Valhalla 4100 SERIES User manual

Valhalla Scientific, Inc.
4100 SERIES
DIGITAL OHMMETER
OPERATION MANUAL
8318 Miramar Mall
San Diego, CA 92121
P: 858/457-5576
F: 858/457-0127
W: www.valhallascientific.com
Advanced Test Equipment Rentals
www.atecorp.com 800-404-ATEC (2832)
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VALHALLA SCIENTIFIC INC. CERTIFICATION
Valhalla Scientific, Inc. certifies that this instrument was thoroughly tested and inspected and found to
meet published specifications when shipped from the factory. Valhalla Scientific, Inc. further certifies
that its calibration measurements are traceable to the Nation Institute of Standards and Technology to
the extent allowed by NIST’s calibration facility.
Due to continuing product refinement and due to possible parts manufacturer changes, Valhalla
Scientific, Inc. reserves the rights to change any or all specifications without notice.
VALHALLA SCIENTIFIC INC. WARRANTY STATEMENT
The warranty period for this instrument is stated on your invoice and packing list. Please refer to these
to determine appropriate warranty dates.
We will repair the instrument during the warranty period provided it is returned to Valhalla Scientific,
Inc. freight prepaid. No other warranty is expressed or implied.
Valhalla Scientific, Inc. is not liable for consequential damages.
Permission and a Return Material Authorization number (RMA) must be obtained directly from the
factory for warranty repairs. No liability will be accepted if returned without such permission.
Due to continuing product refinement and due to possible parts manufacturer change, Valhalla
Scientific reserves the right to change any or all specifications without notice.
4100 Digital Ohmmeter User Manual
Edition 1
Copyright © 1996 Valhalla Scientific, Inc. All rights reserved

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Documentation History
All Editions and Updates of this manual and their creation date are listed below. The first Edition of
the manual is 1. The Edition Number increments by 1 whenever the manual is revised. Updates,
which are issued between Editions, contain replacement pages to correct or add additional information
to the current Edition of the manual. Whenever a new Edition is created, it will contain all of the
Update information for the previous Edition. Each new Edition or Update also includes a revised copy
of this documentation history page.
Edition 1 ………………………………………………….November, 1995
Safety Symbols
Instruction manual symbol
affixed to product.
Indicates that the user must
refer to the user manual for
specific WARNING or
CAUTION information to
avoid personal injury or
damage to the product
Alternating current (AC)
WARNING, RISK OF
ELECTRICAL SHOCK.
Direct current (DC)
Indicates the field wiring
terminal that must be
connected to ground before
operation the equipment ---
protects against electrical
shock in case of fault.
WARNING
Calls attention to a procedure,
practice, or condition that could
cause bodily injury or death.
Frame or chassis ground
terminal --- typically
connects to the equipment’s
metal frame.
CAUTION
Calls attention to a procedure,
practice, or condition that could
possibly cause damage to
equipment or permanent lost of
data.

4
WARNINGS
The following general safety precautions must be observed during all phases of operation, service, and
repair of this product. Failure to comply with these precautions or with specific warnings elsewhere in this
manual violates safety standards of design, manufacture, and intended use of the product. Valhalla
Scientific assumes no liability for the customer’s failure to comply with these requirements.
Ground the equipment: For Safety class 1 equipment (equipment having a protective earth terminal), an
interrupted safety earth ground must be provided from the main power source to the product input wiring
terminals or supplied power cable.
DO NOT operate the product in an explosive atmosphere or in presence of flammable gases or fumes.
For continued protection, replace the line fuse(s) only with fuse(s) of the same voltage and current rating
and type. DO NOT use repaired fuses or short-circuited fuse holders.
Keep away from live circuits: Operating personnel must not remove equipment covers or shields.
Procedures involving the removal of covers or shields are for use service trained personnel only. Under
certain conditions, dangerous voltage may exist even with the equipment switched off. To avoid dangerous
electrical shock, DO NOT perform procedures involving cover or shield removal unless you are qualified
to do so.
DO NOT operate damaged equipment: Whenever it is possible that the safety protection features built
into this product have been impaired, either through physical damage, excessive moisture, or any reason,
REMOVE POWER and do not use the product until safe operation can be verified by service-trained
personnel. If necessary, return the product to Valhalla Scientific for service and repair to ensure that safety
features are maintained.
DO NOT service or adjust alone: Do not attempt internal service or adjustment unless another person,
capable of rendering first aid and resuscitation, is present.
DO NOT substitute parts or modify equipment: Because of the danger of introducing additional
hazards, do not install substitute parts or perform any unauthorized modification to the product. Return the
product to Valhalla Scientific for service and repair to ensure that safety features are maintained.
Measuring high voltage is always hazardous: ALL multimeters input terminals (both front and rear)
must be considered hazardous whenever inputs greater than 42V (dc or peak) are connected to ANY input
terminal.
Permanent wiring of hazardous voltage or sources capable of delivering grater than 150VA should be
labeled, fused, or in some other way protected against accidental bridging or equipment failure.
DO NOT leave measurement terminals energized when not in use.

