Siemens SITRANS LG250 Operating Instructions Manual page 15

Measuring range
Pressure
Steam boiler applications
PBD-51041056
The reference plane for the measuring range of the sensors is the
sealing surface of the thread or flange.
Keep in mind that a min. distance must be maintained below the refer-
ence plane and possibly also at the end of the probe - measurement
in these areas is not possible (dead band). These dead bands are
listed in chapter "Technical data". Keep in mind for the adjustment that
the default setting for the measuring range refers to water.
The process fitting must be sealed if there is gauge or low pressure in
the vessel. Before use, check if the seal material is resistant against
the measured product and the process temperature.
The max. permissible pressure is specified in chapter "Technical
data" or on the type label of the sensor.
Vapours, superimposed gases, high pressures and temperature dif-
ferences can change the spreading speed of radar impulses.
There are two possibilities to correct these deviations.
Corrective value in the process control system
In the technical data under "Influence of superimposed gas and pres-
sure on accuracy" you can find a table with deviation values in some
typical gases or in steam.
In the control system (DCS) you can correct the measurement results
of the SITRANS LG250 with these values.
The prerequisite is constant temperature and pressure in the vessel.
Automatic correction via the reference distance
The SITRANS LG250 can be equipped optionally with a running time
correction via reference distance. The probe can carry out an auto-
matic running time correction with it.
The reference point must hence not be overfilled. The upper dead
band is hence 450 mm (17.7 in).
SITRANS LG250 - Operating Instructions 15