F3 – Setup Menu
Gem-5 User’s Manual 115
Allow Bkg Reset default is “Yes”. Set this to “No” for situations where large
Background Average Period times are used (as set in the F2 - Wait Timeouts). If
background rate is varying, then change this setting back to “YES” and reduce the
Background Average Period. These settings affect how long it takes the monitor to
recognize changing Background conditions.
The effect of the selected K Alpha value is shown opposite the “Bkg False Alarm (K
Alpha)” setting. Three values are listed:
1. The probability of a false alarm when only one zone channel is considered and
it is counted for the time calculated from setting ATP equal to the LLD;
2. The probability of a false alarm when all zone channels are considered and they
are all counted for the time calculated from setting ATP equal to the LLD;
3. The probability of a false alarm when all zone channels are considered using the
count time that will actually be used. The last two items reflect the sum zone
channel handling choice. The number of zone channels used in the
contamination decision (Yes or Check) and the number of zone channels
considered when setting the monitoring time (Yes) are shown next. The frisker
detector is treated independently and does not figure in these calculations. A
reminder is to see the Information Status screen (i.e. Monitor Zone Status
screen) for more details.
The default K Alpha setting is 3.000. This results in a false alarm rate of 1:370 for a
detection zone that is counted for the time calculated from setting its ATP equal to its
LLD, as discussed above.
The default K Beta setting is 2.000. This results in an Alarm Confidence of 95.45%,
as discussed above.
Allow Bkg Reset: The choices are “Yes (Initialize Background)” (default), “No”
and “Yes (Quietly)”. “Yes (Initialize Background)” forces Initialize Background
when a reset occurs.
“Yes (Quietly)” setting the background reset is done quietly while displaying the
scrolling logo. Only when the count time is greater than the Monitoring Time
Maximum due to a low T
b
term is an Initializing Background forced.
“No” setting prevents background over K Delta value from resetting the Background
Average. It also hides F4 = Show/Hide ±K∆ on the Background History and
Background Trend screens.
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