Contents
Safety Symbols 3
WARNINGS 4
Chapter 1 General Information 7
Introduction 7
Manual Description 7
Instrument Description 8
Instrument Identification 8
Chapter 2 Unpacking & Installing 9
Inspection 9
Line Voltage / Fuse Selection 9
Bench Use 9
Rack Mounting 9
Safety Considerations 10
Chapter 3 Specifications 11
General 11
Accuracy 11
General Specifications 13
Environmental Requirements 13
Recommended Calibration Interval 14
Chapter 4 Optional Equipment 15
General 15
Available Options 15
Test Leads 15
Interface 17
Chapter 5 Front Panel Controls 18
General 18
Power Switch 18
Range Switches 18
STD/T.C. Switches 18
Temperature Compensator
Connection 18
Voltage & Current Terminal 19
Zero Control 19
Open Circuit Voltage Switches 19
Polarity Reverse Switch 20
Print/Send Switch 20
Resistance Window 20
Chapter 6 Rear Panel Connectors 21
General 21
Power Connector 21
Fuseholder 21
BCD Interface 21
Other Interfaces 21
Chapter 7 Manual Operations 22
General 22
Connections 22
4100ATC & 4150ATC Operations 23
4165 Operations 24
4165-1344 Operations 24
Temperature Compensation 25
Chapter 8 Interface Operations 26
General 26
BCD Output 26
Other Interfaces 27
Chapter 9 Routine Maintenance 28
General 28
Required Test Equipment 28
Pre-calibration 28
4100ATC Calibration Procedure 29
4150ATC Calibration Procedure 31
4165 and 4165-1344 Cal. Procedure 33
Periodic Maintenance 35
Chapter 10 Theory of Operation 36
Troubleshooting 36
General Circuit Descriptions 37
Detailed Circuit Descriptions 37
Power Supplies 37
Constant Current Source 38
Analog to Digital Converter 39
Optional Interfaces 39
Chapter 11 Special Procedures 40
Noisy Readings 40
Connection to Inductive Load 41

Chapter 12 Addendums 42
Addendums 42
Chapter 13 Parts List 43
4100ATC Main Board Assembly 44
4150ATC Main Board Assembly 47
Final Assembly 51
4100/4150 Display Bd. Assembly 52
4165 Clamp PCB Assembly 53
4165-1344 Main Board Assembly 54
4165-1344 Clamp PCB Assembly 58
Option BCD Interface Assembly 59
Chapter 14 Schematics/Drawings 60
4100-074 1 of 4 a
4100-074 2 of 4 b
4100-074 3 of 4 c
4100-074 4 of 4 d
4165-070 1 of 1 e
4165-071 1 of 1 f
2053-076 1 of 1 g
4100-407 1 of 1 h

