Model 4100 - Valhalla Scientific, Inc

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
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
2
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.
Frame or chassis ground
terminal --- typically
connects to the equipment’s
metal frame.
3
WARNING
Calls attention to a procedure,
practice, or condition that could
cause bodily injury or death.
CAUTION
Calls attention to a procedure,
practice, or condition that could
possibly cause damage to
equipment or permanent lost of
data.
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.
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Contents
Safety Symbols
WARNINGS
3
4
Chapter 1 General Information
Introduction
Manual Description
Instrument Description
Instrument Identification
7
7
7
8
8
Chapter 2 Unpacking & Installing
Inspection
Line Voltage / Fuse Selection
Bench Use
Rack Mounting
Safety Considerations
9
9
9
9
9
10
Chapter 3 Specifications
General
Accuracy
General Specifications
Environmental Requirements
Recommended Calibration Interval
11
11
11
13
13
14
Chapter 4 Optional Equipment
General
Available Options
Test Leads
Interface
15
15
15
15
17
Chapter 5 Front Panel Controls
General
Power Switch
Range Switches
STD/T.C. Switches
Temperature Compensator
Connection
Voltage & Current Terminal
Zero Control
Open Circuit Voltage Switches
Polarity Reverse Switch
Print/Send Switch
Resistance Window
18
18
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18
18
18
19
19
19
20
20
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Chapter 6 Rear Panel Connectors
General
Power Connector
Fuseholder
BCD Interface
Other Interfaces
21
21
21
21
21
21
Chapter 7 Manual Operations
General
Connections
4100ATC & 4150ATC Operations
4165 Operations
4165-1344 Operations
Temperature Compensation
22
22
22
23
24
24
25
Chapter 8 Interface Operations
General
BCD Output
Other Interfaces
26
26
26
27
Chapter 9 Routine Maintenance
General
Required Test Equipment
Pre-calibration
4100ATC Calibration Procedure
4150ATC Calibration Procedure
4165 and 4165-1344 Cal. Procedure
Periodic Maintenance
28
28
28
28
29
31
33
35
Chapter 10 Theory of Operation
Troubleshooting
General Circuit Descriptions
Detailed Circuit Descriptions
Power Supplies
Constant Current Source
Analog to Digital Converter
Optional Interfaces
36
36
37
37
37
38
39
39
Chapter 11 Special Procedures
Noisy Readings
Connection to Inductive Load
40
40
41
Chapter 12 Addendums
Addendums
Chapter 13 Parts List
4100ATC Main Board Assembly
4150ATC Main Board Assembly
Final Assembly
4100/4150 Display Bd. Assembly
4165 Clamp PCB Assembly
4165-1344 Main Board Assembly
4165-1344 Clamp PCB Assembly
Option BCD Interface Assembly
42
42
43
44
47
51
52
53
54
58
59
Chapter 14 Schematics/Drawings 60
4100-074
4100-074
4100-074
4100-074
4165-070
4165-071
2053-076
4100-407
1 of 4
2 of 4
3 of 4
4 of 4
1 of 1
1 of 1
1 of 1
1 of 1
a
b
c
d
e
f
g
h
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 6 – Rear Panel Connections
Chapter 6 describes the use of the rear panel
connections such as power connector, fuseholder
and interface connectors.
Chapter 2 – Unpacking and Installing
Chapter 2 contains information for unpacking
and inspection the equipment. Also contains
power requirements and installation procedure.
Chapter 7 – Manual Operations
Chapter 7 describes all operations including
connections, zero adjustments and temperature
compensation.
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.
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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.
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.
