Berthold LB 444 - Interference Radiation Detection

Density Meter LB 444 SECTION 6. BASICS OF DENSITY MEASUREMENTS
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6.3 Interference Radiation Detection
Select the function Radiation Interference (Parameter menu, page 18) to sup-
press interfering radiation (e.g. weld seam testing).
Caution:
When this function is on (Interference Radiation Detection <On>)
•
the automatic switchover of the time constant (function Rapid switch-over) is
always off.
When turning this function on, you have to define a Sigma value which defines a
window for the measuring signal. If the detector signal suddenly exceeds this
threshold,
•
the measurement is aborted
•
the error message "Interference Radiation" appears on the display.
The measured value and the current outputs are held on the last value.
Reset the error message and start the measurement via the keyboard by ac-
knowledging the error message with <
enter
> and start the measurement with
<
run
> or externally via the digital input.
Note:
To rule out false alarms with sufficient statistical safety, you should enter n > 5.
The mathematical correlation shows that the distance from the alarm threshold
is dependent upon the respective mean pulse rate I
m
.
For calculation it holds: Sigma =
Is/
Example:
Countrate I
m
= 300 I/s, n = 6
I
S
= I
m
+ n *
Im
I
S
= 300 + 6 *
300
= 404 I/s
Thus, an alarm is signaled as soon as I
S
exceeds the value of 404 cps
Note:
Due to the dynamic behavior of the interfering radiation detection, a quick in-
crease of the pulse rate due to operative factors (e.g. very fast emptying of the
vessel or major short-term density changes caused by stirrers) can be inter-
preted as interfering radiation.
For example, opening the active beam channel on the shielding can also cause
a quick increase of the pulse rate. You have to reset the alarm that is then trig-
gered, or better, do not enable the interfering radiation detection at first. Enable
the interfering radiation detection only after the calibration has been performed.