Endress+Hauser Levelflex FMP56 Technical Information page 6

Levelflex FMP56, FMP57
Dielectric constant
The dielectric constant (DC) of the medium directly affects the degree of reflection of the high-
frequency pulses. In the case of large DC values, such as with water or ammonia, there is strong
pulse reflection while, in the case of low DC values, such as with hydrocarbons, pulse reflection is
weak.
Input
The reflected pulses are transmitted from the probe to the electronics. Here, a microprocessor
evaluates the signals and identifies the level echo which was caused by the reflection of the high-
frequency pulses at the product surface. This clear signal detection system benefits from over 30
years of experience with pulse time-of-flight procedures that have gone 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,
with c being the speed of light.
Based on the known empty distance E, the level L is calculated:
L = E – D
The Levelflex has functions for interference echo suppression that can be activated by the user. They
guarantee that interference echoes from internal fixtures and struts, for example, are not interpreted
as level echoes.
Output
The Levelflex is preadjusted 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, based on a table entered either manually or semi-automatically, can be
activated locally or remotely. This function allows the level to be converted into units of volume or
mass, for example.
6 Endress+Hauser