8
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
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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
.2Ω
.19999 Ω
10µΩ
1A
2Ω
1.9999 Ω
100µΩ
100 mA
20Ω
19.999 Ω
1mΩ
10 mA
200Ω
199.99 Ω
10mΩ
1 mA
2kΩ
1.9999 kΩ
100mΩ
100 µA
20kΩ
19.999 kΩ
1Ω
10 µA
Full Scale Test Voltage: 200mV
Range Maximum Input Resolution
20mΩ
19.999 mΩ
1µΩ
200mΩ
199.99 mΩ
10µΩ
2Ω
1.9999 Ω
100µΩ
20Ω
19.999 Ω
1mΩ
200Ω
199.99 Ω
10mΩ
2KΩ
1.9999 kΩ
100mΩ
Full Scale Test Voltage: 20mV
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Model 4150ATC
Test Current
1A
100 mA
10 mA
1 mA
100 µA
10µA
Accuracy
±0.02% of rdg ±2 digits
±0.02% of rdg ±2 digits
±0.02% of rdg ±2 digits
±0.02% of rdg ±2 digits
±0.02% of rdg ±2 digits
±0.02% of rdg ±2 digits
Accuracy
±0.03% of rdg ±3 digits
±0.03% of rdg ±3 digits
±0.03% of rdg ±3 digits
±0.03% of rdg ±3 digits
±0.03% of rdg ±3 digits
±0.03% of rdg ±3 digits
Range Maximum Input Resolution
.2Ω
.19999 Ω
10µΩ
2Ω
1.9999 Ω
100µΩ
20Ω
19.999 Ω
1mΩ
200Ω
199.99 Ω
10mΩ
2kΩ
1.9999 kΩ
100mΩ
20kΩ
19.999 kΩ
1Ω
Full Scale Test Voltage: 20mV
Model 4165
Test Current [1]
100 mA
10 mA
1 mA
100 µA
10 µA
1 µA
Accuracy
±0.03% of rdg ±3 digits
±0.03% of rdg ±3 digits
±0.03% of rdg ±3 digits
±0.03% of rdg ±3 digits
±0.03% of rdg ±3 digits
±0.03% of rdg ±3 digits
[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]
.2Ω
.19999 Ω
10µΩ
100 mA
2Ω
1.9999 Ω
100µΩ
10 mA
20Ω
19.999 Ω
1mΩ
1 mA
200Ω
199.99 Ω
10mΩ
100 µA
2kΩ
1.9999 kΩ
100mΩ
10 µA
20kΩ
19.999 kΩ
1Ω
1 µA
Full Scale Test Voltage: 20mV
Accuracy
±0.03% of rdg ±3 digits
±0.03% of rdg ±3 digits
±0.03% of rdg ±3 digits
±0.03% of rdg ±3 digits
±0.03% of rdg ±3 digits
±0.03% of rdg ±3 digits
[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 .2Ω range 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".
15
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 springloaded 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.
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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.
18
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.
19
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:
thermals =
rdgA − rdgB
µV
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.
20
Chapter 6
Rear Panel Connectors
General
This chapter outlines the use of each of the rear panel controls and connectors. This chapter should be
used in conjunction with Chapter 5 and 7 for complete operating instructions.
Power Connector
The 3-prong power connector mounted on the rear panel of the product is for the application of AC
power to the unit. Refer to Chapter 2 for available voltages and safety precautions.
Fuseholder
This item is located internally on instruments manufactured with serial numbers lower than 8-3637.
This item is used to provide access to the main power fuse. Fuse values are listed below:
105VAC - 125VAC = ¼ amp slo-blo *
210VAC - 250VAC = .125 amp slo-blo *
*Fuse values are doubled if the IEEE, RS232C or Printer interface has been installed. Refer to rear-panel markings.
Replace blown fuses with their exact equivalent only!
BCD Interface
This connector is provided on units fitted with Option "BCD" and may be used to interface with the
Valhalla Model 1248 Comparator, or with other types of data acquisition equipment. The individual
pin functions of this connector are shown in Chapter 8.
Other Interfaces
The 4100 Series is available with a choice of three common interfaces for remote data acquisition.
These include GPIB (IEEE-488.2), RS232C, or a Centronics parallel printer interface. These interfaces
are for data acquisition only, and do not allow remote range control of the ohmmeter. If your ohmmeter
has been fitted with one of these optional interfaces, please refer to Chapter 12 for operating
instructions.
21
Chapter 7
Manual Operations
General
This Chapter contains operating instructions for the ohmmeter Models 4100ATC, 4150ATC, 4165, and
4165-1344. The information contained in this chapter should be used along with the descriptions in
Chapter 5 and 6 to become completely familiar with the various methods of operation using the
different ohmmeters.
Connections
Connections to the ohmmeter are made via 4 binding posts on the front panel of the instrument. When
using Valhalla test leads, the tabbed side of each banana jack is connected to the CURRENT terminals
(see below). This ensures that current is carried in the largest conductor of the cable, and that the
voltage input is shielded.
VHI ☼
☼ IHI ←Tab
VLO ☼
☼ ILO ←Tab
NOTE: If the VHI and IHI terminals are not shorted together the display will roll around and may or
may not indicate an overrange. This is a characteristic of the voltmeter and does not indicate a fault in
the instrument.
