Endress+Hauser Levelflex M FMP40 Operating Instructions Manual page 85

Levelflex M FMP40 with HART/4...20 mA
Endress+Hauser
11.3.1 Input
The reflected pulses are transmitted from the probe to the electronics. Here, a microprocessor
analyzes 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 detection system benefits from over
30 years' experience with pulse time-of-flight procedures that went into the development of the
PulseMaster® software.
The distance D to the product surface is proportional to the time-of-flight t of the pulse:
D = c · t/2,
where c is the speed of light.
Since the system knows the empty distance E, the level L is calculated as:
L = E – D
Reference point for "E", see diagram → ä 84.
The Levelflex possesses functions for interference echo suppression that can be activated by the
user. They ensure that interference echoes from internal fittings or struts, for example, are not
interpreted as level echoes.
11.3.2 Interface measurement
When the high-frequency pulses hit the surface of the medium, only a percentage of the
transmission pulse is reflected. In the case of media with a low DK
penetrates the medium. The pulse is reflected once more at the interface point to a second medium
with a higher DK . The distance to the interface layer can now also be determined taking into
2
account the delayed time-of-flight of the pulse through the upper medium.
DK
DK
11.3.3 Output
The Levelflex is precalibrated at the factory to the probe length ordered so that in most cases only
the application parameters that automatically adapt the device to the measuring conditions need to
be entered. For models with a current output, the factory adjustment for zero point E and span F is
4 mA and 20 mA, and 0 % and 100 % for digital outputs and the display module. A linearization
function with a maximum of 32 points, which is based on a table entered manually or semi-
automatically, can be activated on site or via remote operation. This function allows the level to be
converted to units of volume or mass, for example.
1
2
Appendix
, in particular, the other part
1
c = c = 300 000 km/s
0
total level
C
0
C =
1
DK
1
interface level
L00-FMP4xxxx-15-00-00-en-007
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