Tegam 1750 Instruction Manual

1750

High Speed Programmable

Microohmmeter

MODEL 1750

NOTE: This User’s Manual was as current as possible when this product was manufactured. However,
products are constantly being updated and improved. To ensure you have the latest documentation,
refer to www.tegam.com.

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Instruction Manual

PN# 1750-900-01

Publication Date: April 2017

REV. S

TABLE OF CONTENTS

TABLE OF CONTENTS

1 INSTRUMENT DESCRIPTION

Instrument Description ............................................................................ 1-1

Feature Overview .................................................................................... 1-1

Accessories Sheet ................................................................................... 1-4

Performance Specifications ....................................................................... 1-5

Accuracy ........................................................................................... 1-6

Measurement Times ........................................................................... 1-7

Reference Current Modes ......................................................................... 1-9

Miscellaneous Specifications ..................................................................... 1-10

Test Lead Requirements ........................................................................... 1-12

Broken Lead Detection ............................................................................. 1-14

2 PREPARATION FOR USE

Unpacking & Inspection ............................................................................ 2-1

Safety Information & Precautions .............................................................. 2-1

Terms in this Manual .......................................................................... 2-1

Terms as Marked on Equipment ........................................................... 2-1

Symbols ............................................................................................ 2-2

Grounding the Equipment .................................................................... 2-2

Danger Arising from the Loss of Ground ................................................ 2-2

Use the Proper Fuse ........................................................................... 2-2

Do not Use in Explosive Environments .................................................. 2-2

Do not Operate without Covers ............................................................ 2-3

Preventive Maintenance ...................................................................... 2-3

Line Voltage Selection ......................................................................... 2-4

3 QUICK START INSTRUCTIONS

General .................................................................................................. 3-1

Power the Unit ........................................................................................ 3-1

Factory Settings ...................................................................................... 3-1

Customizing Parameter Settings ................................................................ 3-2

Test Lead Requirements ........................................................................... 3-2

Measuring Resistances Greater than 200kΩ ................................................ 3-2

4 OPERATING INSTRUCTIONS

Basic Operation ....................................................................................... 4-1

Default Parameters .................................................................................. 4-1

Front Panel Description ............................................................................ 4-2

Rear Panel Description ............................................................................. 4-3

Display Modes ......................................................................................... 4-4

Resistance Mode ................................................................................ 4-5

Figure 4.5 Over Range or Open Lead Condition ...................................... 4-5

Open Lead Detection .......................................................................... 4-5

Reading Hold ..................................................................................... 4-6

Absolute Comparator Mode .................................................................. 4-7

% Comparator Mode ........................................................................... 4-8

Navigating the Menus .............................................................................. 4-9

Keypad Functionality .......................................................................... 4-9

Figure 4.8 Menu ................................................................................. 4-9

Ranges .................................................................................................. 4-10

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I

TABLE OF CONTENTS

TABLE OF CONTENTS

Trigger Modes ......................................................................................... 4-11

Delay Time ............................................................................................. 4-11

Display Mode .......................................................................................... 4-12

Absolute Comparator Limits ...................................................................... 4-12

% Compare Limits ................................................................................... 4-13

Communication Interface ......................................................................... 4-13

Store Setup ............................................................................................ 4-14

Recall Setup ........................................................................................... 4-14

Line Frequency ....................................................................................... 4-14

PIN Function ........................................................................................... 4-15

Calibration .............................................................................................. 4-15

Auto Correct ........................................................................................... 4-15

The PIN Function ..................................................................................... 4-16

Enabling or Disabling the PIN Function .................................................. 4-16

Changing a PIN Number ...................................................................... 4-16

Disabling an Unknown PIN ................................................................... 4-16

5 PROGRAMMING & INTERFACING

Interfacing to the 1750 ............................................................................ 5-1

Front Panel ............................................................................................. 5-1

Figure 5.1 Lemo Connector .................................................................. 5-1

Rear Panel .............................................................................................. 5-2

Trigger Input Connector ...................................................................... 5-2

Trigger Out Connector ........................................................................ 5-3

Using the Trigger Outputs ................................................................... 5-4

Connector J8 .......................................................................................... 5-5

RS232 Communication ............................................................................. 5-8

RS232 Settings .................................................................................. 5-8

RS232 Interface Command Summary ................................................... 5-9

RS232 Device Dependent Commands Supplementary Information ............ 5-11

Table 5.4 –RS232 Status Command Summary ....................................... 5-12

RS232 Hierarchy of Commands ............................................................ 5-13

Power Up and Device Clear Defaults .......................................................... 5-13

