KROHNE BM 102 Handbook - Manual (Page 53)

BM 102 53
Setting the level threshold
If the level threshold is set too high, i.e. it is greater than the amplitude of the level reflection, the
device will not find any level even with maximum amplification.
If the level threshold is set too low, i.e. it is below the amplitude of some of the interference signals,
the device will identify and indicate one of these interference signals as a level reflection only if the
tank is empty.
Precise setting of the level threshold is especially important when the dielectric constant is low.
• To set, the level (amplitude of the reflection) must be known.
• The level threshold should be half-way between the invalid interference signals and the level
reflection signal.
• The reflection from the probe tip, which is clearly identifiable at a low εr value, does not need to
lie below the level threshold.
Take a look at all the reflections over the entire probe length and then change the level threshold
and/or the amplification factor in the “Dynamic configuration (F11)” menu.
Typical signal trends
The following diagrams show characteristic signals that have been recorded with the oscilloscope
function.
Rod or cable probe with gain 1 Rod or cable probe with gain 2
Coaxial probe with gain 1 Coaxial probe with gain 2
The signal from coaxial probes does not include the flange reflection, due to the mechanical setup
which does not produce any change in impedance at the flange.
The amplitude of reflection from the product surface increases as the level rises and decreases as
the level falls.