Appendix A Algorithms
280
If continued monitoring is permitted while the background is elevated, it should be
noted that this option provides reduced accuracy since the system would require more
than the specified Maximum Monitor Time. As stated above, “High Background”
may be superimposed over all monitoring display screens to alert the user in this
circumstance.
Krypton mode offers features that allow the monitor to operate in an environment that
periodically experiences high background conditions, such as when Krypton or other
radioactive gas might be present. Krypton Mode Service, is an alternative to Normal
Service for handling these specific high background conditions (see on page 66).
In selecting the appropriate action to be taken during elevated background conditions,
the High Background Rate settings are set in conjunction with the Excessive
Background Rate settings. Figure 130 shows the relationship between the different
background levels and the confidence of alarm.
Figure 130 Automatic Background Capability for Mirion Tec
hnologies (Canberra CA) Ltd. Monitors
There are clearly many choices for handling high background rates using the settings
in the F3 – Detection Zones; F2 – Wait Timeouts and F4 – Out of Service Causes
screens. These alternatives include the following suggestions:
1. If high activity sources frequently move past the monitor it would be desirable
to take the monitor out of service temporarily with auto-recovery in effect. To
accomplish this:
Set the Excessive Bkg Rate, High Bkg Rate and High Count Time to
“AUTO” on the F4 – Out of Service Causes screen (on page 141). Set the
High Background Rate and the Excessive Background Rate to some fixed
count rate on all the F2 – (Zone) Settings screens. The default is 900,000 cpm
(15,000 cps). When the unit requires more than the allowed Maximum
Monitor Time to meet the operational parameters, it will take itself out of
service and display the High Background Out of Service screen.
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