Ludlum Measurements 25024424, Manual

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C
H
A
P
T
E
R
8
A
DVANCED
F
EATURES
8.1 Dead Time Correction
All pulse counting detectors have a "dead time" in which the detector is unable to register
another event. In relatively low fields this is not an issue. However, as the field strength
approaches the high end of the detector’s range, dead time causes the pulse rate to become
non-linear with respect to the real radiation field. Dead time correction is used to linearize
the measurements, allowing a wider linear response range for a given detector.
This instrument uses a second order dead time correction using the below equation:
r at e
c
=
r at e
m
/[1 − (
DT C
1
∗
r at e
m
) + (
DT C
2
∗
r at e
2
m
)]
Where DT C
1
and DT C
2
are the dead time correction coefficients, r at e
m
is the measured
count rate, and
r at e
c
is the corrected rate.
Dead time correction coefficients are configured through the device setup menu or through
Lumic Calibration software. Lumic Calibration software also includes a wizard that will au-
tomate finding and setting the correct coefficients.
DT C
1
is represented in microseconds (
µ
s) on the device setup menu and in the software. The
equation must be calculated in terms of seconds (s) and must be scaled appropriately.
DT C
2
has more complex units and are not shown. However, the representation of the coefficient
on the setup menu and in software do not require scaling.
ò
Setting the
DT C
2
to zero will disable the second order correction, while setting
DT C
1
to zero will disable both, regardless of the value of DT C
2
.
8.2 Units
Depending on the chosen display units, different features will affect value of the reading.
The following table lists the features that apply to each of the display units.
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