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Chapter 1 General Information
Introduction
This manual has information to perform Inspection, Installation, Measurement Operations, and
Troubleshooting for Valhalla Scientific 4100 Series. Also included in this manual are:
Specifications, Parts Lists and all Schematics.
The following instruments are part of the 4100 Series Ohmmeters: 4100ATC, 4150ATC, 4165
and 4165-1344
Manual Description
This manual is separated into the 14 following Chapters.
Chapter 1 – General Information
Chapter 1 contains a brief description of the
instrument and other general information.
Chapter 2 – Unpacking and Installing
Chapter 2 contains information for unpacking
and inspection the equipment. Also contains
power requirements and installation procedure.
Chapter 3 - Specifications
Chapter 3 contains all specifications, including
range, resolution, test current, accuracy, general
and physical specifications for Valhalla 4100
Series.
Chapter 4 – Optional Equipment
Chapter 4 contains information on all available
options and test leads for the Valhalla 4100
Series.
Chapter 5 – Front Panel Controls
Chapter 5 describes the function of the front
panel button, switches, adjustments, terminals
and visual display.
Chapter 6 – Rear Panel Connections
Chapter 6 describes the use of the rear panel
connections such as power connector, fuseholder
and interface connectors.
Chapter 7 – Manual Operations
Chapter 7 describes all operations including
connections, zero adjustments and temperature
compensation.
Chapter 8 – Interface Operation
Chapter 8 contains information on the optional
interface outputs.
Chapter 9 – Routine Maintenance
Chapter 9 contains maintenance information,
such as calibration procedures.
Chapter 10 – Theory of Operation
Chapter 10 describes the theory of operation of
all circuits and sub circuits used on Valhalla
4100 Series.
Chapter 11 – Special Procedures
Chapter 11 includes special for noisy readings
and inductive loads.
Chapter 12 – Addendums
Chapter 12 lists updates and addendums for this
manual.

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Chapter 13 – Parts List
Chapter 13 contains all parts used in the
assembly and sub assembly of any 4100 Series
Ohmmeters. The parts are listed with a
Reference Designator, Valhalla Part Number,
Description, and Manufacturers Part Number.
Chapter 14 – Schematics
Chapter 14 contains all schematics and drawings
for Valhalla 4100 Series Ohmmeters.
Instrument Description
Welcome to the world of low resistance measurement! The precision instrument you have just
purchased offers super-stable measurement capability for hard-to-test items such as transformers,
coils, shunts, and even the resistance of wire itself. Other features include automatic temperature
compensation and recently added interfacing options (Chapter 8). Please read this manual
thoroughly and all accompanying addendums before attempting to operate this instrument.
The 4100 Series Ohmmeters are available with a variety of test probes, accessories, and data
output (see Chapter 4).
Instrument Identification
Valhalla Scientific instruments are identified by a two part serial number. The Serial Tag is
located on the rear or bottom of the instrument. The number is in a form of 00-0000. The first
two digits, called the serial number prefix, indicate the model. It changes only when a change is
made to the instrument. The last 3 or 4 digits, called the serial number suffix, are unique for each
individual unit.
Be sure to include the entire serial number, both prefix and suffix, in any correspondence about
your instrument.
The serial number can also be found on the Main Board, Calibration Tag and Certificate of
Calibration.

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Chapter 2 Unpacking and Installing
Inspection
If the shipping carton is damaged, request that the carrier's agent be present when the unit is
unpacked. If the instrument appears damaged, the carrier's agent should authorize repairs before the
unit is returned to the factory. Even if the instrument appears undamaged, it may have suffered
internal damage in transit that may not be evident until the unit is operated or tested to verify
conformance with its specifications. If the unit fails to operate or fails to meet the performance
specifications of Chapter 3, notify the carrier's agent and the nearest Valhalla Sales Office. Retain
the shipping carton for the carrier's inspection. DO NOT return equipment to Valhalla Scientific or
any of its sales offices prior to obtaining authorization to do so.
Line Voltage / Fuse Selection
The only adjustments required before placing the unit in operation are to verify that the instrument
has been set for the proper local AC line voltage and to verify that the proper fuse for this voltage
has been installed as follows: 105 to 125 VAC = ¼ Amp Slo-blo; 210 to 250 VAC = 0.125 Amp
Slo-blo.
Note: These fuse values are doubled if any of the interfaces (IEEE, RS232, or Printer) are installed.
Refer to rear-panel markings.
On older models the AC line voltage is selected internally by the configuration of the jumpers on
pads 9 through 12. Pads 9-10 and 11-12 are jumpered together for 115VAC operation. Pads 9&12
only are jumpered for 230VAC operation.
On newer models the AC line voltage is selected via a sliding switch mounted on the rear panel of
the instrument. The appropriate fuse values remain the same.
Bench Use
The unit is supplied with all the hardware required for bench use and special instructions for use in
this manner are not necessary. The user should become familiar with Chapters 5, 6 and 7 before
attempting to operate the ohmmeter.
Rack Mounting
Optional brackets are available for mounting the ohmmeter in a standard 19" equipment rack.
These are listed in Chapter 4. The size of the unit and the location of its center of gravity dictate

