A5E33329501 SITRANS LUT400 (HART) – OPERATING INSTRUCTIONS Page 259
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App. A - Technical Ref.
Algorithm
The true echo is selected based on the setting for the Echo selection algorithm. For a list
of options see Algorithm (2.12.2.1.) on page 182. All algorithms ultimately use confidence
to select the true echo. However, when applications report a low confidence value, the
TR algorithm (which tracks the moving echo) can be used to predict the primary variable.
Confidence
Confidence (3.2.9.2.) describes the quality of an echo. Higher values represent higher
quality.
Echo Threshold
Echo Threshold (2.12.2.2.) defines the minimum confidence value required for an echo to
be accepted as valid and evaluated.
Algorithm Echo Determination Suggested Usage
TF True First echo
Selects the first echo that crosses TVT
curve.
Use in liquids applica-
tions free of obstruc-
tions when confidence
of first echo is high.
TR TRacker
Selects the echo that is closest to the
transducer, and is moving. (If echo loca-
tion is steady, BLF algorithm should be
used.)
Only use TR algorithm in
process applications
with continuous level
changes, and a risk of
fixed obstructions that
could interfere with true
level, resulting in low
confidence.
LLargest echo
Selects the largest echo above the TVT
curve.
Use in long range liq-
uids applications with
large (tall) material
return echoes.
BLF
Best of First and
Largest echo
Selects the echo (first and highest) with
the highest confidence value.
Default and most com-
monly used. Use in all
short to mid range gen-
eral liquids and solids
applications where there
is a relatively large (tall),
sharp echo.
ALF
Area, Largest,
and First
Selects the echo with the highest confi-
dence value based on the three criterion
(widest, highest, and first).
Use in mid to long range
solids applications
where the material
return echo is wide and
large, and where com-
peting smaller echoes
challenge BLF.
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