EPD/HB/40521/000
ISSUE 5
EPD TECHNICAL HANDBOOK Page 78
A change in EPD calibration is usually indicative of a fault in the EPD and, due to the
complexity of achieving calibration over the full energy range, it is recommended that
any EPDs that fail calibration checks are returned to Thermo Electron for repair,
recalibration or replacement.
During calibration the calibration constants, and the threshold levels for each of the
four channels are set. The threshold levels determine the minimum pulse size that
will be considered a "count". The calibration constants ensure that the channels are
combined in the correct fashion to give correct dose readings.
Calibration Constants. Calibration constants convert the counts accumulated on
the four detector channels into dose equivalents. These constants are:
HGSens10
SGSens10
HGSens07
SGSens07
FBSens07
BCSens07
Detector Thresholds. Detector thresholds discriminate between radiation pulses
received by the EPDs detectors. These thresholds are set as course and fine values
measured as:
Hard Gamma (HG)
Soft Gamma (SG)
Full Beta (FB)
Beta Compensating (BC)
EPD calibration may be checked using a Thermo Electron irradiator, or by exposure
to a known radiation field, in a manner approved by the appropriate regulating
authority or local rules. It is recommended that calibration is checked annually.
A change in EPD calibration is usually indicative of a fault in the EPD and, due to the
complexity of achieving calibration over the full energy range, it is recommended that
any EPDs that fail calibration checks are returned to the manufacturer for repair or
replacement.
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