 100 pF

Greater than 60 dB at 50 Hz and 60 Hz
(1

kR

in either lead)

3.0
200 mV and 2V ranges:

500V rms or 700V peak ac (continuous)
750V rms,
less than 10

20V, 200V and 750V ranges:
750V rms, 1 IOOV peak ac or

1100V peak ac or lo7 volt-hertz (whichever is less), for

sec.

+

2

digits)

IOOV

lo7

volt-hertz (whichever is less)

DC mA

Ranges:
Accuracy:
Voltage Burden:
Maximum Input:

AC Current (True rms, ac + dc)

Ranges:
Accuracy:

range to full range)
200
45 Hz to 20 kHz

2000 mA range:
45 Hz to 3 kHz

....................................

(6 months, 18" to 28°C)

...............

.............................

.............................

....................................

(6 months, 18" to 28"C, from 5% of

pA, 2 mA, 20 mA and 200 mA ranges:

...........................

..............................

+200 PA, 2 mA, 20 mA, 200

-t(0.3% of reading +3 digits)

0.25V rms max. except 0.7V rms max. on 2000 mA range
2 amps (fuse protected)

200 pA,2 mA,20 mA,200 mA,2000 mA

f

(1.0% of reading +lo digits)

+(1.0% of reading +10 digits)

mA,

2000 mA

,

Voltage Burden:
Crest Factor:
Maximum Input:

Resistance

Ranges:(AutorangingorManual).

Accuracy:

Maximum CurrentThrough Unknown:
Open Circuit Voltage:
Maximum Inputvoltage:

General

Maximum Common Modevoltage:
Operating Temperature Range:

Temperature Coefficient:

StorageTemperatureRange:

Relative Humidity:

Line:

Battery:

(6 months, 18" to 28°C)

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..............

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........................

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............

...............

.....................

.................

...........................

.........

0.25V rms max. except 0.7V max. on 2000 mA range

3.0
2 amps rms (fuse protected)

2000, 2 kn, 20 k0, 200 k0, 2000 kfl, 20 Mf2

f

(0.2% of reading +3 digits) except 20 M0 range

f

(0.5% of reading +3 digits)

0.5 mA on 200n range
5 volts
All ranges, 25OV ac or IOOV dc

500V dc or peak ac
0°C to +50°C
<I 1 10 of applicable accuracy specification per

(0°C to 18"C, 28°C to 50°C)

-40°C to +70°C (without batteries), -40°C to +50°C (with
Ni-Cad batteries)

0 - 80% to +35"C, 0 - 70% to +50°C

1001 115/230V, 48-66

8W (charging) max.

Rechargeable Ni-Cad pack
charge, typical recharge time 14 hr. of ambient temperature
<30°C to achieve full charge). Non-rechargeable 4 alkaline
"C" cells provide 14 hr. operation (typical).

Hz,

I W (instrument only)

(8

hr. typical operation from full

oc

Size:

Weight:

.......................................

.....................................

6.4 cm high x 14.5 cm long x 12.4 cm wide
(2.5" x 5.7" x

1.0 kg (2.2 pounds)

4.9")

Section

2

2-1. INTRODUCTION

2-2.
regarding the correct operation of the Model

Multimeter. It is recommended that the contents of this
section be read and understood before attempting to
operate the instrument. Should any difficulties arise
during operation, please contact your nearest John Fluke
Sales Representative, or the John Fluke Mfg. Co., Inc.,

P.O. Box 43210 Mountlake Terrace WA, 98043,
Telephone [phone]
is located at the back of this manual.

2-3. SHIPPING INFORMATION

2-4. The 8040A was packed and shipped in a foam
container especially designed to provide adequate
protection. Upon receipt, inspect the instrument for
possible shipping damage.

2-5. If reshipment of the instrument is necessary, the
original container should be used. If the original
container is not available, a new one can be obtained
from the John Fluke Mfg. Co., Inc. Please reference the
instrument model number when requesting a new
shipping container.

