IET Labs HARS-X Troubleshooting guide

♦PRECISION INSTRUMENTS FOR TEST AND MEASUREMENT ♦
Email: inf[email protected]
TEL: [phone] • FAX: [phone]
www.ietlabs.com
IET LABS, INC.
HARS-X and X2
High Accuracy Resistance
Substituter
User and Service Manual
Copyright © 2018 IET Labs, Inc.
Visit www.ietlabs.com for manual revision updates
HARS-X im/October 2018

Email: inf[email protected]
TEL: [phone] • FAX: [phone]
www.ietlabs.com
IET LABS, INC.

i
HARS-X
Table of Contents
WARRANTY
We warrant that this product is free from defects in material and workmanship and, when properly used,
will perform in accordance with applicable IET specifications. If within one year after original shipment,
it is found not to meet this standard, it will be repaired or, at the option of IET, replaced at no charge when
returned to IET. Changes in this product not approved by IET or application of voltages or currents greater
than those allowed by the specifications shall void this warranty. IET shall not be liable for any indirect,
special, or consequential damages, even if notice has been given to the possibility of such damages.
THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, IN-
CLUDING BUT NOT LIMITED TO, ANY IMPLIED WARRANTY OF MERCHANTABILITY OR
FITNESS FOR ANY PARTICULAR PURPOSE.

ii
HARS-X and X2
WARNING
OBSERVE ALL SAFETY RULES
WHEN WORKING WITH HIGH VOLTAGES OR LINE VOLTAGES.
Dangerous voltages may be present inside this instrument. Do not open the case
Refer servicing to qualified personnel
HIGH VOLTAGES MAY BE PRESENT AT THE TERMINALS OF THIS INSTRUMENT
WHENEVER HAZARDOUS VOLTAGES (> 45 V) ARE USED, TAKE ALL MEASURES TO
AVOID ACCIDENTAL CONTACT WITH ANY LIVE COMPONENTS.
USE MAXIMUM INSULATION AND MINIMIZE THE USE OF BARE
CONDUCTORS WHEN USING THIS INSTRUMENT.
Use extreme caution when working with bare conductors or bus bars.
WHEN WORKING WITH HIGH VOLTAGES, POST WARNING SIGNS AND
KEEP UNREQUIRED PERSONNEL SAFELY AWAY.
CAUTION
DO NOT APPLY ANY VOLTAGES OR CURRENTS TO THE TERMINALS OF THIS
INSTRUMENT IN EXCESS OF THE MAXIMUM LIMITS INDICATED ON
THE FRONT PANEL OR THE OPERATING GUIDE LABEL.

iii
HARS-X
Table of Contents
Contents
Chapter 1: Introduction
1.1 Introduction..................................................................................1
Chapter 2: Specifications
Specifications .....................................................................................2
Ordering Information.........................................................................3
Chapter 3: Operation
3.1 Initial Inspection and Setup .........................................................5
3.2 Connection ...................................................................................5
3.2.1 General Considerations......................................................5
3.2.3 Four-Wire Kelvin Lead Connections.................................5
3.2.4 Thermal emf Considerations..............................................6
3.3 Dial Setting ..................................................................................6
3.4 Environmental Conditions ..........................................................6
Chapter 4: Maintenance
4.1 Verification of Performance .........................................................7
4.1.1 Calibration Interval............................................................7
4.1.2 General Considerations......................................................7
4.1.3 Calibration Procedure ........................................................7
4.2 Schematic.....................................................................................8
4.3 Replaceable Parts List..................................................................9

iv
HARS-X
Table of Contents
Figures and Tables
Figure 1-1. HARS-X Series High Accuracy Resistance Substituter..........1
Figure 1-2. Single-Decade HARS Unit .....................................................1
Figure 2-1. Typical Operating Guide Affixed to Unit ...............................4
Figure 3-1 Optimal 4-Wire Kelvin Lead Connection ................................6
Figure 4-1. HARS Series Schematic Diagram ..........................................8
Table 4-2: Replacement List......................................................................9
Figure 4-2. HARS-X Replaceable Parts....................................................9

