Endress+Hauser Levelflex FMP51 Modbus Technical Information page 9

Levelflex FMP51 Modbus
Endress+Hauser
Dielectric constant
The dielectric constant (DC) of the medium has a direct impact on the degree of reflection of the
highfrequency pulses. In the case of large DC values, such as for water or ammonia, there is strong
pulse reflection while, with low DC values, such as for hydrocarbons, weak pulse reflection is
experienced.
Input
The reflected pulses are transmitted from the probe to the electronics. There, 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 have been integrated into the
development of the PulseMaster® software.
The distance D to the product surface is proportional to the time of flight t of the impulse:
D = c · t/2,
where c is the speed of light.
Based on the known empty distance E, the level L is calculated:
L = E – D
The reference point R of the measurement is located at the process connection. For details see the
dimensional drawing:
FMP51: →  53
The Levelflex possesses functions for interference echo suppression that can be activated by the user.
They guarantee that interference echoes from e.g. internals and struts are not interpreted as level
echoes.
Output
The Levelflex is preset 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, for digital outputs and the display module 0 % and 100 %. A linearization function
with max. 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 into units of
volume or mass, for example.
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