Reading Via RS232 Interface ............................................................... 5-14

IEEE-488.1 / GPIB Operation .................................................................... 5-15

GPIB Command Summary ................................................................... 5-16

GPIB Device Dependent Commands Supplementary Information .............. 5-18

Serial Polling ...................................................................................... 5-19

Self Test ........................................................................................... 5-21

Hierarchy of GPIB Commands .............................................................. 5-21

Power Up and Device Clear Defaults ..................................................... 5-23

Reading from the IEEE-488 Bus ........................................................... 5-23

Sample Programs ............................................................................... 5-24

6 SERVICE INFORMATION

Cleaning ................................................................................................. 6-1

Calibration Procedure ............................................................................... 6-1

Calibration Verification Procedure ......................................................... 6-3

Performance Verification Procedure ...................................................... 6-4

Internal Jumpers ..................................................................................... 6-5

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(continued)

II

TABLE OF CONTENTS

TABLE OF CONTENTS (continued)

Calibration Enable Jumper ................................................................... 6-5

RS232/RS422 Configuration Jumper ..................................................... 6-5

Figure 6.1 Internal Jumpers ................................................................. 6-5

Repair Parts ............................................................................................ 6-6

Instructions for Fuse Replacement ........................................................ 6-6

Figure 6.2 Fuse and Filter Assemblies ................................................... 6-6

Troubleshooting ...................................................................................... 6-7

No Display ......................................................................................... 6-7

Reading Drifts .................................................................................... 6-7

Unstable Reading ............................................................................... 6-7

Preparation for Repair or Calibration Service ............................................... 6-8

Expedite Repair and Calibration Form ........................................................ 6-9

Warranty ................................................................................................ 6-10

Warranty Limitations .......................................................................... 6-10

Statement of Calibration ..................................................................... 6-10

Contact Informat ion ........................................................................... 6-10

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III

INSTRUMENT DESCRIPTION

SECTION 1

INSTRUMENT DESCRIPTION

The Model 1750 is a highly versatile, precision digital Microohmmeter designed to provide unmatched

measurement speed and accuracy for production test and quality control applications up to 23 MΩ.

The 1750 microohmmeter automatically rejects thermal and electromagnetic line noise to provide error
free measurements for micro Ohm measurements down to 100 nΩ resolution. The 1750 also
incorporates a single command set to make integration easy for IEEE-488, RS-422 and RS-232
applications.

FEATURE OVERVIEW

The 1750 microohmmeter is desi gn ed a s a c omp l ete bu ndl ed s olu ti on for a wi d e vari ety of r esi stan ce
measurement applications. Listed below are some of the features.

0.02% Basic Accuracy with 4½ digit resolution

The 1750 microohmmeter is de signed to perf orm resi stance m easurem ents wi th a 0.02% basic
accuracy. The 4 ½ digit display produ ces readi ngs from 100 nΩ resolution to 23 MΩ maximum
resistance values.

Bipolar Test Si gnal Eliminat es Thermal EMF errors
The unit is designed to eliminate junction EMFs by introducing a bipolar test signal, which when
combined with digital signal processing, produce an accurate resistance measurement minus
thermal offset errors.

Closed Box Calibration
Full digital calibration is performed within minutes without having to make any internal
adjustments. A calibration enable/disable jumper is accessible by removing the top panel. All
adjustments are made digitally.

Programmable Delay Mode
Settling times are programmable from 1-250 ms to allow measurements of devices with extended
time constants.

Continuous and One-Shot Triggering
The 1750 microohmmeter provides two user-selectable, trigger modes, One-Shot and Continuous
for greater flexibility and optimization of test processes.

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1-1

INSTRUMENT DESCRIPTION

Selectable Reference Currents from 100 nA – 1 A
For power sensi ti ve appl ica tion s such as fuse s a nd resi st ors, mu lti pl e test cur rent select ion s a re
available.

Percent or Absolute Comparator with HI-GO-LO contact and TTL outputs
The 1750 microohmmeter d esign m akes it easy to integra te into n ew or existi ng desi gns. There
are three compar ator outputs which doub le as output b ins 1, 2, and 3. The 1750 inter face include s
relay and TTL outputs for comparator and bin functions.

Rear Panel TTL & Relay outputs for PLCs and interfacing
In addition to GPIB and RS232 interfaces, the 1750 provides a variety of TTL and relay contact
I/O’s designed to make integrating the 1750 into a test stand as versatile as possible.

1 year calibration cycle (after initial 6 month calibration)
After the initial 6 month calibration, the recommended calibration interval for the 1750 is every
twelve months.

