Keithley 174 Service manual

INSTRUCTION MANUAL

MODEL 174

DIGITAL MULTIMETER

COPYRIGHT, 1977, KEITHLEY INSTRUMENTS, INC.

THIRD PRINTING, AUGUST, 1980, CLEVELAND, OHIO, U.S.A.

DOCUMENT NO. 28263, REV. 8

CONTENTS

INSTRUCTION MANUAL

Digital Multlmeter

Model 174

kction

:ONTENTS.

LLUSTRATlbNs : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : i;i

iPECIFICATIONS.

. GENERAL INFORMATION

I-1. INTRODUCTION. l-2. l-3. l-4.

.. INITIAL PREPARATION

2-l. 2-2. 2-3.

o--- .- .._ .

i.

FtKAIlNti INSTRUCTIONS. 3-l. G ~iENERAL 3-2. HOW TO SELEC-

3-3. 3-4. 3-5. 3-6. 3-J. 3-8.

ACCESSORIES

..

4-l. G

4-2. 4-3.

4-4. 4-5. 4-6.

4-7.

;I,“: 4-10. MODEL 1723 IEEE INTERFACE

FEATURES.

WARRANTY INF6RMA;I6N: : : : : : : : : : : : : : : : : : : : : : : : : : : l-l

CHANGE NOTICE

GENERAL

INSPECTION.

PREPARl iTION FOR USE

HOW TO SELECT FUNCTION. HOW TO SELECT RANGE HOW TO MEASURE VOLTAGE. HOW TO MEASURE RESISTANCE HOW TO MEASURE CURRENT. .

FURTHER MEASUREMENT CONSIDERATiOk: : : : : : : : : : : : : : : : : : . . 3-g

,ENERAL

,^__.

MuutL I/ZU KECHAKG MODEL I

RACK MC PROBES AND SHUNTi : : : : : : : : : : : : : : : : : : : : : : : : : : : : 4-23 CONVENIENCE CABLES AND CONNECTORS LOW-THERMAL CABLES. . MODEL MODEL

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

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

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

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

..

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

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

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

--T POWER.

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

.-z, ................................

---~~---EABLE BATTERY PACK.

I722

DIGITAL INTERFACE.

XJNTING

1727

DIGITAL OUThi cAeLE iE+ ’ ’ ’ ’ : : : : : : . * * * ’ ’ ’ ’

1743

MAINTENANCE KIT.

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

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

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

........

.......

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

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

.... : : : :

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

: : : : : : :

: : : : : : : : : : : : : : : : :

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

......

...........

: : : : : : : :

.....

,: : : : : 2-l

. . 3-9

. 2

: 4-24 .

Page

iv l-l I’-1

l-l

l-1

2-1 2-l

2-l

3-l

3-1

3-3 3-5 3-6

3-8

4-l

4-6

4-21

4-24 4-24

4-26

4-25

!

ii

AA

INSTRUCTION MANUAL Dlgllel Mulllmeler

Model 174

CONTENTS (Cont'd)

#ection

. THEORY OF OPERATION . . . . . . . . . . . . . . . . . . . . . .

15

5-l. GENERAL.........................::::::::5-,

5-2. 5-3.

5-4.

5-8. ANALOG-TO-DIGITAL CONVERTER (Schematic

5-9.

5-10. DIGITAL BOARD (Schematic 28209E). . : : : : : : : : : : : : : : 1 : : : . 5-23

5-l

MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . . . : : : : : : : : : 6-1

’ 6-1.

6-2. 6-3.

6-4. 6-5.

REPLACEABLE PARTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-l

7

* J-l.

7-2. 7-3.

SIGNALFLOW...............................

SWITCHING (Schematic NANOVOLT PREAMP (Schematic

MODEL MODEL

MODEL

1740

AC OPTION (Schematic

1744

OHMS OPTION (Schematic

1745

AMMETER OPTION (Schematic

27935E). . . . . . . . . . . . . .

279370

E block diagram, Figur; i2.j : : : : : . 5-4

279440) 27941Cj : : : : : : : : : : 1 : : : : . 5-8

2794OC). .

2J936F). : : : : : : : : : : : : , 5-12

DISPLAY BOARD (Schematic

I. POWER SUPPLY (Schematic 279380) . . . . . . . . . . . .

GENERAL.................................6-I

REQUIRED TEST EQUIPMENT . . . . . . . . . . . . . . . . . . . . . , . . . 6-1

PERFORMANCE VERIFICATION . . . . , , . . . . . . . . . . . . . , . . , . 6-1

ADJUSTMENT/CALIBRATION PROCEDURE . . . . . . . . . . . . . , . . . . . .

TROUBLESHOOTING. . . . . . . . . . . . . . . . . . , . . . . . . . . . .

GENERAL...... . . . . . . . . . . . . . . . . . . . . . . . . ...7-I

ORDERING INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . 7-l

SCHEMATICS . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-l

279391)). .

Page

5-l

. 5-2 . 5-5 . 5-12 . 5-21

5-25

6-g 6-21

i

AA

ii;

ILLUSTRATIONS

INSTRUCTION MANUAL

Dlgital

Multlmeter

Model174

igure No.

I

2

T,

65

ii

9

IO

Ila Connector Pin Identification For Model 174/1722. ...........

lib

6

14 15 16

17

18

I9

20

21 Diagram of Signal Flow

22 23

24

2

27 28

:: :: ;t

35 36

37

38

2’0

41

::

2:

:;

48

49

50

Title

Dimensional Data Rear Panel Connections

View of Chassis With Cover Removed . .

Installation of Models

Typical Display For Non-Valid Function ................

Front Panel Controls and Input Terminals ...............

Manual Ranging on the Model Model

Installation of Model 1728 ......................

Installation of Model

Connector Pin Identification For Model

Installation of Model 1722 Digital Interface .............

Location of Jumpers t Pull-Ups For Model Model 1722 Block Diagram

Model 1007 Dual Rack Mounting Kit.

Model 2000 Rack Mounting Kit .....................

Model 1746A Low-Thermal Shorting Plug

Model 1747A Low-Thermal Cable Set ...................

Model 1743 Maintenance Kit ......................

Typical Installation of Extender Card on Model 1722. .........

Simplified Diagram of Nanovolt Preamp. ................

Diagram of AC Attenator (Model

Diagram of AC/DC Converter (Model 1740). ...............

Simplified Diagram of Model 1744 Ohms Option .............

Detailed Diagram of Model 1744 Ohms Option .............. 5-IC

Basic Functional Blocks of A/O Converter ...............

Basic Charge Balance Converter ....................

Operating Waveforms of A/D Converter .................

Simplified Schematic

Simplified Diagram of Complete A/O Converter .............

A/O Converter System Timing. ..................... 5-21

Digital Display Multiplex Scheme ...................

Test Circuit For

Test Circuit For 3uA Verification. .................. 6-7

Model Model

Waveform For A/D Calibration .....................

Model Model

Component Layout, PC-412 (Part I). ....................... : : 1 : : : :

Component Layout, PC-412 (Part 2).

Component Layout, PC-421 .......................

Component Layout, PC-410 .......................

Component Layout, PC-414

Component Layout, PC-408 .......................

Component

Componen r. Layout,

Component Layout, Model

Component

1728

Rechargeable Battery Pack .................

I74

Top View With Cover Removed.

I74

Calibration Adjustments. ..................

I74

Chassis Assembly ......................

I74

Bottom Cover Assembly.

Layout,

Layout, Model

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

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

1740,

1744, 1745: : : : : : : : : : : : : : : :

174. ...................

1722

Digital Interface .............

174/1722. ........... 4- I(

1722. ............

....................... 4-I(

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

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

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

1740) .................

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

30

mV DC Accuracy Check ............... 6-3

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

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

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

~~-409

Model 1728 .....................

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

1722, 1722,

Upper Board (PC-415) . * * . . * . + ' ' 7-67 Lower Board (PC-416) * * * * . * * ' ' *

Page

v

1-2

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

3-5 4-3

4-4

4-7 4-9

4- 11

4-l:

4- 2C 4-2; 4-Z: 4-Z! 4-2; 4-2t

5-l 5-4 5-5

5-7 5-9

5-1: 5-IL

5-11 5-1; 5-2C

5-

2i

6-1~

6-11 6-11

6-25 6-21 7-53

7-54 7-57 7-58

7-59 7-60

7-61

7-62

J-65

iv

BB

SPECIFICATIONS

AS AN AUTOJMANUAL RANGINQ DC VOLTMETER

INSTRUCTION MANUAL

Dlgital MullimeIer

Model 174

WITI AUTO/MANUAL RANGING AC VOLTAGE OPTION ,740

vi

ASANACAMMSTER WlTHOPTlONSl740ANO~7~5

AA

INSTRUCTION MANUAL DigItat MultImeter

Model 174

t

8.5" (217mm)

I

FIGURE I.

Dimensional Data.

INSTRUCTION MANUAL DigItal MultImeter

Model 174

GENERAL INFORMATION

SECTION I.

l-l. INTRODUCTION.

measuring instrument,

l-2. FEATURES.

Standard

a.

Sensitivity to 0.1 microvolt dc.

I.

30000

2.

0.013% basic dc accuracy

t :

Manual, automatic or remote ranging. Lo to CASE isolation to 10’0.

5.

Optional.

b.

1. Model 1728 Rechargeable Battery Pack. Model 1722 Digital Interface. Model 1723 IEEE Iriterface.

;:

Model 1740 AC Option.

5:

Model 1744 Ohmmeter Option.

6. Model 1745 Ammeter Option.

l-3.

manua I .

ized repair facility as given on the inside front cover of this manual.

WARRANTY INFORMATION.

count display for high resolution.

If there is a need for service,

The Model 174 Digital Multimeter is a wide-range, general purpose

capable of measuring ac/dc voltage, ac/dc current, and resistance.

The warranty is stated on the inside front cover of the

GENERAL INFORMATION

contact your Keithley representative or author-

l-4.

the manual will be explained on a change notice sheet attached to the inside back cover

of the manual.

CHANGE NOTICE.

The A symbol can be found in various places in this Instruction Manual.

fully read the associated

ling of the instrument. Damage to the instrument may occur if these precautions

are ignored.

The\ symbol can be found in various places in the Instruction Manual. symbol indicates those areas on the instrument which are potential shock hazards.

Carefully read the associated WARNING statements with regard to proper use and

handling of the instrument.

cautions are ignored.

Improvements or changes to the instrument not incorporated into

IMPORTANT

Care-

CAUTION

statements with regard to proper use and hand-

This

Serious personal injury may result if these pre-

AA

1-l

GENERAL INFORMATION

INSTRUCTION MANUAL

Digital Multimeter

Model 174

'HILLIPS iCREWS

3mV DC, REMOVE TOP COVER 30mV DC, TO GAIN ACCESS ANALOG TO CHASSIS (4 SCREWS)

OUTPUT

CONNECTION TO MODEL 1722 OR

1723 INTERFACE

PHILLIPS SCREWS

l-2

LINE FUSE

F401

FIGURE 2. Rear Panel Connections.

LiNE

INPUT

P405

AA

INSTRUCTION MANUAL

Dlgltat MultImeter

Model 174

GENERAL INFORMATION

TABLE I-l

Summary of Options and Accessories

ptions:

Model 1740 AC Option

Model 1744 Ohmmeter Option

Model 1745 Ammeter Option

upplied Accessories:

Model 1746~ Low-Thermal Short

mther Accessories:

Model 1600 High Voltage Probe Model 1651 50-Ampere Shunt Model Model 1685 Clamp-On AC Current Probe

Model

Model 1723 IEEE Interface

Model 1727 Digital Interface Cable Set

1682

RF Probe

1722

Digital Interface

Remarks: Factory or Field-Installed. To field-

install, refer to Section

Factory or Field-Installed.

install, refer to Section 2, paragraph Z-3d

Factory or Field-Installed. install, refer

See ACCESSORIES, Section 4, paragraph 4-7a.

See ACCESSORIES, Section 4, paragraph 4-5a. See ACCESSORIES, Section 4, paragraph 4-5b. See ACCESSORIES, Section 4, paragraph 4-5~. See ACCESSORIES, Section 4, paragraph 4-jd. See ACCESSORIES, Section 4, paragraph 4-3. Described in separate Instruction Manual. See ACCESSORIES, Section 4, paragraph 4-8.

to

Section 2, paragraph

2, paragrap” 2-3~

To field-

2-3e

Model 1728 Rechargeable Battery Pack Model 1743 Maintenance Kit Modell747A Low-Thermal Input Leads

See ACCESSORIES, Section See ACCESSORIES, Section 4, paragraph 4-9. See ACCESSORIES, Section 4, paragraph 4-7b.

4, paragraph

4-2.

BB

l-3

GENERAL INFORMATION

LINE SWITC :HES -

INSTRUCTION MANUAL

Digital Multimeter

Model 174

-MOUNTING BRACKET

SHIELD FOR

'NANOVOLT

PREAMP

l-4

MODEL

1740

1744

1745

VIOLET WIRE

,TO MODEL

1740

-FUSE

FIOOI

FIGURE 3. View of Chassis With Cover Removed.

AA

INSTRUCTION MANUAL Dlgltal Multlmeter

Model 174

INITIAL PREPARATION

SECTION 2. INITIAL PREPARATION.

2-l.

preparation for use.

2-2.

ly before shipment. Upon receiving the instrument,

may have occurred during transit.

the electrical specifications,

2-3. PREPARATION FOR USE. The Model 174 may require soie preparation before placing the

instrument in use, depending on the field-installable options or accessories to be used.

For line operation the Line Voltage switches and Line Fuse should be checked to verify

correct settings or value for the line power voltage to be used. Models 1722, 1723, or 1728 are to be field-installed, the top cover will need to be removed.

See ACCESSORIES, Section 4 in this manual.

are to be field-installed,

in following paragraphs c, d, and e must be used.

GENERAL.

INSPECTION.

a. How to Set the Internal Line Voltage Switches (S4Ol and 5402). The Model 174

has two slide switches located on the main circuit board as shown in Figure 3. The

top cover must be removed to gain access to the circuit board as shown in Figure 2.

This section provides information needed for incoming inspection and

The Model 174 was carefully inspected both mechanically and electricai-

check for any obvious damages which

Report any damages to the shipping agent. To verify

follow the procedures given in Section 6.

If any one of accessory

If any of the Models 1740, 1744, 1745 Options

the top cover must be removed and the installation procedures

WARNING

Disconnect the line cord before removing the top cover of the instrument. voltage is present at various points on the circuit board and represents a SHOCK HAZARD.

TABLE 2-l.

Summary of Line Voltage Settings

Line Fuse Requirement.

b.

line-operated power supply.

fuse rating is 1/2A for 90-125V range, l/4A for IgO-250V range. The line fuse is

located on the rear panel as shown in Figure 2.

The Model 174 uses a single line fuse to protect the

The fuse is a 3 AE, slow-blow type.

Verify that the

Line

2-l

INITIAL PREPARATION

INSTRUCTION

Digital MultImeter

MANUAL

Model 174

C.

How to Install the Model 1740 AC VOLTS Option.

wire.

Install the plug-in board for the Model 1740 on the Model 174 chassis at PSOI and P502

as shown in Figure 4. edge guides which support the board.

instrument.

d. How to Install the Model 1744 OHMS Option.

1744 is installed on the Model I74 chassis at P503 as shown in Figure 4.

side of ~~-408 faces the front of the Instrument.

e.

Model 1745 is installed on the Model I74 chassis at P504 and P505

The component side of PC-409 faces the front of the instrument. Check fuse FIOOI for

proper rating and condition. rating.

The AMPERES circuit must be calibrated prior to use as in Section 6-49.

Connect the “violet” input lead (P301) coming from the Function Switch to Jl203.

The plug-in board (PC-414) edges should mate with the teflon card

The component side of PC-414 faces the front of the

IMPORTANT

The AC VOLTS circuit must be calibrated prior to use as in Section 6-4e.

IMPORTANT

The entire 174 Calibration Procedure must be performed prior to use as in Section 6-4.

How to Install the Model 1745 AMPERES Option.

Replacement fuse is a Keithley Part No. FU-39; 4 amperes

IMPORTANT

Cut the tie wrap holding the “violet”

The plug-in board (PC-408) for the Model

The component

The plug-in board (PC-409) for the

as

shown in Figure 4.

2-2

AA

INSTRUCTION MANUAL Digital Mulllmeler

Model

174

INITIAL PREPARATION

FIGURE 4.

Installation of Models 1740, 1744, 1745.

2-3

NITIAL PREPARATION

Summary of Detailed

INSTRUCTION MANUAL

Digital Multimeter

Model 174

TABLE 2-2.

74 Max Rating at Input Terminals

I-

FUNCTION DC VOLTS

300 mV - 1 KV 3 mV and 30 mV

AC VOLTS

OHMS

AMPS

3OOpA-3A

30~A 3uA

HI TO LO MAXIMUM

12OOV Peak

250V RMS sine, <60Hz Peak

. <lO'V~Hz

IOOOV RMS, ,<lO'V.Hz

240V RMS sine, ~60Hz or 350~ Peak

, <lO'V*Hz

~250~ PK or c60Hz RMS if

4A,

fuse blows

25mA or 25OV RMS on fixed range

2.5mA or 25OV RMS on fixed range

or

250~

2-4

AA

INSTRUCTION MANUAL

DIgItal MultImeter Model 174

OPERATING INSTRUCTIONS

SECTION 3.

3-l.

measurement of voltage, current, and resistance,

3-2.

able nickel-cadmium batteries.

tion. The I ine-voltage supply is built-in. (2 m) long.

four ranges, from a ininimum of 90 V rms to a maximum of 250 V rms. Table 2-1 (pg 2-l) summarizes the I ine voltages permitted.

GENERAL.

HOW TO SELECT POWER.

The

accessory

purchase of the Model 174 or may be purchased and field-installed at a later time

if so desired.

a. How to Operate From Line Power.

Set the internal line voltage switches (S4Ol and 5402) to the appropriate position

1.

as described in Section 2, paragraph 2-3a.

2. Attach the line cord (CO-7) to the Model I74 at power input receptacle (P405) on

the rear panel. If a shorter I ine cord is desired,

Cord (2 foot long).

This section provides information needed to operate the Model 174 for

The Model 174 may be powered from line voltage or recharge-

The Model 1728 must be installed to permit battery opera-

Model 1728 Rechargeable Battery Pack may be ordered at the time of

OPERATING INSTRUCTIONS.

when the appropriate option is

The power cord is detachable and is 6 feet

NOTE

The Model 174 can be powered from line voltage over

order Keithley Model 7003 Power

installed.

Check the line fuse for proper rating as described in Section 2, paragraph 2-3,

3.

4. Plug the line cord into a source of line power.

Depress LINE pushbutton.

5.

NOTE

Power on will be indicated by a lighted display with one or more digits and measurement units showing.

b. How To Operate From Battery Power.

Install the Model 1728 Rechargeable Battery Pack. (See Section 4, paragraph 4-Z.)

I.

2. Depress BAT pushbutton.

If the LOW BAT indicator is lighted in BAT mode, refer to Section 4-2~ for re-

3.

charging;

otherwise, the Model 174 may be used for measurements.

3-l

OPERATING INSTRUCTIONS

NOTE

The Model 1728 is shipped from the factory in uncharged condition. Therefore, the Model 1728 should be installed and charged prior to use. been charged for at least I6 hours, at least 3 hours.

Summary of Operation in Line and Bat Modes

the Model 174 can be powered continuously for

TABLE 3-2.

Condition of Instrument

After the Model 1728 has

INSTRUCTION MANUAL

Digital Multimeter

Madei 174

Line Power Connected

Button Depressed 1728 Not Installed

LINE ON

BAT

NEITHER

LINE NOR BAT

OFF

Line Power Connected Line Power Not Connected

1728 Installed 1728 Installed

ON

Batterv trickle charaed.

