14
Getting a new background
The user may run background calibration to adjust
the alarm threshold for the new background during
the normal operation of the instrument. It is
recommended to run the background calibration
any time the radiation background significantly
changes, e.g. upon entry or exit from the building,
changing locations, etc.
If the instrument’s background radiation level is not
updated, the alarm may be set off more frequently
in the Search Mode even without the presence of
any radioactive sources. Or conversely, the
instrument’s ability to alarm to the presence of a
radiation source becomes worse. Under these
circumstances it is necessary to run the background
calibration so that the instrument recalculates the
alarm thresholds based on the new environment.
To update the background radiation levels and
recalculate the thresholds, press and hold down on
the Mode button until the message “CAL”
appears on the display. The unit is now acquiring
new background. In total, this process requires 60
seconds. When the LCD screen display returns to
the normal numeric display, the unit has modified
its background radiation levels to the new
environment and is ready for normal operation.
NOTE: The instrument can also adjust to gradually
changing levels of gamma-radiation background
automatically to make operation with the unit more
convenient. By default this function is enabled by the
manufacturer.
False alarms
Occasionally, the instrument may produce random
signals, called “false alarms”. Such alarms (visual,
audible and/or vibration) are irregular and can,
therefore, be easily distinguished from true alarm
signals produced by the gamma radiation sources
which tend to have continuous repetition rate or
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