KROHNE BM 102 Handbook - Manual (Page 73)

BM 102 73
Level measurement as signal amplitude over time since signal was emitted
1 Flange reflection
2 Level measurement
6.1.1 Level measurement of one product
The pulse is emitted by the instrument and guided along the probe. It reflects off the first product
surface it meets and returns to the instrument.
The distance from the gauge flange to the product is proportional to the time taken:
Distance = c
0
. time taken , where c
0
is the speed of light in air.
2
Level is determined by subtracting the distance to the product from the tank height. Note that the
instrument is normally delivered with level being measured from the end of the probe, where the
tank is taken to be empty once the product falls below this point.