Tegam 1750 User manual

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1750
High Speed Programmable
Microohmmeter
MODEL 1750
Instruction Manual
PN# 1750-900-01
Publication Date: April 2017
REV. S
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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I
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
2PREPARATION 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
3QUICK 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
4OPERATING 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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TABLE OF CONTENTS
TABLE OF CONTENTS (continued)
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
5PROGRAMMING & 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
6SERVICE 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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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 Information ........................................................................... 6-10

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1-1
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 designed as a complete bundled solution for a wide variety of resistance
measurement applications. Listed below are some of the features.
0.02% Basic Accuracy with 4½ digit resolution
The 1750 microohmmeter is designed to perform resistance measurements with a 0.02% basic
accuracy. The 4½ digit display produces readings from 100 nΩ resolution to 23 MΩ maximum
resistance values.
Bipolar Test Signal Eliminates 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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INSTRUMENT DESCRIPTION
Selectable Reference Currents from 100 nA – 1 A
For power sensitive applications such as fuses and resistors, multiple test current selections are
available.
Percent or Absolute Comparator with HI-GO-LO contact and TTL outputs
The 1750 microohmmeter design makes it easy to integrate into new or existing designs. There
are three comparator outputs which double as output bins 1, 2, and 3. The 1750 interface includes
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 programmed manually or via communication interfaces. These settings are
stored in non-volatile RAM locations.
Fast Mode for high-speed 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 market. This is obtained by using
a patent pending DSP technique developed by TEGAM.
½ Rack Width
Two 1750 microohmmeter units 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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INSTRUMENT DESCRIPTION
Auto- Correct Function
The auto- correct function compensates for time or temperature drift by reading high accuracy
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 leads produce exceptional 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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INSTRUMENT DESCRIPTION
ACCESSORIES SHEET
17501- Kelvin Klip™ Leads
Provides a solid four- terminal
connection to components under test.
These clips are particularly useful for
manual resistance measurement.
Cable length – 3 ft.
17504 – Kelvin Probes
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.
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.
17502- Spade Lug Adapter
Used for connections between the
1750 front panel LEMO and existing
test fixtures.
Cable length – 3 ft.
17505 - Male LEMO Connector
& Strain Relief
For the repair or construction of 1750
test leads.
KK100- Kelvin Klip™ Rebuild Kit
Kelvin Klip™ replacements for construction
or repair of Kelvin Klip leads.
1583 - GPIB (IEEE-488) Cables
1583-3 – 1-meter GPIB buss cable
1583-6 – 2-meter GPIB buss cable
1583-9 – 3-meter GPIB buss cable
17503-Sorting Fixture
This sorting fixture allows for
efficient four-wire measurement of
leaded parts. The test fixture
features spring action contacts for
easy insertion and removal of test
components.
Cable length – 3 ft.
17507 – Large Kelvin Klip™
Leads
Provides a solid 4-terminal connection
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.
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.

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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. The unit is allowed to warm up for a period of at least 30 minutes before measurements are taken.
A warm-up period of 60 minutes is recommended after exposure to or storage in a high humidity,
(non-condensing), environment.
4. The Kelvin series lead resistances must not exceed the limitations as defined in Table1.1 or Table
1.7.
Table 1.1 below is a summary of the ranges and resistances 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. Absolute maximum lead resistances for each of the reference current ranges are 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 Ω100 μΩ 200 mV 20 mV
20 Ω1 mΩ 200 mV 20 mV
200 Ω10 mΩ 2 V 200 mV 20 mV
2 kΩ 100 mΩ 2 V 200 mV
20 kΩ 1 Ω2 V 200 mV
200 kΩ 10 Ω2 V
2 MΩ 100 Ω2 V
20 MΩ 1 kΩ 2 V
Max. Lead Resistance 500 mΩ 5 Ω50 Ω100 Ω100 Ω100 Ω100 Ω100 Ω
Table 1.1: Full Scale Voltage as a Function of Reference Current

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INSTRUMENT DESCRIPTION
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
.02%+5ct
20 mΩ
.02%+4ct
.02%+5ct
200 mΩ
.02%+2ct
.02%+4ct
2 Ω
.02%+2ct
.02%+4ct
20 Ω
.02%+2ct
.02%+4ct
200 Ω
.02%+2ct
.02%+2ct
.02%+4ct
2 kΩ
.02%+2ct
.02%+2ct
20 kΩ
.02%+2ct
.02%+2ct
200 kΩ
.02%+2ct
2 MΩ
.04%+2ct
20 MΩ
.04%+2ct
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 ranges. If the unit is in
Fast Mode and a range is selected that Fast Mode is not available, 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
NA
20 mΩ
NA
NA
200 mΩ
.05%+5ct
NA
2 Ω
.05%+5ct
NA
20 Ω
.05%+5ct
NA
200 Ω
.05%+5ct
.05%+5ct
NA
2 kΩ
.05%+5ct
.05%+5ct
20 kΩ
.05%+5ct
NA
200 kΩ
NA
2 MΩ
NA
20 MΩ
NA
Table 1.3: Fast Mode Accuracy with Respect to Reference Current