The 4-Wire configuration of all Valhalla ohmmeters eliminates errors normally caused by test lead and
contact resistances. In many applications the contact resistance can exceed the value of the load by
several orders of magnitude. The 4-Wire ohmmeter bypasses this potential error source by providing
two terminals of constant current and an additional two terminals for high impedance voltage
measurement. The result is a fast, accurate resistance measurement of the load, independent of the
resistance of the current carrying leads.
Figure 1 illustrates how the 4-wire principle is used to eliminate lead, wire and contact resistances as
potential error sources. The internal current source inherently overcomes all series resistance (within
compliance voltage limits) and delivers a precise constant current. The internal high-impedance DVM
senses the voltage drop across the load. There is negligible contact and lead resistance error created by
the voltage measurement because the high input impedance of the DVM limits current flow in the
voltage leads.
22
Figure 1 Error Sources in Resistance Measurements
4100ATC and 4150ATC Operations
The guidelines below should be followed for taking measurements using Models 4100ATC and
4150ATC:
1)
Connect the test leads to the ohmmeter as described in the last section of this chapter.
2)
Select the highest resistance range (20KΩ for 4100ATC or 2KΩ for 4150ATC).
3)
Select the STD mode unless a compensator is attached to the connector on the front panel.
4)
Zero Adjustment. This adjustment may be performed at any time but does not need to be
performed before each measurement. To make the adjustment, select the 200Ω range and
connect the ohmmeter to a precision 0.1Ω resistor. Adjust the front panel ZERO
potentiometer so that the display indicates 000.10.
5)
Connect the test leads to the load using a 4-wire configuration.
6)
Select the most precise reading by downranging the ohmmeter until the display flashes
(indicating an overrange condition) and then moving back up one range.
NOTE:
23
It is recommended that the ohmmeter be placed in the highest resistance range (far
right switch) prior to connecting or disconnecting the test leads to avoid drawing an
arc.
4165 Operations
The guidelines below should be followed for taking measurements using the Model 4165 Contact
Resistance Ohmmeter:
1)
Select the 50mV maximum open-circuit voltage. This limits the maximum voltage that will
be present at the CURRENT terminals in a no load situation to ensure a dry measurement.
2)
Select the 20KΩ range.
3)
Connect the test leads to the ohmmeter as described in 6-2.
4)
Zero Adjustment. This adjustment may be performed at any time but does not need to be
performed before each measurement. To make the adjustment, select the 200Ω range and
connect the ohmmeter to a precision 0.1Ω resistor. Adjust the front panel ZERO
potentiometer so that the display indicates 000.10.
5)
Connect the test leads to the load using a 4-wire configuration.
6)
Select the most precise reading by downranging the ohmmeter until the display flashes
(indicating an overrange condition) and then moving back up one range.
7)
Select the 2V clamp. The resistance reading will be indicated on the display. It is
recommended that the OPEN-CIRCUIT VOLTAGE selector be placed in the 50mV
position before changing ranges or disconnecting the test leads.
4165-1344 Operations
The guidelines below should be followed for taking measurements using the Model 4165-1344
Contact Resistance Ohmmeter:
1)
Select the 20mV maximum open-circuit voltage. This switch limits the maximum voltage
that will be present at the CURRENT terminals in a no load situation to ensure a dry
measurement.
2)
Select the 20KΩ range.
3)
Connect the test leads to the ohmmeter as described in 6-2.
4)
Zero Adjustment. This adjustment may be performed at any time but does not need to be
performed before each measurement. To make the adjustment, select the 200Ω range and
connect the ohmmeter to a precision 0.1Ω resistor. Adjust the front panel ZERO
potentiometer so that the display indicates 000.10.
5)
Connect the test leads to the load using a 4-wire configuration.
24
6)
Select the most precise reading by downranging the ohmmeter for maximum resolution.
7)
Select the 2V clamp. The resistance reading will be indicated on the display.
8)
Note the reading on the display and reselect the 20mV clamp.
9)
Reverse the polarity switch and reselect the 2V clamp.
10)
Note the reading on the display. The true-ohms value is calculated by averaging the two
noted readings together.
It is recommended that the OPEN-CIRCUIT VOLTAGE selector be placed in the 20mV
position before changing ranges or disconnecting the test leads.
