Fluke Biomedical 942A-200L-M4 - Manual (Page 60)

942A-200L-M4 & 942A-200L-M5 UDR
Operator Manual
3-20
Statistical Accuracy
T he normal mode of operation is to sample the radiation value, in units of Counts per Minute (CPM) once
per second, and display the average of the 60, one second values. This provides a maximum response
time of 1 minute to a step change in radiation value. At low counting rates, however, the displayed value
will exhibit statistical fluctuations, even though the mean emission rate is not changing.
Note:
In this mode of operation, the alarm response time may
exceed 1 minute. This mode of operation is NOT
recommended for Safety-Related applications.
To reduce count rate fluctuations at low count rates, a 2% statistical accuracy function is provided. When
enabled (via jumper selection), the 60 value average is replaced with a 9604 value average. In this
mode, the 1/second update is replaced with a 1/minute update. If the new value differs from the old value
by a 2 standard deviations, the new value is displayed and the display and alarm logic are updated
1/second. When the change in radiation value is less than 2 standard deviations, the update rate returns
to once per minute. In this mode, the maximum integration time is 20 minutes (20, 1 minute averages).
To reduce count rate fluctuations at low count rates, a 5% statistical accuracy function is provided. When
enabled (via jumper selection), the 60 value average is replaced with a 1537 value average. In this
mode, the 1/second update is replaced with a 1/minute update. If the new value differs from the old value
by a 2 standard deviations, the new value is displayed and the display and alarm logic are updated
1/second. When the change in radiation value is less than 2 standard deviations, the update rate returns
to once per minute. In this mode, the maximum integration time is 20 minutes (20, 1 minute averages).
To reduce count rate fluctuations at low count rates, a 10% statistical accuracy function is provided.
When enabled (via jumper selection), the 60 value average is replaced with a 384 value average. In this
mode, the 1/second update is replaced with a 1/minute update. If the new value differs from the old value
by a 2 standard deviations, the new value is displayed and the display and alarm logic are updated
1/second. When the change in radiation value is less than 2 standard deviations, the update rate returns
to once per minute. In this mode, the maximum integration time is 20 minutes (20, 1 minute averages).