IET Labs SRC-10T-Tnetwork Troubleshooting guide

¨PRECISION INSTRUMENTS FOR TEST AND MEASUREMENT ¨
Email: inf[email protected]
TEL: [phone] • FAX: [phone]
www.ietlabs.com
IET LABS, INC.
SRC-Tnetwork
Resistance Standard
User and Service Manual
Copyright © 2022 IET Labs, Inc.
Visit www.ietlabs.com for manual revision updates
SRC-100T-Tnetwork im/August 2022

¨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 speci•cations. 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 speci•cations 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 de•nitions 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.
O• 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 a!xed 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 classi•ed 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 land•lls 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 speci•c 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 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.
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Contents
Chapter 1 Introduction .................................................................................1
1.1 Introduction...............................................................................................1
Chapter 2 Specifications ..............................................................................3
Specifications ...................................................................................................3
Label .................................................................................................................4
Chapter 3 Operation ....................................................................................5
3.1 Initial Inspection and Setup ...................................................................... 5
3.2 Connections.............................................................................................. 5
3.3 Thermal emf Considerations.....................................................................5
3.4 Environmental Conditions......................................................................... 5
3.4.1 Operating Temperature ................................................................... 5
3.4.2 Storage Temperature.......................................................................5
3.5 Shipping and Handling ............................................................................. 5
Chapter 4 Maintenance................................................................................7
4.1 Maintainability and Reliability ...................................................................7
4.2 Preventive Maintenance ........................................................................... 7
4.3 Calibration ................................................................................................7
4.3.1 Calibration Interval ..........................................................................7
4.3.2 General Considerations ..................................................................7
4.3.3 Required Equipment .......................................................................8
4.3.4 Calibration Procedure .....................................................................8
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1
SRC-Tnetwork
1Introduction
Chapter 1
INTRODUCTION
1.1 Introduction
The SRC-Tnetwork is a standard resistor de-
signed for calibration of various electrometers and
megohmmeters.
The SRC-Tnetwork is a high resistance standard
that uses 3 lower value resistors configured in a T
network to create a higher resistance.
1.2 T-Networks
For high resistance measurements a T-network is
often used with instruments such as electrometers
and megohmmeters equipped with a guard termi-
nal.
A T-network uses low value resistors to achieve
what electronically looks like a high value resistor.
The basic operation of a T-network is three resis-
tors are place in a T configuration and connected
to the positive, negative and guard terminals of the
megohmmeter.
The ratio of the resistors then determines the effec-
tive resistance value that will actually be displayed
by the megohmmeter.
The advantages of the T network is that low value
resistors are used that can be easily and accurately
measured as compared with trying to calibrate a
single high value resistor.
This technique is used quite often in calibration
where it is difficult to accurately calibrate a resistor.
A T-network is illustrated in Figures 1.2 and 1.2
along with the formula to calculate the effective
resistance.
Guard
Positive Negative
R1
R2
R3
It In
Ig
Effective R = R1 + R2 R3
R2 R3 *R3
Figure 1.1: T-Network Model
Figure 1.2 illustrates an example T-network com-
prised of two 1 GΩ resistors and a single 10 kΩ
resistor to create a T-network that has an effective
resistance of 100 TΩ.
Figure 1.2: T-Network Example

2
SRC-Tnetwork
2 Specifications
Figure 1-1: SRC-Tnetwork Standard Resistor
100 TW
RESISTANCE STANDARD
MODEL SRC-100T T-network
SOURCE OUTPUT
CENTER TAP
GUARDGND

3
SRC-Tnetwork
3Specifications
Chapter 2
SPECIFICATIONS
For convenience to the user, the pertinent specifications are given in an OPERATION GUIDE,
Calibration conditions:
At 23°C, low power, accredited calibration traceable to SI
Using T-network calculation based upon calibration of the 3 internal
resistors at a maximum of 200 V.
Terminals:
3 gold plated, low thermal-emf binding posts for Source, Output and
Guard, 1 binding post for Ground and one bnc for Center Tap.
Dimensions: 9 cm W x 11.5 cm L x 5 cm H
(3.5" x 4.5" x 2”)
Weight: 0.45 kg (1 lbs)
Operating temperature range: - 55 to 70°C < 80% RH
Altitude: <2000 m
Enclosure: Cast Aluminum housing to minimize noise
Model
SRC-
Nominal
(W)
Initial
Adjustment to
Nominal
(ppm)
Calibrati on
Uncertainty
(Typical)
(ppm)
Stability
1 year (ppm)
Tempco
(ppm/°C)
Voltage
Coef.
(ppm/V)
Resistor
type
Max. Voltage
(V)
10T-Tnetwork 10 T
±1%
750
± 500 ± 25 1
precision thick
film resistors in a
T-Network
5000
20T-Tnetwork 20 T
50T-Tnetwork 50 T
100T-Tnetwork100 T