2-6. INPUT POWER

2-7. Operating power for the standard 8040A
instrument comes from four, non-rechargeable, alkaline

"C"

hours of instrument operation. Optionally available
power sources include rechargeable Ni-Cad batteries and
a battery
with rechargeable batteries will typically operate for 8
hours; recharging, using the
approximately

This section of the manual contains information

8040A

I. A list of sales representatives

size batteries. The power source typically provides 14

charger/eliminator. The instrument equipped

charger/eliminator, takes

14

hours with the instrument turned off.

Operating

2-8. OPERATING FEATURES

2-9.
and connectors is shown in Figure 2-1. A description of
the control, indicator, or connector is provided in Table
2-1.

2-10. OPERATING NOTES

2-11. The following paragraphs describe various
conditions which should be considered before operating
the

2-12. Fuse Replacement

2-13.
fuse to protect the instrument circuitry from inadvertent
applications of current in excess of 2 amps. This fuse is
located behind the
pressing in lightly on the jack then turning it

counterclockwise
is necessary, use a

2-14. Overrange Indication

2-15. When the full scale capability of the selected

range for any function is exceeded, the display will blink.
The overrange indication does not necessarily mean that
the instrument is being exposed to a damaging input
condition.

2-16. Input Overload Protection

The location of the 8040A controls, indicators,

8040A.

The 8040A is equipped with a current overload

Exceeding the maximum input overload

conditions can damage the
Tables
the instrument.

2-2

l

nst ructions

rnA input jack and is removed by

1/4

turn to release. When replacement

2

amp

AGX

replacement fuse.

CAUTION

8040A.

before attempting to operate

Read

1

2

8

LEFT SlDE

RIGHT SlDE

2-2

Figure

12

2-1.

CONTROL, INDICATOR AND CONNECTOR LOCATIONS

11

10

9

Table

2-1.

CONTROL, INDICATOR AND CONNECTOR DESCRIPTION

8040A

ITEM

NUMBER

1

2

3

4

5

6

7

NAME

POWER switch

Display

Range switches

ka
V

mA

YY

AC

-

---

DC

DESCRIPTION

Separates the power source (batteries or battery eliminator) from
8040A circuitry.

A 4% digit display (19999 maximum) of the measured input,
including decimal point and polarity sign when appropriate.
The units annunicators
applicable range

Provide pushbutton selection of one of five ranges for each
function,
DC Voltage: 200 mV, 2,20,200,1 IOOV, or AUTO
AC Voltage: 200
AC or DC Current: 200

Resistance: 200s2, 2,20,200,2000 ka, or 20 M8IAUTO

Selects resistance measurement mode of operation.

Works in conjunction with the DC and AC switches to select the
voltage function (out position) or current function (in position).

This switch, in conjunction with item 5, selects ac voltage or
alternating current measurement capability.

This switch, in conjunction with item
direct current measurement capability.

i.e.,

(Ma or FA. mV 8) light when the

is

selected.

mV, 2,20,200,750V rms, or AUTO

PA, 2,20,200, or 2000 mA

5,

selects dc voltage or

8

10
11

12

BATTERY CHARGER/
ELIMINATOR

9

V-s2

COMMON

m

A

Sunshade

Jack provided for connection of the chargerleliminator
accessory.

Jack for high (red) lead connection to
and resistance measurements.

Jack for low (black) lead connection to
Jack for high (red) lead

measurements (2A FUSE behind; push in and twist

to remove).
Shade slides forward to improve the readability of the displays in

bright light environments.

2-17. The overload protection varies with the range
and function selected. The maximum allowable input
overload condition for each function and range is given in

r able

2-2.

2-18.

