8. Basis of Calculation LB 124 Scint
80
The weighting factor W is determined as follows in the rateme-
ter function:
τ
1
=
W
with
= the number of seconds since the start of averaging.
The number of seconds used for the averaging depends on the
measurement mode and can therefore determine whether a
high accuracy with slower reaction time to changes is obtained,
or a faster adaptation to changes involving a lower accuracy.
If the count rate changes significantly with respect to statistics
within a short period of time, n will be reset to 1, so that the new
measured values will then be weighted more.
The reject criterion can be individually set in each measurement
mode. For this purpose, the standard deviation
n=
σ
is used
as a measure for the statistical significance. If the difference be-
tween the current measured value and the current mean value
is greater than a definable number of standard deviations, the
averaging will be restarted and t will be reset to 1.
8.2 Ratemeter Function
The weighting factor W described in chapter 8.1 can either be
determined in dependence on the time or the accuracy:
a) Preset time:
The number of seconds entered indicates the maximum period
of time for which an average is obtained, i.e. given a preset time
constant of 100, the weighting factor is calculated with
W=1/100 after 100 s. The accuracy that can be reached in this
case therefore depends on the count rate.
b) Preset accuracy:
When a relative accuracy of ε =
n/1
in percent is reached,
the current number of seconds since the start of the averaging
is put in for n. The preset accuracy is recommended for higher
count rates (from 100 cps on).
The reject criterion is preset to 4 σ; this means that whenever
the difference between the current measured value per second
and the mean value obtained with respect to the last measuring
interval is greater than four times the standard deviation, n will
be reset to 1 and the averaging interval will be restarted.
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