IET Labs SRac Series Troubleshooting guide

♦PRECISION INSTRUMENTS FOR TEST AND MEASUREMENT ♦
Email: inf[email protected]
TEL: [phone] • FAX: [phone]
www.ietlabs.com
IET LABS, INC.
SRac Series
Resistance Standard
User and Service Manual
Copyright © 2019 IET Labs, Inc.
Visit www.ietlabs.com for manual revision updates
SRac im/January 2019

♦PRECISION INSTRUMENTS FOR TEST AND MEASUREMENT ♦
Email: inf[email protected]
TEL: [phone] • FAX: [phone]
www.ietlabs.com
IET LABS, INC.

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,
INCLUDING BUT NOT LIMITED TO, ANY IMPLIED WARRANTY OF MERCHANTABILITY OR
FITNESS FOR ANY PARTICULAR PURPOSE.
i

ii
Safety Symbols
General definitions of safety symbols used on the instrument or in manuals are listed below.
Caution symbol: the product is marked with this symbol when it is necessary for the user to
refer to the instruction manual.
Hazardous voltage symbol: the product is marked with this symbol when high voltage maybe
present on the product and an electrical shock hazard can exist.
Indicates the grounding protect terminal, which is used to prevent electric shock from the
leakage on chassis. The ground terminal must connect to earth before using the product
Direct current.
Alternating current.
Frame or chassis terminal. A connection to the frame (chassis) of the equipment which
normally includes all exposed metal structures.
On supply.
Off supply.
Hot surface. Avoid contact. Surfaces are hot and may cause personal injury if touched.
Disposal
Waste Electrical and Electronic Equipment (WEEE) Directive 2002/96/EC
This product complies with the WEEE Directive (2002/96/EC) marking requirements.
The affixed label indicates that you must not discard this electrical/ electronic product in domestic
household waste.
Product Category: With reference to the equipment types in the WEEE directive Annex 1, this product
is classified as a “Monitoring and Control instrumentation” product.
Do not dispose of electrical appliances as unsorted municipal waste, use separate collection facilities.
Contact your local government for information regarding the collection systems available. If electrical
appliances are disposed of in landfills or dumps, hazardous substances can leak into the groundwater
and get into the food chain, damaging your health and well-being.
When replacing old appliances with new one, the retailer is legally obligated to take back your old ap-
pliances for disposal.
Proposition 65 Warning for California Residents
WARNING: Cancer and Reproductive Harm - www.P65Warnings.ca.gov.
This product may contain chemicals known to the State of California to cause cancer, birth defects, or
other reproductive harm

iii
SAFETY PRECAUTIONS
The following general safety precautions must be observed during all phases of operation, service,
and repair of this instrument. Failure to comply with these precautions or with specific WARNINGS
elsewhere in this manual may impair the protection provided by the equipment. Such noncompliance
would also violate safety standards of design, manufacture, and intended use of the instrument.
IET Labs assumes no liability for the customer’s failure to comply with these precautions.
This is an indoor use product.
DANGEROUS PROCEDURE WARNINGS
Comply with all WARNINGS - Procedures throughout in this manual and instructions on the
instrument prevent you from potential hazard. These instructions contained in the warnings must
be followed.
BEFORE APPLYING POWER
Verify that all safety precautions are taken. Make all connections to the instrument before applying
power. Note the instrument’s external markings described under “Safety Symbols”.
• DO NOT Operate in an Explosive Atmosphere
• Do not operate the instrument in the presence of inflammable gasses or fumes
• Operation of any electrical instrument in such an environment clearly constitutes a safety
hazard
• Use Caution around live circuits and whenever hazardous voltages > 45 V are present
• Operators must not remove instrument covers
• Component replacement and internal adjustments must be made by qualified maintenance
personnel only
• DO NOT substitute parts or modify the instrument
• When working with high voltages; post warning signs, train personnel and keep unauthorized
personnel away.
To avoid the danger of introducing additional hazards, do not install substitute parts or perform
unauthorized modifications to the instrument.
Return the instrument to an IET Labs for service and repair to ensure that safety features are maintained
in operational condition.