10 Preset Storage Locations
Storage location 0 is reserved for recalling factory default settings. Locations 1-9 are user
definable and may be program med manually or via communicat ion interf aces. Thes e settings a re
stored in non-volati le RAM locations.

Fast Mode for high-sp eed measurement
Fast Modes allow speedy measurements of up to 100 reading per second. The time to first reading
is approximately 12 ms, faster than any other Ohmmeter in the mar ke t. This is o btained by us ing
a patent pending DSP technique developed by TEGAM.

½ Rack Width
Two 1750 microohmmeter uni ts are able to be rack mounted, side-by-side, in a standard 19”
rack without modification to the 1750 case.

Manual or Auto Ranging
User defined ranging allows AUTO range or 19 user-selectable ranges of resistance and test
current. All ranges have a 15% over-ranging capability.

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1-2

INSTRUMENT DESCRIPTION

Auto- Correct Function

The auto- correct function compensates for tim e or temp erature d rift b y readin g high ac curacy
internal references and automatically calculating correction coefficients for all ranges. During this
software correction process, the 1750 will delay one reading for 50 ms. The auto correct routine
is performed at power up, after 30 seconds of operation, after 30 minutes of operation, and after
every 65,536 “delayed trigger” readings, (approximately 2 hours).

High Noise Immunity
Built in line cycle integration in combination with shielded test lea ds produce exception al noise
rejection.

GPIB, RS232, or RS-422 Communication Interfaces
Standard GPIB, RS232, or RS422 user-selectable interfaces are standard communications for all
1750 units. A simple command sets ease the task of integration while the use of device dependent
commands allows for specialized function execution.

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1-3

INSTRUMENT DESCRIPTION

connection to components under test.

Kelvin Klip™ replacements for construction

ACCESSORIES SHEET

17501- Kelvin Klip™ Leads

Provides a solid four- terminal
These clips are particularly usef ul for

manual resistance measurement.
Cable length – 3 ft.

17504 – Kelvin Pr obe s

These probes are excellent for
making four-wire surface resistance
measurements on films and other flat
metallic surfaces. Each probe has two
spring-loaded, replaceable tips that
are easily removed and replaced.
Cable length – 3 ft.

17502- Spade Lug Ada pter

Used for connections between the
1750 front panel LEMO and existing
test fixtures.
Cable length – 3 ft.

17503-Sorting Fixture

This sorting fixture allows for
efficient four-wire measur ement of
leaded parts. The test fixture
features spring action contacts for
easy insertion and removal of test
components.
Cable length – 3 ft.

17505 - Male LEMO Connector

For the repair or construction of 1750
test leads.

& Strain Relief

17507 – Large Kelvin Klip™

Leads

Provides a solid 4-terminal connection

KK100- Kelvin Klip™ Rebuild Kit

or repair of Kelvin Klip leads.

to large components hat cannot be
measured with conventional Kelvin
clips. It is robust in construction,
ensuring a firm grip. Used for
connection with large bolts, cables,
plates, etc.
Cable length – 8 ft.

17510 –Chip Tweezers

Four-terminal tweezers make solid
connections to chip components in
manual sorting applications. Capacity of
jaws is 12.7 mm (0.5 in.). Contact tips
are replaceable (part no. 47422)
Cable length – 5 ft.

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1583 - GPIB (IEEE-488) Cables

1583-3 – 1-meter GPI B buss cable
1583-6 – 2-meter GPI B buss cable
1583-9 – 3-meter GPI B buss cable

1-4

CA-22-36 – RS-232 Straight

Cable 9 pin

Male to Female DB9 straight cable used
to connect the 1750 to a PC via RS-

232.
Cable length – 3 ft.

INSTRUMENT DESCRIPTION

PERFORMANCE SPECIFICATIONS

The advertised specifications of the model 1750 are valid under the following conditions:

1. The instrument must be calibrated using the methods and intervals as described in the calibration
section of this user’s manual.

2. The instrument must be in an environment, which does not exceed the limitations as defined under
“Environmental” in the Miscellaneous Specifications in Section 1.

3. T he un i t i s all ow ed to w arm up for a pe ri od of a t lea st 3 0 mi nu tes bef o re me asu rem en ts ar e ta ken .
A warm-up p eriod of 60 min utes is re commend ed after exposur e to or sto rage in a high humidity,
(non-condensing), environment .

4. T he Kelvin seri es lead resi stances must not exceed th e limitati ons as defined in Table1.1 o r Table

1.7.