1
HARS-X and X2
1Introduction
Chapter 1
INTRODUCTION
1.1 Introduction
The High-Accuracy Resistance Substituter (HARS)
series of resistance decade substituters is a family of
instruments providing a very broad choice of high-
performance resistance sources. Any number of
decades from one to eleven is available in a choice
of accuracies. See Figures 1-1 and 1-2.
The HARS substituter is a precision resistance source
with excellent characteristics of stability, temperature
coefficient, power coefficient, and frequency re-
sponse.
The HARS Series employs very-low-resistance
switches with silver-alloy contacts. A special design
keeps zero resistance to less than 1 mΩper decade.
Self cleaning keeps the silver contacts from becoming
tarnished when unused, or when only low currents
are passed through them. This is most often the case
when only minute test currents are drawn by digital
multimeters or other test instruments. Contact resis-
tance is stable and remains low and repeatable.
High-quality gold-plated tellurium-copper binding
posts serve to minimize the thermal emf effects which
would artificially reflect a change in dc resistance
measurements. All other conductors within the in-
strument, as well as the solder employed, contain no
metals or junctions that could contribute to thermal
emf problems.
The standard models offer a choice of one through
eleven decades. The panels are clearly labeled show-
ing the step size and maximum voltage and current
limitations for each decade.
With a resolution as low as 1 mΩand a maximum
available resistance of over 111 MΩ, the HARS se-
ries may be used for exacting precision measurement
applications requiring high accuracy, good stability,
and low zero-resistance. They can be used as compo-
nents of dc and ac bridges, for calibration, as transfer
standards, and as RTD simulators.
Single-decade units may be panel-mounted and
combined with additional units to form potentiometer
circuits or other configurations.
The larger units may be rack-mounted to serve as
components in measurement and control systems.
Figure 1-1. HARS Series High Accuracy Resistance
Substituter
Figure 1-2. Single-Decade HARS Unit.

2
HARS-X and X2
2 Specifications
Chapter 2
SPECIFICATIONS
For convenience to the user, the pertinent specifications are given in an OPERATING GUIDE affixed to the
case of the instrument. Figure 2.1 shows a typical example.
Accuracy:
≤1 MΩsteps: ±(0.01% + 2 m)
10 MΩsteps: ±0.03%
After subtraction of zero-resistance, at 23°C;
traceable to SI
Zero resistance:
≤1 MΩsteps: 1 mper decade
10 MΩsteps: 3 m
Switch type:
Multiple solid silver alloy contacts, continuous
rotation
Switch capacitance:
<1 pF between contacts
SPECIFICATIONS
Operation:
If switches have not been operated for an extended
period of time, they should be rotated a few times
in both directions to restore contact resistance to
specifications.
Environmental conditions:
Operating conditions: +10 to +40°C, <80% RH
Storage conditions: -20 to +65°C
Terminals:
3 Low-thermal-emf tellurium-copper binding
posts with standard 3/4 inch spacing, plus shield
terminal; connections on the rear of the instrument
are available (RO option). -K Option: Kelvin
connection is available as an option with 5 binding
posts
Resistance
per step
Total
decade
resistance
Stability
(±ppm/yr)
Long-term
stability
(±ppm/3 yrs)
Temperature
coefficient
(±ppm/°C)
Resistor type
HARS-X HARS-X2
Max
current
Max
voltage
(per step)
Max power
(per step)
Max
current
Max
voltage
(per step)
Max power
(per step)
1 mΩ10 mΩ50 75 50
Resistance
wire
8.0 A 5 mV 0.04 W 9.0 A 9 mV 0.08 W
10 mΩ100 mΩ50 75 20 4.0 A 40 mV 0.16 W 6.3 A 63 mV 0.4 W
100 mΩ1 Ω50 75 20 1.6 A 0.16 V 0.25 W 2.2 A 0.3 V 0.5 W
1 Ω10 Ω20 25 20
Wirewound,
non-inductive
0.8 A 0.8 V 0.6 W 1.1 A 1.1 V 1.2 W
10 Ω100 Ω20 25 15 0.25 A 2.5 V 0.6 W 0.35 A 3.5 V 1.2 W
100 Ω1 kΩ20 25 5 80 mA 8 V 0.6 W 110 mA 11 V 1.2 W
1 kΩ10 kΩ20 25 5 23 mA 23 V 0.5 W 35 mA 35 V 1.2 W
10 kΩ100 kΩ20 25 5 7 mA 70 V 0.5 W 11 mA 110 V 1.2 W
100 kΩ1 MΩ20 25 5 2.3 mA* 230 V* 0.5 W* 3 mA* 500 V* 1 W*
1 MΩ10 MΩ20 25 5 0.7 mA* 700 V* 0.5 W* 1 mA* 1000 V* 1 W*
10 MΩ100 MΩ50 100 10 Metal oxide film 0.1 mA* 1000 V* 0.1 W* 0.1 mA* 1000 V* 0.1 W*
*Subject to maximum of 2000 V to case