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 PRESENTAT 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.
iv

Contents
Chapter 1 Introduction .................................................................................1
1.1 Introduction...............................................................................................1
Chapter 2 Specifications ..............................................................................2
Specifications ...................................................................................................2
Label .................................................................................................................4
Chapter 3 Operation ....................................................................................6
3.1 Initial Inspection and Setup ...................................................................... 6
3.2 Connections.............................................................................................. 6
3.2.1 Connections for values ≤190 kΩ.....................................................6
3.2.2 Connections for values > 190 kΩand <100 MΩ.............................6
3.2.3 Connections for values ≥100 MΩ....................................................7
3.3 Thermal emf Considerations.....................................................................7
3.4 Environmental Conditions......................................................................... 7
3.4.1 Operating Temperature ................................................................... 7
3.4.2 Storage Temperature....................................................................... 7
3.5 Shipping and Handling ............................................................................. 7
Chapter 4 Maintenance................................................................................8
4.1 Maintainability and Reliability ...................................................................8
4.2 Preventive Maintenance ........................................................................... 8
4.3 Calibration ................................................................................................8
4.3.1 Calibration Interval ..........................................................................8
4.3.2 General Considerations ..................................................................8
4.3.3 Required Equipment .......................................................................9
4.3.4 Calibration Procedure .....................................................................9
4.4 Replaceable Parts List.............................................................................. 9
v

Figures and Tables
Figure 1-1: SRac Series Resistance Standard............................................1
Table 2-1: SRac Specifications....................................................................2
Figure 2-1: Sample label affixed to unit.......................................................3
Figure 3-1: Connections for values..............................................................6
Table 4-1: Replaceable Parts List................................................................9
Figure 4-1: SRac Replaceable Parts..........................................................9
vi

1
SRX/SRC Series
1Introduction
Chapter 1
INTRODUCTION
1.1 Introduction
The SRac Series (Figure 1.1) are stable, laboratory
or portable resistance standards. Their ruggedness
and small size plus their low temperature coefficient
makes the SRac Series ideal for any applications
outside of laboratory environment within the tem-
perature range of 18°C to 28°C. Because of the
low temperature coefficient, they require no oil-or-
temperature bath.
The SRac series units are available in values ranging
from 1 mΩto 10 MΩ, with custom values available,
to satisfy any requirement. The SRac series feature
excellent stability and low temperature coefficient.
To reduce errors caused by temperature changes, the
SRac units are built with a low temperature coef-
ficient at 23°C.
The 5-way binding posts are constructed of low-
thermal emf material.
Figure 1-1: SRac Series Resistance Standard

2
SRX/SRC Series
2 Specifications
Chapter 2
SPECIFICATIONS
For convenience to the user, the pertinent specifications are given in an OPERATION GUIDE, shown in Figures 1-1.
Model
SRac-
Nominal
(Ω)
Initial
adjustment to
nominal
(ppm)
Stability
1 year
(ppm)
Tempco
(ppm/°C) Resistor type
Calibration
uncertainty
dc
(Typical)
(ppm)
dc to ac
change at
1 kHz
(Typical)
(ppm)
Max.
power
(W)
Max.
voltage
(V)
Max.
current
(A) Terminals
0.001 0.001 200 50 20
Manganin
strip
200
25
0.2 0.015 14
4 bp's + gnd
0.01 0.01 200 50 20
Manganin wire 100 0.6 0.15 4.5
0.1 0.1
100 20
1
Foil
60 0.3 0.17 1.7
11110 0.3 0.54 0.54
10 10 2 5
0.6
2.45 0.245
100 100 1 5 24.5 0.024
1K 1 k 1 5 77.5 7.7 mA
10K 10 k 1 2 245 2.5 mA
100K 100 k 1 2 300 2 mA
1M 1 M 5 Wirewound 5 250 0.5 700 0.7 mA
10M 10 M 15 Film 10 2500 0.1 1000 0.1 mA
Foil resistors have a power coefficient of resistance (PCR) of ±5ppm at rated power due to internal heating
Foil resistors have a voltage coefficient (VC) of < 3ppm/V
SPECIFICATIONS
Calibration conditions:
At 23°C, low power, traceable to SI units.
Connections as indicated in table.
Terminals:
Gold plated, tellurium copper, high current, heavy
duty,low thermal-emf binding position standard 3/4 inch
spacing. A case GROUND terminal is provided on all
units.
Dimensions: 8.6 cm H x 10.5 cm W x 12.7 cm D (3.4"
x 4.15" x 5")
Operating temperature range: 15 to 30°C.
Transit case:
Optional Model SRC-100 lightweight transit case
with handle, suitable for transporting and storing
two units. The case provides mechanical protec-
tion and insulation from temperature changes
during transportation or shipping.
Optional Model SRC-100-5 lightweight transit
casewithhandle,suitablefortransportingandstor-
ing 5 SRC/SRX resistance standards.
bnc option:
Option -bnc changes Hi and Lo binding posts to 4
x bnc connectors plus the ground binding post. SRC-100-5 Lightweight transit case for 5 standards