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INSTRUMENT DESCRIPTION
RANGE REFERENCE CURRENT
1 A 100 mA 10 mA 1 mA 100 μA 10 μA 1 μA 100 nA
2 mΩ
.004%rdg
+1 count
20 mΩ
.004%rdg
+.5 counts
.004%rdg
+1 count
200 mΩ
.002%rdg
+.1 counts
.004%rdg
+.5 counts
2 Ω
.002%rdg
+.1 counts
.004%rdg
+.5 counts
20 Ω
.002%rdg
+.1 counts
.004%rdg
+.5 counts
200 Ω
.002%rdg
+.1 counts
.002%rdg
+.1 counts
.004%rdg
+.5 counts
2 kΩ
.002%rdg
+.1 counts
.002%rdg
+.1 count
20 kΩ
.002%rdg
+.1 count
.002%rdg
+.1 counts
200 kΩ
.002%rdg
+.1 counts
2 MΩ
.008%rdg
+.5 counts
20 MΩ
.008%rdg
+.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)
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
Table 1.5: Measurement Times
Table 1.5 provides approximations of measurement times and reading rates for delayed and fast modes.
Note that the time to first reading is longer than subsequent readings. Examples are provided for various
delay settings. The Delayed Mode Measurement Time is calculated by the following equation:
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.
Delayed Mode
Measurement
=
2 X (Line Period + Programmed Delay + Process Time)

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INSTRUMENT DESCRIPTION
Table 1.6: Table of Trigger Modes
In Table 1.6, the availability of Fast, (F), or Delayed, (D), Mode Triggering is illustrated. Delayed mode
is available for each of the 19 resistance / reference current ranges. The Fast Triggering mode is limited
to 8 of the ranges.
RANGE REFERENCE CURRENT
1 A 100 mA 10 mA 1 mA 100 μA 10 μA 1 μA 100 nA
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

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INSTRUMENT DESCRIPTION
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.
+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
A
CB
B C D
SAMPLE
COMPLETE READING
SAMPLE
+ REF
0 A
- REF
A
A B
B
C
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 rejection.
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 reference current from + REF to
– REF.
“A” represents the programmable delay time from 1 to 250 mS.
“B” represents the line cycle time
- 1/f (Sampled Input for Line
Cycle
Integration)
“C” is the time required for broken lead detection to take place
“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 current.
Delayed One-Shot
(Triggered Via Front Panel)
Alternating reference current from + REF to
–
REF.
Triggering via the front panel. Once triggered, two reference
cycles are released of which the latter pulse will be used to
take the actual reading.

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INSTRUMENT DESCRIPTION
MISCELLANEOUS SPECIFICATIONS
Display Modes:
•Resistance; Absolute Comparator; % Comparator
Digital Interfaces:
•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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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 Contact Specifications:
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 adjustments.
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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INSTRUMENT DESCRIPTION
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 lead resistance. This is done by designating two of the four conductors as
source leads. These source leads provide the precision test current that will be referenced in making
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.
V
REFERENCE
CURRENT
SOURCE
VOLTAGE
SENSE
DUT
= SERIES LEAD RESISTANCE
CONTACT
POINTS
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, volt measurement circuit. When these leads are terminated at the points of contact, an
exact resistance reading may be calculated by the 1750 microprocessor. The series lead resistance of
the voltage sense leads is negligible with respect to the high impedance of the voltage measurement
circuitry within the 1750 microohmmeter.
Four-wire Kelvin measurements are mainly used for low resistance measurements where lead
resistance errors must be eliminated.
Even though the four-wire Kelvin measurement minimizes the effect that lead resistance has 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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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 Ω50 Ω100 Ω100 Ω100 Ω100 Ω100 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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1-14
INSTRUMENT DESCRIPTION
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 characteristics. The illustration below represents the Kelvin leads and the
connection across a device under test. Note that there are three loops drawn with the arrows. 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.
V
+
-
Positive Kelvin Loop
Negative Kelvin Loop
Fig 1.2: Continuity Test Paths for Broken Lead Detection
DUT

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2-1
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 following 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 personal 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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2-2
PREPARATION FOR USE
SAFETY INFORMATION & PRECAUTIONS (Continued)
Symbols
As Marked in This Manual:
This symbol denotes where precautionary information may 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 shock
or other potential safety hazards, plug the power cord into a properly wired receptacle before using this
instrument. The proper grounding of this instrument is essential for safety and optimizing instrument
operation.
Danger Arising from Loss of Ground
If the connection to ground is lost or compromised, a floating potential could develop in the instrument.
Under these conditions all accessible parts, including insulating parts such 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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