Endress+Hauser Levelflex FMP51 Modbus Technical Information page 10

10
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
penetrates the medium. The pulse is reflected once more at the interface point to a second medium
with a higher DC . The distance to the interface layer now can also be determined taking into
2
account the delayed time-of-flight of the pulse through the upper medium.
DK ( DC
1
DK (DC )
2
 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. 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).
• Emulsion layers in the area of the interface can strongly attenuate the signal. However, emulsion
layers up to 50 mm (2 in) are admissible.
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)
)
1
2
Levelflex FMP51 Modbus
, in particular, the other part
1
R
c = c = 300 000 km/s
0
L
L
C
0
C =
1
DK
1
L
I
Endress+Hauser
A0011178