BERTHOLD TECHNOLOGIES LB4710-050, User Manual

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Chapter 5 Explanations
Mini-Switch LB 471
58
Chapter 5. Explanations
5.1
Zero Count Rate
The zero count rate is the count rate caused by natural environ-
mental radiation. In contrast to radiation coming from the source,
the zero count rate remains constant. The zero count rate is large-
ly dependent on the scintillator volume. An error in measuring the
zero count rate may result in switching errors.
If no zero count rate values have been entered or read-in, the de-
vice works with the standard value set in the factory. The standard
value is an approximate value defined by the current detector
code. Since background radiation is dependent on the geographical
location, this value should be read in as soon as possible.
The zero count rate is needed for the correct calculation of the
decay compensation.
When reading in the zero count rate, please keep in mind that "re-
sidual radiation", even from a closed shielding container, may dis-
tort the empty count rate value. Gross falsification may lead to
false alarms being triggered over a longer period of operation
(months/years).
5.1.1 Determining the Zero Count Rate
The zero count rate is determined according to the best method.
Often, however, the best method cannot be employed, depending
on the conditions during production or start-up. Below, we will de-
scribe three methods for determining the zero count rate.
a) Best method
With empty or full container, but without source.
Figure 6:
Determining the
zero count rate
with no source
installed
with empty container with full container