KROHNE BM 102 Handbook - Manual (Page 52)

52 BM 102
The following factors apply to the set gain:
Gain Amplification
factor
0 1.05
1 2.10
2 4.37
3 8.93
Level threshold
The level threshold suppresses interference signals so that only the reflections from the product
surface (level signal) are shown. The factory setting of the level threshold is suitable for standard
applications. The threshold will need to be adjusted in the case of very low dielectric constants,
multiple interference reflections or unfavourable installation conditions.
The illustrations below show interference signals when the oscilloscope function is used. These
reflections can be due to various causes, e.g. tank internals or multiple reflections within the
measuring range.
Even though the interference signals
are very weak, the threshold should
nevertheless be set to a value above
these signals.
1 Emitted
pulse
2 Flange reflection
3 Level signal
4 Interference signal
1 Emitted pulse
2 Flange reflection
3 Level signal
4 Interference signal
5 Threshold
In the diagram above it can be seen that the level of the threshold is not constant: 400 mV at 1 m or
3.3 ft, and only 250 mV at 10 m or 33 ft.
No attenuation is required at a probe length ≤ 3 m or 10 ft. The form of the threshold is dependent
on attenuation and is automatically adjusted by the device over the measured length.