ON

Battery slowly discharged.

OFF

Battery charged at maximum

rate.

OFF

ON

OFF

3-2

LIGHTED DECIMAL 60lNTS.

FIGURE 5.

Typical Display For Non-Valid Function.

AA

INSTRUCTION MANUAL

Dlgltal MultImeter

Model 174

OPERATING INSTRUCTIONS

3-3.

switch (5302).

ac voltage function.

voltage function.

to

HOW TO SELECT FUNCTION.

a. V AC (~1.

The Model Option 1740 is installed. If this option is not installed the Model I74 will display all four decimal points to indicate a non-valid function as shown in Figure

b. vDc(=)

res 1 stance ohms) function.

-9

The Model

installeo:

mal points to indicate a non-valid function as shown in Figure

1. HIR. When the FUNCTION Switch is set to Hln, the Model I74 permits resistance

measurements in

2.

measurements in 6 ranges from 300~ to 30MR.

I74

174

LOR. When the FUNCTION Switch is set to LOQ, the Model I74 permits resistance

When the Function Switch is set to V AC the Model 174 will be set to

Refer to paragraph 3-6 for operating information.

can be used to measure ac voltage only when the Averaging AC Voltage

. When the Function Switch is to V DC the Model 174 will be set to dc

Refer to paragraph 3-b for operating information.

When the Function Switch is set to HI0 or LOR the Model I74 will be sef

can be used to measure resistance only when the Ohmmeter Option 1744 is

If this option is not installed,

6

ranges from 3K0 to 300MO.

Function is selected by means of a front panel rotary

IMPORTANT

5.

Refer to paragraph 3-6 for operating information.

IMPORTANT

the Model 174 will display all four deci-

5.

Full range voltage is 3 V.

Full ranoe voltage is 300 mv.

d. A DC (ZJ. When the FUNCTION Switch is set to A DC the Model 174 will be set to dc

current function. Refer to paragraph 3-7 for operating information. Neither auto-

ranging nor remote ranging are available on Amperes.

IMPORTANT

The Model I74 can be used to measure dc current only when the DC Amneter Option I745

is installed.

decimal points to indicate a non-valid function as shown in Figure 5.

e. A AC (“J). ac current function. Refer to paragraph 3-7 for operating information. autoranging nor remote ranging are available on Amperes.

The Model I74 can be used to measure ac current only when both the AC Voltage Option

1740 and the DC Amneter Option 1745 are installed. If these options are not installed

the Model

as shown In Figure

If this option is not installed the Model 174 will display all four

Whkn the FUNCTION Switch is set to A AC the Model I74 will be set to

Neither

IMPORTANT

I74

will display all four decimal points to indicate a non-valid function

5.

AA

3-3

OPERATING INSTRUCTIONS

INSTRUCTION MANUAL

Digital Multimeter

Model 174

LOW

BATTERY

mv

ZERO

FUNCTION

-‘ITCH

3-4

LINE BAT

PZN

SEE FIGURE 7

FOR RANGE SELECTION

DETAILS

FIGURE 6.

Front Panel Controls and Input Terminals.

VALID FOR VOLTS AND

OHMS ONLY

CASE

GROUND LO HI

J304 J303

INPUT INPUT

J302

AA

INSTRUCTION MANUAL

OPERATING INSTRUCTIONS

Digllsl MulIlmeIar

Model 174

3-4. HOW TO SELECT RANGE. On VAC, VDC, and :1 the Model I74 provides automatic, remote, or manual ranging. Remote ranging is available only when the Model 1722 or 1723 is

installed.

Manual Ranging. (Al I functions).

a.

ing the appropriate range pushbutton.

ranging.

If A AC or A DC is selected and none of the valid current range pushbuttons

are depressed the Model 174 will be placed in the following condition: The input

resistance will be 100 KR in parallel with overcurrent protection diodes.

174 display will read near zero (independent of the signal applied) and the decimal

position will be the same as for the 3 uA range (0.0000).

b.

Remote Ranging. (V AC, V DC, and OHMS only).

the Model 1722 or Model 1723 is installed and the REM oushbutton is depressed.

Section 4 ACCESSORIES for information regarding Models I722 or 1723.

The REM pushbutton determines range control only, Trigger, Hold, and Trigger Mode.

C.

Autoranging. (V AC, V DC, and OHMS only).

ranging mode under the following conditions.

The Model 174 can be set to Hanual Mode by depress-

See Figure 7 for detailed explanation of manual

NOTE

The Model

Remote ranging is available only when

Refer to

NOTE

and does not affect timing controls,

The Model I74 will be placed in Auto-

If AUTO is depressed the Model I74 will be set to autoranging mode.

I.

2. If none of the manual range nor REM pushbuttons are depressed (that is, all are

released),

then the Model 174 will be set to autoranging mode as a default condition.

AA

FIGURE 7.

Manual Ranging on the Model 174.

3-5

OPERATING INSTRUCTIONS

NOTE

The following rules govern the autoranging feature:

a) When the display exceeds 29999, the Model 174 upranges (that is, it changes to

less sensitivity and the decimal point and measuring unit changes appropriately).

b) When the display reaches 02599 the Model I74 downranges (that is, it changes

to greater sensitivity and the decimal' point and measuring unit changes appropriately)

until it reaches the most sensitive range (except 3mV dc and 30 nV dc).

INSTRUCTION MANUAL

Digital Multimeter

Yodet~74

3-5. 30mV, 300mV, 3V, 3OV, 3OOV, and IOOOV DC.

Model 174 measures ac voltage in five ranges, 300 mV, 3V, 3OV, 3OOV, and IOOOV.

HOW TO MEASURE VOLTAGE.

Maximum input voltage depends on the range selected. allowable continous input for each range on AC and DC. Do not exceed these voltages or damage to the instrument will occur.

The Model 174 measures dc voltage in seven ranges:

When the Model 1740 Option is installed, the

CAUTION

Table 3-3 gives the maximum

TABLE 3-3.

Maximum Allowable Continuous Input

IOOOV rms (<lO'V.Hz 1000~ rms (<lO'V.Hz IOOOV rms IOOOV rms (<lO'V*Hz 1OOOV rms

(*107V.Hr

(<lO'V~Hz

*NOTE

12OOV Peak 1200V Peak 12OOV Peak 12OOV Peak

3mV,

When 3mV or 30mV range pushbuttons are depressed, and thus the allowable input will be 1000 V rms

DC Voltage. The Model 174 detects dc voltages from f0.1 microvolts/digit to t1200

voy;s (1200.0 display). The maximum display is 29999. When the display exceeds 29999, a 3 remains lighted, but ail other digits are blanked. volts on the highest range.

Select V DC on Switch 5302.

1.

2. Depress AUTO, REM or desired Manual Range pushbutton. Connect the signal to be measured between HI and LO terminals. The terminals are

3.

designed to accept banana or "bunch pin" plugs,

1747 Low-Thermal coaxial input cable.

below IO microvolts dc resolution.

4. Observe the displayed digits, polarity sign,

ment unit (mV or V).

A "zero" reading will always be displayed as -.OOOO.

3-6

If no polarity sign is indicated,

These leads are recommended for measurements

the 300mV range will be selected

(<IO'V*Hz).

The display blinks above 1200.0

such as the accessory Keithley Model

decimal point location, and measure-

a positive polarity is implied.

AA

INSTRUCTION MANUAL Digital Multimeter Model 174

OPERATING INSTRUCTIONS

On the 3 mV and 30 mV DC ranges the front panel "mV ZERO" control must

5.

adjusted to obtain rated accuracy.

Make low-thermal connections to the Model

a)

Model 1747 cable or satisfactory equivalent is recommended.

b) Set the Model 174 to the 3 mV range.

Allow the thermal emfs generated by the input connections

C)

d) Some circuits may need to be enclosed in polyurethane foam, a cardboard box, or other suitable enclosure to prevent zero fluctuations due to air movement at the connection point.

Make certain that a "Zero Signal"

e)

be measured (e.g., a zero current condition for a resistance thermometer measurement).

f) Adjust the "mV ZERO" control for a display indication of-.0000 mV f .OOOl mV.

The "mV ZERO"

effect on any

Proceed

9)

h) The "mV

control operates only on the 3 mV DC and 30 mV DC ranges.

other range or function.

with the measurement and apply the signal.

ZERO" control setting will also be valid for the 30 mV range if used.

condition is established for the circuit to

NOTE

174

as described above. Use of tne

to

stabilize.

be

It has no

AC Voltage.

b.

(1000.0 display).

The Maximum display is 29999.

all other digits are blanked.

Maximum input voltage is 1000 V rms or

I.

Select V ac on Switch 5302. Depress AUTO, REM or desired Manual Range pushbutton.

2. Connect the signals to be measured between HI and LO terminals.

3.

are designed to accept banana or "bunch pin" plugs,

1747 Low-Thermal coaxial input cable.

4.

Observe the displayed digits, decimal point location,

v) .

The Model 174 detects ac voltages from IO microvolt5 to 1000 volts

The Model

174

is average-reading, When the display exceeds 29999, a 3 remains lighted, but The displa

blinks above 1000.0 volts on the highest range.

7

10 V*Hz on all ranges.

calibrated in terms of rms sinewave

(The terminals

such as the accessor Keithley Model

and measurement unit (mV or

3-7

OPERATING INSTRUCTIONS

INSTRUCTION MANUAL

Digital Multimeter

Model 174

3-6.

measures resistance from IO milliohms/digit to 300 megohms. The maximum display is 29999. When the display exceeds 29999, a 3 remains lighted, Maximum allowable input voltage is 240V rms or 350 V peak up to 60 Hz.

the resistance under test at full range is 3 volts. The Model 174 measures from 3Kn to

300 megohms full range in HI mode.

the resistance under test at full range is 300 millivolts. 3OOC to 30 megohms full range in LO Mode.

HI and LO terminals. For measurement on low resistance ranges where lead resistance may cause an error the following procedure should be performed.

HOW TO MEASURE RESISTANCE. When the Model 1744 Option is installed, the Model 174

but all other digits are blanked.

a. HI Ohms Measurement.

I. Select Hlfl on Switch 5302.

2. Connect the resistance under test between HI and LO terminals. Depress AUTO, REM, or the desired Manual Range pushbutton.

3.

4. Observe the displayed digits, decimal point location, and measurement unit (Kfi or

MR) . b. LO Ohms Measurement. When Switch 5302 is set to LOO,

1. Select LO n on Switch S302.

2. Connect the resistance under test between HI and LO terminals. Depress AUTO, REM, or the desired Manual Range pushbutton.

3.

Observe the displayed digits, decimal point location, and measurement unit (iI,

4.

KR, or Mn).

Lead Resistance Compensation.

c.

When Switch S302 is set to HIR, the voltage developed across

the voltage developed across

The Model 174 measures from

The Model I74 measures the total resistance between

1. Connect the measuring circuit to the INPUT terminals on the 174 using appropriate

test leads or cables.

2. Substitute a temporary short circuit in place of the circuit to be measured. fn the case of the Model 1747, temporarily clip together the alligator connectors.

3.

4.

Record the reading on the Model 174 as RO (residual lead resistance under a

shorted condition).

Remove the shorted condition and connect the active circuit to be measured.

5.

6. Record the new reading in the Model 174 as R,.

The true value of “Ri’ is R = R - Rg, within the stated accuracy of the Model

7.

174.

method.

No additional errors in theTresi:tance measurement are added when using this

3-8

AA

INSTRUCTION MANUAL

Digital Multlmeler

Modal 174

OPERATING INSTRUCTIONS

3-7.

measures dc current in seven ranges: both the Model I740 and 1745 Options are installed, the Model 174 measures ac current over

the same ranges. Range selection is via manual range pushbuttons only.

peres. The maximum display is 29999. When the display exceeds 29999, a 3 remains lighted but all other digits are blanked.

HOW TO MEASURE CURRENT.

The Model I74 DMM is protected by a 4 ampere fuse on all ranges except 3uA and

3OuA.

250V input voltage. If the fuse is blown, should be installed in the fuse holder on the 1745 option.

MAINTENANCE, Paragraph 6-5, for fuse replacement.

a. DC Current.

I. Select A dc on Switch S302.

2.

3.

4.

ment unit (uA,. mA, or A).

implied.

On the 3uA and 30uA ranges the maximum allowable input corresponds to a

The Model 174 DMM detects dc currents from to.1 nanoamperes to ?3 am-

Depress the desired Manual Range pushbutton. Connect the signal to be measured at the HI and LO terminals.

Observe the displayed digits, polarity sign, decimal point location, and measure-

A "zero" reading will always be displayed as -.OOOO.

When the Model 1745 option is installed, the Model 174

3uA, 30uA, 300pA, 3mA,

CAUTION

a replacement Keithley Part No. FU-39

If no polarity sign is indicated, a positive polarity is

30mA, 300mA, and 3A. When

Refer to Section 6,

b. AC Current. The Model I74 DMM detects ac currents from 0.1 nanoamperes/digit to

3 amperes in AC function. The Model 174 is average reading calibrated in rms of a sine

wave. The maximum display is 29999. When the display exceeds 29999, a 3 remains lighted,

but all other digits are blanked.

Select A AC on Switch S302.

I.

Depress the desired Manual Range pushbutton.

2.

Connect the signal to be measured at the HI and LO terminals.

3.

Observe the displayed digits, decimal point location, and measurement unit (PA,

4.

ma or A).

3-8.

FURTHER MEASUREMENT CONSIDERATIONS.

Grounding Considerations.

a.

the line cord are provided to avoid electrical shock in the event of an electrical

malfunction. The ground (CASE) terminal,

ground, ground is at a safe potential at all times.

Always ensure that the instrument Is grounded either through the third wire on

the line cord or through a separate connection between CASE terminal and reliable

earth ground.

injury due to electrical shock.

serves as a return current path and ensures that the instrument chassis

Failure to follow these precautions could result in serious personal

The CASE terminal and the third wire ground on

when properly connected to a reliable

WARNING

AA

3-9

OPERATING INSTRUCTIONS

INSTRUCTION MANUAL

Digital Multimeter

Model 174

How to Use the Model 174 Off-Ground.

b.

at’potentials of up to ilOO volts.

(CASE terminal) is specified at 103n shunted by less than O.OluF. In general, the LO

terminal should be connected to the point in the measurement circuit which has the lowest

impedance to power I ine ground or the “effective guard” or “shield” mode in the circuit. If the measurement circuit is independent of power line ground LO and CASE should be

connected to a cornnon point in the circuit.

c.

3mV/30mV Accuracy. The 3mV/30mV accuracy specifications assume that the instrument

has been in thermal equilibrium with the environment for I hour or more, and that the

front panel

obtain a “zero” indication of -.OOOO mV ? .OOOl mV. The “mV Zero” control is used in

this manner to compensate for thermal emfs generated in the circuits connected to the

input terminals. These externally generated thermal emfs must re,nain constant during

the measurement in order to obtain stated accuracy.

d.

300mV Accuracy. The 300mV accuracy is given down to 1% of range. Below 1% of range an additional . the 1% level, but gradually as the level is decreased below 3OOuV.

e.

mV Analoq Output.

is specified.

ranges and functions output voltages up to +l5V may exist.

varying within this span, Analog Output” point is the output of the nanovolt preamp, which has a fixed gain of 100,

and no switching is done, the “mV Analog Output” provides continous Xl00 output for signal levels as low as the

Model 174 noise level (typically IOOnV to 15OnV p-p, up to 30mV).

“mV ZERO” control has been used imnediately prior to the measurement to

l5mV is added to the accuracy. This does not occur immediately at

This output is active only on 3mV and 30mV ranges. No accuracy

Typically the output is within 2 (2 x accuracy spec + digit). On other

or have step changes within this span. Notice that the “mV

except in the A/D converter between 3mV and 30mV ranges. Thus,

Isolation from the

The “LO” terminal can be operated off ground

“LO” terminal to power I ine ground

Output may be randomly

f. Overload on 3mVdc and 30mVdc.

from DC up

lO7V *

exceed the overload specification on the 3mV/30mV ranges until IO ms after the range change command is given. (e.g. IOms after Load Range goes active or a new range pushbutton is depressed).

4.

Offset Current. The offset current is adjusted to IOpA at the factory or by executing the calibration procedure given in Section 6-4.

with time and temperature, but is is unlikely to exceed 200pA at any environment within

the specified region up to 6 months after calibration. that peak-to-peak noise in the Model 174 will be larger (than that exhibited with a short circuit) for source resistances in excess of about 30KG to 70Kfi.

Settling Time. Table 3-4 gives typical and worst expected settling times express-

h. ed as the number of conversions (320 ms) for the Model 174. The numbers in the table assume that the proper range and function have been selected and previous transients have “settled” before a “step change” in the signal is applied. effects of input cabling time constants.

to

60HZ.

HZ product. When switching from 3mV/30mV to higher ranges the voltage must not

Up to 180~ RMS may be applied continuously at any frequency up to

Up to 250V may be continuously applied at frequencies

Offset current wi 1 I change

Short term variations are such

The numbers do not include

3-10

AA

INSTRUCTION MANUAL Digltsl MultImeter

Model 174

OPERATING INSTRUCTIONS

TABLE

Source R

3mV, 30mV 3mV, 30mV

OHMS

DC AMPS AC VOLTS AC AMPS

particular Model I74 will have repeatable settling time characteristics for a fixed

or low) source resistance. oft instruments ('Itypical values") and the maximum settling time of a "slow" but properly

peratinq instrument ("worst expected values").

All except 3OOMn HI

30Mn LO

3OOMn HI

30MR LO All All All

<lOKn

i-OOKn LEnd Range

End Range

Any <lOOKn

Any

The above is a rough indication of what can be expected of

-4.

Number of Conversions Required to Settle to Within 0.01% of a "Step Change".

Tvpical

I

20

AA

3-11

INSTRUCTION MANUAL Dlgllel Multimeter

Model 174

ACCESSORIES

SECTION

4-l.

Model

1722 Digital Interface, probes, test leads, only be installed and used one at a time.

4-2.

use, or for complete freedom from ac power lines for critical measurements where near-

infinite commonmode rejection is needed.

recharging is needed from the built-in charger. operation from full charge. The Model I728 recharges completely in I6 hours with instrument off.

screwdriver and adds I,

-25°C to +35’C when installed in the Model 174.

“NC--

GENERAL. This section describes various accessories available for use with the

174.

Models Section 2 INITIAL PREPARATION and Section 3 OPERATING INSTRUCTIONS.

MODEL

These accessories include the Model 1728 Rechargeable Battery Pack, the Model

the Model 1723 IEEE Interface,

and other convenience accessories.

1740, 1744,

1728

RECHARGEABLE BATTERY PACK.

Trickle char

Model 1722. 1723 and

and

1745

are field-installable options which are described in

es with instrument on.

;i

kg

(3

pounds) to

1728

can only be installed and used one at a time.

4.

ACCESSORIES

rack mounting kits and various

Model 1722, 1723 and 1728 can

NOTE

The Model 1728 powers the 174 for portable

A front panel low-battery indicator shown when

174.

NOTE

Ni-Cd rechargeable batteries give

The Model 1728 is field installable with Storage and ambient operating temperatures

3

hours

The Model 1728 Rechargeable Battery Pack can be installed by the user within the Model I74 at any time. However (

1723 IEEE Interface is already installed,the Model 1728 cannot be used simultaneously

a, How to l’nstall the Model I728 Recharqeable Battery Pack. nished with the Model 1728 are already installed in the battery pack. pack includes 7 rechargeable “C” cells (1.2V, 2 AMP tir) and two 19.2 volt packs

(sixteen l.2V cells per pack). See Figure 8.

Check she fuses on the Battery Pack.

I .

F403. All are 1 ampere, 3AB or 3AG, Slo-Blo types, Keithley Part No. FU-IO.

Check for proper installation of batteries in the Battery Pack.

2.

battery cells are to be installed see paragraph 4-2d.