3
SRX/SRC Series
3Specifications

4
SRX/SRC Series
4 Specifications
SRX Series RESISTANCE STANDARD
Stability:
Maximum Power
:
Temp. Coefficient:
Power Coefficient
:
Temperature Range:
Storage Temperature
:
20 ppm/year
0.25 W
10 ppm/°C
0.5 ppm/mW
15°C to 30°C
0°C to 40°C
REPORT #: 82893
Tech: 21-Oct-2015Date:CTS
23.5
Temp(°C): Due:
Cert No:
2073.01
Calibrated Resistance (R)
999.996 48 mȍ
Meas. Uncertainty: 9.6 ppm
Long Island, NY
Email: info@ ietlabs.com · Tel: [phone]
www.ietlabs.com
IET LABS, INC.
Model: SRX-1 SN: J1-XXXXXXXX
Figure 1-1: Typical Operating Guide Affixed to Unit

5
SRX/SRC Series
5Operation
Chapter 3
OPERATION
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 OPERATION GUIDE is attached to the case
of the instrument to provide ready reference to
specifications.
3.2 Connections
All SRac have four insulated low thermal emf bind-
ing posts for four-terminal measurements as shown
in Figure 3-1. As an option -bnc is available which
replaces the 4 binding posts with bnc connectors.
The fifth binding post GND is connected to the case.
Figure 3-1: Connections
1 Ω
RESISTANCE STANDARD
MODEL SRac-1
LO
HI
LO
HI
SENSE
CURRENT
GND
HI INPUT
HI SENSE
LO INPUT
LO SENSE
GROUND
Binding Post Function
CURRENT HI Current input from source (e.g. ohmmeter)
CURRENT LO Current return to source (e.g. ohmmeter)
SENSE HI Measurement point for a four-wire ohmmeter
SENSE LO Measurement point for a four-wire ohmmeter
GND Guard or shield
Table 3-1: Connections
3.3 Thermal emf Considerations
High-quality, gold-plated, tellurium-copper bind-
ing posts serve to minimize the thermal emf effects
which would artificially reflect a change in ac resis-
tance measurements. All other conductors within
the instrument, as well as the solder used, contain no
metals or junctions that could contribute to thermal
emf problems.
There nevertheless may be some minute thermal emf
generated at the test leads where they contact the gold
banana jacks. This voltage will also be eliminated if
a meter with so called “True Ohm” capability is used.
Otherwise the generated emf may represent itself as
a false component of the dc resistance measurement.
Always use low emf test leads when working with
SRac models. In particular, avoid brass or steel
conductors.