ASSEMBLY AND INITIAL OPERATION

2-19. It is recommended that the assembly and initial
operation of the

8040A be done in accordance with the

following procedure. No test equipment is required to

8040A for voltage (ac or dc)

8040A for all functions.

conrlection to 8040A for current (ac and dc)

'/4

turn and pull

perform this procedure; all signals observed are gener­ated by the
instrument operational evaluation when the

8040A. This procedure may be used as an

8040A is

being used in locations away from normal calibration
equipment.

2-20. Assemble the 8040A as follows:

a. Remove the contents of the box marked

BATTERY COVER. (Four

"C" size batteries, a

8040A

Table

2-2.

8040A MAXIMUM ALLOWABLE INPUT OVERLOAD CONDITIONS

battery cover, and two mounting screws for
non-rechargeable batteries; an assembled pack
and two mounting screws for rechargeable
batteries.

CAUTION

Do not operate

8040A

without battery
cover in place (batteries do not have to
be installed).

b.

The four non-rechargeable alkaline batteries are

to be mounted in the battery clips (position as
indicated on

8040A case) then the battery cover
secured in place with the two screws provided.
When installing the battery pack note the guide
tab on the edge of the cover and match it with
the recess in the bottom center of the

8040A

case.

2-21.
the basic operation of the

The following procedure may be used to check

8040A. It is not intended to be
used as a verification of calibration accuracy. Proceed
with the operational check as follows:

a. Turn the 8040A on.

c.

(Check DC Volts Operation)

Select volts dc
function (see Function Selection Examples) and
the 20 range.

d.

Insert the test lead probe into the

BTRY

TEST

hole, located on the bottom of the 8040A case.

e. The 8040A display will indicate the battery

voltage; between 4.0 volts and 5.8 volts.

f.

(Check

AC

Volts Operation)

Select the volts

ac function and 200 mV range.

€5 The 8040A display will indicate the ripple

voltage created by the inverter. This voltage will
be as much as 60

mV ac (battery operation) or

150 mV ac with the charger/eliminator as power

source.

NOTE

Due to the charging oJ the inpur c~oupling
capacitor it will take 5 to

I

reading

h.

o settle.

(Check Resistance Operation)

10

secondsfbr this

Select the

resistance function and 2 range.

b. Connect the red test lead to the V-0 input

terminal.

I.

Insert the test probe tip into the mA input
terminal.

j.

k.

The 8040A display will indicate 0.100

(Check

test lead to the

DC

mA Operation)

mA input terminal.

+2

Connect the red

1. Select the dc mA function and 2 range.

digits.

0.

P.

(Check AC mA Operation)

Select the ac mA

function.

The 8040A display will indicate the same as step

n

(mA input is dc coupled).

m. Place the test probe tip into the BTRY TEST

2-22.

FUNCTION SELECTION EXAMPLES

hole.

n. The 8040A display will indicate between 0.400

the 0.580

milliamps. (The current depends upon

the battery voltage measured in step d and e.)

Pushbutton Out Input LO Lead Connection

Pushbutton In

Operators Cho~ce

DESIRED SWITCH INPUT

FUNCTION POSITIONS CONNECTIONS

Volts DC

2-23.

switch positions and input connections for each
function.

Figure

Input HI Lead Connection

NO

Connection

2-2

provides a graphic illustration of

8040A

0

O

Volts AC

D~rect Current

Alternating

Current

Res~stance

Figure

80401

2-2.

MULTIMCTCR

FUNCTION SELECTION EXAMPLES

-.

.

-

Section

3

3-1.

3-2.

arranged under two major headings. The first, titled
OVERALL FUNCTIONAL DESCRIPTION, discusses
the overall operation of the instrument in terms of the
functional relationships of the major circuits. The
second section is titled CIRCUIT DESCRIPTION and
deals with the internal operation of each major circuit in
more detail. Block diagrams and simplified circuit
diagrams are included, where needed, to aid in
understanding the theory. The complete schematic
diagrams are located in Section

INTRODUCTION

The theory of operation for the Model 8040A is

7.

