BERTHOLD TECHNOLOGIES LB 444, Operating Manual

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04/03
347
LB 444
80
The following calculation only applies to detectors working with Cs-137 or Co-60.
For detectors working with Am-241 the plateau should be recorded at the measuring lo-
cation with product.
The thickness of steel plates can be calculated as follows:
d
d
d
St
m
W
= +
ρ
*
. 7 8
d
St
= thickness of steel plates in mm
ρ
m
= average product density
d = measuring path in product in mm
d
w
= double wall thickness of measuring pipe
The purpose of all these provisions is to generate the same count rate in the scintillation
counter as under actual operating conditions.
Select
Plateau / Measure Plateau in the Service menu .
Upon completion of the plateau measurement, you may invoke the function Request Pla-
teau to display the value pairs HV-steps/count rate.
The detector works properly if a clear plateau is visible; the position of the plateau is ir-
relevant.
Figure 31: Plateau curve
Plot the count rate vs. the high voltage, as shown in the diagram above.
If the count rate in the flat part of the curve changes by more than 5% per 100 V high
voltage, the scintillation counter will operate unstable. The detectors or at least the crys-
tal multiplier combination have to be replaced.
0
2000
4000
6000
8000
10000
12000
14000
16000
500 600 700 800 900 1000 1100 1200 1300
HV in V
cps