Thermo EPD Mk2, Technical Handbook

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EPD/HB/40521/000
ISSUE 5
EPD TECHNICAL HANDBOOK Page 55
4.6.7 Dose Quality Flags
There are 7 dose quality flags set within the EPD. Dose quality can only be read and
cleared via the IR communications link. They are normally cleared at the start of an
Issue period. The dose quality flags are as follows:
(i) Reset Count
The reset count flag is a count of the number of times the unit has been reset, either
by:
(a)
removing and re-fitting the battery,
(b)
by a commanded reset via the IR communications link,
(c)
by a software reset.
(ii) Shock Time Seconds
The EPD detectors are susceptible to large mechanical shocks. This is overcome
by detecting the shock with a piezo detector. The EPD continues to accumulate
dose during the shock period, but at the dose rate that was present immediately
before the shock was detected. However, if the dose rate is greater than
approximately 4mSv/h the counts caused by the shock will be small relative to the
radiation counts and therefore all counts are used in the calculation of dose. Shock
Time is the time period over which shock processing has taken place. Continuous
Shock detection for greater than 45 seconds will cause an abuse alarm (see
Abuse
Warning ).
(iii) Dose Over-range
The dose over-range flag indicates that one of the dose stores has exceeded 1Sv
(100 rem) . Dose continues to accumulate above this value to a maximum of
16.777215 Sv (1677.7215 rem).
(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