11)
Temperature Compensation
Automatic Temperature Compensation (ATC) simulates a constant ambient temperature chamber
for materials which are normally subject to varying ambient temperatures. When the ATC mode is
selected, the temperature sensor (Options "AL" and "CU") automatically senses the ambient
temperature and adjusts the reading to indicate what the actual resistance value would be in a
controlled 20°C or 25°C environment. The Option "CU" compensator simulates the coefficient of
copper while Option "AL" simulates aluminum.
The ATC mode is selected by pressing the T.C. push-button. The temperature sensors are
connected to the ohmmeter via the front panel BNC connector. The temperature sensor may be may
be placed in closer proximity to the device under test using a Valhalla Option "CK" compensator
extension cable. Selecting the T.C. mode with no sensor connected will yield invalid
measurements.
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.
25
Chapter 8
Interface Operations
General
The 4100 Series of ohmmeters is now available with a choice of two data outputs. The standard
output provides data in a binary-coded-decimal format. The latest data output available is a parallel
printer port for connecting directly to a Centronics compatible printer. Both interfaces are described
below.
BCD Interface
Pin Number
Data
1
2
3
4
6
7
8
9
11
12
13
14
16
17
18
19
21
22, 40
26
50
1
2
4
8
10
20
40
80
100
200
400
800
1000
2000
4000
8000
10000
20000 (overrange)
+5 VDC supply
0 VDC common
35
End of Conversion on negative transition
(A high signifies "Busy")
45
Display Hold Line (+5V or open = Run; 0V = Hold)
The BCD outputs are fully compatible with the Valhalla Model 1248 BCD Comparator. When
connecting to the comparator using the standard IDC-2 interface cable, the end of the cable
possessing the wire break-outs is connected to the Model 1248.
26
Other Interfaces
The 4100 Series is available with your choice of three common interfaces for remote data
acquisition. These include GPIB (IEEE-488.2), RS-232C, and a Centronics parallel printer
interface. These interfaces are for data acquisition only, and do not allow remote range control of
the ohmmeter.
The Centronics print-out option allows the ohmmeter to be connected to a variety of standard printer
types. The print-out style may be configured in a label format to include company name, model
number, serial number, time, date, test number and the measured data.
If your ohmmeter has been fitted with one of these optional interfaces, please refer to Chapter 12 for
operating instructions.
27
Chapter 9
Routine Maintenance
General
This Chapter provides general maintenance information and a procedure for calibrating the
ohmmeter. The Model 4100 Series ohmmeters should be calibrated on a routine basis (every 12
months is recommended) to ensure continued accuracy.
Before performing the calibration procedure below, the ohmmeter should be allowed to warm up at
a stable temperature for at least 30 minutes with the covers in place.
Required Test Equipment
The following equipment is required to perform calibration of the product:
1)
Precision Resistors with known values to within ±0.005%, having the following values:
0.01Ω[1], 0.1Ω[1], 1.0Ω[1], 10Ω[1], 100Ω[1][2], 1KΩ[2] and 10KΩ[2]
[1] May be replaced by Valhalla Model 2575A.
[2] May be replaced by Valhalla Model 2724A.
2)
DC Voltage source with available outputs of 0 to 200mV ±2µV (Valhalla Model 2701C)
3)
Four-terminal test lead set (Valhalla Option "K" or Option "C")
4)
For 4165 & 4165-1344 only:
a voltmeter capable of measuring 20mV within ±1mV, 50mV within ±5mV, and 2V within
±10mV.
Note: If this equipment is not available, the ohmmeter may be returned to Valhalla Scientific for
calibration traceable to NIST.
Pre-Calibration Procedure
The calibration adjustments are accessed by removing the top cover of the instrument. If the
ohmmeter has been fitted with any of the optional interfaces (IEEE, RS232C, or printer), the blue
interface PCB will cover the adjustments. This installation has been designed to facilitate
calibration by using hinged stand-offs to allow access to adjustments. To enable this board to tilt
upward, remove only the black screw in the rear corner of the interface PCB. Replace this screw
when finished with calibration.
28
The locations of the adjustment potentiometers are shown on the drawing number 4100-600 at the
back of this manual. Leave the cover in place as much as possible. After each adjustment is made,
the cover should be replaced and the instrument allowed to stabilizing.
CAUTION!
Dangerous AC line voltages exist inside the instrument. Use caution when making
adjustments to avoid contact with these voltages.
4100ATC Calibration Procedure
Voltage Zero Adjustment
1) Connect the voltage standard (2701C) at 0 volts to the VOLTAGE HI and LO terminals.
2) Select the 200Ω range and the STD mode.
3) Adjust the front panel ZERO potentiometer so that the display indicates 000.00.