To install the Battery Pack,

3.

shown in Figure 2. circuit board. Temporarily remove the plastic spacers installed on the Mode) I74 chassis. Separate the two halves of the spacer and reinstall on the Model 1728 board as shown in Figure assembly.

(P401, P402) taking care to orient the connectors as shown. If the Model 1740 AC

Option is installed,

to permit access to connector P4Ol as in Fiaure 9.

on the spacers with the pack oriented as shown in Figure 9 and tighten down the four

screws which hold the Model

tighten down the four Phillips screws.

Plug the two 5-wire connectors (J401, J402)

Carefully renwve the top cover to gain access to the printed

9.

it will be necessary to temporarily renwve the 1740 pc board

1728

if the Model I722 Digital Interface or the Model

The batteries fur-

The battery

Three fuses are used, F401, F402, and

If replacement

loosen four Phillips screws on the top cover as

The rubber “0” ring retains the spacer and screw

into the mating receptacles

Place~the Model 1728 in position

to the Model I74 chassis. Replace the top cover and

AA

4-l

ACCESSORIES

b.

How to Check Batteries.

INSTRUCTION MANUAL

Digital MultImeter

Modal 174

IMPORTANT

The Model 1728 is shipped from the factory in an uncharged condition.

the pack should be installed in the Model 174 and charged prior to usa

The Model

I.

battery condition.

The LOW BAT indicator will be lighted when the

2.

operating voltage.

LINE or OFF to permit recharging of the Pack.

c. How to Charge the Batteries. The Model 1728 provides built-in recharging circui try. rapid rate when the Model

and may shorten the life of the batteries.

d. rechargings before replacement is necessary.

batteries,

the batteries used in the Model 1728.

The Model 174 must be connected to line voltage.

Overcharging the batteries will raise the internal temperature of the battery pack

How to Replace Batteries.

use only the equivalent types as supplied by the factory. Table 4-l summarizes

I74

has a built-in LOW BAT indicator

When the indicator turns on, the

I74

is set to OFF.

CAUTION

The rechargeable batteries will normally provide many

TABLE

Summary of Batteries Used in the Model 1728.

However,

4-l.

to permit easy determination of

Battery Pack goes below normal

Model I74 should be switched to

Recharging occurs at the most

if it is necessary to replace the

Therefore,

Description

I .2v “C” ccl I (2 AMP-HR)

+19.2V pack

(16-l.2V cells)

-19.2V pack (16-l .2v ccl IS)

Quantity Vo I tage Keithley Part No.

7

I +19.2V BA-31

I -19.2v BA-3 I

8.4~

BA-30

4-2

AA

INSTRUCTION MANUAL

Digital MultImeter

Model 174

J4Ol

ACCESSORIES

(MATES WITH)

P4Ol

F401

r,uunc 0.

PIO(I~I I/L" nechargeable Battery Pack.

ACCESSORIES INSTRUCTION MANUAL

Digital MultImeter

Med.4

174

4-4

FIGURE 9.

Installation of Model 1728.

AA

INSTRUCTION MANUAL

Dlgltal Mulllmeter Model 174

e. Circuit Description. (See also Schematic 26758c.j

The Model 1728 provides il9.2 volts and +8.4 volts from nickel-cadimum bat-

I .

teries. BT401 and ET402 are 19.2 volt, by IA, 3AG Slo-Blo fuses. and is also fused by a IA, 3AG, Slo-Blo fuse. charging circuit which is operated from i29.5V unregulated supplied by the DMM linepower supply.

2. BT40l Charging. CR401 and CR402 and resistor ~402 place a diode drop across R401. current is the maximum charging current. plying current through Q401.

is set to OFF. A trickle charge is maintained when the DMH is line operated.

reduced current is obtained by inserting a limiting resistor in series with the charging circuit (not shown on Schematic 26758C). charged at a C/IO rate (45 mA for ET401 & BT402, & 2OOmA for BT403). When trickle charged, the charge rate varies according to line voltage t battery condition from a minimum of C/l00 rate to a maximum of C/20 rate. Thus,

fully charge the batteries, but is intended to put sufficient charge into them for short intermittent use.

ET403 is an 8.4~ pack composed of seven 1.2 volt “C” cells

‘BT401 is

charged

The maximum charging current occurs only when the DHH

.45 AH nickel cadmimum packs which are Fused

The Model 1728 has a built-in re-

via a constant current from Q401. Diodes

Diode CR403 prevents the battery From SUD-

In full charge,

trickle charge may never

ACCESSORIES

The resulting

the batteries are

The

3. ET402 & ET403 Charging. Q402 or Q4Ol respectively. except that they are powered by unregulated ?29.5V.

BT402 G ET403 are charged via a constant current from

These circuits operate similarly to the above circuit.

AA

4-5

ACCESSORIES

4-3. MODEL 1722 DIGITAL INTERFACE.

General.

a.

control lines. This accessory is available either "factory installed" or "field-installable". Model 1722 consists of a two-layer circuit with card-edge and mating output connectors.

Installation.

b.

Disconnect the Model 174,line cord from line voltage.

I.

Depress LINE pushbutton to discharge any voltages on power supply capacitors, etc.

2. Loosen and remove the four Phillips screws on the top cover as shown in Figure 2.

3.

4. Lift off the top cover and set aside.

Temporarily remove the four spacer assemblies held down by a slotted strew.

5.

Reassemble the spacers as shown in FigurelO.Be careful to install the "0" ring

6.

over the screw to hold the assembly together prior to installing the Model I722 board,

The Model 1722 provides binary coded decimal outputs (8421) and range Outputs are open-collector positive true unless otherwise specified.

INSTRUCTION MANUAL

Digital Multimeter

The

Model 114

Place the Model 1722 in the location shown in FigureIOwith the cables oriented

7.

properly.

8. Plug the Model 1722 connectors JlOO3, JIOOI, and J1002 into mating connectors

P403, P404, and P701 respectively.

9.

T401 as shown in Figure 10.

IO.

Diaital Output Connector Terminations.

~lk6 ('to-pin) and PI101 (26-pin).

(IO-ft. long) cables mate with PIoo~/PIIOI connectors. See Figure 1, for pin

identification.

See detailed view for orientation of connectors.

See detailed view for orientation of connectors

Connect the ground return wire from the Model 1722 to the screw on transformer

Reinstall the top cover.

The Model 1722 uses two card-edge connectors

Accessory Model 1727-03 (3 ft. long) or Model 1727-10

4-6

AA

INSTRUCTION MANUAL DigItal

Model174

Multimeter

ACCESSORIES

Jim,

1

I II

I I II 7.

2 TOP SPACER

\

.F BOTTOM SPACER (27812

~"0" RING (GA-j)

ABOVE HARDWARE

IS FURNISHED

WITH MODEL 174.

(27812a)

kltiUHt IO.

Installation of Model 1722 Digital Interface.

ACCESSORIES

TABLE 4-2.

General Characteristics of Model 1722 Digital Interface.

IGITAL OUTPUTS:

Logic: BCD (8421) Open-collector positive true unless otherwise specified.

Data: 4 full digits, I partial digit (0,

Function: 4-bit code (0, AC VOLTS)

Polarity: HIGH 3+. Overflow: Autorange: Automode:

-AG (m): HIGH (logic "0" 5 no output change occuring.) Logic Levels: HIGH : open collector to output LO. LOW Z closure to output LO. Output device (2N5134) greater than 20V breakdown, pull-up resistors may be installed on these open collector outputs.

is reconnnended when using internal 5 volt power supply.

JTPUT TIMING: Data is updated typically every 320 msec (non-trigger mode).

is typically 1.2 msec. Data will appear at an output only if its respective strobe is

active. The FLAG will go low (Logic "0") typically 2 tnsec before update and go high

typically 100 vsec after update. flag is high. If FLAG RESET is activated, the FLAG will reset (go to Logic "0") until the end of the next data update.

fMOTE CONTROLS:

Strobe: Strobe lines permit word serializing in 4-bit increments or multiples thereof. HIGH inhibits controlled output lines from conduction, LOW enables conduction. Range In: 4-bit exponential code. Load Range: Hold:

conversions).

Printer Hold: Same as hold but grouped with outputs for convenience in inte;facing

printer. Trigger Mode: LOW enables TRIGGER control. Trigger Mode Disable: Trigger: Flag Reset: LOW sets FLAG jFLAG) to LOW (HIGH). Control Logic Levels t Source Requirements:

voltaqe between +2.4V and 5V referred to output LO.

w_jthin O:~V while sinking +I.6 milliamperes (ITTL load). The Hm, Tm, TRIGGER MODE DISABLE, TRIGGER, and FLAG RESET lines control the Model 174 regardless

of front panel setting.

in "V" and "Sl" functions, when the front panel "REM" (remote) pushbutton is depressed

LOW q > 29999.

LOW ; range change.

HIGH : autorange mode.

Data can be expected to be unchanging so long as the

Low enables remote ranging as set by Range code.

LOW inhibits display update,

LOW disables TRIGGER.

LOW to HIGH transiti initiates a new A/D conversion.

LOAD RANGE and Range Input Codes control range selection onl

output update and autorange (A/D continues

I, 2, 3) and exponential range code.

<0.5V at 5mA sink (3TTl loads).

HIGH 5 either an open circuit or a

LOW ! closure to output LO

INSTRUCTION MANUAL

Digital Mulllmeler

Internal

4.7K minimum value

Update time

Model174

jOLATION:

by IO9 n and 5OOpF, 1200 VDC, IOOOV runs AC maximum. controls are located from chassis ground by IO6

4-8

All digltal outputs and remOte controls are isolated from 174 analog input

All digital outputs and remote

R and O.OlpF; 250V runs maximum.

INSTRUCTION MANUAL Dlgttal Multlmeter

Model 174

ACCESSORIES

TABLE 4-3.

Sumnary of Remote Commands at PllOl

(See also Figure 12)

Pin No. Comnand

I

2

3 4

5

6

CASE GND COMMON COMMON

AUTORANGED STROBE TRIGGER MODE

AUTOMODE STROBE

7 HOLD

a 9 LOAD RANGE

IO II 12

OVERFLOW STROBE

FLAG/FLAG STROBE RI FUNCTION STROBE

13 R2

Pin No.

14

15 16

17

la

19

20 IO3 STROBE

21

22

23

24

25 26

Command

RANGE STROBE

R4

POLARITY STROBE R8

IO' STROBE

TRIGGER

FLAG RESET

IO' STROBE

TRIGGER MODE DISABLE

lOI STROBE

AUTORANGED

IO0 STROBE

PI006

AA

PIIOI

I

,

t

L ----- --------__- ---- J

----__----------------------,

r

i

I

L

---a--------- 1 3 9 1315 ----------------- 17 19 212325 27 29 31 I

FIGURE Ila. Connector Pin Identification For Model 174/1722,

2 4 6 6 1012141616 20222426

I,, ,

1 3 5

2 4 6 6 10121416162022242628303234363'340 I

I, , , , ( , , ( , , , , , , , , , , ,-q

7 , 9

, , 1 , , , , , .d

11131c17192123-25

5 7 11 33 35 37 3g

i

1

4

I

4-P

ACCESSORIES

-

- Y

Pin No.

20

I

*

2 ii

9

IO

I1

I2

13 I4

15 I6

17 18

19

TABLE 4-4.

Suwnary of Digital Output at ~1006

(See also Figure 12.)

Signal

CASE GND COMMON COMMON COMMON

COMMON PRINTER HOLD AUTOMODE VEXT R8 VOLTS R4 AMPS R2

AC

RI

OHMS

lo’+-8

103-e

104-4

103-4

INSTRUCTION MANUAL

Digital Multimeter

Model 174

Signal

104-Z lD3-2 104-l 103-l 102-8

101-8

102-4 IO’-4 102-Z

100-4

FLAG

100-z

OVERFLOW

100-I

POLARITY

4-10

--m-m--- -------- -----~

r

I

PI101

t

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

l-

i

PI006 )

I

L

-----.-------------------------

FIGURE lib.

t ; 2 8 1012141616 20222426

1

11v1.11.11**

a 3 5 7 9 11131E1719212325

2 4 6

7 I I I I ( , I 1 I , , 1 , , , , I , I 1 3 5 7 9 111315

8 10 121416162022242626 303234 36 3840 I

1?1921232527293133353739 I

Connector Pin identification For Model 174/1722.

1

i

I

-

---1

,

I

1

AA

INSTRUCTION MANUAL

Dlgltal Mulflmeter Model174

(Mode

1722 Ran

TABLE 4-5.

d Function Cod

g For MO

in

ACCESSORIES

1 174)

'UNCTION

IC VOLTS

.ow R

OUTPUT FUNCTION

CODE (1) VAAC R

100 0

IO1 0 rC VOLTS

000 I

RANGE

3 mV

30 mV

300 mv

303 i

300 v

1200 v

300 mV

3 v

30 v

300 v

1000 v

300 R

3 kn

30 kR

300 kn

3 MR

30 MO

OUTPUT RANGE

CODE (I)

R8 R4 % Rl

0011 0 1 0 0 0 I 0 I 0 I,0 0 I I I

0 0 0 0 0 1

0 I 0 I

0 II0

0 Ill

IO 0 0 IO 0 I

0 0 I 0

0011 0 I 0 0

0 IO 1 0 II0 0 1 II

(EXP)

INPUT

RANGE

CODE (I) (2)

R8 R4 R2 Rl

III1 I IO 0 IO II I 0 I 0 I 0 0 1 I 0 0 0

0

II I

0 110

I I I I

IO IO 1 0 0 I

IO 0 0 0 III 0 II0

Ill1 110 I I I 0 0 IO II IO IO IO 0 I

IO 0 0

AUTORANGE AUTORANGE

II R 001 0

3 kn

30 kQ 0 I 0 0

300 kn

3 Mn

30 Mfl

300 MR

11) Coding in this table is defined to be HIGH (POSITIVE) TRUE. "1" = HIGH and "0" = I LOW. Refkr to output and remote control logic levels for definitions of HIGH t LOW.

,2) Note that except for AUTORANGE CODE,

PUT RANGE CODE, I.=. the INPUT RANGE CODE is the LOW TRUE BCD code of (EXP).

(3) Note that (EXP) is oiiectly the exponent of IO if the numerical readings are

defined as follows:

VOLTS: Unit = uV OHMS: AMPS:

AA

0011

0 10 I 0 II0 0 III

IO 0 0

INPUT G RANGE CODE is the compliment of the OUT-j

Uni~t = R Unit = nA

1111 I IO0 IO I I IO IO IO 0 I IO 0 0

0 III

AUTORANGE AUTORANGE

4-11

ACCESSORIES

INSTRUCTION MANUAL

Dlgltal Multimeter

Model 174

TABLE 4-5. (Con't)

(Model 1722 Range & Function Coding For Model 174)

OUTPUT FUNCTION CODE (I)

UAACQ

010 0

011 0

d.

HOW to Select Vext Using Internal Jumper.

internal or external voltage references and internal pull-up resistors. (See Figure 16.)

LANGE

3 UA

30 IJA

100 PA

3 mA

30 mA

100 mA

3 A 3 uA

30 uA

100 PA

3: 2

;OO mA

3 A

OUTPUT RANGE CODE (I)

RB RI, Rz Rl

0 0 1 I 0 1 0 0 0 IO I 0 110 0 Ill

10 0 0 IO 0 I

001 I 0 IO 0 0 IO I 0 II0 0 III

IO 0 0 10 01

The Model 1722 may be wired for use with

(EXP)

3 4

===l==-

INPUT RANGE CODE (I) (2)

Ra R4

NO AUTORANGE OR REMOTELY PROGRAMMED CURRENT RANGES.

R2

RI

I

I. Jumper A.

the external reference Vext (pin 8, ~1006).

2.

Jumper B.

the internal reference (+5V .

Jumper C.

3.

reference. reference is rated at 40 mA maximum.

The pull-up resistors are not connected in this instance. The +5 volt

When this jumper is installed,

When this

When this jumper is installed, Vext is connected to internal t5V

'urnper is installed,

j

the pull-up resistors are connected to

4-12 AA

INSTRUCTION MANUAL

Olgllrl Mulllmeter Model 174

ACCESSORIES

TABLE 4-6.

Digital Output Lines Grouped By Function.

Name

IO0 STROBE

100-l 100-2 100-4 100-8

IO1 STROBE

101-l 101-2

IO’-4

lo’-8

IO2 STROBE

102-l 102-2

102-4

102-8

IO3 STROBE

IO’-, 103-2

103-4

IO4 STROBE

104-l 104-2 104-4

104-8 ‘OLARITY STROBE {ANGE STROBE

-RI

-R2

-R4

-R8

Pi006

Name

FUNCTION STROBE

-VOLTS

-AMPS

-AC

-OHMS 16

OVERFLOW STROBE

-OVERFLOW

AUTOMODE STROBE

-AlJTOMODE

AUTORANGED STROBE

-AUTORANGED

PRINTER HOLD

TRIGGER MODE

-tEiD LOAD RANGE

NO.

10 I2

14

38

7

6

RI

R2

R4 R8

--

I8

23

21

I9

I7

--

i

--

16

I4

15 13

II

TRIGGER

FLAG RESET

TRIGGER MODE DISABLE COMMON

,CASE

FLAG/Fm STROBE

FM

FLAG

VEXT

2,3,4,5

I

--

36 34

8

PI101

NO.

-

12

8

6

4

25

:

9

II 13

15 17 I9

:: 2,3

I

IO

AA

4-13

ACCESSORIES

INSTRUCTION MANUAL

Digital Multimeter

Model 174

PI006 Pl,lOl

.,,

3=

GND

JlOOl

1

4-14

JIOOZ

JlOO3

FIGURE 12.

Models 1722 Digital Interface.

AA

INSTRUCTION MANUAL

DigItal MultImeter Model 174

ACCESSORIES

PI006

~---3 =

GND

,L

S

JlOO2

FIGURE 13.

NOTE : UPPER BOARD PC-4

NOT SHOWN.

JlOO3

Location of Jumpers and Pull-Ups For Model

16

1722

4-15

ACCESSORIES

INSTRUCTION MANUAL

Digilal Multimeler

Model 174

Detailed Explanation of Model 1722.

e.

end of the Manual .)

1. TRIGGER MODE AND TRIGGER (Timing Diagram 23248E): When TRIGGER MODE is active

(Low),

Conversion starts within 1.6 milliseconds after RISING TRIGGER.

120 milliseconds after start of conversion.

not be updated and the FLAG will stay at HIGH (unless reset by FLAG RESET).

RANGE IN code (Table65) at the beginning of the next conversion. As long as LOAD

RANGE is held low the instrument will remain on its programmed range, provided the “REM” pushbutton on the front panel is depressed. of Table 4-5 will result in the nearest valid range to that programmed. always set the DMM to the newly programmed range.

will be held until the end of the first complete conversion on the new range.

a REMOTE CONTROL update prior to data output. case of HOLD. change could result in erroneous data.

the FLAG be examined no sooner than IO psec after activation of the HOLD bit.

is low wait until it goes to HIGH before expecting the mbit to have been accepted. Other REMOTE CONTROL bits such as -and TRIGGER, code can be kept active for longer than an output data update time, I.e. >3.2 msec to

insure proper REMOTE CONTROL acceptance.

output data and display will not be updated.

2. m:

LOAD RANGE: When LOAD RANGE is low the 174 will go to the range as set by the

3.

4.

REMOTE CONTROLS:

If either ITOlIYor PRINTER HOLD is low,the output data and the display will

Referring to timing schematic 2824913 it is possible to just miss

A HOLD just missed (unknown to the user) just before data begins to

(Schematics and Timing Diagrams are at the

TRIGGER MODE enables TRIGGER.

