User's Manual

Appendix A: Technical reference
A.2 Echo processing
SITRANS LR250 (FOUNDATION FIELDBUS)
232 Operating Instructions, 01/2014, A5E32221411-AB
Position Detect (2.5.7.2.)
The echo position detection algorithm determines which point on the echo will be used to
calculate the precise time of flight, and calculates the range using the calibrated propagation
velocity [see
Propagation Factor (2.5.3.)
for values]. There are three options:
●
Center
●
Hybrid
(Center and CLEF)
●
CLEF
(Constrained Leading Edge Fit)
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.