MAINTENANCE
PRS-200 Series
15
Chapter 8
MAINTENANCE
8.1
Verification of Performance
8.1.1 Calibration Interval
The PRS-202 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.
8.1.2 General Considerations
It is important, whenever testing the PRS-202 Series
Decade units, to be very aware of the capabilities
and limitations of the test instruments used. Such
instruments would have to be significantly more ac-
curate than the specified accuracy for all applicable
ranges, in order to perform this task, allowing for a
band of uncertainty of the instrument itself, consult
IET Labs for information.
It is important to allow both the testing instrument
and the PRS-202 Substituter to stabilize for a number
of hours at the nominal operating temperature of 23
0
C,
and at nominal laboratory conditions of humidity.
There should be no temperature gradients across the
unit under test.
In the case of a resistance substituter, substantial
Kelvin type 4-wire test terminals should be used to
obtain accurate low resistance readings. It is conve-
nient, 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.
Steps should be taken to minimize emf effects, by
maintaining an even temperature, by using only low
emf connectors. Using meters with a “True Ohm”
function is recommended.
Proper metrology practices should be followed in per-
forming this verification.