Integration starts

RANGE IN codes programed outside the limits

LOAD RANGE will

However,

This can be misleading especially in the

To check If this occurred, it is suggested that

the display and output data

If flag

wand the RANGE IN

TRIGGER MODE DISABLE: When in TRIGGER MODE and triggering the autorange mode,

5.

normal operation will give an output for each range encountered during the autoranqe.

However,

-and m. This will prevent the FLAG from being set and ignore further triggering until the final range is reached.

after the second conversion on the final range.

trigger mode operation.

f. Circuit Description.

I . Overal I Block Diagram.

associated clock lines are first isolated.

split. to parallel form and then to the output buffers.

block which decides where the data is going, out or in, and also generates the flag. Control input data and strobes are first buffered by the input buffer block.

strobes go to the output buffer to gate the outputs.

the input register and control block where they are converted from parallel to serial form and sent to the isolation block.

decides, based on control data input, whether there is to be an output update.

isolation for the I722 is provided by transformer TIOOI which is powered by a second-

ary winding of the DMM power transformer.

SEiCLK and INCLK each drive an emitter follower made up of transistors 41036, Q1035, and 41037 whose loads are LED’s in the opto-isolators are pulled up by resistors RIOIO, RI009 and ~1018, which is driven by QlO34 similar to the three just mentioned. The output pullup on ~1018 is on the DMM mainframe.

isolation is taken directly from the DMMc5 volts through RlOl6 and Cl018 and CTOl7,

which provide the coupling.

if this is undesirable the

As shown in Figure 14 Serial data from the DMM and its

Output data DOWNDAT goes to the output register block where it is converted

Signal Isolation.

The bidirectional data line SERDAT and the two clock lines

-output bit can be tied to TRIGGER MODE

The FLAG will indicate a valid reading

Then operation will revert to normal

Bidirectional data line SERDAT is then

The clock lines go to the control

The

The control data inputs go to

The input register and control block also

Power

Power for the DMM side of the

4-16

56

INSTRUCTION MANUAL Dlgltal Mulllmeter

Model 174

ACCESSORIES

Power Supply.

3.

plied via pins B and C on JIOIA. Switching for the power for TlOOl provided at JlOO3 Pins A and B and comes

mainframe through its Power On switch. and run through an integrated circuit +5V regulator TRIOOI, by ClOl5, CIOOZ, ClOO3, C1004, 1~1014. ground by a green wire to a screw on the DMM mainframe or transformer. Also common mode filtering is performed by RI008 and Cl006 between output low and chassis ground.

4.

Control Block. UPCLK, the isolatra form of INCLK,

of El017 timer.

threshhold input of UlOl7. edge goes into trigger. ever, since this threshhold is clamped low through diode CRIOOZ.

to time out in the time period of the clock pulses on INCLK until the last rising edge of INCLK, at which time it will clock out at 30 microseconds, therefore UPTIME, the output of UlOl7, will be length of the INCLK pulse stream plus approximately 30 microseconds, This is done by clocking DOWNCLK with UPTIME in flip-flop UlOl5A. downtime also defines the time when the flag is set high, that is when data has finished’being updated. Setting the flag low during data change time, or resetting

the flag, thru UlOl4C d U1014D where it is called GATECLK and goes to the output register.

5. Output Register.

l009A & 8, IOIA & 8, IOIIA f, B. are used. Serial data enters U1008B and is clocked through all of the shift registers by the parallel clock, GATECLK. At the end of the clocking time all 30 bits have been shifted in and are presented in parallel to the output buffer.

6.

Output Drive and Buffer. gates UIOOI thru 1007 and UlO12 and 1013. and drive transistors QIOOI through 1030 to output connector Rl006.

7. Input Buffers. Strobe lines are buffered by UIIOI and UllO2 and go out to the output drive and buffer block. UllO5.

false triggering.

UllO4 is a Schmitt trigger and is put on certain control lines to prevent

which is the time in which data will be flowing from the 174 to the DhH.

is accomplished in two ways:

LOW voltage ac ~rorn the seconddry of the DMM transformer is sup-

via the D"M

The secondary of TlOOl is rectified, filtered

where it is again filtered

The core of TIOOI is connected to chassis

is run to the trigger input

A buffered version of UPCLK is also run via diode gate CR1002 to the

UlOl7 is such that its output will go high when a falling

A filter made up of RI007 and Cl008 will try to charge, how-

It will not be able

The beginning of

FR or UPDATE.

The output register is made up of shift registers Ul008A & 8

It is a 32-bit shift register, of which only 30 bits

Parallel data on the output registers goes to output

Here they are gated with the output strobes

Remote control inputs are buffered by Ul104, ullll,

Downtime also gates DOWNCLK

AA

4- I 7

ACCESSORIES

INSTRUCTION MANUAL

Digital Mullimeter

Model 174

- ---. I~--- I-- I

4-18

FIGURE

Mod~el 1722 Block Diagram

14.

INSTRUCTION MANUAL

Dlgltsl MultImeter

MQdd 174

ACCESSORIES

4-4. either single or dual mounting configuration,

Description:

The Model 2000 is a rack mounting kit which converts any half-rack style “Ml’ instrument

from bench mounting to rack mounting in a standard IT-inch rack. The dimensions are 3-l/2 in. high x I9 in. wide. panel and angle bracket which can be mounted on either side of a half-rack instrument.

I tern

UO.

RACK MOUNTING.

Description

21

22

27 28

Angle Bracket

Screws, #6-32 x 5/E, Phillips

Blank Panel

Screws , 46-32 x l/2, Phillips

The Model 174 can be rack mounted in a full rack (19 inch width) in

MODEL 2000 SINGLE RACK MOUNTING KIT

The hardware included in this kit consists of a blank

TAI 3LI

E

4-7.

Parts List

FI

3r Model ;

Qtv

Req ’ d

I

too

0. Kei thley

Part No.

267380

__

247818

--

T

Illustration

29

30

31

1

Screws, X10-32 x 3/E, Socket Hd.

Angle Bracket (Staked)

Kep Nut, 16-32

--

267418

--

I

AA

4-19

ACCESSORIES

Assembly Instructions: (Refer to Figure 15)

I. Before assembling the rack kit,

rack frame (either left or right position).

Once the position of the instrume,lt has been determined, the “side dress” panels

(I:;m II) on each side of the instrument should be removed.

24) to a’llow the side dress panels to slide toward the rear.

with longer screws (I tern 22) furnished with the kit.

The bottom cover feet and tilt bail assemblies may be removed if desired. Orig-

3.

inal hardware,

future conversion back to bench mounting.

Attach “angle bracket” (Item 21) to left and right side of instrument using two

4.

#6-32 x 5/8 inch Phillips screws (Item 22).

l/2 inch Phillips screw (Item 28) furnished with the kit,

use two #6-32 x 5/8 inch Phillips screws and two Kep nuts.

Attach “blank panel” (Item 27) using two #IO-32 x 318 inch Socket Hd screws (Item

5.

29) furnished with the kit.

side dress panels, feet and tilt bail assemblies should be retained for

determine the position of the instrument in the

For I4 inch instrument use one #6-32 x

INSTRUCTION MANUAL

DIgital MultImeter

Model 114

Remove four screws (Item

The screws are replaced

For II inch long instruments

4- 20

FIGURE 15.

Model 2000 Rack Mounting Kit.

AA

INSTRUCTION MANUAL Digital MultImeter

Model 174

ACCESSORIES

MODEL 1007 DUAL RACK MOUNTING KIT

Description: The Model 1007 is a dual rack mounting kit

with overall dimensions 3-l/2 in. (64 mm)

high and I9 in. (483 mm) wide. ware included in this kit consists of two Angle Brackets,

extra mounting screws.

one Mounting Clamp, and

The hard-

Application:

The Model 1007 converts any half-rack, style I’M” instrument from bench .?ounti”g to rack

mounting in a standard l9-inch rack.

kit may also be used for rack mounting IV-

inch ful I rack ividth instruments.

The

The Model 1007 Rack Mounting Kit can be tised to mount instruments of II inch or I4 incn depth. The user should decide the position of the instruments to be rack mounted. Assembly Instructions refer to instruments positioned as above and identified as instrument “A” and “8”.

TABLE 4-8.

Parts List

I

N

-

0.

22

23 24

25

26

27

28

Description

I

Angle Bracket

Screw, ,#6-32 x 518, Phillips Pan Hd

Mounting Cl amp

Screw, 16-32 x I, Phillips Pan Hd

Kep Nut #6-32

Screw, #6-32 x l/2, Phillips Pan Hd

Screw, ,#6-32 x 718, Phillips Pan Hd

: F

or ModI

Req’d

!

Qtv

2

6

1

I

3

2

I

1007. Keithley

Part No.

274108

247988

-_

--

__

--

Tile

1 i

AA

I

1

4-21

ACCESSORIES INSTRUCTION MANUAL

Digital Multimeter

Modal 174

Assembly Instructions: (Refer to Figure 16)

Before assembling the rack kit,

I .

the instruments can be mounted in either location, their position should be determined by the user’s measurement. sitioned as shown. For mounting IY-inch full rack width instruments, disregard steps 2 through

2. Once the position of each instrument has been determined, the “side dress” panels

on both sides of each instrument should be removed.

the screws (Item 8, original hardware) in two places.

the rear of the instrument to remove.

*,?

(Item 7) and replace the screws to hold the mounting clamp in place.

4. Tighten the screws (Item 8) on instrument “6”.

the “corner bracket”

5.

The mounting clamp is installed on instrument

With the screws removed, insert the “mounting clamp” behind the “corner bracket”

The following instructions refer to instruments “A” and “B” po-

(Item 7) on instrument “5” as shown.

deternine the position of each instrument. S i “ce

Removal is accomplished by loosening

Slide the “side dress” panels to

“A” using the original hardware (Item

Insert the “mounting clamp” behind

When mounting instruments having the same depth,

5.

26) are required to secure the two instrument together.

different depth, do not use kep nut (Item

6.

Attach a” “angle bracket” (It em 22) on each instrument using hardware (Item 23) in

place of the original hardware (Item

ets using 1!6-32 x l/2 Phillips screws (Item 27). For II in. long instruments use :6-32

x

5/8

Phillips screw (Item 23) The bottom cover feet and tilt bail assemblies nay be removed if necessary.

7.

8. The original hardware, side dress panels,

retained for future conversion back to bench mounting.

with -6-32 kep nut (I tern

8).

26)

but substitute shorter screw (Item 28).

For 14 in.

feet and tilt bail assemblies should be

a screw (I

When mounting instruments of

long instruments fasten angle brack-

tell

25)

and kep nut (I ten

26).

4-22

FIGURE

Model 1007 Dual Rack Mounting Kit.

16.

AA

INSTRUCTION MANUAL

DlglW MuMmeter

Model 174

ACCESSORIES

4-5.

Model

The Model 1600 is a divider probe for measurement of high voltage up to 40 kilovolts dc. The probe is optimized for use with a dc voltmeter having a 10 megohms input resistance.

Thus,

SPECIFICATIONS:

Voltage Range:

Input Resistance: Division Ratio: 1000:1 Ratio Accuracy (with IOMQ Load):

Ratio Stability: +O.Ol% per 'C; +O.l% per year.

Heating Effects: Self-heating due to application of high voltage for periods in excess

"AC response at 1kV is flat within ?lO% from 20Hz to 120 Hz.

on input impedance of multimeter used.

PROBES AND SHUNTS.

174.

the Model 1600 should be used on 30V or high dc voltage ranges.

of I minute will cause a maximum of 0.2% additional error at 40kV (error is less at

lower voltages).

They are intended for use on various voltage or current ranges.

0 to

1000 megohms.

The following probes and shunts extend the capabilities of

MODEL 1600 HIGH VOLTAGE PROBE

40,000

volts dc."

C1.5%

?2.0% at 20kV and 30kV

+3.0%

i4.0%

MODEL 1651 CURRENT SHUNT

at 25kV, decreasing to

at IOkV and 40kV, and at IkV.

Division ratio is dependent

the

The Model

least 100 microvolts resolution. be used on the 30mV dc range on the Model 174, however, zero instability.

The Model

for use with a DC voltmeter having IO megohms input resistance.

used on the 300mV or

to reduce the effective input resistance.

SPECIFICATIONS:

Voltage Range:

Transfer Accuracy: +5%,

ing,

Input Impedance: 4Mfi shunted by 2 pF. Maximum Allowable Input: 30V rms ac, 2oOV dc. Accessories Supplied:

adapter.

1651

calibrated in rtns of a sine wave.

is a 0.001 ohm shunt (+I%) for use with an AC or DC voltmeter having at

The shunt is rated at up to 50 amperes.

MODEL 1682 RF PROBE

1682

is an RF probe for measurement up to IOOHHz.

shunt the input terminals with a IOMR metal-film resistor

0.25

3V

ranges,

to

30

volts f-m.

1OOkHz to IOOMHz (20"-3O'C); usable IkHz to IGHz; peak respond-

Straight tip, hook tip, ground clip, hf adapter, banana plug

heating effects may cause some

The shunt can

The Model 1682 is optimized

If the Model 1682 is

AA

4-23

ACCESSORIES

MODEL 1685 CLAMP-ON AC CURRENT PROBE

The Model 1685 is a clamp-on current probe for measurement of ac current up to 200 amperes. The Model 1685 is used with an AC Voltmeter and provides an output of 0.1 volt rms per ampere.

SPECIFICATIONS: Range:

Accuracy:

Temperature Coefficient:

ampere range. Maximum Allowable Current: 300 amperes rms. Maximum Conductor Voltage: 600 volts rms. Conversion Ratio:

2, 20 and 200 amperes rms.

?4% of range at 60 Hz. +6% of range at 50 Hz.

+O.O5%/"C on the 20 and 200 ampere ranges.

0.1 volt rms per ampere.

INSTRUCTION MANUAL

Digital Multimeter

Model 174

+0.3%/"C on the 2

4-6. CONVENIENCE CABLES AND CONNECTORS. effective use of the Model 174 on the 300mV and higher ranges.

MODEL 1681 CLIP-ON TEST LEAD KIT

The Model 1681 is a set of test leads, 48 in. (1,2m) in length, terminated by a banana

plug and spring-action clip-on probe.

MODEL 1683 UNIVERSAL TEST LEAD KIT

The Model 1683 is a set of flexible test leads, 40 in. (lm) in length, with interchangeable screw-on adapters.

4-7,.

LOW-THERMAL CABLES.

MODELl746A LOW THERMAL SHORT

The Model17464 is supplied with each Model

connectors make a sliding contact along the inside of the input terminal.

This minimizes variations in thermal emfs and resistance. The low thermal

short is used to verify proper operation on the 3mV DC and 3OOD LO ranges.

The following cables and connection kits enable

174.

The "bunth pin" type

MODELl747A LOW THERMAL INPUT CABLE

The Modell747A is a low-thermal input cable with "bunch pin" type connectors

to mate with the Model 174 input, and copper alligator clips for convenient

connection to the circuit under test. The cable is 3 feet long and is tested

to 1011 0 insulation resistance during manufacture.

Since many other types of banana plugs may create thermal emfs which vary in excess of the Model 174 input variations,

low voltage dc measurements on 3mV DC and 30mV DC ranges. The cable is also

useful as a shielded high impedance cable for AC or high resistance measurements.

4-24

the Model1747A is recommended for

BB

INSTRUCTION MANUAL Dlgltal MultImeter

Model 174

ACCESSORIES

FIGURE 17.

FIGURE 18.

Modell746A Low-Thermal Shorting Plug

Modell747A Low-Thermal Cable Set

4-8. 26- and 40- conductor ribbon cable terminated by mating card-edge connectors to the Model 1722.

long (3,l m).

4- 9 . 488-1975 gus Interface that provides the logic and control functions necessary to inter-

face the Keithley Model 174.

within the Model 174.

Model 1723 Instruction Manual.

BB

MODEL 1727 OIGITAL OUTPUT CABLE SET.

The Model 1727-03 is 3 feet long (I m), and the Model 1727-10 is ten feet

The pins on the connectors are identified in Figure Il. (page 4-9).

MODEL 1723 IEEE INTERFACE.

The Model 1723 has a single interface board that mounts

installation and operating instructions are furnished in the

The Model 1723 is a microprocessor-based IEEE Standard

The Model 1727 is a cable set consisting of

4-25

ACCESSORIES

INSTRUCTION MANUAL

Dlgital Multimeter

Model 174

4-10. MODEL 1743 MAINTENANCE KIT. sary for adjustment/calibration and troubleshooting of the Model 174.

Summary of Items Furnished With the Model 1743.

This kit contains the following items which are neces-

TABLE 4-10.

r

'tern

I

la

lb

IC

Id

2

3

4

5

6

7

8

9

IO

II

12

I3 I4

15

Description

-

-I-

Extender cable set for Digital Board, PC-421.

9 brown,1 gray conductors.

and PVOZ on PC-412.

9 yellow1 brown conductors.

and P903 on PC-412.

9 gray, l'blue conductors.

and P904 on PC-412. 9 blue, 1 yellow conductors. and PqO5 on PC-412.

Extender card for Model 1744 Ohms Board (PC-408). This extender card is labeled as PC-439 and enables the ohms board to be extended for access to circuit test points, etc. Extender card for Model 1745 Current Board (PC-409).

This extender card is labeled as PC-440 and enables the

Current Board to be extended for access to circuit test points,

etc.

Extender card for Model 1740 AC Board (PC-414). This extender card is labeled as PC-441 and enables the AC Board to be extended for access to circuit test points, etc. Extender card for upper board (~~-416) of Model 1722 Digital

Interface. This extender card is labeled as PC-437 and

enables the upper board to be extended for access to the

lower board (PC-415).

card assembly in Figure 20. PC Card Extractor. servicing. Cable Assembly. 2 brown,1 white conductors. Connects between JlOD2 on Model 1722 and P7Ol on PC-421. Cable Assembly, I brown,1 white conductors. Connects between J1003 on Model 1722 and P403 on PC-412. Cable Assembly, 3 brown,1 white conductors. Connects

between JIOOI on Model 1722 and P404 on PC-412. Test Lead Assembly, I red,1 black conductors. Connects

between TPlOl and TP102 on PC-412 and Oscilloscope. See Section 6, MAINTENANCE. Test Lead Assembly, I green conductor. Connects between

TP702an PC-421 and Oscilloscope LOW as described in

Section 6, MAINTENANCE.

Test Lead Assembly.

the Model 1740 AC Option is installed. Extends the violet

wire connection from function switch to

Calibration Cover (requires thumb screws).

Thumb Screws (4 pieces). Used to fasten the Calibrati.on

Cover.

Instruction Manual. Verification and Adjustment/Calibration information in

Section 6. MAINTENANCE.

See the illustration of the extender

Enables the removal of pc boards for

I violet conductor. Used only when

Model 174 (Contains Performance

Connects between J702 on PC-421

Connects between J703 on PC-421

Connects between J704 on PC-421

Connects between J705 on PC-421

Model

1740.

Keithley Part No.

28706C

286968

286VVB

28702~

286106

21257A

287098

287108

287118

28623~

28622~

28707A

287121)

28263

4-26

BB

INSTRUCTION MANUAL

DIgital MultImeter Model 174

ACCESSORIES

AA

FIGURE 13.

Model

1743

Maintenance Kit

I4

-27

ACCESSORIES INSTRUCTION MANUAL

Digital MultImeter

Model 174

w-416

~

-EXTENDER CARD

2861oe(~c-437)

4-28

FIGURE 20. Typical Installation of Extender Card on Model

1722.

AA

INSTRUCTION MANUAL Digital

Model 174

Multimeter

THEORY OF OPERATION

SECTION 5.

5-l. GENERAL. and options.

5-2.

fr:nt) ) components and switching details are shown on the Switching schematic 27935E.

circuits shown in Figure 21,

rear), and relays K50l and K502. (UYOI, Zone M-3) to the A/D input (A/D SIG).

“AZI” and “A/D CAL” to autocal ibrate the A/D converter. “A/D SIG” which autozeros the A/D and integrates the signal for 200ms.

