User's Manual

Appendix A: Technical reference
A.2 Echo processing
SITRANS LR250 (FOUNDATION FIELDBUS)
236 Operating Instructions, 01/2014, A5E32221411-AB
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 85).
•
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.
Auto False Echo Suppression Range must be set to a distance shorter than the distance to the
material level when the environment was learned, to avoid the material echo being screened out.