iET PRS-330 series, Operation Manual, Page: 16 / 67

SPECIFICATIONS
PRS-330 Series
4
2.2 General Specifi cations and Stability
Warm-up:
This unit utilizes custom designed low thermal
emf relays for high stability and low-level signal
applications. This thermal voltage is nominally
less than 15
μ
V under laboratory conditions.
Please note that a change in this thermal emf will
give a false drift in resistance as measured by a
dc ohmmeter, since the ohmmeter will interpret
this emf as an effective resistance. The worst
case such effective drift after warm-up is less than
±25 ppm, primarily due to stabilization of this
emf at the relay contacts as settings are changed.
Unit should be allowed to stabilize for
one hour. For maximum stability, allow
u n i t t o w a r m - u p o v e r t w o h o u r s .
Recommended Calibration Interval:
Typical calibration interval 12 months.
Adjustment can easily and automatically be
accomplished using IET’s PRS-DMM software
Adjusting the PRS-330 can improve accuracy
associated with the drift of the resistors.
Environmental:
This product complies with the
W E E E D i r e c t i v e ( 2 0 0 2 / 9 6 / E C )
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
I, this product is classed as a “Monitoring
and Control instrumentation” product.
Effects of Humidity:
Exposure to humidity >60% for a periods of weeks
can cause the resistors to drift some of that is
reversible. It is recommended that the PRS-330 be
stored at humidities less than 50% to minimize this.
Short-term Stability:
The PRS-330 was tested for extended periods
of time. Based upon this testing the following
stability information was determined. These
specifications apply for the PRS-330 in 4
terminal mode with shorting links removed
and without switching to another value.
Typical short-term stability without
switching:
< ±(4 ppm + 100 μΩ ) / 10 minutes
Typical 24 hr. Accuracy after Adjustment:
After performing an adjustment per 8.1.4
of this manual using a Fluke 8508A and
then performing a calibration veri
fi cation per
8.1.3 within 24 hours the typical accuracy is:
±(30 ppm + 300 μΩ ) for values <1 M Ω
±60 ppm for values > 1 M Ω
See graph below for actual performance,
shown in blue, with 6 digit resolution
across resistance range. The red lines
represent tolerance of ±(30 ppm + 300
μΩ ).
Figure 2-1 Error versus Resistance up to 1 M Ω