(Deck 3) accomplishes the necessary switching for AZI, AZZ, and A/D CAL. The A/D converter is shown on schematic 27936F which includes the LSI device (UlO3). The A/D converter and

switching are located on the Mother board (PC-412).

of segment and timing lines a through g, dp, Ml, and NMC.

a clock line (SERCLK), which provides appropriate timing signals for a shift register, connect to the Model I722 or 1723 digital interface through the digital board (PC-421, schematic 28209E, Zone H-l, I-l).

SIGNAL FLOW.

The “input switching”

relay K503, and the rear 2 sections of range pushbuttons (S3Ol). All these

b. The “input switching”

c. The A/D makes 2 sequential measurements during each conversion. The first is betweer

d. The output of U103 goes to the display board (PC-410, schematic 279390) in the form

This section contains circuit descriptions for the Model 174 mainframe

The overall flow diagram is shown in Figure 21.

network consists of switch 5302 (deck 4 front and deck l

connects the signal to one of the various signal conditioning

then to the output switching consisting of 5302 (deck I,

The signal then goes through an active ac filter

THEORY OF OPERATION.

The second is between “AZZ” and

Switch 5302

A serial output (SERDAT) and

THEORY OF OPERATION

INSTRUCTION MANUAL

Digital Multimeter

Model174

In addition to these signal flow schematics,

ise;hown on schematic 279380.

schematic 26758C.

Each separate model number (e.g.

designations. Mating connector numbers are noted on the various Model 174 schematics.

5-3.

provides six positions: summarized in Table 5-l.

SWITCHING (Schematic 27935E).

a. Function Switch 5302.

ECK NO. FRONT/REAR

I I

Front Switches INPUT LO.

Rear

The optional battery pack, Model 1728 is shown on

NOTE

174, 1728) has any independent set of schematic

The front panel rotary function switch has four decks and

ACV, DCV, HIR, LOR, DCA, ACA.

TABLE 5-l.

Summary of Function Switching

ACTION OF SWITCH

Selects signal conditioning output for A/D converter.

the power supply (located on PC-412)

The purpose of each deck is

2

3 3 4 4

b. Range Switch S3Ol.

Manual Range Pushbuttons (3OOQ through IOOOV, 3A): Pins l-2-3 and 7-8-V on all

I.

pushbuttons, pins 4-5-6 of 300 (V-Ma-mA) pushbutton, pushbutton encode 4-bit, low-true, 1248 BCD range code on NRIS, NRZS, NR4S, and NR8S.

Pins 4-5-6 and 10-11-12 of 3A pushbutton, pins 10-11-12 of 300mA pushbutton, and pins

10-11-12 of 3OuA pushbutton connect AMPS input (5302, deck 4, front, pin 8) to the

specific current range input on P504 or P505.

in this set are depressed, AMPS input is connected to the 3uA input.

30uA pushbutton and 10-11-12 of the 3uA pushbutton connect the "current protect" line

to amps input if neither of these ranges is selected. ors are diode protected on the 300uA through 3A ranges. button connect the A/D input (via S302, deck I, rear, pin 5) to the "3uA input"

when that range is selected,or to the "30uA input"

when 30uA or higher range is selected.

REM is depressed, pushbuttons are mechanically interlocked so that only one may be depressed at a given

time.

Front Encodes the 3-bit function code to integrated circuit UlO3

on VI, AC DC and R lines.

Rear Selects inputs for "NBI" indication. section 5-Ye.

Front Selects A/D CAL and AZ1 input. Rear Selects AZ2 input. Front Switches INPUT HI. Rear Connects AC input to on DC.

with ZMR.

Notice that if none of the pushbuttons

(via 30uA pushbutton pins 11-12)

When no range is selected or 3000, AUTO, or

the A/D input is open,

and the display reads near zero.

Loads the Model 1745 output

and pins 10-11-12 of 30 (V-Mfi-mA)

Pin 4-5-6 of the

Thus the current sensing resist-

Pins 4-5-6 of the 3uA push-

All range

5-2

AA

INSTRUCTION MANUAL

THEORY OF OPERATION

Dlgltsl Multimeter

Model 174

2. “AUTO” Pushbutton. Electrically this switch does nothing. Mechanically it is

interlocked with the other range pushbuttons,

range code is selected (NRIS = NRZS = NR4S = NR8S = t5V).

“REM” Pushbutton. When this pushbutton is depressed “NREM” is active (OV).

3.

other range pushbuttons are mechanically interlocked, c. Relay Operation.

Relay K503 (Zone B-3) connects INPUT HI to the nanovolt preamp input on 3mV DC and

I. 30mV DC ranges. The relay is constructed with two coils; one of the coils is always energized.

2. Relay K502 (Zone G-4) connects the nanovolt preamp output to the A/D input

(through CLAMP) when on 3mV DC and 30mV DC ranges, where is is energized.

connects the CATT line to CLAMP when not energized on other DCV ranges.

Relay K501 (Zone H-5).

3.

so that when it is depressed, the AUTO

The relay

The

a) 300mV and 3V Ranges:

through overload protection resistors R523 and R524.

b) 30V through IOOOV Ranges:

the attenuator through ~516.

DC Volts Zero Controls.

d.

Potentiometer R509 (Zone L-3) is a 300mV Zero adjustment which develops a small

I.

current (< +I5 PA) through R5ll. The control is used to set AZ1 (in DC V function) equal to the voltage at INPUT LO.

2. Potentiometer R513 (Zone F-7).

to make the voltage at R507 equal to the voltage at

e.

DC Attenuator.

1. Overload Protection. (R523, R5.24, R522, C503, 3V DC ranges if an overload is applied to Input HI, The remainder of the overvoltage will be dissipated on a shield to the rear of the display board.

protect KS01 from transients with a large V-Hz product.

1OO:l Ratio. (R515, R503, R505, in Zone G-5, F-5, and F-6) If Q5Ol is off, this

2.

is a simple lOO:l divider.

1000: I Ratio.

fo&d by the ratio of R515 to the parallel combination of CR503 + R505) and CR504 +

R506 + Q501 on resistance.)xThis ratio is independently adjusted using R506.

When Q50i is turned on (by control line H) a lOOO:l divider is

K50l is not energized and connects CATT to DCV INPUT HI

K501 is energized and connects CATT to the output of

The same circuit as used for 300mV zero is used

Input LO on 3OV DC range.

in Zone H-4, H-5) On 300mV DC and

CATT will clamp at t (4 to 7V).

in R523 and R524 which are mounted

and C503 as well as C501 and C502

R522

The ratio is adjusted by R505.

j-4. NANOVOLT PREAMP (Schematic 279370 and block diagram, Figure 22).

a. Input Fi 1 ter. The preamplifier filter is a 2-stage R-C filter designed to with-

stand 250 rms sinewave or 250 v dc. Diodes CR601 and CR602 provide overload protection for the modulator stage that follows.

b. Modulator. The FET modulator (Q604) is a monolithic “Series-Shunt” chopper.

Additional filtering is included to protect against fast-rise inputs and spikes generated by the chopping action. The “chopped” with an amplitude of (VIN - V,) peak-to-peak.

AA

signal at the modulator output is a square-wave

5-3

THEORY OF OPERATION

The

AC Amplifier.

by%pacitor pair (Q603) followed by operational amplifier U602. and is set by a feedback resistor newtork ~612 and 17613. DC gain is unity.

C609

and resistor

square-wave output is capacitively coupled to the ac amplifier

R614.

The ac amplifier consists of a differential FET

Fedback ac gain is nominally 1000,

INSTRUCTION MANUAL

Digital Multimeter

Model 174

d. Demodulator. switch Q602). and proportional to (V,N - VF).

Closed Loop Gain. Overall dc gain is lOO:i and is adjusted via potentiometer R604.

Components which determine the dc gain are resistors ~604, R615, and R616.

Millivolt Zero. The zero circuit consists of I megohm resistor (R617), potentio-

rneE,r

is factory set for optimum zero span.

through feedback resistor R616.

Q6Oi A, B and ~602. means of potentiometer R603 which sets the rise time to the gate of FET Q604A.

st>ng of resistor divider taps R622A through R622P. zero span.

which develops the compensating zero offset voltage at the input.

wiz tailored rise and fall times,

current is adjusted by means of tailoring the rise time to the gate of the series switch (Q604A) using R603.

~623

FET Driver Circuit.

q

h. The mV Zero circuit consists of I megohm resistor (R617) potentiometer ~623 and a

i.

The oscillator and FET drive generates complementary 520 Hz square wave drives,

The output of the demodulator is a square wave referenced to signal common

and a string of resistor divider taps R622 (A-P).

The zero circuit generates a zeroing current through feedback resistor ~616,

The ac output is direct coupled to the half-wave demodulator (FET

The moveable jumper J601

The zero circuit generates a zeroing current

Complementary 520 Hz square waves are generated for driving

Rise and fall times are tailored.

to drive the modulator and demodulator.

Offset current is adjusted by

The moveable jumper J6Ol selects

Offset

Figure 22.

Simplified Diagram of Nanovolt Preamp.

AA

THEORY OF OPERATION

5. Amplifier Ul203 is powered from +3V (+15V-VR1204 voltage) and -15V. When the amplifier is overloaded, DC voltage off capacitors Cl210 and Cl2.11. ranging.

the average voltage at the output is -6 volts which keeps

TABLE 5-2.

1740

Gain Chart.

INSTRUCTION MANUAL

Dlgital Multimeter

Model 174

This minimizes settling time when auto-

RANGE CONTROL LINES

/ A/D GAIN ATTENUATION

300

mV

3

300

1000 v

v

il

;I $10 %I00

t1000

-L

b.

AC/DC Converter.

I. The AC/DC converter is a transconductance amplifier. The simpl’ified circuit

shown in Figure 24 illustrates the basic operation. converted to a current (Ii”) as a result of the summing amplifier configuration.

Current lin flows through FET Ql2Ol when negative and through diode CR1201 when

positive.

flowing through Rout.

referenced to a negative voltage (-l5V)

2. The AC converter consists of dual FET Ql203, operational amplifier UIZOI, MOS FET Q1201, diode CRl201, and transistor Q1202. RI215 and R1212.

is located in the feedback loop of the converter amplifier.

driven from the output of the amplifier for negative current input.

Thus Eout is a halfwave rectified signal. Eout is developed by IIN

The positive (+) terminal of the converter amplifier is

The output resistance is determined by RI207 and R1201.

Xl0

Xl Xl

to

allow voltage swing across FET 41201.

ov

+5v

I-t

The input resistance is determined by

DIOO

ov

ov ov ov

ov ov

ov

+5v

The AC input voltage (Ein) is

DIOOO DIQ

ov ov ov ov

+5v

FET Q1201

The gate of this FET is

3. For positive input current the feedback path for lJl201 and FET Ql2O3 (a, b) is through diode CR1201 and transistor Q1202. side of Rl215,

the gate of Ql203 (pin 3).

This turns on the base emitter junction of Ql202 and pulls current throuqh diode CRl201,

so that the connection path is through Rl215, Rl212, CR1201, and Q1202 (emitter to collector) to the -15V supply.

is to equalize the output load on amplifier Ul2Ol for each polarity, and to avoid

parasitic oscillation which might occur in Ul201,

loading.

current flows into the summing junction of the amplifier, which is

This current causes the output of Ql20l to go negative.

The reason for using transistor Ql202 and not a diode

When the signal is positive at the input

because of unequal output current

5-6

AA

INSTRUCTION MANUAL Digital Multlmeter Model 174

THEORY OF OPERATION

4. When the input voltage is

Rl215, causing Ql201 output to go positive and forward bias QIZOI gate.

turns on QIZOI, pulling current through resistors RI207 and RI201 from signal grotind Thus Ql2Ol only conducts for negative input signals; the output current is a halfcycle negative going sinewave. which provides fi I tering. The action of the filter allows a 3V output with only 6

volts available from Ql201. The transfer gain of the AC/DC converter is unity. causes a I volt DC output.

5. Ql2O3 is a dual FET, used as source followers with source resistors RI213 ana Rl214. The IOmV adjustment feeds a small correction current to the summing junction to adjust for leakage current errors.

system gain on the 300mV and 3V ranges.

the DC filter (whose input is RI206 and Cl205 in this case.)

Cl210 and Cl211 are the only blocking capacitors needed on the AC/DC converter

6.

input.

reaching the output.

7. The AC/DC system common is the -6 volt reference. It is composed of voltage follower lJl202 and input divider RI210 and Rl2lI.

impedance AC path between -6V and signal low to minimize AC noise pickup.

The capacitors keep voltage offsets produced by Ul203, Ql203, and Ul201 from

negative,

This output current flows through Cl201 and RI207

Without Cl201 more than a 9 volt swing would be needed.

current will flow 0t1t resistor RI212 and

This ac:lor!

A one volt AC RMS sinewave input

The I volt (I kHz) adjustment calibrates the

Additional output filtering is provided by

Cl206 is used to provide a low

Ein

o--)

41202

RI RI

207

201

THEORY OF OPERATION

INSTRUCTION MANUAL

Dlgilal Multimeter

Model 174

5-b.

shown in Figure resistor Rx.

unknown resistor value and the value of the constant current. voltage (VREF) and resistors (R) determine the value of the constant current which deter-

mines full range resistance sensitivity.

Range

300 R

3OOKn

3OOMn

MODEL 1744 OHMS OPTION. (Schematic 2794113)

a. Simplified Description. The basic philosophy for the Model 1744 ohms circuit is

3KQ

30Kn

3MR

30Mn

25.

The output voltage of the operational amplifier is proportional to the

HI OHMS

m

3.3v .33v 3v

3.3v .33v

l-m

A constant current equal to VREF : R is forced through the unknown

Properly scaled reference

TABLE 5-3

Summary of Ohms Ranges

LO OHMS

Full Range

Volts at

A/D Input

.3v

‘R

ImA

I OOnA

I OpA 0 I

IpA

IOOnA 0 0

IOnA 0 0

Range Logic

A] B/ C

I 0

0 I

- --

3v

3v 3v 3v 3v

‘R

ImA

I OOpA

IOvA

IPA

I OOnA

IOnA

Range

LO

1

gic

-_

I

‘REF

C

3.3v .3v

1

0

I

0

I

0

.33v

3.3v .3v .33v

3.3v .3v .33v .3v

-

l

0

I

0

I

0

-

b. Detailed Description.

A more detailed diagram of the ohms converter is shown in Figure

I.

surement scheme is based on a “pseudo four-terminal” method.

is made possible by the four modes of operation of the A/D converter:

(AZI), AUTO CALIBRATE (ACAL), AUTO ZERO 2 (AZ’,?), and SIGNAL INTEGRATE. AZI input is measured for 40 ms and this zero level is stored. calibration voltage is measured for 40 ms.

between A/D reference calibration and AZI.

across R. also flows through Rx the calibration is fixed. defined as the zero level for signal measurement and is stored in the A/D.

measures the input at the bottom of Rx for 200 ms.

ference between signal input and AZ2 which is the voltage across Rx. the value of Rx and is displayed after appropriate scaling.

essentially a ratio measurement between the voltage across R

Notice that the voltage at the top of R,

ment (rU1102 offset and lead resistance drop) and the voltage at the bottom of R

negative. at high resistance values.

Since R is a fixed, stable resistor,

Thus, the HI terminal is guarded and relatively fast response is achizved

The A/D calibrates itself to the difference Thus,

is essentially at signal low of the instru-

During ACAL the A/D reference

it is calibrated to the voltage

the value of IR is now known. Since IR

AZ2 is measured for 40 ms. This is

The A/D thus measures the dif-

The four-terminal scheme

The: measurement is

x and the voltage across R.

26.

The mea-

AUTO ZERO I

The A/D

This represents

is

5-8

AA

INSTRUCTION MANUAL Dlgllal MultImeter

Model 174

THEORY OF OPERATION

4bvb

+

INPUT

INPUT LO

V

REF

R

IR

i

A

OPERATIONAL AMPLIFIER

vO

= lRRX

AA

FIGURE 25.

Simplified Diagram of Model 1744 Ohms Option.

5-T

THEORY OF OPERATION

3.3 o

INSTRUCTION MANUAL

Digital Multimeter

Model 174

‘REF

.33

CURRENT HI

__j A/D CAL

5- 10

LO

0

CURRFNT LO

FIGURE 26.

)A/D SIG

Detailed Diagram of Model 1744 Ohms Option.

AA

INSTRUCTION MANUAL Dlgltsl Mulllmcler

Model 174

2.

The ranging is accomplished by selecting one of six current steps:

IuA, IOuA, lOOvA, ImA.

ohms ranges is possible.

THEORY OF OPERATION

IOnA,

Since the A/D Converter has ranges 0.3~ and 3V. a total of 12

I OOnA,

Switching of VREF is performed by FET switches QllO3 and Ql104.

3.

(A, B, C) is controlled by the U103. volts or +.33444 volts depending on the logic level of “C” (JIIOI, pin 2). circuit IJIIOI is a buffer.

Resistors RIIOZ, RIIOI, and the “on”

4.

“W

what is called “R5” in Figure

“R6” in Figure 26.

“mirror” 41108 and Ql109, common-base transistor 41107, and load resistors RI112 and Rl113.

provided by resistor network Rll20,

UllO2 forces a current through resistor Rlll9, transistor all09 (connected as a diode), and resistor Rlll6.

bias resistor RI114 and reference voltage of VRIIOI. biasing. Capacitor Cl102 decreases output noise and assures loop stability.

in Figure

if they are switched into the circuit.

5. The operational amplifier is composed of integrated circuit UllO2, current

U1102 is a differential FET input operational amplifier. Offset adjustment is

The base of transistor Qll07 is held at approximately -4 volts by the action of

The diode CR1102 from the junction of RI112 and RI113 limits the amount of

6.

power delivered to them and the current injected to the +15V supply under overload conditions. The diode CR1103 in the collector of QllO7 is likewise for overload protection and

keeps the base-collector junction of QllO7 from ever being forward biased, as this

could cause too much current to be drawn through RI114 and Rlll5. QIIIO, CR1106 and

Qllll protect UllO2 during overload as seen in Figure 26.

When the ohms circuit is functioning properly,

7.

exists, an alternate feedback loop comes into play, thus keeping the AZ1 point near

ground.

input terminals are open circuited, the output of UllO2 starts going positive, increasing the current through QIIOY which is mirrored in Qll07. current to Qll07 is limited,

resistor Rill4, turning on Qll06 ..Lich pulls current through Qllll keeping the AZ1

point near ground.

26.

RI112 and RI113 determine open circuit voltage at the input terminals.

Qlll in conjunction with RI118 and QllO6 provide for this. When the

Resistors Rl103, R1105, and the “on”

26.

Notice that RREF is the parallel combination of R6 and R4 or R5

This current is then “mirrored” in the collector of QllO8.

additional base current in QllO7 flows through its base

Switches QllO3 and 41104 select either +3.3444

resistance of QIIOI make up what is called

resistance of Qll02 make up

Resistors RI104 and RI107 make up what is called

RIIZI, Rll23, Rll22, and Rll06. The output of

Resistor RI115 is used for zener

and an open circuit condition

Since the collector

Lange logic

Integrated

AA

5-i I

THEORY OF OPERATION

INSTRUCTION MANUAL

Digital

Multimeter

Model 174

5-7.

the range pushbuttons (5301) and are arranged in a four-terminal measuring scheme.

A/D converter sensitivity is 300 millivolts full range.

the input is protected by a 4 ampere fuse (FIOOI), the input to 2 diode drops for either positive or negative inputs. UIOOI guards the center connection of the diode bridge.

r

MODEL 1745 AMMETER OPTION (Schematic 27940C).

