Siemens SITRANS LG270 Operating Instructions Manual page 11

Prerequisites for inter-
face measurement
PBD-51041066
h2
h1
Fig. 4: Interface measurement
1 Sensor reference plane (seal surface of the process fitting)
d1 Distance to the interface (HART value 1)
d2 Distance to the level (HART value 3)
TS Thickness of the upper medium (d1 - d2)
h1 Height - Interface
h2 Height - Level
L1 Lower medium
L2 Upper medium
L3 Gas phase
Upper medium (L2)
•
The upper medium must not be conductive
•
The dielectric constant of the upper medium or the actual distance
to the interface must be known (input required). Min. dielectric con-
stant: 1.6. You can find a list of dielectric constants on our home
page: www.siemens.com/sitranslg.
•
The composition of the upper medium must be stable, no varying
products or mixtures
•
The upper medium must be homogeneous, no stratifications
within the medium
•
Min. thickness of the upper medium 50 mm (1.97 in)
•
Clear separation from the lower medium, emulsion phase or detri-
tus layer max. 50 mm (1.97 in)
•
If possible, no foam on the surface
Lower medium (L1)
•
The dielectric constant must be 10 higher than the dielectric
constant of the upper medium, preferably electrically conductive.
Example: upper medium dielectric constant 2, lower medium at
least dielectric constant 12.
Gas phase (L3)
•
Air or gas mixture
•
Gas phase - dependent on the application, gas pahse does not
always exist (d2 = 0)
SITRANS LG270 - Operating Instructions
d2
L3
L2
TS
L1
1
d1
11