10
that it must be supported on both sides along its entire length through the use of trays or slides. If it
is to be transported while mounted in a rack, it should be supported so as to prevent upward or
downward movement.
It is recommended that blank panels at least 1.75 inches high be installed between this and any other
units in the rack to ensure freedom of air flow. Under no circumstances should the ambient air
temperature around the unit exceed 50°C while the unit is in operation or 70°C when power is
removed.
Safety Considerations
The power plug must be a three-contact device and should be inserted only into a three-contact
mating socket where the third contact provides a ground connection. If power is provided through
an extension cable, the ground connection must be continuous. Any discontinuity in the ground
lead may render the unit unsafe for use!
The testing of inductive loads such as transformers requires that special precautions be taken to
avoid damage to the instrument and/or injury to the operator! Please refer to Chapter 11.

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Chapter 3 Specifications
General
The specifications for the 4100 Series of Ohmmeters are listed in the following paragraphs. In all
cases the specifications are valid for full Kelvin Four-Terminal measurements using connections
having less than 20 milliohms of lead resistance per wire.
Accuracy
The accuracy specifications listed below are valid following a 30 minute warm-up at an ambient
temperature between 15°C and 35°C for a period of 1 year following calibration, and include the
effects of line voltage variations within the allowed range.
Model 4100ATC
Range Maximum Input Resolution Test Current Accuracy
.2Ω.19999 Ω10µΩ1 A ±0.02% of rdg ±2 digits
2Ω1.9999 Ω100µΩ100 mA ±0.02% of rdg ±2 digits
20Ω19.999 Ω1mΩ10 mA ±0.02% of rdg ±2 digits
200Ω199.99 Ω10mΩ1 mA ±0.02% of rdg ±2 digits
2kΩ1.9999 kΩ100mΩ100 µA ±0.02% of rdg ±2 digits
20kΩ19.999 kΩ1Ω10 µA ±0.02% of rdg ±2 digits
Full Scale Test Voltage: 200mV
Model 4150ATC
Range Maximum Input Resolution Test Current Accuracy
20mΩ19.999 mΩ1µΩ1 A ±0.03% of rdg ±3 digits
200mΩ199.99 mΩ10µΩ100 mA ±0.03% of rdg ±3 digits
2Ω1.9999 Ω100µΩ10 mA ±0.03% of rdg ±3 digits
20Ω19.999 Ω1mΩ1 mA ±0.03% of rdg ±3 digits
200Ω199.99 Ω10mΩ100 µA ±0.03% of rdg ±3 digits
2KΩ1.9999 kΩ100mΩ10µA ±0.03% of rdg ±3 digits
Full Scale Test Voltage: 20mV

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Model 4165
Range Maximum Input Resolution Test Current
[1] Accuracy
.2Ω.19999 Ω10µΩ100 mA ±0.03% of rdg ±3 digits
2Ω1.9999 Ω100µΩ10 mA ±0.03% of rdg ±3 digits
20Ω19.999 Ω1mΩ1 mA ±0.03% of rdg ±3 digits
200Ω199.99 Ω10mΩ100 µA ±0.03% of rdg ±3 digits
2kΩ1.9999 kΩ100mΩ10 µA ±0.03% of rdg ±3 digits
20kΩ19.999 kΩ1Ω1 µA ±0.03% of rdg ±3 digits
Full Scale Test Voltage: 20mV
[1] The Model 4165 uses reduced test currents and incorporates a user-selectable clamp-on
current source for making "dry" measurements. The clamp may be set to 50mV or 2V.
Model 4165-1344
Range Maximum Input [2] Resolution Test Current [1] Accuracy
.2Ω.19999 Ω10µΩ100 mA ±0.03% of rdg ±3 digits
2Ω1.9999 Ω100µΩ10 mA ±0.03% of rdg ±3 digits
20Ω19.999 Ω1mΩ1 mA ±0.03% of rdg ±3 digits
200Ω199.99 Ω10mΩ100 µA ±0.03% of rdg ±3 digits
2kΩ1.9999 kΩ100mΩ10 µA ±0.03% of rdg ±3 digits
20kΩ19.999 kΩ1Ω1 µA ±0.03% of rdg ±3 digits
Full Scale Test Voltage: 20mV
[1] The Model 4165-1344 uses reduced test currents and incorporates a user-selectable clamp on
the current source for making "dry" measurements. The clamp may be set to 20mV or 2V. The
4165-1344 also has a reverse current mode that may be used to ensure a dry, true-ohms
measurement.
[2] If the clamp is set to "20mV", the Maximum Input specification is changed to: 20% of range
for the .2Ωrange or 50% of range for all other ranges.

