Principle Of Operation - Siemens SITRANS LG250 Operating Instructions Manual

Application area
Functional principle -
level measurement
Functional principle - in-
terface measurement
PBD-51041388
– Safety Manual (SIL)
– Test certificate measuring accuracy (optional)
– Operating instructions manual "Display and adjustment mod-
ule" (optional)
– Supplementary instructions manual "Plug connector for con-
tinuously measuring sensors" (optional)
– Ex-specific "Safety instructions" (with Ex versions)
– if necessary, further certificates
3.2

Principle of operation

The SITRANS LG250 is a level sensor with cable or rod probe for
continuous level or interface measurement, suitable for applications
in liquids.
Due to the qualification up to SIL2 or homogeneous redundant up
to SIL3 (IEC 61508) the SITRANS LG250 is suitable for the use in
safety-instrumented systems (SIS).
The safety function (SIF) can be a monitoring of the max. or min. level
or a combination of both.
High frequency microwave pulses are guided along a steel cable or
a rod. Upon reaching the product surface, the microwave pulses are
reflected. The running time is evaluated by the instrument and output-
ted as level.
h
Fig. 2: Level measurement
1 Sensor reference plane (seal surface of the process fitting)
d Distance to the interface (HART value 1)
h Height - Level
High frequency microwave impulses are guided along a steel cable or
rod. Upon reaching the product surface, a part of the microwave im-
pulses is reflected. The other part passes through the upper product
and is reflected by the interface. The running times to the two product
layers are processed by the instrument.
SITRANS LG250 - Operating Instructions
1
d
9