F3 – Setup Menu
Gem-5 User’s Manual 107
Measurement Variance Ratio, which is used in turn to determine if background
changed during measurement.
Note: The Monitor Time Minimum, Monitor Time Maximum, and Monitor Time
are all forced to the next higher integer multiple of Measurement Collect
Time.
Excessive Background in Service After: This sets the time delay before a unit can
return to service automatically following an Out of Service condition caused by
excessive background. The default time is 300 seconds, while the shortest time
allowed is 60 seconds. To be in effect, Excessive Bkg Rate must be set to “Auto” in
the F4 – Out of Service Causes screen (on page 141).
Low Background Minimum Average Period: At every background update the
average background count rate for each detector section (i.e. single zone) is compared
with its Low Background Rate alarm level, provided that the time used to calculate
the average background rate is not less than the Low Background Minimum
Average Period. This check is used to determine whether a detector has failed due
to decreasing efficiency (e.g. due to PMT tube degradation, slow leak, loss of gas,
hole in window, etc.). The allowable range is 10 seconds to 600 seconds (10
minutes). Selecting a very short average period could result in false alarms due to
poor counting statistics. The default value is 20 seconds; this allows a low
background check to be completed during background initialization, which takes 25
seconds with default settings.
Low Background Rate Setting and Strategy on page 282 or a discussion of the low
background count rate alarm.
Zero Count Period: This is used to trigger a Zero Count fault if the current reading
has at least this much time and there are no counts in any of the counting channels.
See F4 – Out of Service Cause for action taken. Maximum value is 300 s since it has
been determined empirically that, for example, zero counts for 10 s can occur in a 1
cps background. Default is 5 s and minimum is 1 s.
Approach Sensor Reset Time: This sets the time after the last activation of the
approach sensor before the monitor returns to Background Update mode, if no other
sensor becomes activated. The default is 3 s.
Occupied Sensor Hold Time/While Positioning: This sets the time from the last
activation of the Occupied Sensor after which the occupant is assumed to have left
the platform. If monitoring is not complete, then the “Monitoring not complete,
please re-monitor!” warning is given after this time has expired.
During Occupied Sensor Hold Time interval, any sensors activated by the
occupant leaving are ignored. Default is 0.25 s while in the “Walkthrough” mode
and “0.5 s” while in the “One-Step” mode. Otherwise its 1 s without barriers and
0 s with barriers. The short time allows the GEM-5 to be immediately available
for the next person to monitor.
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