3
HARS-X and X2
3Specifications
Mechanical:
Model Dimensions Weight
1 decade
7.7 cm W x 7.7 cm H x 8.4 cm D
(3" x 3" x 3.3") 0.45 kg (1 lb)
2-3 decade
31 cm W x 8.9 cm H x 10.2 cm D
(12.2" x 3.5" x 4") 1.7 kg (3.8 lb)
4-5 decade
37.5 cm W x 8.9 cm H x 10.2 cm D
(14.75" x 3.5" x 4") 2.0 kg (4.3 lb)
6 decades
43.9 cm W x 8.9 cm H x 10.2 cm D
(17.3" x 3.5" x 4") 2.2 kg (4.8 lb)
7 decades
2.4 kg (5.3 lb)
8 decades
48.3 cm W x 17.8 cm H x 17.8 cm D
(19" x 7" x 7")
3.4 kg (7.5 lb)
9 decades
3.5 kg (7.7 lb)
10 decades
3.6 kg (7.9 lb)
11 decades
3.7 kg (8.1 lb)
ORDERING INFORMATION
OPTIONS
-RM Rack mountable case for standard 19” rack
-K Kelvin type 4-terminal binding posts
-RO Rear output binding posts
Model* Total resistance
(Ω)
No of
Dials
Resolution
(Ω)
HARS-X-1-0.001 0.01 1 0.001
HARS-X-1-0.01 0.1 1 0.01
HARS-X-1-0.1 1 1 0.1
HARS-X-1-1 10 1 1
HARS-X-1-10 100 1 10
HARS-X-1-100 1 k 1 100
HARS-X-1-1K 10 k 1 1 k
HARS-X-1-10K 100 k 1 10 k
HARS-X-1-100K 1 M 1 100 k
HARS-X-1-1M 10 M 1 1 M
HARS-X-1-10M 100 M 1 10 M
HARS-X-2-0.001 0.11 2 0.001
HARS-X-2-0.01 1.1 2 0.01
HARS-X-2-0.1 11 2 0.1
HARS-X-2-1 110 2 1
HARS-X-2-10 1.1 k 2 10
HARS-X-2-100 11 k 2 100
HARS-X-2-1K 110 k 2 1 k
HARS-X-2-10K 1.1 M 2 10 k
HARS-X-2-100K 11 M 2 100 k
HARS-X-2-1M 110 M 2 1 M
HARS-X-3-0.001 1.11 3 0.001
HARS-X-3-0.01 11.1 3 0.01
HARS-X-3-0.1 111 3 0.1
HARS-X-3-1 1.11 k 3 1
HARS-X-3-10 11.1 k 3 10
HARS-X-3-100 111 k 3 100
HARS-X-3-1K 1.11 M 3 1 k
HARS-X-3-10K 11.1 M 3 10 k
HARS-X-3-100K 111 M 3 100 k
Model* Total resistance
(Ω)
No of
Dials
Resolution
(Ω)
HARS-X-4-0.001 11.11 4 0.001
HARS-X-4-0.01 111.1 4 0.01
HARS-X-4-0.1 1.111 k 4 0.1
HARS-X-4-1 11.11 k 4 1
HARS-X-4-10 111.1 k 4 10
HARS-X-4-100 1.111 M 4 100
HARS-X-4-1K 11.11 M 4 1 k
HARS-X-4-10K 111.1 M 4 10 k
HARS-X-5-0.001 111.11 5 0.001
HARS-X-5-0.01 1.1111 k 5 0.01
HARS-X-5-0.1 11.111 k 5 0.1
HARS-X-5-1 111.11 k 5 1
HARS-X-5-10 1.1111 M 5 10
HARS-X-5-100 11.111 M 5 100
HARS-X-5-1K 111.11 M 5 1 k
HARS-X-6-0.001 1.111 11 k 6 0.001
HARS-X-6-0.01 11.1111 k 6 0.01
HARS-X-6-0.1 111.111 k 6 0.1
HARS-X-6-1 1.111 11 M 6 1
HARS-X-6-10 11.1111 M 6 10
HARS-X-6-100 111.111 M 6 100
HARS-X-7-0.001 11.111 11 k 7 0.001
HARS-X-7-0.01 111.1111 k 7 0.01
HARS-X-7-0.1 1.111 111 M 7 0.1
HARS-X-7-1 11.111 11 M 7 1
HARS-X-7-10 111.1111 M 7 10
HARS-X-8-0.001 111.111 11 k 8 0.001
HARS-X-8-0.01 1.111 111 1 M 8 0.01
HARS-X-8-0.1 11.111 111 M 8 0.1
HARS-X-8-1 111.111 11 M 8 1
HARS-X-9-0.001 1.111 111 11 M 9 0.001
HARS-X-9-0.01 11.111 111 1 M 9 0.01
HARS-X-9-0.1 111.111 111 M 9 0.1
HARS-X-10-0.001 11.111 111 11 M 10 0.001
HARS-X-10-0.01 111.111 111 1 M 10 0.01
HARS-X-11-0.001 111.111 111 11 M 11 0.001
* Use “X2” for higher power model