TABLE 5-4

Summary of the Model

Cal

Range

3uA

3OuA

3OOuA

3mA

30mA

300mA 1 R

3A

hunt Resistance

I OOKR

IOKn

I KR

100 n

IO n

0.1 R

Adjustment

RIOOI

RI002 RI003

RI004

RI005

RI006

RI 007

The shunt resistors are switched by

On the 300 PA through 3A ranges

and by diode bridge CRIOOI which clamps

Unity gain amplifier

1745 Ranges

Current

Protect Ci rcui t

Input Pin

JIOOI, pin I

JIOOI, pin 2 JIOOI, pin 3 JIOOI, pin 4 JIOOI, pin 5

JlOO2, pin I JlOO2, pin 2

Active

NO NO YES YES YES YES YES

The

-I

5-8.

ANALOG-TO-DIGITAL CONVERTER. (Schematic 27936F)

a.

Introduction.

1.

The A/D converter, digital representation of an analog voltage applied to its input. The basic functional blocks involved in this process are shown in Figure 27. has several distinct rodes of operation, broadly grouped as “signal-measurement mode” and “error-correction mode”. voltage input to display output occurs in two major blocks. Converter) generates a digital pulse train whose frequency is proportional to the

input voltage. The second block (digital chip) contains circuitry which counts the incoming pulses for a fixed time period, producing a total count which is proportional

to the average of the input voltage over that time period.

2.

The digital chip (a custom MOS LSI circuit) which performs the pulse counting function also performs a number of other functions necessary for the analog-todigital converter, and for other portions of the DMM.

this digital subsystem will not be given in the following discussion.

various of its outputs which are necessary for the operation of the remainder of the

A/D converter wi I I be referred to when necessary.

The first step of the A/D conversion process,

3.

tion,

put pulse train has the property that its average frequency bver a given time period

is proportional to the average of the input voltage over the same time period.

the charge balance technique has the property that the digital output is a representation of the true integral of the analog input over any specified sampling time.

circuitry which performs the V/F function is explained in detail in Section 5-8b.

is performed using a principal known as charge balancing.

as its name implies,

It can be seen that the transformation from

performs the function of generating a

This A/D converter

The first block (V/F

Details of the operation of

However ,

the Voltage-to-Frequency conver-

The resulting out-

Thus,

The

5-

I2

AA

INSTRUCTION MANUAL Dlgllal MultImeter Model 174

THEORY OF OPERATION

SlGNAL

INPUT

\

rl”LlIPLklL”

A

-.-

,tH*RGE-BALANCE

SYSTEM)

> <

A I

CONTROL SIGNALS

V

OlOlTAL

LSI

CH I P

FRONT PANEL

CORRECTION SIGNAL

<

PULSE NAlN OUTPUT

CONTROL 5

<

>

AUTO-ZERO

AN0

AUTO-CALIBRATE

SYSTE"

I’\

! I

I

IGNALS

> DISPLAY IHFORnATlO”

>OlGlTAL INTERFACE ,NFOR”ATlOH

FIGURE 27.

Basic Functional Blocks of A/D Converter.

4. The charge-balance circuitry described in Section 5-8b, although highly linear, has certain intrinsic scale factor and zero offset errors. verter these errors are corrected for by the use of additional circuitry.

In the complete A/D con-

This so-

called Auto-Zero and Auto-Calibrate circuitry is described in Section 5-7~.

5-7d contains a description of overall A/D converter system operation, combining the

circuit functions described in sections

5-7b

and 5-7~ into a complete A/D conversion

cycle.

b. Voltage-to-Frequency Converter.

The simplified circuit shown in Figure 28 illustrates the basic principles of the

I.

charge-balance V/F converter.

the integrating capacitor voltage,

current Ix is integrated by the capacitor, V

positive than the threshhold of the comparator (time tl in Figure 29).

output voltage Vc. which is a logical variable,

Its operating waveforms are shown in Figure 29. Assume

Vi, to be initially negative.

As the input signal

i rises and eventually becomes nwre

The comparator

then rises to a logic ‘one’.

next positive-going edge of the clock CID (time t2 in Figure 29), this ‘one’ is

latched by the flip flop and appears as the latched output QR. At t3, the out-of-

AA

Section

At the

5- I

THEORY OF OPERATION

INSTRUCTION MANUAL

Digital Mullimeter

Modal 174

COMPARATOR

b

L

+

VC

2-Y QR

CID

IrP

(CLOCK) -ii

klti”Kt 28. Basic Charge-Bala,Ke

phase clock, Cl, goes high and enables the output of the AND gate, thereby turning on

the current switch.

current lr bringing Vi

Vi crosses the comparator threshhold in a negative direction and V, goes to a logical

‘zero’.

is still a zero and therefore the flip flop output also becomes a zero. current consequently is not turned on during that clock period, and in fact stays off until the next time the integrator voltage once again rises abode the comparator

threshhold.

is forced to flow out of the integrating capacitor, discharging it and

to a negative value. Sometime (t4) during this reference current pulse,

At the next positive-aoina e’qe of clock CID,

For the next half clock period, from t3 to ts, the reference

Converter.

(t6), the comparator voltage V,,

The reference

5- 14

AA

INSTRUCTION MANUAL

Digital Multlmeler

Model

174

THEORY OF OPEAATIO

2. For relatively large values of the input,

capacitor to be recharged above the comparator threshhold is relatively small, and

the charging-discharging cycle described will occur at a high frequency.

values of input current,

ingly longer and the events described will occur at a lower rate.

rate of reference current pulses (and digital output pulses) is a function of the

input current.

Notice that the amOunt of charge removed from the integrating capacitor during

3.

each discharge cycle is equal to the product of the reference current, Jr, and onehalf the clock period.

time period is equal to the total charge that flowed in during the same time period

(within a resolution of one discharge increment) the uniformity of size of the

reference current pulse guarantees that the total number of such pulses is precisely

proportional to the time-integral of the input current.

the recharging time of the integrator will be correspond-

Since the total charge removed from the capacitor in any giver

the time required for the integrating

For lower

Thus the repetitior

AA

CUTPUT PULSE

CID

J

L-i 1 A

1 I

FIGURE ,29. Operating Waveforms of A/D Converter.

1

I

1

r

5-l 5

THEORY OF OPERATION

INSTRUCTION MANUAL

Digital Multimeter

Model 174

4. Figure 30 is a simplified

to perform

already discussed, Figure 30 shows three major circuit elements not previously

mentioned.

=) high impedance input to the A/D converter. gain of IO, giving the A/D converter in effect two voltage ranges, selected tiy the

line labeled GIO (an output from the LSI chip).

b) The transconductance amplifier, MOS FET (QlO4) and resistors, buffer amplifier LIZ02 into a proportional current,

integrating capacitor.

C)

of op amp UIOI provide a fixed current component of Ix, in addition to the variable

component Is (which is proportional to the input voltage).

rent, labeled lo, allows the overall A/D converter to handle both positive and nega-

tive input voltages. With this arrangement,

of its maximum possible value when the input voltage to the entire converter is

zero.

subtracting a fixed number from the accumulated count before displaying it.

d) The remaining circuitry in Figure 30 is functionally equivalent (with some added details) to the basic charge-balance loop shown in Figure 28. output signals QR and CLK are used by the digital subsystem, in effect, to recon-

stitute the pulse train discussed in connection with Figure 29.

the V/F conversion.

The input buffer amplifier, U202, serves two functions. First is provides a

The reference diode and the resistor connected from it to the summing junction

This transposition is accounted for in the digital subsystem (LSI chip) by

schematic

In addition to some added details of the circuitry

converts the voltage which appears at the output of

diagram of the circuitry actually employed

Second,

consisting of op amp UIOI and its associated

the output pulse frequency is one half

it provides a selectable voltage

Ix, which is used to charge the

This fixed offset cur-

The digital

c.

Auto-Zero and Auto-Cal ibrate Circuitry.

I . The charge balance system shown in Figure 28 is inherently highly linear, but

both its zero and full-scale calibration (scale factor) are susceptible to drift with

time and temperature, due to a variety of effects.

related circuit functions, intrinsic et-rors can be cancelled, resulting in a.system whose scale factor is

essentially as stable as the voltage of a reference zener diode and whose zero sta-

bility is limited principally by thermo-electric offsets.

achieve this performance are described in this section.

2.

It can be shown that all zero-error sources in the charge balance system (such as offset voltage drift of amplifiers LIZ02 and UIOI, UIOI, etc.) can be represented as a total effective error current at the summing junction of amplifier UIOI.

error current at the emitter of the reference current output transistor, QIOZB. It

is thus possible to correct for all such errors by introducing an appropriate COTrection current at each of these two locations in the circuit.

Auto-Cal and Auto-Zero circuitry, then,

two currents and to supply them during the measurement of the input signal.

3. The method used to “discover

follows: Consider first the Auto-Zero operation.

volt input would cause the charge-balance loop to deliver reference-current pulses to

the integrator at exactly l/2 the clock frequency (see Section 5-7b4c). Zero mode, digitally forced to deliver reference-current pulses at precisely l/2 the clock

frequency. amplifier (lx) does not exactly match thins forced reference current; the difference

the buffer input is supplied with zero volts, and the current switch is

The current being delivered to the integrator through the transconductance

referred to as Auto-Zero and Auto-Calibrate, these

In a similar way, all gain errors are equivalent to an

is to discover the proper values of these

” the proper value of the correction signals is as

Through the use of a pair of

The techniques.used to

input current drift of amplifier

The function of the

In an error-free system, a zero-

In the Auto-

5-16

AA

INSTRUCTION MANUAL

Digital Multimeter

Model 174

THEORY OF OPERATION

AA

FIGURE 30.

Simplified Schematic.

5-l

THEORY OF OPERATION

INSTRUCTION MANUAL

Digital Multimeter

model 174

exactly equals the correction current required to cancel the dffset errors.

inteqrator voltage, Vi, exhibits a charge balance sawtooth waveform like that shown

in Figure 29,

difference current.

flows into the summing junction of amplifier UIOI so that the slope of the ramp is

equal to zero.

The Auto-Calibrate system works in an analogous manner, with three differences

4.

of detail:

The voltage supplied to the input of buffer amplifier U202 is

a)

voltage which the charge balance system can measure.

b) The current switch is forced to a frequency equal to the clock frequency

rather than one half of it.

The feedback correction current is delivered to the emitter of the reference

Cl

current output transistor (QlO2B).

The circuitry which performs the operations described above is shown in Figure 3lF’together with most of the charge balance system redrawn from Figure 28. circuitry is grouped in five major blocks:

Input Multiplexer,

a)

b) Reference current forcing circuitry,

Comparator fi I ter,

c)

d) Auto-Zero feedback and storage circuitry,

superimposed on a much slower ramp whose slope is proportional to this

The auto-zero feedback system adjusts a correction current which

In this way,

all zero errors are precisely cancelled.

the

Thus the

exact amount

The added

Auto-Cal feedback and storage circuitry.

e)

This circuitry will be described block by block with reference to the above

6.

description of its basic mode of operation.

The input multiplexer supplies the necessary

a) the buffer amplifier at appropriate times, signal source when that signal is to be measured. The multiplexer consists of JFET

switches controlled by signals from the LSI chip. The two adjustable capacitors

shown in Figure 31 are used primarily to neutralize the JFET switching charge in

order to minimize the A/D input current.

b) The reference current forcing circuitry controls the input of the comparator

latch flip flop. In the Auto-Zero mode, it forces the output of this flip flop to

alternate between one and zero on successive clock periods. The resulting reference

current pulse rate is equivalent to an output frequency from the charge balance system of l/2 the clock frequency.

one constantly with the result that the reference current is on at every opportunity;

reference-current pulse frequency thus equals the clock frequency.

FON and COFF, are used to control these two operating modes:

both Auto-Zero and Auto-Calibrate, and COFF is a logic “0” during Auto-Zero and “I” otherwise.

The block labeled “Comparator Filter”, not previously mentioned, serves an

C)

important function in the Auto-Zero and Auto-Calibrate feedback loops. As discussed above, and Auto-Cal purposes is the slow ramp arising from the effective error currents. Because this t-amp has superimposed on it a relatively high frequency triangle wave-

form,

the component of the integrator voltage which is of interest for Auto-Zero

the combination of comparator and comparator-filter functions as a switching-

In the Auto-Calibrate mode QR is forced to a

and connects the buffer amplifier to the

“known” voltages to the input of

Two chip outputs,

FON is a logic “1” during

5-18

BB

INSTRUCTION MANUAL

THEORY OF OPERATION

Dlgltel MultImeter

Model 174

mode (class D) amplifier for the ramp voltage, with gain equal to tne ratio of the -

Vc switch to the triangle amplitude. the switching output of the comparator so that only the low-frequency amplified ramp

signal is passed on to the remainder of the Auto-Zero (or ACAL) feedback loop.

d) The Auto-Zero feedback and storage block completes the control loop used to generate the Auto-Zero correction current. capacitors and consider only the direct signal path via the Auto-Zero loop switch and the JFET source follower. ductance amplifier, comparator fi I ter), FET source and UIOI summing junction. constitute a simple low-frequency and dc feedback loop which will strive to adjust the voltage across the integrating capacitor to a value near zero. tion has been achieved,

on the desired value,

must now be exactly balanced by the switched reference current.

The remainder of the auto-zero system operation is quite simple. Once the stable

closed loop condition has been achieved, one of the two capacitor switches is then closed and the gate voltage on the source follower (which has the value necessary to produce the correct value of IAZ) is stored on that capacitor. When the loop

finally opens at the end of the Auto-Zero phase,

lished during the Auto-Zero phase thus remains in effect until the next Autc-Zero

operation.

integrating capacitor,

auto-zero loop switch,

then the Auto-Zero correction current IAZ must have taken

since the total current being fed to the integrating capacitor

Consider the following circuit elements:

The comparator-filter’s function is to srwoth

lgnqre for the moment the two storage

Transconswitching rode amplifier (comparator and source follower and the resistor between

Examination shows that these circuit elements

Once this condi-

the value of IAZ which was estab-

switch

The Auto-Cal feedback and storage block works in a manner identical to that of

e)

the Auto-Zero feedback and storage block,

is fed to the emitter of Ql028 instead of the summing junction of UIOI. Al though the Auto-Zero and Auto-Cal correction operations interact to some degree, a few sequential iterations of these operations suffice to establish the correct values of the two correction currents.

Overall A/D System Operation.

d.

In the preceeding two sections the structure and function of each major analog

I.

circuit block has been explained.

in which these elements are combined in a complete A/D conversion. is based on Figure

conversion.

The first major division of the conversion period is into an error-correction

2.

segment (120 ms long) and a signal-measurement segment (200 ms long).

former, the input multiplexer supplies known reference voltages to the V/F block,

and (as described in Section 5-7~) the correction currents IAZ and IACAL are estab-

I ished. During the latter, signal voltage applied to its input, chip. count and displays the result.)

3.

three 40-msec. phases.

gain is held constant at either IX or IOX (depending on DHM range and function).

During the AZ1 phase,

voltage, and the Auto-Zero feedback loop is closed.

correct any system zero-errors is established,

(see Figure

(As the next conversion period begins,

The error-correction segment of the conversion cycle is further divided into

31)

causes the source-follower gate voltage which produces this current

an overall A/D converter timing diagram showing one complete

32,

the now error-corrected V/F converter has the unknown

During the first two of these phases, the buffer amplifier

the input multiplexer supplies the buffer with a zero-reference

This section contains a description of the manner

and its output pulses are counted by the digital

with the exception that its output current

The description

During the

the chip processes the resulting pulse-

The value of IAZ required to

and the closure of the AZCI switch

THEORY OF OPERATION

INSTRUCTION MANUAL

Digital Mulfimeter

Model 174

5-27

Figure 31.

Simplified Diagram of Complete A/D Converter

AA

INSTRUCTION MANUAL

THEORY OF OPERATION

Dlgltal MultImeter

Model 174

to be stored on the corresponding Auto-Zero storage capacitor,

4. During the ACAL phase, the multiplexer connects the buffer input to a full-scale

reference voltage (either 3.34 or 0.334V, depending on buffer gain), and a similar process results in a scale-factor correction voltage being stored in the Auto-Cal storage capacitor.

5. Buffer gain during the AZ2 phase is always the same as it is during the signal-

measurement phase; it may differ from its value during AZI and ACAL.

(possibly) changed buffer gain,

second Auto-Zero operation is required to prepare the V/F converter for an errorcorrected signal measurement.

stored on the capacitor controlled by the AZCZ switch (Figure 31).

the effective system offsets may have changed so the

This new value of the Auto-Zero correction voltage is

ONE A/D CONVERSION

Because of the

-4

L

ERROR SIGNAL CORRECTION MEASUREMENT

FIGURE 32. A/D Converter System Timing.

5-Y.

drivers, and timing mux generator. The entire display, function indicators are fully multiplexed.

(timing mux).

generated by LSI UlO3 (Schematic 27936F).

t3, t4, and t5. The cornnon anodes of the digits and function indicators are driven by

the appropriate "mu&' line. The "mux" timing is also used with the Model 1722 or 1723 digital interfaces. are 191.5 microseconds, while to and tl are twice as long (383 microseconds).

and function indicators.

DISPLAY BOARD (Schematic 279390).

a. This schematic shows the display digits, the LED function indicators, alI display

The "mux" times are generated by shift register ~801.

The total "mux" cycle is I.53 milliseconds.

b.

The data "mux" lines drive the cathodes of the display segments (a,b,c,d,e,f,g,dp)

The data "mux" signals are generated by UlO3.

A

SIGNAL INTEGRATE

200ms

/

including (polaritv) sign and

This is accomplished with six time slots

Inputs to ~801 are

The time slots are identified at to, tl, t2,

Periods t2 through t5

c. The tl period controls the IO4

brightness compared to other dlgits the data"mux 'I lines are activated for one half the

tl period or 191.5 microseconds.

digit and the polarity sign. To keep constant

The IO" digit is blanked unless it is a I, 2, or 3.

AA

5-2'

THEORY OF OPERATION

The anode driver transistors are saturating switches (Q810 through Q815). The seg-

me:; driver transistors are emitter followers (Q802 through Q809).

resistors are R802A throuah R802H. Resistor ~803 and capacitor

itor ~801 decouples integrated circuit ~801 from the power supply.

resistor R808 prevent parasitic oscillation of segment driver transistors.

Pin I5 NfJI line will turn on all decimal points when the function selected Is not

e.

installed.

~801 is turned on by ~804.

LEGMENT

LINES

~801 and ~804 accomplish this when the appropriate option is not insta!lcd;

~802

DRIVES DISPLAY SEGMENT OF

Segment current is approximately 30 milliamperes peak.

decouple current spikes'from the 5 volt supply.

TABLE 5-5

Display Data MUX Lines.

INDICATOP LIGHT DURING

INSTRUCTION MANUAL

Digital Multimeter

Model174

The current limiting

Capac-

Diode CR801 and

a for last 'r.of tl,

mV indicator

V indicator

MR indicator

5-22

FIGURE 33. Digital Display Multiplex Scheme.

AA

INSTRUCTION MANUAL Digital

Multimeter

MO&l 174

THEORY OF OPERATION

S-10.

a. Circuit Partitioning on Schematic 2820YE.

J7b; (pins 10,

circuit to Zone K, not including Q7'22, Q719, or Q720.

schematic. b. Detailed Circuit Description.

4,'i; J705, pins 9, connector J704, pins 2, 6; J705, pins 7, IO; J702, pins 3, 7, 6, 2 (near the bottom of

the schematic).

DIGITAL BOARD (Schematic 28209E).

Relay Drive Circuit. This circuit is located from Zone A to Zone H not including

8, I, 4),

2. Interface Logic. This circuit is located from the right edge of the relay drive

Phase Lock Loop Circuit. This circuit is located on the remainder of the

3.

