iET PRS-330 series, Operation Manual, Page: 49 / 67

MAINTENANCE
PRS-330 Series
37
Chapter 8
MAINTENANCE
8.1 Verifi cation of Performance
8.1.1 Calibration Interval
The PRS Series instruments should be veri fi ed
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 Series
Decade units, to be very aware of the capabilities
and limitations of the test instruments used. Such
instruments have to be signi
fi cantly more accurate
than the speci fi ed accuracy for all applicable
ranges in order to perform this task, allowing for
a band of uncertainty of the instrument itself, the
test setup and the environment; consult IET Labs
for information.
It is important to allow both the testing instrument
and the PRS-330 to stabilize for a number of
hours at the nominal operating temperature
of 23
o
C, and at nominal laboratory conditions
of humidity. There should be no temperature
gradients across the unit under test.
In the case of the PRS-330 a Kelvin type 4-wire
test terminals should be used to obtain accurate
low-resistance readings.
Steps should be taken to minimize thermal-emf
effects, by maintaining an even temperature and
by using only low-emf connectors. Use of meters
with a “True Ohm” function is recommended.
Proper metrology practices should be followed
in performing this veri
fi cation.
8.1.3 Calibration Procedure
Equipment Required:
Keysight 3458A, Fluke 8508A or equivalent
KK-100, TL-600 Kelvin Cable or equvalent.
Procedure:
Fluke 8508A or Keysight 3458A using 7 ½ digits
of resolution or better is connected to the binding
posts of the PRS-330 using a 4 terminal Kelvin
connection.
The gold shorting links must be removed on the
binding posts of the PRS-330.
The PRS-330 consists 43 internal resistors
which are combined in either series or parallel
to achieve the programmed resistance. The gold
shorting links must be removed on the binding
posts of the PRS-330.
These resistors require periodic measurement to
keep the PRS-330 within published speci
fi cations.
The resistors are measured using a DMM. The
measured value is then stored in a table within