Prosonic M
Endress+Hauser 3
Function and system design
Measuring principle
L00-FMU4x-15-00-00-xx-001
E: Empty distance; F: Span (full distance); D: Distance from sensor membrane - product surface; L: Level; BD: Blocking
distance
Time-of-flight method
The sensor of the Prosonic M transmits ultrasonic pulses in the direction of the product surface. There, they
are reflected back and received by the sensor. The Prosonic M measures the time t between pulse transmission
and reception. The instrument uses the time t (and the velocity of sound c) to calculate the distance D between
the sensor membrane and the product surface:
D = c ⋅ t/2
As the device knows the empty distance E from a user entry, it can calculate the level as follows:
L = E - D
An integrated temperature sensor compensates for changes in the velocity of sound caused by temperature
changes.
Interference echo suppression
The interference echo suppression feature on the Prosonic M ensures that interference echos (e.g. from edges,
welded joints and installations) are not interpreted as a level echo.
Calibration
Enter the empty distance E and the span F to calibrate the device.
Blocking distance
Span F may not extend into the blocking distance BD. Level echos within the blocking distance cannot be
evaluated due to the transient characteristics of the sensor.
20 mA
100%
4mA
0%
D
L
F
E
BD
Sensor BD Max. range fluids Max. range bulk materials
FMU40 0.25 (0.8) 5 (16) 2 (6.6)
FMU41 0.35 (1.1) 8 (26) 3.5 (11)
FMU42 0.4 (1.3) 10 (33) 5 (16)
FMU43 0.6 (2.0) 15 (49) 7 (23)
FMU44 0.5 (1.6) 20 (66) 10 (33)
m (ft)
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