Table 1.1 below is a summary of the ranges and resi stances available with the model 1750. It also
shows the full-scale voltage for each of the reference current ranges. The default ranges are printed in
BOLD. Absol ute maximum lead resist ances for each of the refe rence curren t ranges ar e included on
the bottom row. If these absolute maximum lead resistances are exceeded then significant error will be
introduced into the measurement.

RANGE RESOLUTION

REFERENCE CURRENT

1 A 100 mA 10 mA 1 mA 100 μA 10 μA 1 μA 100 nA

2 mΩ 100 nΩ 2 mV

20 mΩ 1 μΩ 20 mV 2 mV

200 mΩ 10 μΩ 200 mV 20 mV

2 Ω 100 μΩ 200 mV 20 mV

20 Ω 1 mΩ 200 mV 20 mV

200 Ω 10 mΩ 2 V 200 mV 20 mV

2 kΩ 100 mΩ 2 V 200 mV

20 kΩ 1 Ω 2 V 200 mV

200 kΩ 10 Ω 2 V

2 MΩ 100 Ω 2 V

20 MΩ 1 kΩ 2 V

Max. Lead Resistance 500 mΩ 5 Ω 50 Ω 100 Ω 100 Ω 100 Ω 100 Ω 100 Ω

Table 1.1: Full Scale Voltage as a Function of Reference Current

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1-5

INSTRUMENT DESCRIPTION

.02%+5ct

.02%+4ct

.02%+5ct

.02%+2ct

.02%+4ct

.02%+2ct

.02%+4ct

.02%+2ct

.02%+4ct

.02%+2ct

.02%+2ct

.02%+4ct

.02%+2ct

.02%+2ct

.02%+2ct

.02%+2ct

.02%+2ct

.04%+2ct

.04%+2ct

NA

NA

NA

.05%+5ct

NA

.05%+5ct

NA

.05%+5ct

NA

.05%+5ct

.05%+5ct

NA

.05%+5ct

.05%+5ct

.05%+5ct

NA

NA

NA

NA

Table 1.2 summarizes the accuracy specifications for the model 1750, in the delayed mode.

RANGE REFERENCE CURRENT

1 A 100 mA 10 mA 1 mA 100 μA 10 μA 1 μA 100 nA

2 mΩ

20 mΩ

200 mΩ

2 Ω

20 Ω

200 Ω

2 kΩ

20 kΩ

200 kΩ

2 MΩ

20 MΩ

Table 1.2: Delayed Mode Accuracies with Respect to Reference Current

(±) ACCURACY; 18-28 °C (64.4-82.4 °F); 1 YEAR (after initial 6 month cycle ).

In the fast mode, the published accuracy for all reference current ranges is +/- (0.05% + 5 counts).
These accuracies are displayed in Table 1.3. Fast Mode is not available for all range s. If the unit is in
Fast Mode and a range is selected that Fast Mode is not ava ilable, then the instrument will default to
Delayed mode.

RANGE REFERENCE CURRENT

1 A 100 mA 10 mA 1 mA 100 μA 10 μA 1 μA 100 nA

2 mΩ

20 mΩ

200 mΩ

2 Ω

20 Ω

200 Ω

2 kΩ

20 kΩ

200 kΩ

2 MΩ

20 MΩ

Table 1.3: Fast Mode Accuracy with Respect to Reference C urre nt

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1-6

INSTRUMENT DESCRIPTION

.004%rdg

+1 count

.004%rdg

+.5 counts

.004%rdg

+1 count

.002%rdg

+.1 counts

.004%rdg

+.5 counts

.002%rdg

+.1 counts

.004%rdg

+.5 counts

.002%rdg

+.1 counts

.004%rdg

+.5 counts

.002%rdg

+.1 counts

.002%rdg

+.1 counts

.004%rdg

+.5 counts

.002%rdg

+.1 counts

.002%rdg
+.1 count

.002%rdg

+.1 count

.002%rdg

+.1 counts

.002%rdg

+.1 counts

.008%rdg

+.5 counts

.008%rdg

MEASUREMENT TIMES

READING RATE

TIME TO FIRST READING

FAST MODE

10ms

100 Readings/ s

12 ms

DELAYED MODE

DELAY=1 ms

36 ms

27 RDG/s

38 ms

DELAY=5 ms

45 ms

22 RDG/s

47 ms

DELAY=10 ms

55 ms

18 RDG/s

57 ms

Delayed Mode

=

2 X (Line Period + Programmed Delay + Process Time)

RANGE REFERENCE CURRENT

2 mΩ

20 mΩ

200 mΩ

2 Ω

20 Ω

200 Ω

2 kΩ

20 kΩ

200 kΩ

2 MΩ

20 MΩ

1 A 100 mA 10 mA 1 mA 100 μA 10 μA 1 μA 100 nA

+.5 counts

Table 1.4: Table of Temperature Coefficients

+/- Temperature Coefficient / °C

(0-18 °C & 28-50 °C; 32-64.4 °F & 82.4-122 °F)