4
HARS-X and X2
4 Specifications
Figure 2-1. Typical Operating Guide Affixed to Unit
1 mȍ10 mȍ8 A 5 mV 0.4 50 75 50 10 mȍ100 mȍ4 A 40 mV 0.16 50 75 20
100 mȍ1 ȍ1.6 A 0.16 V 0.25 50 75 20 1 ȍ10 ȍ.8 A 0.8 V 0.6 20 25 20 10 ȍ100 ȍ.25 A 2.5 V 0.6 20 25 15 100 ȍ1 kȍ80 mA 8 V 0.6 20 25 5 1 kȍ10 kȍ23 mA 23 V 0.5 20 25 5 10 kȍ100 kȍ7 mA 70 V 0.5 20 25 5
100 kȍ1 Mȍ2.3 mA* 230 V* 0.5* 20 25 5 1 Mȍ10 Mȍ0.7 mA* 700 V* 0.5* 20 25 10
10 Mȍ100 Mȍ0.1 mA* 1000 V* 0.1* 50 100 10 Metal oxide film
*Subject to maximum of 2000 V to case
Total
deacde
resistance
Max
current
Resistance
per step
Power
per/step
(W)
Max
voltage
Resistance
Wire
Wirewound,
non-inductive
Stability
(±ppm/yr)
Long-term
stability
(±ppm/3 yrs)
Temp.
coeffieient
(±ppm/°C)
Resistor
type
HARSXCLBL/p1/HARS-X gen'l/55%/03-02-2010
Observe all safety rules when working with high voltages or line voltages. Connect the (G) terminal to earth ground in order to maintain the case at a safe voltage. Whenever hazardous voltages (>45 V) are used, take all measures to avoid accidental contact with any live components: a) Use maximum insulation and minimize the use of bare conductors. b) Remove power when adjusting switches. c) Post warning signs and keep personnel safely away.
IET LABS, INC.• 534 Main Street, Westbury, NY 11590 • [phone] • [phone] • Fax: [phone]
CAGE CODE: 62015 www.ietlabs.com
Accuracy:
≤≤ ≤≤
≤1 MΩΩ
ΩΩ
Ω steps: ±(0.01% + 2 mΩ)
10 MΩΩ
ΩΩ
Ω steps: ±0.03%
After subtraction of zero resistance, at 23°C; traceable to SI
Zero Resistance:
≤≤ ≤≤
≤1 MΩΩ
ΩΩ
Ωsteps: ≤1 mΩper decade
10 MΩΩ
ΩΩ
Ω steps: approx. 3 mΩ
Switch Type:
Multiple solid silver alloy contacts, continuous rotation
Switch Capacitance:
<1 pF between contacts
Operating Conditions:
+10 to + 40°C, <80% RH
Operation:
If switches have not been operated for an extended period, they should be rotated a few times to restore contact resistance to specifications.
CONSULT INSTRUCTION MANUAL FOR PROPER INSTRUMENT OPERATION
HARS-X SERIES HIGH ACCURACY DECADE RESISTANCE SUBSTITUTER
WARNING
MODEL: HARS-X-6-0.01 SN: C3-09404334