6
SRX/SRC Series
6 Operation
3.4 Environmental Conditions
3.4.1 Operating Temperature
For optimal accuracy, SRac Models should be used
in an environment of 23°C. They should be allowed
to stabilize at those temperatures after any significant
temperature variation.
3.4.2 Storage Temperature
The SRac Series should be maintained within the
storage temperature range of 0°C to 40°C to retain
its accuracy within the specified limits.
3.5 Shipping and Handling
The SRac Series should not be exposed to any ex-
cessive shock or temperature extremes. The option
SRC-100, a lightweight transit case capable of stor-
ing two SRac units, is recommended for shipping or
transporting the models.
3.6 Frequency Response
The SRac Series was designed to have minimal
change between dc values and ac values at 1 kHz.
This also makes calibration easy as the SRac can be
calibrated at dc rather than ac.
For resistance values below 1 MΩit is recommended
to use the dc value for the ac value at 1 kHz. This is
due to the uncertainty for the dc measurement is sig-
nificantly better than the ac measurement uncertainty.
For resistance values of 1 MΩand 10 MΩit is recom-
mended to use the ac value.
The frequency response of the foil resistors is based
upon the formula below;
Figure 3-2 Rs and Rp formulas for foil
resistors
It is important to realize that when measuring using
an LCR meter or similar device that Rs or Rp should
be selected depending upon the resistance value.
Rs should be used for values < 100 kΩas the model
for the resistor is a resistance with a series inductance.
Figure 3-3 Equivalent circuit for Rs
Rp should be used for values of 100 kΩand higher. as
the model is a resistance with capacitance in parallel.
Figure 3-4 Equivalent circuit for Rp

7
SRX/SRC Series
7Maintenance
Chapter 4
MAINTENANCE
4.1 Maintainability and Reliability
It is possible to maintain SRac units indefinitely.
They are reliable due to their closed, rugged design
and sealed resistors. The units are resistant to elec-
tromagnetic interference (EMI) because of their metal
enclosure.
4.2 Preventive Maintenance
Keep the SRac units in a clean environment. This
will help prevent possible contamination.
The front panel may be cleaned to eliminate any leak-
age paths from near or around the binding posts. To
clean the front panel:
Wipe the front panel clean using alcohol and a
lint-free cloth.
4.3 Calibration
The SRac units may be employed as stand-alone
instruments or as an integral components of a system.
If used as part of a system, they should be calibrated
as part of the overall system to provide an optimum
system calibration.
If an SRac model is employed as a stand-alone de-
vice, the following should be observed:
• Calibration Interval
• General Considerations
• Required Equipment
• Calibration Procedure
4.3.1 Calibration Interval
The recommended SRac Series calibration interval
is twelve (12) months.
If the instrument is used to transfer resistance values
only, recalibration is not required, assuming that there
has been no drastic change of value.
4.3.2 General Considerations
Before starting the calibration procedure, you need
to consider the following:
• Calibration environment should be 23°C and
less than 50% relative humidity.
• Test instruments should be sufficiently more
accurate than the SRac unit, and/or the un-
certainty of the measurement instrumentation
has to be considered in the calibration Test
Uncertainty Ratio (TUR).
• The testing equipment and the SRac unit
should stabilize at laboratory conditions for
at least 24 hours.
• Kelvin type 4-wire test leads should be
used to obtain accurate low resistance
measurements.
• Steps should be taken to minimize thermal
emf effects, such as using a meter with “True
Ohm” capacity.
• Accepted metrology practices should be
followed.

8
SRX/SRC Series
8 Maintenance
4.3.3 Required Equipment
Many combinations of standards, transfer stan-
dards, meters, and bridges may be used to calibrate
this instrument. The following are some possible
choices:
• Resistance Standards or Transfer Standards
for the required values with traceable cali-
brations, such as the following standards
available from IET Labs
• SR-102 100 Ω
• SR-103 1 kΩ
• SR-104 10 kΩ
• SRL series
• Precision resistance measurement bridge
or multimeter, with a transfer accuracy
of ±l ppm. Options include:
• Guildline Model 9975
• Measurements International Model
6010C
• ESI model 242, 242A, 242C, or
242D
• A high-precision, high-stability digi-
tal multimeter (e.g. Fluke 8508A)
along with a set of resistance stan-
dards for ratio mode.
4.3.4 Calibration Procedure
To calibrate an SRac unit, proceed as follows:
1. Set up the calibration equipment in the resis-
tance measurement mode.
2. Confirm the resistance of the unit.
3. Confirm that the resistance is consistent with
historical measurements.
4.4 Replaceable Parts List
Reference IET Pt No Description
1BP-1000-RD Binding Post, Red
2BP-1000-BK Binding Post, Black
3BP-1000-GN Binding Post, Green
Not Shown SRac-*-Res SRac resistor assembly
Replace * with nominal resistance value
Table 4-1: Replaceable Parts List
Figure 4-1: SRac Replaceable Parts
1
2
3