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Erratic readings or readings that seem to fluctuate may indicate
a problem with the gauge. In the event the readings are
“suspect” the Stat Test may be executed to validate the normal
operation of the gauge.
A Stat Test consists of twenty 1-minute counts. Although other
count times are available (4, 8 and 16 minutes) they are not
recommended, since the temperature correction process is not
utilized during a stat test. Long count times (causing the stat test
to run overnight) could result in the gauge undergoing
temperature changes. It is very important that the ambient
temperature remain the same during the stat test. The longer
count times, however, can be used to check long-term gauge
operation.
After the 20 counts, the gauge calculates the standard deviation.
This standard deviation is compared to a theoretical standard
deviation value. Ideally this ratio should be one. However, the
3241 prescale (or divide) for one minute counts is 4. This results
in an ideal ratio of (0.5). The acceptable limits for the ratio are
from (0.35) to (0.71). The gauge is considered to be unstable if
the ratio is outside these limits. The table below gives the limits
for other count times.
Ratio Table
Table 2. Range of Standard Deviation Ratios
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