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Appendix A: Technical reference
A.2 Echo processing
SITRANS LR250 with FOUNDATION FIELDBUS
238
Operating Instructions, 09/2021, A5E32221411-AH
A.2.5 Echo Threshold
Confidence (2.5.9.1.) describes the quality of an echo. Higher values represent higher
quality. Echo Threshold (2.5.7.3.) defines the minimum confidence value required for an
echo to be accepted as valid and evaluated.
A.2.6 Echo Lock
If the echo selected by Algorithm is within the Echo Lock window, the window is centered
about the echo, which is used to derive the measurement. In radar applications, two
measurement verification options are used:
Lock Off
SITRANS LR250 responds immediately to a new selected echo (within the restrictions set by
the Maximum Fill / Empty Rate), but measurement reliability is affected.
Material Agitator
A new measurement outside the Echo Lock Window must meet the sampling criteria before
the window will move to include it.
The other available options, Maximum Verification and Total Lock are not recommended
for radar.
A.2.7 Auto False Echo Suppression
Note
• For detailed instructions on using this feature via AMS see TVT (time varying threshold)
(Page 82).
• For detailed instructions on using this feature via the handheld programmer see Auto
False Echo Suppression (2.5.10.1.).
Auto False Echo Suppression is designed to learn a specific environment (for example, a
particular vessel with known obstructions), and in conjunction with Auto False Echo
Suppression Range to remove false echoes appearing in front of the material echo.
The material level should be below all known obstructions at the moment when Auto False
Echo Suppression learns the echo profile. Ideally the vessel should be empty or almost empty,
and if an agitator is present, it should be running.
The device learns the echo profile over the whole measurement range and the TVT is shaped
around all echoes present at that moment.
Auto False Echo Suppression Range (2.5.10.2.)
Auto False Echo Suppression Range specifies the range within which the learned TVT is
applied. Default TVT is applied over the remainder of the range.
The learned TVT screens out the false echoes caused by obstructions. The default TVT allows
the material echo to rise above it.