Function And System Design; Measuring Principle - Endress+Hauser Levelflex M FMP41C Technical Information

Levelflex M FMP41C, FMP45

Measuring principle

Endress+Hauser

Function and system design

The Levelflex is a "downward-looking" measuring system that functions according to the ToF method (ToF =
Time of Flight). The distance from the reference point (process connection of the measuring device (→ Page
30-31) to the product surface is measured. High-frequency pulses are emitted and guided along the probe. The
pulses are reflected by the product surface, received by the electronic evaluation unit and converted into level
information.
This method is also known as TDR (Time Domain Reflectometry).
Probe length
LN
Reference point of measurement, details → Page 30-31
Input
The reflected pulses are transmitted from the probe to the electronics. There, a microprocessor analyses the
signals and identifies the level echo, which was generated by the reflection of the high-frequency pulses at the
product surface. This clear signal finding benefits from the more than 30 years of experience with pulse time-
of-flight procedures that have been integrated into the development of the PulseMaster
The distance D to the product surface is proportional to the time of flight t of the impulse:
D = c · t/2,
with c being the speed of light.
Based on the known empty distance E, the level L is calculated:
L = E – D
Reference point for "E" see above diagram.
The Levelflex possesses functions for the interference echo suppression that can be activated by the user. They
guarantee that interference echoes from internal objects and struts are not interpreted as level echoes.
Flange:
reference point of
measurement
D
L
20 mA
100%
E
F
4 mA
0%
L00-FMP4xxxx-15-00-00-en-006
®
Software.
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