Voltage Full-scale Adjustment
1) Set the 2701C to output 100mV for 4100ATC. The ohmmeter uses negative voltages therefore
the VOLTAGE HI terminal should be negative with respect to the VOLTAGE LO terminal.
2) Adjust RV101 for a display indication of 100.00.
3) Remove all connections to the terminals.
Current Zero Adjustment
1) Using the 4-wire test leads, connect the input terminals of the ohmmeter to the 0.1 ohm standard
resistor and select the 200Ω range.
2) Adjust the front panel ZERO potentiometer for a display indication of 000.10 ohms ±1 digit.
.2Ω Range Adjustment
1) Connect the ohmmeter to the 0.1 ohm standard resistor and select the.2Ω range.
2) Adjust R60 for a display indication of .10000 ±2 digits.
2Ω Range Adjustment
1) Connect the ohmmeter to the 1 ohm standard resistor and select the 2Ω range.
2) Adjust R64 for a display indication of 1.0000 ±2 digits.
29
20Ω Range Adjustment
1) Connect the ohmmeter to the 10 ohm standard resistor and select the 20Ω range.
2) Adjust R66 for a display indication of 10.000 ±2 digits.
200Ω Range Adjustment
1) Connect the ohmmeter to the 100 ohm standard resistor and select the 200Ω range.
2) Adjust R70 for a display indication of 100.00 ±2 digits.
2KΩ Range Adjustment
1) Connect the ohmmeter to the 1Kohm standard resistor and select the 2KΩ range.
2) Adjust R74 for a display indication of 1.0000 ±2 digits.
20KΩ Range Adjustment
1) Connect the ohmmeter to the 10Kohm standard resistor and select the 20KΩ range.
2) Adjust R76 for a display indication of 10.000 ±2 digits.
End calibration for 4100ATC. „
30
4150ATC Calibration Procedure
Voltage Zero Adjustment
1) Connect the voltage standard (2701C) at 0 volts to the VOLTAGE HI and LO terminals.
2) Select the 200Ω range and the STD mode.
3) Adjust the front panel ZERO potentiometer so that the display indicates 000.00.
Voltage Full-scale Adjustment
1) Set the 2701C to output 10mV. The ohmmeter uses negative voltages therefore the VOLTAGE
HI terminal should be negative with respect to the VOLTAGE LO terminal.
2) Adjust RV101 for a display indication of 100.00.
3) Remove all connections to the terminals.
Current Zero Adjustment
1) Using the 4-wire test leads, connect the input terminals of the ohmmeter to the 0.1 ohm standard
resistor and select the 200Ω range.
2) Adjust the front panel ZERO potentiometer for a display indication of 000.10 ohms ±1 digit.
20mΩ Range Adjustment
1) Connect the 4150ATC to the 0.01 ohm standard resistor and select the 20mΩ range.
2) Adjust R60 for a display indication of 10.000 ±2 digits.
200mΩ Range Adjustment
1) Connect the ohmmeter to the 0.1 ohm standard resistor and select the 200mΩ.
2) Adjust R64 for a display indication of 100.00 ±2 digits.
2Ω Range Adjustment
1) Connect the ohmmeter to the 1 ohm standard resistor and select the 2Ω range.
2) Adjust R66 for a display indication of 1.0000 ±2 digits.
20Ω Range Adjustment
1) Connect the ohmmeter to the 10 ohm standard resistor and select the 20Ω range.
2) Adjust R70 for a display indication of 10.000 ±2 digits.
31
200Ω Range Adjustment
1) Connect the ohmmeter to the 100 ohm standard resistor and select the 200Ω range.
2) Adjust R74 for a display indication of 100.00 ±2 digits.
2KΩ Range Adjustment
1) Connect the ohmmeter to the 1Kohm standard resistor and select the 2KΩ range.
2) Adjust R76 for a display indication of 1.0000 ±2 digits.
End calibration for 4150ATC. „
32
4165 and 4165-1344 Calibration Procedure
Voltage Zero Adjustment
1) Connect the voltage standard (2701C) at 0 volts to the VOLTAGE HI and LO terminals.
2) Select the 200Ω range and the 2V clamp and NORMAL polarity.
3) Adjust the front panel ZERO potentiometer so that the display indicates 000.00.
Voltage Full-scale Adjustment
1) Set the 2701C to output 100mV for 4100ATC. The ohmmeter uses negative voltages therefore
the VOLTAGE HI terminal should be negative with respect to the VOLTAGE LO terminal.
