ELECTRONIC PERSONAL DOSEMETER HANDBOOK
EPD/HB/40521/000
TECHNICAL DESCRIPTION
ISSUE 5
Thermo
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 with the
dose and detector counters at the start of an Issue period, e.g. by Access Control
or Issue/Return software. In ‘dose of record’ systems, EPD dose, detector
counters and quality factors are all read together and stored on the system
database to allow later integrity checking of the dose recorded. The dose quality
flags are as follows:
(i) Reset Count
The reset count is a count of the number of times the unit has been reset, either
by:
(a)
removing and re-fitting the battery, or battery cap,
(b) use of an unsuitable or passivated Lithium battery,
(c)
by a commanded reset via the IR communications link,
(d)
by a software reset,
(e)
by a fault condition.
Note that the EPD loses recent dose received since the last log of dose to non-
volatile memory, as described in section 4.6.5.
(ii) Knock Time Seconds
The EPD detectors are susceptible to large mechanical shocks. This is overcome
by detecting the shock with a piezo ‘knock’ detector. The EPD continues to
accumulate dose during the shock period, but at the dose rate that was present
immediately before the knock was detected. However, if the dose rate is greater
than approximately 4mSv/h the counts caused by the knock will be small relative
to the radiation counts and therefore all counts are used in the calculation of dose.
Knock Time is the time period over which knock processing has taken place.
Continuous Knock detection for greater than 15 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).