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General Specifications
Display Type: ............................................................................................4½ digit LED (20000 counts)
A-to-D Conversion Rate:.............................................................................................. 400 milliseconds
ATC Mode (4100 and 4150 only):................................... Add ±0.05% + 0.001%/°C to accuracy spec
Compensator Accuracy: ............................................................±0.1% of rated temperature coefficient
Overrange: ............................................................................. 100% of range (19999 counts on display)
Overrange Indication: ...................................................................................................... Display flashes
Terminal Configuration: ...............................................................................................Four-wire Kelvin
Temperature Coefficient:............................................................... ±0.002% /°C (0-15°C and 35-50°C)
Test Current Polarity: ...................................Negative (flows Low to High). 4165-1344 is selectable.
Test Current Compliance Voltage (4100,4150): ......................................................... 5 volts minimum
Test Current Compliance Voltage (4165):...............................selectable clamp at 50mV or 2V (±5%)
Test Current Compliance Voltage (4165-1344):.....................selectable clamp at 20mV or 2V (±5%)
Settling Time:........................................................... 300 milliseconds + 1 conversion to within ±0.1%
Environmental Requirements
Common Mode Rejection Ratio: .......................................................................... 60 db at DC to 60Hz.
Power Supply: ......................................... 115VAC or 230VAC ±10% @ 50Hz to 400Hz; 25VA max
Operating Temperature Range: ............................................................................................ 0°C to 50°C
Storage Temperature Range: .......................................................................................... -40°C to +85°C
Humidity:................................................................................ 80% RH max. at 40°C (non-condensing)
Dimensions: ........................................................................ 15"(38cm)W x 10"(26cm)D x 3½"(9cm)H
Dimensions (serial# 8-3637 and higher):......................17"(43cm)W x 11½"(29.5cm)D x 4"(10cm)H
Weights:...................................................................................11lbs(5kg) NET; 15lbs(7kg) SHIPPING

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Weights (serial# 8-3637 and higher):...............................12lbs(5.5kg) NET; 16lbs(7.5kg) SHIPPING
Recommended Calibration Intervals
The above accuracy specifications are valid for a period of 1 year following calibration, thus for
maintenance of these specifications a calibration interval of 1 year is recommended. More frequent
calibrations may be performed as desired.

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Chapter 4 Optional Equipment
General
The 4100 series of Ohmmeters are shipped with a detachable power cord and an Operation Manual
as standard equipment. This Chapter lists several items that may be desirable for special
applications.
Available Options
Listed below are the options available for use with the 4100 Series of Ohmmeters.
Temperature Compensators
Models 4100ATC and 4150ATC may utilize a compensating sensor to provide resistance
readings that have been corrected for temperature changes. Options AL and CU simulate
a constant-temperature chamber referenced to either 20°C or 25°C. The temperature
coefficient of Option CU is 3931ppm/°C. The temperature coefficient of Option AL is
4030ppm/°C.
Option CK: Compensator Extension Cable
This option is a shielded extender cable to allow an Option "CU" or "AL" to be mounted
up to 48" away from the ohmmeter
Option RX3: Rack Mount Adapter
The 4100 Series of ohmmeters may be mounted in a standard 19" equipment rack using
these optional rack ears. The standard rack ears are designated as Option RX3.
Test Leads
Option K: 4-Wire Kelvin Lead Set
Option "K" is a shielded, 4-wire Kelvin cable set, forty-eight inches in length terminated
in "KCS" gold-plated clips. Option "K" is the recommended general purpose lead set for
most applications.
Option KCS: Kelvin Clips
Option "KCS" are the gold-plated Kelvin clips used on the Option "K" lead set for 4-wire
measurements of smaller components and leads. Clips open to 1/2 inch and
accommodate test currents of up to 10 amperes.
Option JAWS: Heavy-Duty Clips
Option "JAWS" are the heavy-duty clamps used to terminate Option "KK".

