10
2.2 Operating Modes
•
Self-Check (Test)
•
Background Calibration
•
Search Mode (count rate indication, s
-1
)
•
Settings
•
PC Communication via IR Interface
2.2.1 Self-Check
The instrument goes into this mode when turned on. Before
the self-tests, an audible alarm is shortly activated, then all
segments and indicators appear on the LCD. The instrument
displays the
“tESt” message and goes through the self-test
sequence: LCD test, detector test, processor test, non-volatile
memory test, alarm test. The analog scale segments count down the test time. After
the self-check, the instrument shortly produces an audible signal, then goes into the
background calibration. The LCD displays "CAL" message and the analog scale with
increasing segments.
2.2.2 Background Calibration
The instrument goes into this mode automatically following
completion of self-check, "CAL" message appears on the LCD. In
the Background Calibration mode the instrument measures
naturally occurring background radiation. The processor counts
pulses coming from the detector for the preset time, and the analog scale segments
increase as the instrument calibrates. The scale completely filled with segments
indicates that the background calibration is complete. Later on when the user makes
the instrument update the background, the background count time will automatically
decrease with increasing the background level.
The processor calculates the alarm threshold value:
N
n
N
Alarm
⋅
+
=
where
N
– the average count time for the calibration time;
n
−
the number of meansquare deviations (coefficient
n
)
The coefficient
n
changes the alarm threshold: the smaller the value of
n
, the
smaller the threshold value, and the greater the instrument’s sensitivity
.
However,
this also increases the probability of false alarms.
The user may run background update whenever it is necessary during normal
operation of the instrument. To do so, press and hold (for more than 2 seconds) the
MODE button 12 (Fig.1) until "CAL" and the analog scale with increasing segments
appears on the display. The instrument is acquiring new background. With connected
