KROHNE BM 100A Handbook - Manual (Page 41)

Handbook BM 100 A 41
Gain and voltage amplitude
As explained in the measuring principle in section 7, the level of a product is converted from a return
signal (the product reflection) received by the gauge: this signal has taken a certain amount of time
to return to the gauge and it has a certain strength / size measured in milli-volts (dependant on the
dielectric constant of the product).
All pulse signals returning to the gauge electronics block (including flange, obstruction and the
product surface reflections) are converted to voltage amplitudes. The gauge’s microprocessor looks
for part of the largest signal that is over a set voltage amplitude, called the “threshold”, and identifies
this as the product being measured. For this signal to be usable by the gauge, the microprocessor
will amplify the signal by increasing the gain. Once the signal is within a set “working” range, the
gauge follows this signal. The gauge registers any changes in time for this part of the signal to return
to the converter and translate this into a displayed level or volume.
Gain is a function of voltage amplitude. This defines the default threshold value when the gauge is
searching for the product level. A strong return signal will be given a low gain (i.e. Gain 0 or a small
amplification). However, if the signal is very weak, then a Gain of 3 (i.e. high signal amplification) is
given.