Endress+Hauser Levelflex FMP55 - Registered Trademarks

Levelflex FMP55
10 Endress+Hauser
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 DC
1
, in particular, the other part
penetrates the medium. The pulse is reflected once more at the interface point to a second medium
with a higher DC
2
. The distance to the interface layer now can also be determined taking into
account the delayed time-of-flight of the pulse through the upper medium.
In addition to this, FMP55 measures the capacitance of the probe. This enables interface
measurements even if the second echo is missing due to an emulsion layer between the two phases.
DK
1
c=c =300000km/s
0
C =
1
DK (DC )
2 2
DK DC
1 1
( )
C
0
L
L
R
L
I
A0011178
 2 Interface measurement with the guided radar
LL Level complete
LI Level interface
R Reference point of measurement
In addition, the following general conditions must be observed for interface measurement:
• The DC of the upper medium must be known and constant
1)
. The DC can be determined with the
aid of the DC manual CP00019F or the "DC Values App". In addition, if the interface thickness is
existing and known, the DC can be calculated automatically via FieldCare.
• The DC of the upper medium may not be greater than 10.
• The DC difference between the upper medium and lower medium must be >10.
• The upper medium must have a minimum thickness of 60 mm (2.4 in).
For dielectric constants (DC values) of many media commonly used in various industries refer
to:
• the Endress+Hauser DC manual (CP01076F)
• the Endress+Hauser "DC Values App" (available for Android and iOS)
When using the capacitive measurement of FMP55:
• Conductivity of the upper medium: < 1 μS/cm
• Conductivity of the lower medium: > 100 μS/cm
1) For FMP55: Under certain conditions measurement is possible even with a changing DC. For details please contact your Endress+Hauser
representative.