Description Of Functions; Function And System Design - Endress+Hauser Fieldbus Levelflex M FMP43 Operating Instructions Manual

Appendix
!
102
11.2

Description of functions

Note!
A detailed description of the function groups, functions and parameters is given in the
documentation BA245F – "Description of Device Functions" on the CD-ROM supplied.
11.3

Function and system design

11.3.1 Measuring principle)
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 → ä 13) to the product surface is measured. High-frequency pulses are injected
to a probe and led 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).
lower edge of the process connection:
reference point of
measurement
Probe length LN
Reference point of measurement, details → ä 14
Fig. 5:
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, details → ä 56.
The Levelflex possesses functions for interference echo suppression that can be activated by the
user. They guarantee that interference echoes from internals and struts, for example, are not
interpreted as level echoes.
Levelflex M FMP43 with FOUNDATION Fieldbus
D D
E E
L L
®
Software.
20 mA
100%
F
4 mA
0%
L00-FMP43xxx-15-00-00-en-001
Endress+Hauser