Table 1.5: Measurement Times

Table 1.5 provides approximations of me asurement times and reading rates for delaye d and fast modes.
Note that the time to first reading is longer than subsequent re adings. Examples are provided for various
delay settings. The Delayed Mode Measurement Time is calculated by the following equation:

Measurement

Where the Line Period is 1/f, f = (50 or 60 Hz) and the Programmed Delay Time may range from 1mS
to 250 ms. The Process Time is the time required to process the read data and is equal to about 1.9
ms.

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1-7

INSTRUMENT DESCRIPTION

2 mΩ

D

20 mΩ

D D

200 mΩ

D, F D

2 Ω

D, F D

20 Ω

D, F D

200 Ω

D, F

D, F D

2 kΩ

D, F

D, F

20 kΩ

D, F D

200 kΩ

D

2 MΩ

D

20 MΩ

D

RANGE REFERENCE CURRENT

1 A 100 mA 10 mA 1 mA 100 μA 10 μA 1 μA 100 nA

Table 1.6: Table of Trigger Modes

In Table 1.6, the availability of Fast, (F), or Delayed, (D), Mode Triggering is i ll ustrat ed. Del ayed mod e
is available for each of t h e 1 9 resistance / reference cu r ren t ran ges. The Fa st T riggering m ode is limited
to 8 of the ranges.

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1-8

INSTRUMENT DESCRIPTION

+

REF

0 A

SAMPLE

SAMPLESAMPLE

SAMPLE

SAMPLES FOR HIGH AND LOW STATES ARE TAKEN

FOR 32 CYCLES, THEN A READING IS PROCESSED.

THE PROCESS IS REPEATED CONTINUOUSLY.

READING COMPLETE

+

REF

0 A

SAMPLE

SAMPLE

SAMPLE

SAMPLE

CONTINUOUS SAMPLES ARE TAKEN FOR 32 CYCLES,

THEN A READING IS PROCESSED

READING COMPLETE

+

REF

0 A

- REF

A

A

A

A

ACB

B

B

B

B

C

C

CD D

SAMPLE

COMPLETE READING

SAMPLE

COMPLETE READING

SAMPLE

SAMPLE

+

REF

0 A

- REF

A

ACBB C D

SAMPLE

COMPLETE READING

SAMPLE

+

REF

0 A

- REF

A

A BBC

C D

SAMPLE

COMPLETE READING

SAMPLE

Fast Continuous:

Readings are taken towards the end of each +REF/ 0A state.
The test signal is an alternating reference current from + REF
to 0A, with automatic thermal and noise rejectio n.

Fast One-Shot:

This mode must receive an external trigger and is a shortened
version of the Fast Continuous mode. A total of 64 data
samples are taken. 32 samples on + cycles and 32 samples
on the 0 Ampere cycles. These samples are digitally processed
to produce reading

Delayed Continuous:

Continuous Alternating refer ence current from + REF to
“A” represents the programmable delay time from 1 to 250 mS.
“B” represents the line cycle time
Cycle
“C” is the time required for broken lead detection to take p lace

“D” is when the reading is processed and updated

Delayed One-Shot

Alternating reference current from + REF to – REF.
Triggering via GPIB, RS232 or rear trigger input will cause a
single cycle of reference curren t .

Delayed One-Shot

(Triggered Via Front Panel)
Alternating reference current from + REF to – REF.
Triggering via the front panel. Once trigg er e d , two reference
cycles are released of which the latter pulse will be used to
take the actual reading.

REFERENCE CURRENT MODES

There are several types of pulses available for making measurements. Below is a summary of
characteristics for each type of trigger mode and the sequence of events that occur during an actual
measurement.

Integration)

- 1/f (Sampled Input for Line

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– REF.

.

1-9

INSTRUMENT DESCRIPTION

MISCELLANEOUS SPECIFICATIONS

Display Modes:

• Resistance; Absolute Comparator; % Comparator

Digital Inte rfaces:

• IEEE-488

• RS-232

• RS-422

• External Trigger Input, and Reading Done TTL Outputs - BNC Connectors

Display:

• 4½ Digit alpha numeric readout; 2 X 16 Characters, Dot Matrix Display with backlight

Measurement Method:

• 4 terminal Kelvin connection to DUT.