-

-

-

-

-

-

-

-

-

- - -

v-n

I

I

I

I

I

I

INPUT

DIVIDER

ANALOG

I

I

OHMS

VOLTAGE

SOURCE

I

I

SHUNTS

SUPPLIES

-

Theory

3-3.

3-4.

3-5.

major sections; an Analog section and a Digital section.
The interconnection of the two major sections of
circuitry, including the subsections within each section is
illustrated in Figure
discuss the operation of the
major sections (and subsections of each) giving a brief
look at the function and interrelationship of these
circuits.

-

OVERALL FUNCTIONAL DESCRIPTION
Introduction

The 8040A circuitry can be divided into two

-

-

1

of

Operation

3-1.

This section of theory will

8040A in terms of the two

---

DISPLAY

A

i

TIMING AND

I

CONTROL SIGNALS

A/D

CONVERTER

I I

II

I

I

I

I

TIMING AND CONTROL

A

1

I

I

I
I

I

I

I

I

I

I

I

I
I

I

I

1

Figure

3-1.

8040A

BLOCK

DIAGRAM

3-

1

3-6. Analog Circuits

3-7. The Analog portion of the 8040A circuitry
consists of an Input Divider, Buffer, RMS Converter,
Ohms Voltage Source, A/ D Reference, Current Shunts,
Power Supplies and
measured are connected to the Analog circuitry via the
V-R or
proportional to the applied input, is developed by the
Input Divider, Current Shunts, Buffer and RMS

Converter and applied to the
voltage equivalent of the applied input charges a
capacitor in the
input. A reference voltage, opposite in polarity to the
voltage representing the applied input, is then connected
to the
at a constant rate. The time it takes the capacitor to
discharge is therefore proportional to the applied input.
the Digital section of
and displays it as a digital representation of the input
circuit.

mA terminals. A dc voltage, directly

A/D causing the charged capacitor to discharge

A/D Converter. The inputs to be

A/D Converter. This dc

AID to a level proportional to the

8040A circuitry measures the time

3-8. Digital Circuits

3-9. The Digital section consists of Timing and
Control and Display circuits. The Timing and Control
Signals connect the dc voltage representing the input
being measured to the A/ D for 100 ms then disconnect
it and apply the reference voltage. At the time the
reference voltage is applied the Timing and Control
circuit starts counting the number of cycles of the
Crystal Oscillator occur until the A/ D sends a signal to
the Timing and Control circuit indicating that the
capacitor has been discharged to zero. The number of
cycles of oscillator signal that occurred is presented on
the display as the value of the unknown input being
measured by the

8040A.

be connected in series with the unknown resistance
applied to the
The Ohms Source Voltage is applied to this voltage
divider and the voltage drop across the unknown

resistance is measured by the
value of the resistance.

V-R terminal to form a voltage divider.

8040A to calculate the

3-15. Current Shunts

3-16. The Current Shunts are a set of series connected
resistors. The unknown current applied to the mA
terminal develops a voltage proportional to the
current, across the portion of the shunt resistors selected

by the range switch. The
developed across the shunt resistor and displays the
value of the input current.

8040A processes the voltage

3-17. Buffer

3-18.
(measurement of dc or ac volts), the
(measurement of resistance) or the Current Shunts
(measurement of dc or ac
Buffer (see Figure 3-2). The gain of the Buffer is changed
to compensate for the changes in the output voltage of
the Input Divider and Current Shunts. A combination
of buffer gain

Divider or Current Shunts is selected so that the output
of the Buffer will not exceed 2V dc (or rms) for any full
scale input in either the dc (or ac) voltage or current
function. Because of changes in the reference voltage
used in the resistance function (explained in the

Reference theory) the output of the Buffer, for full scale
inputs, changes when the range changes. Table 3-1
provides the gain and Buffer output information for
each range.