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Option KK: 4-Wire Kelvin Lead Set
Option "KK" is a heavy-duty 4-wire Kelvin cable set, 48-inches in length terminated in
"JAWS" clamps for measuring large motors, bushings, etc. Opening is 2".
Option MP-1: Kelvin Micro-Probes
Option "MP-1" is a 48-inch shielded Kelvin 4-wire cable set with a 1-ampere test current
capacity employing a set of Kelvin Micro-Probes. The probes are equipped with spring-
loaded stainless steel tips with 0.05" spacing.
Option MP-2: Kelvin Mini-Probes
Option "MP-2" is a 48-inch shielded 4-wire cable set equipped with Kelvin Mini-Probes
having spring-loaded stainless steel tips with 0.18" spacing.
Option MP-3: Kelvin Micro-Probes
Option "MP-1" is a 48" shielded lead set (dual banana), handheld pencil type, terminated in
spring loaded steel tips with .08" separation (1 amp max.). Special orders or modified
versions available upon request.
Option MP-4/MP-5: Surface Probes
These probes permit rapid, repeatable bonding testing on a variety of screened or flat
surfaces. Test current is evenly distributed through the probe base while sensing is
accomplished via a spring loaded center contact. The MP-4 target area is 1" in diameter.
The MP-5 target area is .4" in diameter.
Option MP-S: Single Probe Lead Set
Option "MP-S" is a 4-wire lead set terminated in single points. The 4-wire configuration is
maintained up to the point of the probe, eliminating most cable resistance effects. Option
MP-S may be used where a single probe tip is a must.
Option BBL: Banana-to-Banana Cable
Option "BBL" is a 48" shielded cable terminated on both ends in dual banana plugs. This
cable may be used for voltage and current connections to the ohmmeter.
Option C: Banana-to-Clip Cable
Option "C" is a 48" general purpose shielded lead set terminated on one end in dual banana
plugs and on the other end in red and black alligator clips.
Option SL-48: Low Thermal Leads
Option "SL-48" is a 48" shielded lead set terminated in gold-plated spade lugs. This lead set
is designed to eliminate problems caused by thermal EMF's and is rated for the maximum
output current of the instrument.

17
Interface
Option BCD: Data Output
This option provides parallel BCD data on p rear-panel 50-pin connector. All outputs are
TTL comparable levels with a drive capability of 1 LS load. The Option BCD may be used to
drive the Valhalla Model 1248. (See Chapter 8)
Model 1248: Dual-Limit Comparator
The Valhalla Model 1248 may be used in conjunction with a 4100 Series Ohmmeter and Option
BCD above. The Model 1248 is a dual-limit BCD comparator that interprets the display
indications of the ohmmeter as either "HI", "LO" or "GO", based on a tolerance that is set by the
user. Relay contact closure is provided to trigger an alarm, counter, batch sorter or other device.
The 1248 also reduces operator workload by allowing him to make an instant determination of
the test results. The mating cable from the ohmmeter to the 1248 is 3' in length and designated
as "IDC-2".
Options IEEE, RS232, and PAR: Data Output
The Valhalla 4100 Series of ohmmeters is available with several of the industry's most popular
remote interfaces. These include a GPIB IEEE-488.2 compatible interface, a serial RS232C
interface, and a Centronics parallel printer interface for direct print-out capability. The
interfaces are for data acquisition only and do not provide range or function control of the
ohmmeter. The interfaces are available in any combination and may be used simultaneously.
Also refer to Chapter 8 and additional Addendums.