Input Connector:

• Heavy Duty Type LEMO Connector for signal integrity and long life.

Input Protection:

• ± 15 V Continuous.

• Maximum Common Mode Input Voltage is 42 V peak.

Overload Current:

• Delayed Mode: 100% Overshoot, <25 μs

• Fast Mode: 200% Overshoot, < 30 μs

Noise Rejection:

• 60 dB Typical at Line Frequency

Maximum Open Circuit Compliance Voltage, (Typical):

Closed circuit compliance voltages are much lower; see Table 1.1, Full Scale Voltage as a
Function of Reference Current

• 18 Vp-p maximum (1 mA-1 A Test Current)

• 14 Vp-p maximum (100 nA-100 uA Test Current)

Environmental:

• Operating Temperature: 0 to 50 °C (32 to 122 °F), <80% RH; (Non-Condensing)

• Storage Temperature: -35 to 60 °C (-31 to 140 °F), <90% RH (Non-Condensing)

EMC:

• EN 61326-1:2013

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1-10

INSTRUMENT DESCRIPTION

MISCELLANEOUS SPECIFICATIONS (Continued)

Dimensions:

• Depth: 13.0” (33.0 cm)

• Width: 8.50” (21.6 cm)

• Height: 5.20” (13.2 cm)

Weight:

• 9.25 lbs (4.20 kg)

Rear Interface Relay Cont act Sp eci fications:
The relay contact I/Os are rated at 125 VAC @ 500 mA or 30 VDC @ 1 A.

Calibration:

Calibration of the 1750 is permitted via the front panel with no internal a d justments.
Calibration requires the temporary placement of a jumper, P9 to the J9 position.

AC Power Requirements:
Input: <100 VA, 108-132 VAC or 216-264 VAC, at 50/60 Hz.

Fuse:

• For 108-132 V Operation; use 0.8 A @ 250 V, 5X20 mm, fast acting, TEGAM PN#FU-800

• For 216-264 V Operation; use 0.5 A @ 250 V, 5X20 mm, fast acting, TEGAM PN#FU-500

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1-11

INSTRUMENT DESCRIPTION

V

REFERENCE

CURRENT

SOURCE

VOLTAGE

SENSE

DUT

= SERIES LEAD RESISTANCE

CONTACT

POINTS

TEST LEAD REQUIREMENTS

From the factory, the 1750 microohmmeter is equipped with the choice of either 17501 Kelvin Klips or
17502 Kelvin Spade Lugs. These are both 4-wire Kelvin input cables. Four-wire Kelvin-type cables must
be used with the 1750 in order to obtain an accurate resistance measurement.

The Kelvin measurement technique allows for a much more accurate reading over the two wire method.
This is because it eliminates l ead resistance. Thi s i s d on e by designatin g two o f th e f ou r con du ctors as
source lead s. These sou rce leads p rovide th e precisi on test curren t that wil l be referen ced in ma king
the resistance measurement. Since current is the same throughout a series circuit, the lead resistance
of the test leads will not have any effect on the reference current.

Figure 1.1: Electrical Representation of a typical Four-Wire Kelvin Measurement

The other two conductors are designated as voltage sense leads. These leads originate from high
impedance, v olt measurem ent circuit . When these l eads are termi nated at the poi nts of contact, an
exact resis ta n ce r ea d ing may be cal cu lated by the 175 0 m icroprocesso r . Th e s eries lead resistance of
the volta ge s ens e l eads i s neg l igi ble w i th resp e ct t o t he hi gh i mp edan ce of t he vol t age m ea sur ement
circuitry within the 1750 microohmmeter.

Four-wire Kelvin measurements are mainly used for low resistance measurements where lead
resistance er ro rs must be elimi nated.
Even though the four-wire Kel vin measurement minimizes th e effect that l ead resistance h as on the
overall measurement, there is a maximum allowable lead resistance. If this value is exceeded, then the
resulting measurement will be erroneous. The test current source dictates this limitation and lead
resistance limits are based on the amount of reference current that is flowing. The table below
summarizes these limitations.

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1-12

INSTRUMENT DESCRIPTION

REFERENCE CURRENT 1 A 100 mA 10 mA 1 mA 100 μA 10 μA 1 μA 100 nA

MAXIMUM LEAD RESISTANCE 500 mΩ 5 Ω 50 Ω 100 Ω 100 Ω 100 Ω 100 Ω 100 Ω

Table 1.7: Maximum Allowable Lead Resistance (per lead).

To assure measurement accuracy, the above lead resistance limits should not be exceeded.