The output voltage of either the Input Divider

V-R terminal

mA) is applied to 48 in the

(XI or X10) and scale factor of the Input

A/D

3-10. CIRCUIT DESCRIPTION
3-11. Introduction

3-12.
look at the subsections of circuitry, as presented in the
block diagram, in more detail. When needed for
explanation, simplified schematic diagrams of the
circuits being discussed will be provided.

This section of 8040A theory of operation will

3-13. Input Divider

3-14. The Input Divider performs two basic functions
when measuring unknown inputs applied to the
terminal. First, when measuring either dc or ac voltages,
the divider is used to scale the input voltages down to a
level that can be handled by the Buffer. The second
function of the divider is to provide resistors which can

V-R

Table

-

3-1.

RANGE

200

2

kfi

20

kfi

200

ka

2000

kc2

20 Ma

BUFFER GAlN CONFIGURATION,

kn

FUNCTION

BUFFER GAIN
AND DIVISION

XIO,

+

XIO,

+

XI,

+

1

XIO,

+

XI,

+I

XI, +I0

3-19. AID Reference

3-20.
to the

After the output of the Buffer has been applied

A/

D Converter for 100 ms the timing and control

1

I

I

FULL SCALE

BUFFER OUTPUT

980 mV
980 mV
833 mV
980 mV
833 rnV
333 mV

signals disconnect the Buffer output and connect the
appropriate

simplified schematic diagram of the
circuit.

3-21.
current the Timing and Control circuit detects the
polarity of the voltage applied to the A/
order to select the reference voltage of the opposite
polarity. If, for example, the input to the
positive the Control circuits would produce a
command which would cause the -VREF gate (part of
U8) to turn on and supply a -1.0 volt reference to the
A/ D Converter. A negative polarity input to the
will cause the Control circuit to provide a DE(+R)
command to turn on the +VREF gate to apply a 4-1.0
volt reference to the A/D Converter.

3-22.
processed by the RMS Converter so that the dc voltage
(proportional to the ac input voltage) applied to the
A/D Converter is always positive polarity. In the AC
function (volts or current) the Control circuit produces a

DE(-R) command to apply the -VREF to the A/D
Converter. In the AC and DC functions the reference
voltage is fixed at 1.0 volt either positive or negative.

A/D Reference voltage. Figure 3-3 is a

AID Reference

When the 8040A is used to measure dc volts or

D

Converter in

8040A is

DE(-R)

8040A

AC voltage or current applied to the 8040A is

3-23.
voltage changes as the input to the
8040A use a ratio ohms conversion technique to
determine the value of the unknown resistance applied
to the input terminals. This technique works on the
principle that when a voltage (Ohms Source Voltage) is
applied across series connected resistors (the Input
Divider resistors and the unknown) the voltage drop
across each will be proportional to the value of each
resistor.

3-24. The 8040A calculates the value of the unknown
resistor. The formula followed to make this calculation
is:

Where RX is the unknown resistance, RREF is the Input

Divider
voltage across the unknown resistance and VREF is the
voltage across the Input Divider

3-25.

Input Divider is fixed for any given range and the
resistance values are a factor of 10 apart, the position of
the decimal point in the Display makes the adjustment

In the resistance

resistor(s) selected by the range relays, Vx is the

Since the value of the reference resistor(s) in the

(KR)

function the reference

8040A changes. The

resistor(s).

+11.5v

T

10k 10k

41

0.47 pF

FROM
INPUT 270 pF

DIVIDER

Q8

FROM

CURRENT

2.67k

+

.

TO

RMS

CONVERTER

1

TO

A/D

CONVERTER

-1 1.5V

Figure

3-2.

SIMPLIFIED BUFFER CIRCUIT

3-3

IN

THE

BUFFER

CIRCUIT

f++!!-ii

-

---

-)-

-

---------

20k

---------------

----

-

3-4

TO OHMS
VOLTAGE

Figure

3-3.