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Chapter 5 Front Panel Controls
General
This chapter outlines the use of each of the front panel controls and connectors. This chapter should be
used in conjunction with Chapter 6 and 7 for complete operating instructions.
Power Switch
This "push-push" switch is used to alternately apply or disconnect the AC power source from the
internal circuitry of the product.
Range Switches
These switches are used to select the required resistance range. The switches are interlocked such that
only one switch may be selected (depressed) at any one time. Use the range and resolution tables of
Chapter 3 to determine which range will provide the greatest accuracy without exceeding its limit.
CAUTION!
Extra care must be taken when working with inductive loads. Always select the highest
resistance range before connecting or disconnecting the test leads.
STD / T.C. Switches
These paragraphs apply only to Models 4100ATC and 4150ATC. These switches are used to select
(T.C.) or deselect (STD) the temperature compensating mode of operation. These switches are
interlocked such that only one may be depressed at any one time.
This switch should be left in the STD position unless a compensating sensor (Option CU or AL) is
attached to the TEMPERATURE COMPENSATOR jack. Depress the T.C. switch to select the
compensator. Selection of the ATC mode of operation when no sensor is fitted will yield invalid
measurements.
Temperature Compensation Connector
These paragraphs apply only to Models 4100ATC and 4150ATC. This BNC connector may be
connected to a temperature sensor (e.g., option "CU" or "AL") for operation of these products in the
T.C. mode via up to 48" of RG58CU cable (Valhalla Option CK). This sensor simulates a constant
temperature chamber and will accurately monitor the ambient temperature and correct the displayed
reading to give the value at the reference temperature of the sensor.

19
To achieve the best results when using the T.C. mode of operation the user should ensure that the sensor
is in the same environment as the test load, and is not in any large air currents which may cause cooling
effects. The user should also note that to reduce the effects of drafts the temperature sensor has been
designed with a long thermal time constant, thus at least 20 minutes should be allowed for thermal
stabilization following any large change in ambient conditions or following handling of the sensor.
CAUTION!
The case of the sensor is electrically connected to internal circuitry in the ohmmeter. The
sensor should have no electrical contact with the load under test.
Voltage and Current Terminals
The four terminals on the front panel provide full 4-wire Kelvin measurement capability. The
CURRENT terminals provide the test current while the VOLTAGE terminals are used to monitor the
voltage drop across the load. Refer to Chapter 7 for more details on connections.
Zero Control
This potentiometer may be used to trim out any offset present on the display. See Chapter 7.
Open Circuit Voltage Switches
These paragraphs apply only to Models 4165 and 4165-1344. The OPEN CIRCUIT VOLTAGE
switches are used to select the desired maximum compliance voltage of the current source. This
function ensures "dry" measurements by clamping the open-circuit voltage at the CURRENT terminals.
For example, if the 20mV switch is depressed the voltage at the CURRENT terminals will not exceed
20mV (±5%). These two switches are interlocked such that only one may be depressed at any one time.
The user should note that in some applications (where the lead resistance is not negligible) it is possible
that the selected voltage may be exceeded even when connected to a low resistance load. In this event,
if it is not possible to reduce the lead resistance in the current carrying leads, the user may wish to select
the higher clamp voltage after connecting to the test load and then re-select the lower clamp voltage
prior to the removal of the test load. This will ensure that the required voltage is not exceeded during
connection or disconnection, but will allow the correct value of the test load to be obtained.
For the 4165-1344 only, the 20mV clamp should be selected prior to reversing the polarity of the test
current.

20
Polarity Reverse Switch
These paragraphs apply to the Model 4165-1344 only. This switch allows the effects of thermal emf's
to be measured and corrected for by averaging the measurements obtained on both polarities. An
estimation of the thermal emf's present may be obtained by the formula:
V
rdgBrdgA
thermals µ
2
−
=
Where reading A and reading B are the readings taken in the NORMAL and REVERSE modes,
disregarding the decimal point.
Print / Send Switch
The PRINT switch, which is labeled "SEND" on later units, is used by the optional parallel printer or
serial RS232C interface to control data transfer. If the printer interface is installed, pressing this button
will generate a print-out of the resistance data. For the RS232C option (without printer), this will send
one reading to the terminal. Please refer to the appropriate Addendum.
Resistance Window
This 4½ (19999 counts) LED display presents the measured resistance value. The units of measure are
determined by the setting of the Range switches, and are either milliohms, ohms, or kilo-ohms. A
flashing display indicates an overrange condition. In this situation the unit should be upranged to obtain
a solid reading.