Fluke 732B - Monitoring Long-Term Stability

Operation
Monitoring Long-Term Stability
3
3-17
2. With a 10 kΩ pullup resistor between pins 3 and 7, monitor the TTL-level signal on
pin 7 with respect to pin 2. A high state on pin 7 corresponds to the front panel IN
CAL indicator being lit. A low state on pin 7 corresponds to the front panel IN CAL
indicator being off.
3
7
2
+V
CC
+5V
10k
COMMON
V
cal
5.95
+11.5V
IN CAL (H)
IN CAL (H)
k14f.eps
Figure 3-10. IN CAL Status Output Circuit
Monitoring Long-Term Stability 3-19.
You can determine the long-term stability of the standard by periodically comparing the
output voltage to a known reference standard and plotting the difference on a control
chart. Output voltage drift, with respect to the legal volt, may be positive or negative and
is a characteristic of the individual 732B. Accumulated test data have shown that, once
established, the measured drift is generally linear, provided the instrument continues to
receive uninterrupted operating power. When drift rate is established, extrapolations of
output voltage are possible, and allow certification of the standard with lower
uncertainty than is obtainable from the stability specifications alone.
A convenient method of performing the needed periodic calibration is to use the Fluke
Direct Voltage Measurement Program, Option 732B-200 (described in Section 1 and the
Fluke Catalog), which provides calibration against a traceable reference standard in your
own laboratory.
Note
A paper has been published that describes a technique for characterizing
drift rate of solid state dc voltage references. Refer to "The Fluke Direct
Voltage Maintenance Program," by Les Huntley, published in the
proceedings of the 1984 Measurement Science Conference.
Due to the possibility of undetected damage or malfunction, there is a risk involved in
relying completely on any single standard. This risk is reduced significantly by using
two or more independent standards (with frequent intercomparisons) to ensure that all
are stable within the range of expected normal deviations. An added advantage of having
multiple, independent standards is the opportunity to use a statistical average of the
individual outputs. You can use multiple 732B 10V outputs, as obtained with model
734A, in this way to gain statistical improvements of your standard’s uncertainty
specification.
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