5
HARS-X and X2
5Operation
Chapter 3
OPERATION
3.2.2 Electrical Considerations
In order to make proper use of the full performance
capabilities of the HARS unit, especially if low resis-
tance or low-resistance increments are important, take
care when connecting to the terminals of the decade
box. In particular, in order to keep contact resistance
to a minimum, take the most substantial and secure
connection to the binding posts. They accept banana
plugs, telephone tips, spade lugs, alligator clips, and
bare wire. The largest or heaviest mating connection
should be made, and, where applicable, the binding
posts should be securely tightened.
These considerations may be relaxed whenever single
milliohms are considered insignificant for the task
being performed.
3.2.3 Four-Wire Kelvin Lead Connections
Whenever possible, 4-wire Kelvin leads, the ideal
connection, should be employed. Such a connection
minimizes the effects of contact resistance and ap-
proaches ideal performance.
If the four terminals are available as clamps similar to
alligator clips, they may be connected to the necks of
the binding posts. If the four terminals are available
separately, the optimal connection is shown in Figure
3.1, where the current leads are introduced into the
top of the binding posts, and the voltage leads at the
necks.
3.1 Initial Inspection and Setup
This instrument was carefully inspected before ship-
ment. It should be in proper electrical and mechanical
order upon receipt.
An OPERATING GUIDE is attached to the case of
the instrument to provide ready reference to speci-
fications.
3.2 Connection
3.2.1 General Considerations
The HARS Series Decade unit provides three ter-
minals labeled H(high), L(low), and G (ground).
The H and L terminals are connected to the ends of
the resistance being set; the G terminal is connected
to the case. The G terminal may be used as a guard
or shield terminal. It may also be connected (using a
shorting link) to the Lterminal to allow two-terminal
as opposed to three-terminal measurements.
In order to make the most stable measurements, de-
termine which is the more sensitive of the two user
leads, i.e. the one going into a higher impedance.
This lead should be connected to the more protected
one of the two HARS terminals. That would either
be the HARS terminal that is shorted to the case, or
the LOW HARS terminal whenever neither is con-
nected to the case.
If switches have not been operated for an extended
period, they should be rotated a few times to restore
contact resistance to specifications.

6
HARS-X and X2
6 Operation
3.2.4 Thermal emf Considerations
The highest-quality low-emf components are used in
the HARS Series. There nevertheless may be some
minute thermal emf generated at the test leads where
they contact the gold-plated binding posts.
This emf will not reflect itself if an ac measurement
instrument is employed. It will also be eliminated if
a meter with a “True Ohm” capability is used. Oth-
erwise it may represent itself as a false component of
the dc resistance measurement. It is also possible to
take a second measurement with the leads reversed
and average the reading.
3.3 Dial Setting
Whenever the dials are used in positions 0-9, the
resulting resistance is read directly. Both the decimal
point and the steps are clearly marked on the panel.
For additional flexibility and range, each decade
provides a “10” position setting. This “10” position
on any one decade equals the “1” position on the next
higher decade. It adds about 11% to the nominal total
decade resistance.
To determine the resistance obtained when one or
more “10” settings are used, simply add “1” to the
next higher decade. For example, a setting of 3-6-
10-0-10 becomes:
3 3 0 0 0 0
6 6 0 0 0
10 1 0 0 0
0 0 0
10 1 0
____________________________
TOT 3 7 0 1 0
and a setting of 10-10-10-l0-10.10 Ωbecomes:
10 1 0 0 0 0 0.0
10 1 0 0 0 0.0
10 1 0 0 0.0
10 1 0 0.0
10 1 0.0
.10 1.0
____________________________
TOT 1 1 1 1 1 1.0
3.4 Environmental Conditions
For optimal accuracy, the decade box should be used
in an environment of 23oC. It should be allowed to
stabilize at that temperature after any significant
temperature variation.
Humidity should be maintained at laboratory condi-
tions. This is especially important if high resistances
are involved.
Figure 3-1 Optimal 4-Wire Kelvin Lead Connection