Relay Drive Circuit. This circuit develops relay drive signals (J704, pins I, 3,

8, 6, 3, 4,

Logic Outputs DIOOO, DIOO, DIO. These signals are HI-true drive lines for

a)

relays on the Model 1740 AC Volts Option. Logic is derived from the "VI" line (J702, pin 7) which is a signal determined by the Function Switch setting, "RL" line (J702, pin 3). "H" from A/D Line "GIO" of UlO3. "GIO" controls the 300mV or 3V A/D sensitivity at

certain portions of the A/D conversion cycle.

during the time when "GIO" is valid, Thus, "GIOL" remains valid until "NAZC2" updates "GIOL" (during the next conversion).

line (J705, pin 71, and "GIOL" line. "GIOL" is buffered and is derived

P701 (pins C, B, A), J705 (Pin 2), or J704 (Pin j).

near the top of the schematic). Logic inputs are from

"NAZCZ" clocks the flip-flop U705B

b) Logic Output ACS. This signal turns on transistor Ql204 (located on Model 1740 AC Option) when on 30 VAC, 300 VAC, or 1000 VAC ranges. Transistor Q712 is on when "RL" is "LOW".

Logic output NH3V: A "LOW" state forces the A/D to 3V sensitivity regardless

C) of "GIOL" state in particular, on 30 V range the A/D is set to 3V sensitivity.

Logic is perfor;ed by U706C, U709A, U7llA, and U707A, D. "Gl OL" , "ACDC", "RL",

d) Logic Output NATTRL: This signal drives relay K501 which is part of the dc attenuator. Logic is the complement of "RL" from UlO3.

Logic Output NVPARL: This signal turns on relay KS02 (Q707 turns on) when on

d

the 3mV DC and 30mV DC ranges.

lines as inputs.

f) Logic Outputs NSET and NCLEAR: ranges only. "NCLEAR" is active on all other ranges and functions. transistors Q708 or Q717 saturate and connect either

(VR701). Logic is performed by U706B (as for NVPARL). U712A generates a complementary signal for Q702 and NSET.

2.

Interface Logic.

to

u103

4 information from either the Model I722 or 1723 (on SDAT, Zone H-3), or range control information from the front panel through shift register U708 (Zone J-7), U7Ol timing logic (Zone l-5) and 4711, which drives "SERDAT".

Transistors Q703 and Q702 drive transistors Q708 and 4717 respectively.

(sERDAT line, zone I-l).

U703 is a bilateral switch (4 in parallel) which selects between range control

and "N3VR5" ("N3VR5"is always pulled up by R744).

Logic is performed by U706B using "RL", "H", and "Z"

"NSET" is active on the 3mV DC and 30mV DC

"NSET" or "NCLEAR" to -12 volts

This circuit controls range selection through the serial input

Input signals used are

When active,

AA 5-23

THEORY OF OPERATION INSTRUCTION MANUAL

Digital Multimeter

Model 174

b) U703 control is performed by Q701 (Zone J-2) whose output is high (U703 on)

whenever Rmis "LOW" (REM pushbutton is depressed).

is controlled by U712C (Zone J-3).

"HIGH" (thus Q701 is "HIGH",

R4, and R8 periods of "SDAT" from the interface controls the timing (through TRIG mode, TRIGGER, and HOLD bits on "SDAT" and "SERDAT"), and the front panel controls range selection when REM

is not depressed.

the

U703 ison) at all time5 except during LOAD RANGE, Rl, R2,

INCLK pulse train. (See timing diagram 28247E). Thus the

Input to U712C is RNG TIM (U702, pin 5) which is

When REM is not depressed, Q701

The right NOR gate (pins 3, 4, 5, 6) of U7Ol

c)

and REML (pin 4). The range control data (RI,

This data is generated by shift register U708 which is clocked by INCLK (Zone I-l)

from UlO3.

d) The other NOR gate (pins II, 12, 13, 4)

range limits in UlO3 by setting SERDAT low during

28247E). controls SERDAT even though U703 is on.

Phase Lock Loop.

3.

U716 (Zone N2) is a phase lock loop circuit whose output (pin 4) operates at

a)

nominally 5.2kH.z.

"locks" this 650 Hz output (pin 3) to tqB (pin 14) after level shifting by Q722

(Zone K-l) and Q72l (Zone L-l).

every 1.53ms.

b) U714 and U713A divide the 5.2 kHz output by 5.

to generate 50% duty cycle, 520 Hz, complementary signals at SYNC I and SYNC 2. These

signals are used to operate the chopper amplifier in the nanovolt preamp.

4.

On-Board Supplies.

supplies to various circuits on PC-421.

Resistors R738 (Zone J-3) and R737 (Zone J-5) adjust level.

SDAT is uncommitted by the Model 1722 or 1723 during t4 time, thus Q7ll

U715 divides this frequency by 8 to 650 Hz at U715, pin IO.

t+8 occurs

Q7lV (Zone K-3) and Q718 (Zone N-6) provide +lIV and -1OV

208

is controlled by RNG TIM (pin 3)

R2, R4, and R8) is on U7Ol pin 5.

of ~701 selects the appropriate end

"ABR" time (See Timing Diagram

times every 32Oms conversion

U713 divides this output by 2

or'

U716

5-24 AA

INSTRUCTION MANUAL

Digltal MultImeter Model 174

5-11. POWER SUPPLY (Schematic 279380).

& This schematic contains the battery switching, line voltage switching, line trans-

former and voltage regulators for the entire instrument. used. delivers +I5 volts to m0st of the circuitry on the Model 174.

regulator which is used as the positive supply to the LSI chip (UlO3 on schematic

27936F). VR40l is a +5 volt regulator which is used to drive the display, the digital

logic circuitry in the A/D converter and most relays.

b

2

complete regulated circuitry and reference elements built in.

transformer T401,

nected to the transformer is a full wave rectifier composed of CR402 and 2 filter capacitors C401 and C402, which supplies about 30 volts to Q403 and Q4Ol and the battery charging circuitry.

L

be charged through the unregulated voltages.

resistors R401, resistors drop the charging current to a trickle charge level.

VR402 is a ?I5 volt regulator (i3% accuracy) with typically 0.1% regulation and

VR402 is a ?I5 volt dual tracking regulator.

or from tl9.2 volt batteries in the Model 1728 Battery Pack.

If the Model 1728 Battery Pack is installed in the Model 174 the batteries will

When the instrument is line powered

R402, and ~408 feed the charge inputs on the battery pack.

It is an integrated circuit with

Three separate regulators are

THEORY OF OPERATION

VR404 is a +8 volt

It is either driven by

These

Con-

d.

The preregulated V+ input to VR402 supplies the +8 volt regulator VR404.

input goes through dropping resistor R403 to further reduce the voltage down to an

acceptable level for VR404.

transformer secondary (pins 7 and 81, full wave rectifier CR401 and preregulator Q402.

This voltage also charges the 8.4 batteries.

e, In BAT mode the’t19.2 volt batteries and the +8.4 volt batteries connect to the

input terminals of YR401 and VR402.

ohm resistor (R403).

the Model 1722 for its regulated 5 volt supply.

off, power is also removed from the Model 1722.

Transformer T40l has two internal shields.

f. IOynd one primary shield is tied to power ground. tion. When switch 5402 is at ll7V position,

connected in parallel and the Model I74 is set for nominal 117V operation.” When switch 5402 is at 234V position,

is set for nominal 234 operation).”

Switch S4Ol has two positions: NORM and LO. If set to NORM, the I ine voltage

range is 105-125 volts or 210-250 volts. is 90-110 or 195-235 volts.

The LINE Switch also supplies ac voltage from the transformer to

The input for VR40l (+5V regulator) is derived from

The 8 volt regulator (VR404) is fed through the 270

Thus, when the Model 174 power is turned

One secondary shield is tied to pin

This shielding provides line isola-

the dual primary windings of T40l are

the primary windings are in series and the Model 174

“NOTE

If set to LO,

the I ine voltage range

Th i s

AA

5-25

INSTRUCTION MANUAL

Dlgilal Multimeter

Model 174

MAINTENANCE

SECTION 6.

6-1.

Included are procedures for electrical Performance Verification, Adjustment/Calibration,

Troubleshooting, and Fuse Replacement.

6-2.

is given in Table 6-l.

Alternate test equipment may be substituted if specifications eoual the stated character-

istics

GENERAL. This section contains information necessary to rsaintain the instrument.

REQUIRED TEST EQUIPMENT.

TEM E

A

DESCRIPTION

DC Calibrator

Test equipment for Adjustment/Calibration is given in Table 6-8.

Test Equipment For Performance Verification

Recomnended test equipment for Performance Verification

TABLE 6-1.

SPECIFICATION

o.zv, zv, zov, zoov, IOOOV

MAINTENANCE.

MFR.

Fluke,

MFR. MODEL

343A

to.ooz% or 2ouv

AC Calibrator

0.2v, 2v, 2ov, zoov

H-P

745A

t0.0228

AC Calibrator/Amplifier

IOOOV @ *0.04x

H-P

745A/746A

Decade Resistor

current Source

Current Source

IMR Resistor

IOOR Per Step k-Terminal

Low Thermal Resistor

6-3.

of the instrument. range of 20°C to 30°C and relative humidity less than 70%. specification at any point, perform a complete calibration as given in paragraph 6-4.

If the instrument is "IN WARRANTY", that is,

of shipment,

It is recommended that this verification be performed every 6 months. of the A/D and I744 Ohmmeter Option, allowable limits, be recalibrated independently from the A/D.

PERFORMANCE VERIFICATION.

All measurements should be made at an ambient temperature within the

contact your Keithley representative or the factory.

only that function need be recalibrated.

2Kfi, lOKn, 20KR, 200KR

IMa, 2Mn, lOMR,20MR, ~0.01%

200Mfi, 0.1% 200uA, 2mA, 20mA, 20.006%

200mA, 2A +0.02%

>1/8w;

kO.Ol% tolerance

Use the following procedures to verify basic operation

tl% tolerance

it has been less than 6 months after date

if the instrument does not indicate within the

ESI

Fluke

K-l

ESI

If the instrument is out of

The 3 and 30 mVdc ranges may

RS725

3330B

382A R-86-inn

SRI010

With the exception

AA

6-l

MAINTENANCE

INSTRUCTION MANUAL

Dlgital Multimeter

Model 174

IMPORTANT

The Performance Verification should be performed by qualified personnel using accurate and reliable test equipment as given in Table 6-l.

taken to avoid electrical shock when the calibration or other maintenance is performed with the line cord connected to ac power.

NOTE

This Procedure is intended to verify only the basic accuracy of the Model I74 in

voltage, current, better than the measurement accuracy. Table

In these instances the Allowable Reading in terms of the “Absolute Accuracy”

should be used.

a. Stabilization.

hour prior to performing the Performance Verification.

b.

I. Select DC V function.

2.

3.

4.

6-l

IS not Xl0 better because such equipment is not commercially available.

Input Resistance Check (DC Volts).

Select the Set the Calibrator (A) to the IO-Volt range. Set the Calibrator output to 0 volts.

and resistance modes.

Recommended verification period is every 6 months.

Allow the Model I74 to stabilize with power on for a least one

3

volt DC range.

Test equipment accuracy should be Xl0

In many cases the equipment listed in

Care should be

Record the Model I74 reading and identify as VOO.

5.

Set the Calibrator output to 2 volts.

6.

Record the Model 174 reading and identify as V20.

7.

a. Connect the I Megohm Resistor (G) between the Calibrator output high and the Model

I74 input HI.

Repeat steps 3,

9.

IO.

Calculate VZO-VOO, and identify as “A”.

Il. Calculate V21-VOI, and identify as “6”.

12.

Verify that

resistance is greater than IO3 ohms.

c. Voltage Accuracy Check.

I. DC Voltage (300mV to IOOOV Ranges).

Select DC V and AUTORANGE.

a) b) Connect the DC Calibrator (A) to the Model

Set the DC Calibrator to the output specified in Table 6-2.

Cl

d) Verify that the Model I74 is within the limits specified under “Absolute

Accuracy”.

Repeat steps c) and d) with negative vol tag=.

e)

4, 5, and 6 except identify the readings as VOI and V2l respectively.

“A”-“B” does not exceed 20 digits.

This will ensure that the input

174.

6-2

AA

INSTRUCTION MANUAL Dlgltal MultImeter

Model 174

MAINTENANCE

TABLE 6-2.

DC Voltage Performance Check (300 mV to IOOOV)

Voltage

Range Applied Relative Accuracy*

300 mV 0.20000 Vdc 199.97

3:

;

2.0000 20.000 Vdc Vdc I.9997 19.997 to to 2.0003 20.003 1.9996 19.996

Allowable Reading ZO'C-30-C

to

300 v 200.00 Vdc 199.97 t0 200.03 199.96 to 200.04

i

;kDoes not include the uncertainty of the DC

Calibrator.

1000 v 1000.0 .Vdc 999.8 to 1000.2 999.7 to 1000.3

2. DC Voltage (30 mV Range).

Select DCV and 30 mV range.

a) b) Connect the DC Calibrator (A), YKQ Decade Resistor (D), and Lcu-

Thermal Resistor (H) as shown in Figure 34.

DC

CA

Absolute Accuracy""

200.03 199.95

**Does include the uncertainty of the DC

Calibrator given in Table 6-1.

to

200.05

to

to 20.004 2.0004

AA

FIGURE 34. Test Circuit For 30 mV DC Accuracy Check.

6-3

MAINTENANCE

Set the DC Calibrator to an output of 0.000000 V.

c)

d) Adjust the Model 174 "mV ZERO" control for -0.0000 mV t.0001 mV display.

Set the DC Calibrator to an output of +2.000000 V.

4

f) Verify that the Model 174 reading is between +19.991 and +20.009 mV dc.

Due to the design of the nanovolt amplifier within the Model 174,the 3 mV range will be in calibration when the 30 mV range is verified as above. specific verification procedure is given for the 3 mV range.

AC Voltage (Model 1740 AC Option).

3. Select AC V and AUTORANGE.

a)

b) Connect the AC Calibrator (6) to the Model 174.

Set the AC Calibrator to the output specified in Table 6-3 (for applied

C)

voltages between 200 mV and 200V.)

d) Set the frequency to 50 Hz. Repeat verification at 20 kHz.

INSTRUCTION MANUAL

Digilal Multimeter

Model174

IMPORTANT

Therefore, no

For the 1000 volt range connect the High Voltage Amplifier to the output of

e)

the AC Calibrator. (See the manufacturers instructions).

f) Set the AC Calibrator/High Voltage Amplifier combination (C) for an output

of 1000 volts ac rms.

Verify the readings given in Table 6-3 (Absolute Accuracy) for frequencies

9)

of 50 Hz and 20 kHz.

TABLE 6-3.

AC Voltage Performance Check

Voltage

Range Applied

300 mv ZOO.OOmV 199.54 to 200.46

3: 1: 20.000 2.0000 v v I.9954 19954 to to 20.046 2.0046.

300 v 200.00 v 199.54 to 200.46

1000 v 1000.0 v 997.4 to 1002.6

Relative Accuracy:'

Allowable Reading 20°C - 30°C

1 Absolute Accuracy**

mv 199.50 to 200.50 mv

V V 1.9950 19.950 to to 2.0050 20.050 V v V 199.42 to 200.58 v

V 997.0 to 1003.0 v

*Does m include the uncertainty of the AC "*Does include the uncertainty of the AC

Calibrator. Calibrator given in Table 6-l.

6-4

AA

INSTRUCTION MANUAL

Dlgltal Mulltmeter

Model 174

MAINTENANCE

d. Resistance Accuracy Check.

1.

HI Ohms.

Select HI OHMS and AUTORANGE.

a)

b) Connect Decade Resistor (D) to the Modal 174.

In order to compensate for lead resistance error,

4

test leads, set the Decade Resistor dials to 0 and subtract the zero reading from the

Model 174 display in the following tests.

d) Set the Decade Resistor to the resistance specified in Table 6-4.

Verify that the Model 174 is within the limits specified under "Absolute

4

Accuracy".

Resistance performance Check (HI OHMS)

Resistance

Range Setting

3

KR 2.0000 KR

30 KR 20.000 KR

300

Kn 200.00 Kn

3 Mfl 2.0000 Mn

30 MR 20.000 Mn'

300

Mn 200.00 MQ

(Model 1744 Ohms Option).

measure the resistance of the

TABLE

Relative Accuracy* Absolute Accuracy""

1.9993 to 2.0007 I.9991 to 2.0009

6-4.

Allowable Reading, 20°C - 30°C

19.993 to 20.007 19.991 to 20.009

199.93 to 200.07 199.91 to 200.09 I.9989 to 2.0011 1.9987 to 2.0013

19.959 to 20.041 19.967 to 20.042

196.59

to 203.41 196.39 to 203.61

*Does not include the uncertainty of the De-

cade Resistor.

i'"Does include the uncertainty of the De-

cade Resistor given in Table 6-l.

AA

6-5

MAINTENANCE INSTRUCTION MANUAL

Digital Multimeler

Model174

2.

LO Ohms.

Select LO OHMS and AUTORANGE.

a) b) Connect Decade Resistor (D) to the Model

Measure the resistance of the test leads by setting the Decode Resistor dials to

C)

0 and subtract this reading from the Model I74 display in the following tests.

d) Set the Decade Resistor to the resistance specified in Table 6-5.

174.

Verify that the Model

4

Accuracy".

Resistance Performance Check (LO OHMS)

Resistance

Range Setting

300 n

3

Kfi

30

KQ

300

Kfi

3 MO

30 Mri

;': Does not include the uncertainty of the

Decadeesistor.

200.00 R

2.0000 KR

20.000 KR

200.00 KR

2.0000 Ma

20.000 MR

174

is within the limits specified under "Absolute

TABLE

Relative Accuracy:'

199.92

1.9993

19.993

199.89

IV.959 IV.799

6-5.

Allowable Reading, 20'~ - 30°C

Absolute Accuracy*"

to 200.08 to 2.0007

to 20.007 to 200.11 to 20.041

to 20.201

""Does include the uncertainty of the

Decade Resistor given in Table 6-1.

199.90 to

I.9991

19.991 to

199.87 to

1.9957 to

19.797 to

2OO.lO

to

2.0009

20..009

200.13

2.0043

20.203

6-6

INSTRUCTION MANUAL

Dlgital MultImeter

Model 174

e. Current Accuracy Check (Model

I.

DC Current (300 UA to 3A Ranges).

Select DC A.

a)

b) Connect Current Source (E) to the Model 174.

c) Set the Current Source to ;he current specified in Table 6-6. d) Select the appropriate range on the Mode! 174.

Verify that the Model I74 is within the limits specified under "Absolute

d

Accuracy".

f) Repeat steps c),

current

Range

uA 200.00 IA

300

2 2.0000 20.000 mA mA

3;

mA 200.00 mA

300

A

3

Applied

1.0000 A

d), and e) using a negative input.

DC Current Performance Check

1745

Current Option).

TABLE 6-6.

Allowable Reading, 20°C - 30'~

Relative Accuracy*

199.87 to 200.13

1.9988 to to 2.0012 20.012

19.988

199.86

1.9982 to 2.0018 1.9978 to 2.0022

to 200.14

Absolute Accuracy;'*

199.86 to 200.14

1.9987 to 2.0013

19.987 to 20.013

198.82 to

201.18

aDoes not include the uncertainty of the

currentsource.

DECADE RESISTOR

I--- --

n,

OC CALIBRATOR (A)

I

----

w

A* Does include the uncertainty of the

Current Source.

r\

HI

MODEL 174

LO

0

CASE

AA

FIGURE 35.

Test Circuit For 3uA Verification.

L-7

MAINTENANCE

DC Current (3uA and 30uA Ranges)

2. Select DC A

a) b) Select 30uA range.

Connect the DC Calibrator (A) and series IMfl Decade Resistor (D) to the Model

Cl

174 input terminals, as shown in Figure 35.

d) Set the DC Calibrator to 20.200 volts dc.

Verify that the Model 174 is within the limits shown in Table 6-7 under

d

"Absolute Accuracy".

