IET Labs SRac Series, User And Service Manual

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7
SRX/SRC Series
7 Maintenance
Chapter 4
MAINTENANCE
4.1 Maintainability and Reliability
It is possible to maintain SRac units inde fi nitely.
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 suf fi ciently 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.