Chapter 7 Retrieving Information
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The text above the graph indicates the count times for the selected zone or detector.
The sum zone will be the zone that is controlling the overall counting time for the
monitor. The actual counting time used would be the time displayed for the Sum
Zone All rounded up to the next highest integer number of seconds.
The vertical green line (at 2775 Bq in the example shown above) indicates the
current alarm set point (release limit) for the selected zone. The required monitor
time for the selected zone is given by the intersection of the green line with the
(yellow) curve. In the example shown above, the alarm release limit of 2775 Bq for
Detector Sum Zone 7-8 requires 1.7 seconds of monitoring time. If the alarm limit
were reduced to 2000 Bq, the required monitoring time would increase to about 3
seconds. The limiting-case zone is Gamma Sum Zone All , which requires 2.4
seconds. In this case, the actual counting time would be rounded up to 3 seconds,
unless “Count Body In Two Steps” has the effect of reducing the required counting
time.
NOTE:
The examples shown above are for explanation purposes
only. Monitoring times may differ on site, and are subjected to
many variables, such as background, shielding, etc.
The two horizontal red lines indicate the minimum (3 s) and maximum (30 s) monitor
times, as set in the F2 – Wait Timeouts screen. The intersect of the maximum
monitor time (30 s) with the (yellow) curve indicates the lowest alarm set point that
would not take the unit out of service due to high background (Maximum Monitor
Time exceeded). For the zone shown in the figure above, this is just less than 700
Bq.
A complete table of counting times required for each detection zone, as well as a
description (makeup of sum zones) of each zone, can be found on the F6 – Monitor
Zone Status screen (below).
F6 – Monitor Zone Status
The Monitor Zone Status screen (Figure 117) displays current average background
count rate, the Lowest Level of Detection (LLD) and count time information for each
detection zone (singles, pairs, triplets, quads, and All, as applicable).
Note : The “LLD Bq” column changes to “DL Bq” when Methodology is set to
“Bayesian”.
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