2) Adjust RV101 for a display indication of 100.00.
3) Remove all connections to the terminals.
Current Zero Adjustment
1) Using the 4-wire test leads, connect the input terminals of the ohmmeter to the 0.1 ohm standard
resistor and select the 200Ω range.
2) Adjust the front panel ZERO potentiometer for a display indication of 000.10 ohms ±1 digit.
.2Ω Range Adjustment
1) Connect the ohmmeter to the 0.1 ohm standard resistor and select the.2Ω range.
2) Adjust R60 for a display indication of .10000 ±2 digits.
2Ω Range Adjustment
1) Connect the ohmmeter to the 1 ohm standard resistor and select the 2Ω range.
2) Adjust R64 for a display indication of 1.0000 ±2 digits.
20Ω Range Adjustment
1) Connect the ohmmeter to the 10 ohm standard resistor and select the 20Ω range.
2) Adjust R66 for a display indication of 10.000 ±2 digits.
200Ω Range Adjustment
1) Connect the ohmmeter to the 100 ohm standard resistor and select the 200Ω range.
2) Adjust R70 for a display indication of 100.00 ±2 digits.
33
2KΩ Range Adjustment
1) Connect the ohmmeter to the 1Kohm standard resistor and select the 2KΩ range.
2) Adjust R74 for a display indication of 1.0000 ±2 digits.
20KΩ Range Adjustment
1) Connect the ohmmeter to the 10Kohm standard resistor and select the 20KΩ range.
2) Adjust R76 for a display indication of 10.000 ±2 digits.
Voltage Clamp Adjustments
1) Set the clamp to the highest voltage setting (2V).
2) Connect the ohmmeter to the 10Kohm standard resistor and select the 2KΩ range (the display
will flash indicating an overrange condition).
3) Attach the voltmeter between the CURRENT HI and LO terminals.
4) Select the 20mV (4165-1344) or 50mV (4165) open-circuit clamp.
5) Adjust the "50mV" potentiometer on the clamp PCB for a voltmeter reading of 20mV (41651344) or 50mV (4165) ±1mV.
6) Select the 2V open circuit clamp, and the 20Ω range.
7) Adjust the "2V" potentiometer on the clamp PCB for a voltmeter reading of 2V ±10mV.
End calibration for 4165 and 4165-1344. „
34
Periodic Maintenance
The 4100 Series of ohmmeters do not require any periodic maintenance other than an occasional
cleaning of the exterior surfaces of the product and routine performance of the calibration
procedure.
Loose dirt or dust which may have collected on the exterior surface of the ohmmeter may be
removed with a soft cloth or brush. Any remaining dirt may be removed with a soft cloth dampened
in a mild soap and water solution. Do not use abrasive cleaners on the ohmmeter!
The front panel may be cleaned with a soft cloth and a "Windex" type cleaner if required. Do not
use petroleum based cleaners on the front panel.
If required, the interior of the product may be cleaned out by blowing with dry compressed air.
If the product has become heavily soiled with dirt or other contaminants it is recommended that the
unit be completely overhauled. Contact Valhalla Scientific Calibration Center for details.
Valhalla Scientific, Inc.
Calibration Center
8318 Miramar Mall
San Diego Ca, 92121
Phone: 858/457-5576
Fax: 858/457-0127
e-mail: valhalla@valhallascientific.com
35
Chapter 10
Theory of Operations
Troubleshooting
Apparent malfunctions are often the result of misinterpretation of specifications or due to an incomplete
understanding of the instrument. A thorough review of the operating instructions for this
instrument is recommended prior to any component replacement. Check to be sure that cables and
other test equipment are in good working order before attempting to troubleshoot the ohmmeter.
If the ohmmeter exhibits problems that cannot be eliminated by reviewing the operating instructions, the
following guidelines have been established to help solve the problem.
Localizing the Problem
The key to successful troubleshooting is to localize the problem as much as possible before trying to pin
the problem down to a specific component. Certain questions should be asked such as "Does the
problem occur on all ranges or on a specific range only?". The power supplies are also one of the first
things that should be checked.
As it is not possible to anticipate all failure modes of the ohmmeter, servicing personnel should become
familiar with this Chapter of the manual to gain a complete understanding of the internal workings of
this instrument.