In order to make accurate measurements on resistances greater than 200 kΩ, it is highly recommended
that the GROUND terminal, located on the rear panel, be connected to the DUT test fixture shield. The
test fixture shield must surround the DUT.
Also, for resistance measurements greater than 200 kΩ, the programmable delay time should be set to
a minimum of 100 ms to allow adequate settling of the reference current.

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1-13

INSTRUMENT DESCRIPTION

V + -

Positive Kelvin Loop

Negative Kelvin Loop

DUT

BROKEN LEAD DETECTION

A broken lead detection feature is enabled for ranges below 200 Ω when operating in either of the two
Delayed trigger modes. This feature is a function of the firmware and detects an open circuit by
monitoring the test current characteristi cs. The ill ustrati on below r epresents the Kel vin lea ds and th e
connection acros s a d evi ce u nd er test. Not e tha t th ere are t hr ee loop s drawn wi th the a rrows . Each of
these arrows shows the continuity test that is effectively performed by firmware during each read cycle.
If either the negative Kelvin loop, Positive Kelvin loop, or connection between the leads is broken, then
a broken lead state will be detected and the message “*****” is displayed on the LCD.

Fig 1.2: Continuity Test Paths for Broken Lead Detection

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1-14

PREPARATION FOR USE

!

SECTION 2

PREPARATION FOR USE

UNPACKING & INSPECTION

Each 1750 microohmmeter is put through a series of electrical and mechanical inspections before
shipment to the customer. Upon receipt of your instrument unpack all of the items from the shipping
carton and inspect for any damage that may have occurred during transit. Report any damaged items
to the shipping agent. Retain and use the original packing material for reshipment if necessary.

Upon Receipt, inspect the carton for the fo llowing items:

Model 1750 Precision Microohmmeter
Model 1750 User’s Manual
Either one of the following: 17501 Kelvin Klips™ or 17502 Spade Lug Adapter

SAFETY INFORMATION & PRECAUTIONS

The following safety information applies to both operation and service personnel . Safety precautions
and warnings may be found throughout this instruction manual and the equipment. These warnings
may be in the form of a symbol or a written statement. Below is a summary of these precautions.

Terms in This Manual

CAUTION statements identify conditions or practices that could result in damage to the equipment or
other property.

WARNING statements apply conditions or practices that could result in pers onal injury or loss of life.

Terms as Marked on Equipment

CAUTION indicates a personal injury hazard not immediately accessible as one reads the marking, or a
hazard to property including the equipment itself.

DANGER indicates a personal injury hazard immediately accessible as one reads the marking.

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2-1

PREPARATION FOR USE

! !

!

SAFETY INFORMATION & PRECAUTIONS (Continued)

Symbols

As Marked in This Manual:

This symbol denotes where precautionary information m ay be found.

As Marked on Equipment:

Attention – Please refer to the instruction manual.

Power ON/OFF switch

Danger – High or hazardous Voltage

Earth Ground Terminal

Grounding the Equipment

This product is grounded through the grounding conductor of the power cord. To avoid electrical shoc k
or other potential safety hazards, plug the po wer cord into a properly wir ed receptacle before using this
instrument. The proper grounding of this instrument is essential for safety and optimizing instrument
operation.

Danger Arising from Loss of G round

If the connection to ground is lost or compromise d, a floating potent ial could develop in the instrument.
Under these conditions all accessible parts, including insulating parts s uch as keypads and buttons could
develop a hazardous voltage and put the user at risk.

Use the Proper Fuse

To avoid fire hazard, use only the correct fuse type as specified for the AC power supply in the
“Miscellaneous Specifications” or “Repair Parts” sections of this manual.

Refer fuse replacement to qualified service personnel.

Do Not Use in Explosive Environments

The 1750 microohmmeter is not designed for operation in explosive environments.

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2-2

PREPARATION FOR USE

!

Do not Operate without Covers

This device should be operated with all panels and covers in place. Operation with missing panels or
covers could result in personal injury.

Preventive Maintenance

Preventive maintenance performed on a regular basis will improve the reliability of this instrument.
It may include cleaning (please refer to Section 6), visual inspection, or even monitoring the operating

environment.

FOR QUALIFIED SERVICE PERSONNEL ONLY

SERVICING SAFETY SUMMARY

Do Not Service Alone

Do not perfo rm servi ce or adj ustm ent on th is produ ct unl ess anoth er per son cap able of renderi ng first
aid is present. In stallati on and mai ntenance proc edures des cribed in this man ual are to be p erformed
by qualified service personnel only.