SlMPLl

FlED

A/D

REFERENCE CIRCUIT

ON FOR

+VREF

I

I

v

d-

TO

A/D

CONVERTER

for the RREF term in the formula. The 8040A directly
reads the value of
output to the
VREF is determined by algebraically adding
positive voltage) to a negative equivalent of the ohms
source voltage. The resulting voltage is VREF and is
applied to the
application of

Vx and applies the resulting Buffer

AID Converter for 100 ms. The value of

VX (a

A/D Converter at the end of the 100 ms

Vx.

3-31.
~ulti~lier-Divider function is performed using a Log­Antilog circuit. The base-emitter voltage of a transistor
is almost perfectly logarithmically related to the
collector current.
obtain two times the log of the input; then by taking the
antilog we obtain a voltage proportional to the square of
the input

In the 8040A implicit conversion method the

By

putting two transistors in series we

(Vi2).

3-26.

3-27.
positive voltage source in the
ational amplifier
schematics in Section 7) make up the unity gain buffer
amplifier that supplies the ohms source voltage. The
Ohms Voltage Source circuit is used exclusively in the
resistance measurement function.

3-28.

3-29. An rrns amplitude is that value of alternating
current or voltage that results in the same power
dissipation in a given resistance as dc current or voltage
of the same numerical value. The mathematical formula
for determining the rms value of an ac voltage is:

Where Vi is the value of the ac voltage at any given
instant. The
instantaneous voltage and computes the rrns value of the
input signal.

3-30. The 8040A uses an implicit method for
computing the rrns value of the input. Figure 3-4 is a
block diagram of
rms value of an ac voltage. The output voltage of the
RMS Converter (VO) is a dc voltage proportional to the
rrns value of the ac voltage applied to the
proven by the following mathematical calculations. As
indicated in Figure 3-4 Vo
multiplying both sides of the equation by Vo we get
Vo2
formula becomes Vo

Ohms

The ohms source voltage is derived from the

Voltage Source

AID reference. Oper-

U1 and associated components (see

RMS Converter

8040A RMS Converter monitors the

the'implicit method of calculating the

8040A. This is

=

(K)/VO ; therefore, by

=

Vi2. By taking the square root of both sides the

=

m.

3-32. The components in the 8040A RMS Converter
that perform the various functions in calculating the rrns

value of the
signal (Vi) to the RMS Converter is first applied to a
circuit which produces a current representative of the
absolute value of the input. The current is then applied
to the collector of the first of the two series connected
transistors that, in conjunction with operational amplifier

U38, produce a voltage output representing two times
the log of Vi. A feedback circuit through U 13 (pins
and 3) and the upper right transistor in array U11
provide a voltage equal to the log of Vo. Subtracting the
log of Vo from two times the log of Vi is equal to the
mathematical function of calculating
final step in determining the rrns value is handled by
U13 (pins
U11 and the output filter (the 47k resistor and 0.47
capacitor). These components calculate the antilo of

V/VO

this voltage being directly proportional to the rms value
of the input applied to the

3-33.

3-34. The AID Converter receives the dc voltage

output, from either the RMS Converter or Buffer,

representing the unknown value applied to the

input terminals. Timing signals from the Timing and

Control circuit cause the RMS Converter or Buffer

output voltage to be applied to the

ms. The amplitude of this input voltage controls the rate

at which a capacitor in the

end of the 100 ms integrate period the charge on the

capacitor is proportional to the unknown applied to the

inpit are illustrated in Figure 3-5. The input

Vi2/Vo . The

7,6,

and

5),

the lower right transistor of array

producing an output voltage equal to&,

8040A.

AID

Converter

A/ D for exactly 100

A/D is charged, so that at the

1,2,

pF

8040A

Vi

O---X

ABSOLUTE

VALUE

CIRCUIT

I

XI

I

Vi

I

ONE-QUADRANT

MULTIPLIER-DIVIDER

-

X

-

Y

XY

z

3

Vi2

-

VO

z

I

Figure 3-4. RMS CONVERTER REPRESENTATION

LOW

FILTER

-

(vi2)

vo

PASS

vo

b