4
SRC-Tnetwork
4 Specifications
Figure 1-1: Typical Operating Guide affixed to the SRC-100T-Tnetwork

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SRC-Tnetwork
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.
3.2 Connections
The SRC-Tnetwork is designed to be connected to
an electrometer or megohmmeter such as the IET
1865 Plus.
1865 Plus Connections
When connecting to the IET 1865 Plus remove the
shorting link between the GND and Guard Terminal
and connect the SRC-100T as shown in Figure 3-1.
Figure 3-1 1865 Plus Megohmmeter Connection
Keithley 6517A/B Connections
When connecting to the 6517A/B make sure the short-
ing link is between the GND and Guard Terminal and
connect the SRC-100T as shown in Figure 3-2.
Figure 3-2 Keithley 6517A/B Connection

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SRC-Tnetwork
6 Operation
3.3 Environmental Conditions
3.3.1 Operating Temperature
For optimal accuracy, SRC-Tnetwork should be used
in an environment of 23°C. They should be allowed
to stabilize at those temperatures after any significant
temperature variation.
3.3.2 Storage Temperature
The SRC-Tnetwork should be maintained within the
storage temperature range of 0°C to 40°C to retain
its accuracy within the specified limits.
3.4 Shipping and Handling
The SRC-Tnetwork should not be exposed to any exces-
sive shock or temperature extremes. The option SRC-100,
a lightweight transit case capable of storing two SRC-
Tnetworks, is recommended for shipping or transporting
the models.

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SRC-Tnetwork
7Maintenance
Chapter 4
MAINTENANCE
4.1 Maintainability and Reliability
It is possible to maintain SRC-Tnetwork indefinitely.
They are reliable due to their closed, rugged design
and resistors. The units are resistant to electro-
magnetic interference (EMI) because of their metal
enclosure.
4.2 Preventive Maintenance
Keep the SRC-Tnetwork 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 SRC-Tnetwork 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 SRC-Tnetwork is employed as a stand-alone
device, the following should be observed:
• Calibration Interval
• General Considerations
• Required Equipment
• Calibration Procedure
4.3.1 Calibration Interval
The recommended SRC-Tnetwork calibration inter-
val 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 su!ciently more
accurate than the SRC-Tnetwork, and/or the
uncertainty of the measurement instrumenta-
tion has to be considered in the calibration
Test Uncertainty Ratio (TUR).
• The testing equipment and the SRC-Tnetwork
unit should stabilize at laboratory conditions
for at least 24 hours.
• Steps should be taken to minimize thermal
emf e"ects, such as using a meter with “True
Ohm” capacity.
• Accepted metrology practices should be
followed.

8
SRC-Tnetwork
8 Maintenance
4.3.3 Required Equipment
Many combinations of standards, transfer standards,
meters, and bridges may be used to calibrate this
instrument. The following are some possible choic-
es:
• A dual source guarded bridge
• A high-precision, high-stability digital multime-
ter (e.g. Fluke 8508A, Fluke 8588A or Keysight
3458A) or other DMM with an accuracy of 20
ppm or better for direct measurements.
4.3.4 Calibration Procedure
To calibrate an SRC-Tnetwork proceed as follows:
1. Set up the calibration equipment in the resis-
tance measurement mode.
2. Measure R1, R2 and R3. The bnc center
tap connection is there to assist in measur-
ing these resistances without opening the
standard. Just measure between the center
conductor of the bnc and the Source, Guard
and Output terminals.
3. Calculate the Effective R using the formula
in Figure 4.1
4. Confirm that the resistance is consistent with
historical measurements to verify stability.
Figure 4-1 Schematic and formulas