Siemens SITRANS LR250 Operating Instructions Manual page 236

Appendix A: Technical reference
A.2 Echo processing
Center
Uses center of the echo.
Hybrid
Uses the Center algorithm for the top part of the vessel, and the CLEF algorithm for the part
nearest the vessel bottom, according to the setting for CLEF range.
CLEF (Constrained Leading Edge Fit)
● Uses the leading edge of the echo.
● Is used mainly to process the echo from materials with a low dK value.
In an almost empty flat-bottomed vessel, a low dK material may reflect an echo weaker than the
echo from the vessel bottom. The echo profile shows these echoes merging. The device may
then report a material level equal to or lower than empty.
The CLEF algorithm enables the device to report the level correctly.
Example: CLEF off: Position set to Hybrid
Vessel height: 1.5 m; CLEF range set to 0 (Center algorithm gives the same result.)
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②
③
④
234
default TVT
material echo
vessel bottom echo selected
echo marker
SITRANS LR250 (PROFIBUS PA)
Operating Instructions, 08/2014, A5E32221386-AC