Component Replacement
If the problem has been identified as a faulty component, the accuracy of the ohmmeter can be
maintained only if the following precautions are taken:
Use only the specified replacement component or its exact equivalent. Spare parts can be
ordered from your nearest Valhalla Scientific Service Center or from the factory directly by
referring to the Valhalla Stock Number listed in the Parts Lists section at the back of this
manual.
Use only 63/37 grade rosin core electronic grade solder with a 50W or lower maximum
power soldering iron.
When soldering, heat the terminal of the component, not the solder. Apply solder smoothly
and evenly. Do not move the component until the solder has cooled. Bad solder joints can
cause additional problems!
Static sensitive parts require special handling procedures. Always treat an unknown part as
if it were static sensitive.
36
General Circuit Descriptions
The ohmmeter may be easily thought of as consisting of two separate parts.
1) A constant-current source. This half of the ohmmeter provides a stable test current that is passed
through the load to develop a voltage across it. The value of this current for each range is indicated
on the front panel of the instrument.
2) A digital voltmeter (analog-to-digital converter). The voltmeter senses the voltage drop across the
load and translates this into the resistance reading on the display.
Use the following guidelines to determine whether the fault lies in the voltmeter or current source
circuitry of the ohmmeter:
1) If the fault occurs on one range only then the fault is probably in the current source section.
2) If the fault is display related (e.g., missing segments, non-numeric data, etc.) then the fault is
probably in the voltage measurement section.
3) If the fault occurs on all ranges, the voltmeter section may be verified as operational by applying a
precise -100mV (4100ATC) or -10mV (all others) to the VOLTAGE terminals. The display should
indicate 10000 counts no matter which resistance range is selected.
Detailed Circuit Descriptions
This series of paragraphs detail the actual operation of the above mentioned circuits, and are provide to
aid the technician in troubleshooting to component level. A basic knowledge of electronics is assumed.
The technician should refer to the schematics at the back of this manual.
Power Supplies
The ohmmeter uses several supplies to power the current source, the voltmeter (A-to-D converter) and
any optional interfaces. All of these supplies are similar in design. A secondary winding of the
transformer provides the basic AC voltage from which the DC supply will be produced. This AC
voltage is rectified using diodes, filtered using electrolytic and tantalum capacitors, and in some cases
regulated using a standard three-pin regulator.
The supplies are shown on the schematic 4100-074 sheet 1 (and sheet 2 for the optional unregulated
+5V supply). The 4150ATC and 4165 models use additional supplies for their preamplifier, shown on
sheet 2.
37
Constant-Current Source
The constant-current source provides the stable current necessary to generate the precise voltage drop
across the load. The design of the current source compensates for all series resistance (within
compliance voltage limits) to overcome the effects of test lead and contact resistances.
Reference Generator
The reference generator is shown on the drawing 4100-074 sheet 2. The precise voltages required by
the A-to-D converter and the current source are provided by the zener reference IC106. IC106 and its
associated components produce a nominal 6.95V. This voltage is attenuated by the resistors R111
through R115 and RV101 to provide the required 100mVDC reference voltage to the A-to-D converter.
RV102 is used to adjust the reference voltage to the current source. In the ATC mode (4100ATC and
4150ATC only) the resistor formed by R114 and R119 is replaced by the temperature compensator to
provide the required corrections for temperature variations.
Reference Inverter Stage
The reference inverter is shown on drawing 4100-074 sheet 1. IC11 and its associated components
form an amplifier stage having a gain of -.144. This stage is used to convert the +6.95 VDC reference
voltage to the negative 1 volt reference required by the current source.
Differential Amplifier
The differential amplifier is shown on drawing number 4100-074 sheet 1. IC12 and its associated
components form a unity gain differential amplifier. The output of the Reference Inverter stage (Vref)
and the output of the Output Amplifier (Vout) form the inputs to this amplifier. The output voltage from
this amplifier is thus given by (Vout-Vref).
Output Amplifier
The output amplifier is shown of drawing number 4100-074 sheet 1. IC13, Q18, Q20 and the range
resistors R60 through R76 combine to form the output amplifier of the current source. The range
resistors determine the value of the output current. The voltage drop across these resistors (Vout) is used
as an input to the Differential Amplifier to provide error correction and to compensate for varying loads.
Output Voltage Clamp
This additional PCB is only fitted in Models 4165 and 4165-1344 and is shown on schematic 4165-070.
The operation of this circuit is as follows:
1)
IC2, IC3, R3 and R4 form a reference circuit providing -2.5V.
