Berthold DUO XPERT LB 470RID, Operating Manual

Page: 136 / 240

7 Main Menu Device Setup LB 470RID Level
136
56925-1BA2 Rev.02, 05/2021
Further information on scenario A
A relative limit value is monitored, i.e. the alarm threshold is reached when exceed-
ing a maximum dose rate (calibration value at empty vessel) at the detector.
False alarms due to operative factors are not possible. However, only stronger in-
terfering radiation is detected.
Further information on scenario B
A differential limit value is monitored, i.e. each fast rise of the dose rate triggers
an alarm.
Even minor outside radiation is detected, when it occurs erratically. Operative fac-
tors such as fast emptying of the vessel or opening the shielding container may
trigger false alarms.
To rule out false alarms with sufficient statistical safety, you should enter n > 5. The
mathematical correlation shows that the distance of the alarm threshold is depend-
ent upon the respective mean count rate in.
For calculation it holds:
Sigma = √ Ips
Example:
Count rate Im = 300 cps, n = 6
Is =Im + n x √In
Is = 300 +6 x √300 = 404 Ips
Thus, an alarm is signaled as soon as Is exceeds 404 cps.
IMPORTANT
Due to the dynamic behavior of the interfering radiation detection, a quick in-
crease of the pulse rate due to operational factors (e.g. very fast emptying of
the vessel or large short-term level changes caused by agitators) can be inter-
preted as interfering radiation. Due to a high Sigma value, false triggering by
these operating conditions can be suppressed. However, the radiation interfer-
ence detection also becomes less sensitive.
For example, opening the useful beam channel on the shielding can also cause
a quick increase of the count rate. You have to reset the alarm that is then
triggered, or better, do not enable the interfering radiation detection at first.
However, it would be better not to enable the interfering radiation detection
at first. Enable the interfering radiation detection only after calibration.