7
HARS-X and X2
7Operation
Chapter 4
MAINTENANCE
4.1 Verification of Performance
4.1.1 Calibration Interval
The HARS Series instruments should be verified for
performance at a calibration interval of twelve (12)
months. This procedure may be carried out by the user
if a calibration capability is available, by IET Labs,
or by a certified calibration laboratory.
If the user should choose to perform this procedure,
then the considerations below should be observed.
4.1.2 General Considerations
It is important, whenever testing the HARS Series
Decade Units, to be very aware of the capabili-
ties and limitations of the test instruments used. A
resistance bridge may be employed, and there are
direct-reading resistance meters or digital multimeters
available that can verify the accuracy of these units,
especially when used in conjunction with standards
that can serve to confirm or improve the accuracy of
the testing instrument
Such test instruments must be significantly more accu-
rate than ±(l00ppm+2 mΩ) for all applicable ranges,
allowing for a band of uncertainty of the instrument
itself. A number of commercial bridges and meters
exist that can perform this task; consult IET Labs.
It is important to allow both the testing instrument
and the HARS Substituter to stabilize for a number of
hours at the nominal operating temperature of 23OC,
and at nominal laboratory conditions of humidity.
There should be no temperature gradients across the
unit under test.
Substantial Kelvin-type 4-wire test terminals should
be used to obtain accurate low-resistance read-
ings. It is convenient, once the zero resistance has
been determined, to subtract it from the remaining
measurements. This can be automatically done in
many instruments which have an offset subtraction
capability.
4.1.3 Calibration Procedure
1. Confirm the zero resistance of the unit.
2. Determine the allowable upper and lower limits
for each resistance setting of each decade based
on the specified accuracy.
For the HARS series, these limits for any
resistance “R” are [R±(0.0001 R + 2
mΩ)].
3. Confirm that the resistances fall within these
limits after subtraction of the zero resistance.
4. If any resistances fall outside these limits, the
associated switch assembly may require service
or replacement.

8
HARS-X and X2
8 Maintenance
Figure 4-1. HARS Series Schematic Diagram
4.2 Schematic
Refer to Figure 4-1 for a schematic of the HARS
decade unit.

9
HARS-X and X2
9Maintenance
4.3 Replaceable Parts List
1
2
3
Table 4.2: Replacement List
Model Ref IET Pt No Description
1 BP-1000-RD Binding Post, Red
2 BP-1000-BK Binding Post, Black
3 BP-1000-GN Binding Post, Green
4 HARS-X-4300-KNB Knob Assembly
Not Shown HARS-X-3100 Foot
Not Shown HARS-4100-X-.001 1 m/step Decade Switch Assembly
Not Shown HARS-4100-X-0.01 10 m/step Decade Switch Assembly
Not Shown HARS-4100-X-0.1 100 m/step Decade Switch Assembly
Not Shown HARS-4100-X-1 1 /step Decade Switch Assembly
Not Shown HARS-4100-X-10 10 /step Decade Switch Assembly
Not Shown HARS-4100-X-100 100 /step Decade Switch Assembly
Not Shown HARS-4100-X-1k 1 k/step Decade Switch Assembly
Not Shown HARS-4100-X-10k 10 k/step Decade Switch Assembly
Not Shown HARS-4100-X-100k 100 k/step Decade Switch Assembly
Not Shown HARS-4100-X-1M 1 M/step Decade Switch Assembly
Not Shown HARS-4100-X-10M 10 M/step Decade Switch Assembly
* Use “X2” for higher power model, for example HARS-4100-X2-100 for 100 /step Decade X2 Switch Assembly
4
Figure 4-2. HARS Replaceable Parts