ELECTRONIC PERSONAL DOSEMETER HANDBOOK
EPD/HB/40521/000
TECHNICAL DESCRIPTION
ISSUE 5
Thermo
Page
53
4.6.5
Dose and Dose Rate
The EPD calculates dose and dose rate. Dose is accumulated in 3 stores:
Dose
,
Total Dose
and
ADS Dose
. Dose rate is the current rate calculated by the EPD.
Dose
The EPD displays Hp(10) (penetrating or deep) dose and Hp(0.07) (superficial or
shallow) dose.
Dose
is regarded as a short-term record of dose received, usually
associated with the issue of an EPD. It is this value that is compared with dose
alarm thresholds and an alarm raised if the value exceeds the thresholds. The
EPD records
Dose, Total Dose
and
ADS Dose
in units of 1/64µSv, although this
is displayed as a decimal equivalent. Total Dose is a store providing a long-term
record of dose accumulated by the EPD.
The LCD display can be set to auto-
range between 1
µ
Sv to 16Sv (maximum resolution 1
µ
Sv).
Accumulated dose is written to non-volatile memory at least every 15 minutes.
Therefore is a reset occurs, due to the battery cap being removed or the EPD
being heavily dropped, or a passivated battery fitted, up to 15 minutes of
accumulated dose may be lost. Such events however are detected and a count of
resets provided as quality data associated with the accumulated dose, see section
4.6.7.
Note that from software version 11 EPDs it is possible to configure the EPD to
make additional logs to the non-volatile memory at 1 minute intervals if the dose
received in the preceding minute exceeds 1 uSv.
Display characteristics that can be set are:
Units
Sv or rem
Decimal Places:
2 or 3 decimal places
Resolution:
µ
Sv or mSv
Default Time:
10 to 99 seconds
Note
: For Gamma dose, two counts are approximately equivalent to 1/64
µ
Sv and
for Beta dose one count is approximately 1/6
µ
Sv. To avoid statistical
inaccuracies doses should only be displayed in micro sieverts (or 0.1 rem),
but when summing a number of doses the full resolution should be used to
minimize rounding errors.
Dose
Rate
This is the current dose rate as calculated by the EPD. It may be viewed on the
display or read via the IR communications link. Dose rates are calculated using
an averaging algorithm to reduce statistical variations to within ±20% under most
conditions. This results in increased averaging time constants at low dose rates.
