EPD/HB/40521/
000
ELECTRONIC PERSONAL DOSEMETER HANDBOOK
TECHNICAL DESCRIPTION
ISSUE 5
Page 56
Thermo
(iv) Dose Rate Over-range
The dose rate over-range flag indicates that the dose rate has exceeded 1Sv/h
(100 rem/h) at some time in the past, (i.e. the recorded dose may be inaccurate,
probably low, due to non-linearity at high dose rates).
(v) Counter Over-range
The counter over-range flag indicates that at least one detector has exceeded the
maximum count rate expected (300,000 counts/second - gamma counters and
26,000 counts/second - beta counters). A possible cause for this flag to set is that
the unit has either been exposed to some kind of extreme interference or has
developed a fault.
(vi) Abuse Warning
The abuse warning indicates that an abuse alarm has been activated. An abuse
alarm is activated if mechanical knocks are detected continuously for greater than
15 seconds (see
Knock Time Seconds
)
(vii) CRC Failure
The CRC failure flag is set as a result of an integrity check on a set of data
indicating that the EPD detected a checksum error in the dose data. Checksum
failures are corrected by retrieving the last stored dose from secure store
(EEPROM). During the correction process up to 15 minutes of dose may be lost.
(viii) Low Voltage (EPD software version 11 and later)
The EPD analogue circuitry detected a low supply voltage condition.
(ix) Detector Fault (EPD software version 11 and later)
The EPD ‘flash LED’ detector test failed.
4.6.8 Dose And Dose Rate Alarm Processing
The EPD performs alarm processing as described in this section. The occurrence
of a dose or dose-rate alarm is recorded by the following internal flags. These
flags make it easy for applications s/w to determine over the IR communications
link whether an alarm has occurred during an issue period. The flags are
therefore normally cleared over the IR communications link at the start of an issue
period:
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