NOTE

The DC Calibrator output is adjusted to compensate for voltage drop across the 1Mn

Decade Resistor. tolerances include the uncertainty of the Decade Resistor (D).

f) Repeat steps d) and e) using a negative input.

g) Select the 3 uA range.

h) Connect the DC Calibrator (A) and series 10~~ Decade Resistor (D) to the

Model

174

input terminals, as shown in Figure 35.

The input voltage across the Model 174 will be 0.2 Volts. The

INSTRUCTION MANUAL

Digital Mullimeter

Model 174

i) Set the DC Calibrator to 20.200 volts dc.

Verify that the Model 174 is within the limits shown in Table 6-7 under

j)

"Absolute Accuracy".

k) Repeat steps i) and j) using a negative input.

TABLE 6-7.

DC Current Performance Check (3pA and 30pA Ranges).

Current

Range

3UA

30~4

*Does not include the uncertainty of

the Current Source.

Applied

7-d

20uA

Allowable Reading, 20°C - 30°C

Relative Accuracy*

I.9978 to 2.0022 I.9988 to 2.0012

**Does include the uncertainty of

Absolute Accuracy**

I.9976 to 2.0024

1.9986 to 2.0014

the Current Source.

6-8

AA

INSTRUCTION MANUAL

Dlgllel Multimeter Model 174

MAINTENANCE

6-4.

when a specification has been determined to be out of tolerance.

instrument to the published specifications, (paragraph 6-3) should be used.

laboratory conditions (25°C ? I’C ambient and relative humidity less than 70%).

ADJUSTMENT/CALIBRATION PROCEDURE.

The calibration procedure should be performed under

If the Model 1744 Ohms Option is field-installed, the entire adjustment

I. procedure must be performed to ensure that rated accuracy is achieved.

2.

If the Model 1740 AC Option is field-installed, section 6-4e must be performed to ensure that rated accuracy is achieved. The other functions are not affected by the installation of the Model 1740.

If the Model 1745 Current Option is field-installed, section 6-49

3.

must be performed to ensure that rated accuracy is achieved.

a. How to Install the Model 1743 Callbratfon Cover.

I. Disconnect the line cord from ac power outlet.

2.

Depress the LINE pushbutton to discharge any voltages developed across

capacitors in the power supply.

Remove the four Phillips screws on the top and lift off the top cover.

3.

4. Temporarily disconnect and remove the Model 1728, 1722, or 1723 options

(if installed at this time).

The following adjustments should be performed

For checking the

the Performance Verification procedure

NOTE

Check the Line Switches 5401 and 5402 for proper setting.

5.

6.. Connect the following calibration leads furnished with the Model 1743 Maintenance

Kit.

Connect the single green wire to Test Lead TP702 (Power Supply Common) shown

a)

in Figure 36.

b) Connect the 2-wire test lead (red, black) to test points TPlOl/TPlO2 shown

in Figure 36..

as viewed from, the front panel.

Before the Calibration Cover is fastened down

7.

red and black wites through the holes in the Calibration Cover corresponding to Tp702

and TPlOl/TPl02 respectively.

8.

Place the Calibration Cover in position and fasten down using the “Thumb S~rews~’

furnished with the klt.

b.

Power-Up and Stabilization.

I.

Connect the line cord to ac power.

2.

Depress LINE.

Allow the Model

3.

place for at least I hour.

It is important that the calibration sequence be followed exactly in the order

given, because the adjustments are interrelated and dependent on prior callbra-

tion steps.

The red lead is positioned on the left side of the instrument (TPIOI)

, pass the free ends of the green,

174

to stabilize with the Model 1743 Calibration Cover in

NOTE

AA

6-g

MAINTENANCE

lNSTWCTlON MANUAL

Digital Multlmeter

Model 174

LINE VOLTAGE jWITCHE5

TPIOI,

IED AND J~REs cc iERE (SE

P402

S4Ol

r

; Ls402

TPl02

BLACK

INNECT :E TEXT

-, I

REAR PANEL

,i

I

-P404

-TP702

GREEN WIRE CONNECTS HEf

NANOVOLT

- PREAMP SHIELD

(LO)

TP70 I

(GIOL)

P701

P403

P40 I

FRONT PANFI

-SIDE

BRACKEl

-INPUT HI TO MODEL 1740 OPTION

FUSE ~1001

(1745

OPT I ON)

CURREF

AA

INSTRUCTION MANUAL Digital Multimater

Model174

MAINTENANCE

R505 ~506

RiO9

R513 .OCATED \PPROX. \S SHOWN :IRCLES.

FtGURE 37.

Model 174 Calibration Adjustments.

MAINTENANCE

INSTRUCTION MANUAL

Digital Multimeter

Model 174

TABLE 6-8.

List of Test Equipment Required For Adjustment/Calibration

TEM DESCRIPTION

A

B

C

D

E

G

H

J

K Maintenance Kit

L

DC Calibrator +0.290005\1

AC Calibrator

AC Calibrator/Amplifier Decade Resistor

Current Source

I

Current Oscilloscope

Microvoltmeter DMM

Test Circuit

Low-Thermal

Test Leads

Source

Minimum SPECIFICATION NEEDED

+2.90005v +29.0005v +2go.o05v +1000.05v c29.2gv

IOmV, IV, IOV, IOOV, +0.022%

@ IkHz, 20kHz

IOOOV +0.04% &' IkHz, 20kHz H-P

2Kfi, 20Kn, 200KR, IMn, 2MR,

IOMfi, 20MG, ro.Ol% 290pA, 2.9mA, IOmA, +0.006% 200mA, IA +0.02%

5mV/Div.,

With IOMRProbe.

IOuV Full Scale, C2%

1.00000 ?O.OOl%

Resistor, 2MR, I%, 0.2W Parallel

Capacitor, IpF, 50V

Calibration Cover, Calibration K-l

Leads, Extender Cards and Cables.

Low-Thermal,

All CO.OOZ%

\

i

Dual Trace, Tektronix 465

Combination K-l ~-215-1~

>

Coaxial Input Leads K-i

MFR

Fluke

H-P

ESI

Fluke Fluke

K-l K-l K-l R-253-2M

MFR MODEL

343A

745A

745A/746A

RSi25

33308

382~

155

5900

1743

1747

M

N

A NOTE: For the 30pA and 300pA ranges,

Low-Thermal Short

IOOR Per Step 4-Terminal 10.01% Tolerance

Low-Thermal Resistor

Calibrator (A) and series connected Decade Resistor (D), as in Figure 35.

(Furnished with the Model 174)

6-12

K-l 1746

ESI SRI010

a Current Source must be composed of the DC

AA

INSTRUCTION MANUAL DigItal Multlmrtar

Model174

c.

A/D Calibration.

NOTE

This procedure must precede the analog section calibration to ens&e that

the Model

I. Capture Range Adjustments.

a) Set to DC V function and 300mV range.

174

will meet all rated specifications.

MAINTENANCE

b) Connect the Model

Make sure the 2 wire test lead (furnished with the Model

C)

connected at TPlOl and TPl02, as described in paragraph b-4 a,

d) Connect Oscilloscope (G) between the following points:

I) Oscilloscope External Trigger to "red" at TPIOI (FON), using lOtIn Probe.

2) Oscilloscope Vertical Input to "black" at TP102 (Prefilter), using IOHn Probe.

3) Oscilloscope GND to "green" ground at TP702 (LOW).

1746

Low-Thermal Short to the input.

1743

6,

Maintenance Kit) is

b).

AA

MAINTENANCE INSTRUCTION MANUAL

Digital Multimeter

Model 174

Set the Oscilloscope controls as follows:

=)

I) Trigger:

2) Vertical:

3) Time Base: 20 ms/division For the following adjustment refer to the trace shown in Figure 38.

f)

g) Adjust potentiometer RI03 (Auto Cal ACAL) for a level of +IV ?-0.2V during

the Auto Cal time period.

Adjust potentiometer R201 (Auto Zero AZI) for a level of +lV +0.2V during

h)

the AZ1 period.

Adjust potentiometer R217 (Auto Zero AZ2) for a level of +lV iO.2V during

i)

the AZ2 period.

Repeat steps h), i), and j) until all levels are within +iV f0.2V simultaneously.

j)

The following steps k) I) through k) 3) are required only if the Model 1744 Ohms Option is installed.

k) Set to LO0 function and 3 k0 range.

I) Adjust potentiometer RI106 (n BIAS) for a level of +lV CO.2V during Auto

Zero AZI and Auto Zero AZ2 periods.

2) Adjust potentiometer ~208 (0.3V Ref) for a level of +lV iO.ZV during Auto

Cal ACAL period.

+, DC coupled

DC, O.SV/division (.OSV/Division x IO in Probe).

NOTE

3) Repeat steps I) and 2) until both conditons are met simultaneously.

SIGNAL INTEGRATION

PREFILTER ,

OUTPUT

FON+

I AZl

I

I I

H----l 20 ms -b/4-200 ms -------+

; ACAL j I

FIGURE 38. Waveform For A/D Calibration

I

AZ2 I

I

-\A+

I I

I

6-14

AA

INSTRUCTION MANUAL

Digital MultImeter

Model 174

2.

Zero and Offset Current Adjustments (300mV range).

Set to V DC function and 300 mV range.

=I b) Connect the Model 1746 Low-Thermal Short to the input.

Record the Model 174 reading.

C)

Remove the Model

d)

Connect the Test Circuit (J) across input HI and LO.

4

f) Adjust variable capacitor C203 (Input Current) to achieve the same Model 174

reading as in step c) within +2 digits+.

Remove the Test Circuit.

9)

The following steps h) through j) are required only if the Model 1744 Ohms Option

is installed.

h) Connect the Model 1746 Low-Thermal Short.

Set to LO R function and 3 KR range.

i)

Adjust variable capacitor C205 (ohms Zero) for a zero reading on the Model 174.

j)

Set to DC V function and 300 mV range.

k)

I) Adjust potentiometer R509 (300 mV Zero) for a zero reading.

1746.

NOTE

MAINTENANCE

Verify that during the 200 ms Integration period the output at TP102 (Prefilter

ml

has no more than IO transitions from positive slope to negative slope (and vice-versa

d.

DC Voltage Calibration.

I * Zero and Offset Current Adjustments (3 mV and 30 mV ranges).

Set to DC V function and 30 mV range.

=) b) Connect the Model

Verify that the mV ZERO Control (Rb23) has a control range of 5OuV ?12uV,

c)

passing through zero no less than 5 digits from either end position of the mV Zero

Control.

If the zero is less than

move jumper

ing capabili'ty. Repeat test JO verify the change.

d) Set to 3 mV range.

Connect the Model 1746 Low-Thermal Short.

4 f) Adjust the mV Zero Control for a zero reading +2 digits.

Remove the Model 1746

9)

h) Connect the 100 KSi Resistor (D) acrc~ss the input.

Jbo3

to the next position in the direction which allows greater zero-

1746

Low-Thermal Short.

NOTE

5

digits from the end position of the mV Zero Control,

,;.

AA

Adjust potentiometer Rb03 (Offset Current) for a zero reading ?2 digits.

i)

Repeat steps e) through i) until both condition; are satisfied.

j)

6-15

MAINTENANCE

Gain Adjustment For 30 mV Range.

2.

Set to DCV function and 3 mV range.

3)

b) Connect the DC Calibrator (A) and (D) 9Kn Decade Resistor and lOOn Low-Thermal

Resistor (M) as shown in Figure 34, on page 6-3.

Set the DC Calibrator for 0.000000 V dc.

C) d) Adjust the "mV ZERO" control for a display of -.OOOOmV.

Select 3OmV Range.

d

f) Set the DC Calibrator for +2.90005 V dc.

INSTRUCTION MANUAL

Digital Multimeter

MQdd 174

g) Adjust potentiometer

d. DC Voltage Calibration.

Zero Adjustments.

3.

Set to DCV function and 300 mV range.

a) b) Connect the DC Calibrator (A) to the Model 174 input.

Set the DC Calibrator for an output of +5uV (See NOTE below).

C)

It may be necessary to compensate for dc offset of the DC Calibrator. if the dc calibrator offset is

to +~711v to compensate for the offset.

with microvoltmeter (H) to set the + 5uV input.

d) Adjust potentiometer

“-00.00” and “+OO.Ol”.

Set the Model 174 to 30 V range.

d

f) Set the DC Calibrator (A) for an output of +.0005V.

g) Adjust potentiometer R5l3 (30V Zero) for a display which flashes between

"-0.000" and "+O 001"

. .

~604 (30

R509

mV Gain) for a display of

NOTE

-2uV dc, then the DC Calibrator should be adjusted Monitor the voltage at the Model 174 input

(3OOmV Zero) for a display which flashes between

+29.000

mV to

~29.001

For example,

mV.

6-16

AA

INSTRUCTION MANUAL Dlgltal Multlmeter

Model 174

4.

Full Range Calibration,

Connect the DC Calibrator to the input terminals.

a) b) Set the instrument to the range given in Table 6-10.

MAINTENANCE

c) Set the DC Calibrator to the"App1ied Input' level given in Table d) Adjust the control given in Table 6-10 to achieve the display specified.

Range Setting

3v

300

v

30

v

1200

v

;**Display should flash alternately between readinqs when

the DC Calibrator is set to the applied input or to

a setting of ~0.1 digit of applied input (e.g. 2.90004

to 2.90006 v).

NOTE

Perform the calibration in the exact order given.

TABLE 6-10

Full Range DC Calibration

Applied Input

+2.90005

+290.005 v +29.0005 v +1000.05 v

V

Control

2.9

V ADJ (R213) 290 V ADJ (R505) Xl0 GAIN (R209)

I KV ADJ (R506)

6-10.

Display Required+:'

+2.9000 +290.00

+29.000 to +29.001 v +1000.0 to +1000.1 v

to +2.9001 v

to

+290.01

v

I

AA

MAINTENANCE

INSTRUCTION MANUAL

Digital Multimeter

Model 174

e. AC Voltage Calibration.

Option is installed.

Set the Model I74 to AC V function and AUTORANGING.

I .

Connect the AC Calibrator (B) to the input terminals.

2.

For voltages greater than 100 volts, the High Voltage Amplifier (C) as per manufacturers operating instructions.

Set the AC Calibrator to the voltage and frequency specified in Table 6-11.

3.

4.

Adjust the control given in the table to achieve the appropriate display.

The steps must be performed in the exact order given in Table 6-11.

Full Range AC Calibration (Model 1740 Only)

Range Setting Applied Input

./300 mV

c 3 v

30 v

300 v 100 v 1000 v 1000 v

(;

3: ;

300 v

1

IO mV

I v

IO v

1000 v 1000 v

I v

IO v

100 v

This procedure is required only if the Model 1740 AC

NOTE

use the AC Calibrator (B) along with

NOTE

TABLE 6-11.

Frequency Control

1kHz RI202 (IkHz Adj) IkHz RI201 (IkHz Adj) 1kHz IkHz RI204 (IkHz Adj) IkHz

20kHz 20kHz Cl218 (20kHz Adj) 20kHz 20kHz Cl214 (20kH.z Adj)

RI205 (IkHz Adj)

RI203 (IkHz Adj) Cl220, Cl219 (20kHz Adj)

Cl213 (20kHz Adj)

Display Required

009.99 to 010.01

0.9999 to 1.0001 ov.ggg to 10.001

099.99 to 100.01

0999.9 to 1000.1

0399.9 to 1000.1

0.9999 to 1.0001 ov.gvv to 10.001

99.99 to

100.01

+ These adjustments are interactive.

twice in order to achieve all conditions simultaneously.

6-18

It may be necessary to perform the adjustments

AA

INSTRUCTION MANUAL Dlgltal Multlmeter

Model I74

Ohms Calibration. This procedure is required only if the Model 1744 Ohms Option is

f.

installed.

Connect Decade Resistor (D) to the Model 174. Set to IOMQ.

1.

MAINTENANCE

2. Set the Model Adjust potentiometer II1104 (10 Ma Adj) for a reading of 10.000 MR.

3.

Set the Model I74 to LOn function.

4.

Adjust potentiometer ~1106 (n Bias) for 10.000 MR.

5.

6.

Repeat steps 2 through 5 until both readings are within 21 digit simultaneously.

7.

Verify that the test leads furnished with the Model 1743 Maintenance Kit are

connected as in paragrapf? 6-4 a. page 6-9.

Connect "green" between LOW and Oscilloscope low.

a) b) Connect "black" between Pre-filter Output and Oscilloscope vertical input using

IO X Probe.

c) Connect "red" between TPIOI (FON) and Oscilloscope trigger.

Set the Oscilloscope controls as follows:

8. Gain:

Time Base: Trigger: EXT.

Set the Model 174 to LO R function and AUTORANGE.

9.

IO. Connect the Model 1746 Low-Thermal Short.

Adjust potentiometer R208 (0.3V Ref) for +IV +O.lV during the Auto Cal time period

II.

as shown in Figure 38,

174

to HIR function and AUTORANGE.

(See also Figure 36.)

.sv/div. (.OsV/Div. X IO in Probe).

20 ms/div.

6-14,

Verify that the Oscilloscope trace is +lV ?0.3V during the Auto Zero time period

al*;hown in Figure 38, Page 6-14.

Check the calibration in steps 1 through 12 to ensure that conditions have not

13.

changed. Readjust potentiometers Rll04, desired conditions.

14.

Set the Model 174 to HI R function and AUTORANGE. Connect Decade Resistor (D) to the Model 174.

15.

16.

Set the Decade Resistor to 290.000K 0. Adjust potentiometer RI103 (290Ka Adj) for a reading of 290.00 +I digit.

17.

Set the Decade Resistor to On.

18. Record the residual resistance (Rg) as displayed on the Model

19.

20. Set the Decade Resistor to 2.9OOfl + R01. Adjust potentiometer RI102 (2.9Kn Adj) for a reading equal to 2.9000K + R,,

21.

*I digit.

Ri106,

and R208 as necessary to achieve the

174.

6-19

MAINTENANCE

INSTRUCTION MANUAL

Digital Multimeter

Model 174

Current Calibration.

9.

Option is installed.

Set the Model 174 to DC A function.

I .

Set the Model I74 to 3A range.

2. Connect Current Source (F) to the Model 174.

3. Set the Current Source (F) for +2A.

4. Adjust potentiometer RI007 for a reading of 2.000A t1 digit.

5. Set the Model 174 to 300mA range.

6. Set the Current Source (F) for 290 mA.

7. Adjust potentiometer RI006 for a reading of 290.00 mA il digit.

8. Set the Model 174 to 3OmA range.

9.

IO. Set the Current Source (E) for 29mA. II. Adjust potentiometer R1005 for a reading of 29.000 mA +I digit.

12. Set the Model 174 to 3 mA range. Set the Current Source (E) for 2.9000 mA.

13.

14. Adjust potentiometer RI004 for a reading of 2.9000 mA ?I digit. Set the Model I74 to 300pA range.

15.

16.

Set the Current Source (E) for 290.00uA.

Adjust potentiometer RI003 for a reading of 290.00vA +I digit.

17.

This procedure is required only if the Model 1745 Ammeter

18. Set the Model 174 to 30pA range. Connect DC Calibrator (A) and IMR Decade Resistor (D) to form a current source

19.

and connect to the Model 174, as in Figure 35 on page 6-7.

20.

Set the DC Calibrator (A) to 29.29V.

21.

Adjust potentiometer RI002 for a reading of 29.000pA fl digit.

22.

Set the Model 174 to 3pA range. Change the Decade Resistor (D) to IDMR.

23.

24.

Check that the DC Calibrator setting is 29.2gV.

25.

Adjust potentiometer RIO01 for a reading of 2.90OOpA ~5 digits.

END OF CALIBRATION/ADJUSTMENT PROCEDURE.

6-20

AA

Keithley 174 Service manual

Specifications and Main Features

Frequently Asked Questions

User Manual