c) The Counter-Timer mode is designed for a high accuracy.
The measurement time or the statistical accuracy can be
chosen as a measure of the duration of a measurement.
In the operating modes "Search" and "Ratemeter", measure-
ments are carried out to find contamination. In this mode, the
display quickly follows a change of the radiation field. In the
search mode, a lower measurement accuracy is accepted in
order to detect changes even faster.
An accurate measurement requires – in contrast to the search
mode – averaging of the count rates over an extended period of
time. The LB 134 is able to do this automatically in the rateme-
ter mode, provided that the average count rate remains within
the statistical significance all the time during this period. This
can be taken for granted, for example, when measuring con-
tamination and the unit is not moved as long as the measure-
ment is running.
However, in order to perform stationary measurements with a
given accuracy for the mean value, you should select the oper-
ating mode Counter-Timer. In this measuring mode, either the
averaging time or the statistical accuracy of the measured value
can be selected.
1.7 Important Measuring Parameters at a Glance
Alarm thresholds Alarm thresholds can be set for each measurement type and for
each nuclide; exceeding of these thresholds is signaled visually
and audibly. Moreover, in this case the measured value flashes
every second. An integral threshold can also be set for the inte-
gral value or dose value; exceeding of this threshold is signaled
visually and audibly.
Calibration factors Contamination monitors include two calibration factors for each
nuclide, since the detectors can be calibrated in accordance
with two different standards (DIN 25415 und DIN ISO 7503
Norm). When purchasing the device, the supervisor determines
the standard according to which the measurements are to be
carried out and selects the appropriate standard in the corre-
sponding menu. For all other probes there is only a single cali-
bration factor for the nuclides or for measurement types. If a
probe cannot be calibrated, we only get raw data and the cali-
bration factor is then 1 for the unit cps or 60 for the unit cpm.
The calibration factor is multiplied by the net count rate to ob-
tain the desired unit of measurement.
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