2)
R5 through R9 provide divided voltages from this -2.5V reference with outputs at -2.0V and
-50mV (for 4165) or -2.0V and -20mV (for 4165-1344). The selected output of this divider is
connected to one input of the comparator formed by IC1, the other input of which is the voltage
38
on the CURRENT HI terminal. The output of this comparator is used to turn off the output
stage of the current source when the selected open-circuit voltage limit is exceeded.
Analog-to-Digital Converter
The A-to-D converter is basically a high-impedance voltmeter that is used to measure the voltage drop
across the unknown load. This voltage is converted to digital form to represent the resistance value of
the load. The A-to-D converter circuitry is shown in the drawing number 4100-074 sheet 2.
A-to-D Converter
The A-to-D conversion is performed by the IC pair IC103-IC104 and their associated components.
IC103 is the digital portion of the converter and IC104 is the analog portion. The required reference
voltage is generated by IC106. IC102 is used to demultiplex the digital outputs of the converter and to
condition it for use by the display LEDs DS1-DS5.
Preamplifier
Ohmmeter Models 4150ATC, 4165, and 4165-1344 use a preamplifier stage consisting of IC101 and its
associated components to boost the voltage input to the A-to-D converter up to the required levels. The
preamplifier is a chopper stabilized x10 amplifier. This stage raises the 20mV full-scale test voltage of
these instruments up to the 200mV full-scale voltage required by the A-to-D converter.
Optional Interfaces
The BCD interface takes multiplexed digital information from the voltmeter and converts it to a parallel
BCD 8-4-2-1 code that is easier to work with. This circuitry is shown on drawing number 2053-076 at
the back of this manual.
The other interfaces (IEEE, RS232C, and printer) are made possible by Valhalla's 1020 Smart Interface
Board. The 1020 takes range information from contacts of the range switches and digital data from the
voltmeter. It decodes this information and makes it available at any of four ports. A complete
description of the operation of this interface is beyond the scope of this manual. Please contact Valhalla
Scientific if problems are encountered.
39
Chapter 11
Special Procedures
Noisy Readings
In general, noisy readings are caused by poor connections either to the input terminals or to the test
load. If noisy readings are encountered, check these connections first.
Inductive Loads
The measurement of highly inductive loads (such as large transformers) may also yield noisy readings.
This is due to the very high impedance to line voltage exhibited by the load causing an excessive
amount of noise pick-up. This effect can be significantly reduced by using fully shielded cables. It may
also be helpful (and will cause the settling time to be reduced) if the unused windings on transformers
being tested can be short- circuited during the measurement. This will significantly reduce the
inductance of the winding under test and will also prevent these windings from producing dangerous
voltages during connection and disconnection of the ohmmeter.
Drifting Displays
All Valhalla ohmmeters use a high impedance voltmeter as part of the resistance measurement process.
This voltmeter is a highly accurate and stable 4½ digit analog-to- digital converter (A to D). Unless it is
receiving a definite input signal, the output display of this A to D is ambiguous. The display may
indicate a randomly wandering number, or it may flash indicating an overrange condition. This
unpredictable display may make it seem to appear that the instrument is experiencing some sort of
malfunction. It is, in fact, just a characteristic of the voltmeter circuit and should not be mistaken for a
fault in the instrument.
The display indications should be ignored unless there is a definite measurement being taken. If this
wandering display is not acceptable, the ohmmeter can be made to indicate an overrange condition
whenever the terminals are opened either by using a 4-wire Kelvin type lead set (Valhalla Option "K")
or by shorting the VHI and IHI terminals together.
The display should indicate a stable reading when the test leads are securely attached to the device
under test. If the display appears to be erroneous when connected to a load, recheck the test leads for
integrity and cleanliness. If all external items appear to be functioning properly, the problem may be
the ohmmeter. In this case, please call the factory.
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Connecting to Inductive Loads
The measurement of inductive loads (transformers, ballasts, coils, magnets, chokes, etc.) requires that
special precautions be taken in order to ensure safety and maximize performance. Other than the noise
considerations mentioned in the last section of this chapter, the following items should be noted:
1) Prior to connecting the unit to the load, select the highest (rightmost RANGE switch) range
possible.
2) Settling times for inductive loads are greater than those of resistive loads. A stable reading
generally indicates that the inductor has been fully charged and an accurate measurement is being
taken.
3) Prior to disconnecting the load, select the highest resistance range and wait for the display to show a
stable reading indicating that the inductor has been discharged. This reduces the possibility of
drawing an arc which may cause injury to the operator and/or damage the instrument.
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