Use Care Wh en Servicing with Power On

Dangerous voltages may exist at several points in this product. To avoid personal injury or damage to
this equipment, avoid touching exposed connections or components while the power is on. Assure that
the power is off when removing panels, soldering, or replacing co m ponents.

Power Source

This product is intended to connect to a power source that will not apply more than 250 V
the supply conductors or between either supply conductor and ground. A protective ground connection
by way of the grounding conductor in the power cord is essential for safe operation.

between

RMS

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2-3

PREPARATION FOR USE

!

LINE SELECTOR

671175400

LINE VOLTAGE SELECTION

CAUTION: DO NOT APPLY POWER TO THE INSTRUMENT BEFORE READING THIS SECTION:

Unless other wise specified, the M odel 1750 microohmmeter i s delivered from TE GAM with its power
supply set for 120 V, 60 Hz operation. However, the 1750 design allows it to operate under 120/240
V @ 50/60 Hz op erati on. It is recomm ended th at th e li ne vol tage, f requ ency setti ng an d fus e typ e be
verified before powering the unit.

The following procedure describes the steps necessary to change the 1750 power settings from factory
default settings to 240 VAC @50 Hz.

1. Verify that there is no power connected to the unit. Remove the top co ve r.

2. Change the line selector switch on the power supply printed circuit board from 120 VAC to 240

VAC. The switch is located toward the rear panel of the 1750 on the top most PCB board. Refer
to the figure below:

3. Replace the top cover and connect the 1750 to its power source. Power the unit by depressing

the power switch located on the front panel.

4. Press the [MENU/CLEAR] key then press the 50/60 Hz key, (Key #1). Scroll the menu by pressing

either the [▲] or [▼] keys. Once 50Hz is displayed on the LCD then press [ENTER]. The 1750 is
now set for 240 VAC @ 50 Hz operation .

POWER SU PPLY

ASSEMBLY

SWITCH

Fig 2.1: Line Voltage Selection Location

NOTE: The 1750 microohmmeter uses line cy cle in t egrat ion in order to p rev ent in ter fer enc e f rom a ff ectin g the
instrument read ings . F or p rop er rea d ing s, th e f req uen cy se tting of th e in stru men t mu st m atc h th e lin e su pply .
You can change th e frequency setting simply by follow ing the instructions in step #4.

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2-4

QUICK START INSTRUCTIONS

Parameter

Setting

Parameter

Setting

1

Range

2 Ω @100 mA

8

Communication

*RS232

2

Trigger

Delay Continuous

9

Store Setup

-

3

Delay Time

111 ms

10

Recall Setup

-

4

Display Mode

Resistance

11

Line Frequency

60 Hertz

5

Compare Limits

19999; 00000

12

PIN Function

*Disabled

6

% Compare Limits

10.00%; 10.00%

13

Calibration

*Disabled

7

Nominal

10000

SECTION 3

QUICK START INS TR UCTIONS

GENERAL

The Model 1750 microohmmeter is a versatile product, which can be used in many different
configurations. De pending on the applicat ion, there are configur ations of the 1750 microohmmeter that
will help optimize te st cond itions invo lving acc uracy, me asurement speed, and v ersatility. The bes t way
to maximize the effectiveness of a pro duct and test setup is by ha ving a thorough unders tanding of the
instrumentation and the test parameters, which can a ffect the readings.
The Quick Start section is designed to give the user a general i n st ru ct i on s et for the speedy setup a n d
measuremen t of resista nce values . Whenever additi onal informat ion is app licable, a r eference w ill be
made to other parts of this manual so that the user, at their discretion, can decide whether or not to
pursue ad d itional informa t io n .

POWER THE UNIT

The power supply of the Model 1750 is designed for 50-6 0 Hz operat ions and a v olt age ran ge of 1 08­132 & 216-264 VAC. Review the line voltage selection procedure on page 2-4 before proceeding.

Power the unit and allow at least 30 minutes for the unit to warm up. Make sure that the safety
precautions on pages 2-2 and 2-3 hav e be en re vi ewed an d un der sto od. Ve ri fy th at t h e en vi ron men tal
conditions, listed on page 1-10 are met.

FACTORY SETTINGS

Before perfor ming t he actual resistance m easuremen t, there a re a num ber of test paramet ers, whic h
must be defined. The factory settings can be used for most general resistance measurements.

The 1750 microohmmeter is shipped from the factory with instrument settings as follows:
These settings can be recalled by sending a device clear command via RS232, RS422 or GPIB interface.

* When a device clear command is sent via communications interface, this value does not change.

CUSTOMIZING PARAM ETER SETTINGS

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Table 3.1: Factory Default Settings

3-1