Confidence; Echo Threshold; Figure Of Merit - Siemens SITRANS LUT400 Operating Instructions Manual

A.2.1.3

Confidence

Confidence (3.2.9.2.) (Page 245) describes the quality of an echo. Higher values represent
higher quality.
A.2.1.4

Echo Threshold

Echo Threshold (2.12.2.2.) (Page 220) defines the minimum confidence value required for
an echo to be accepted as valid and evaluated.
A.2.1.5

Figure of Merit

Figure of Merit (3.2.9.1.) (Page 244) measures the quality of the reported process value:
higher values represent better quality. Even when a low confidence value exists, a high FOM
will ensure the true echo has been selected. Approximately 20 readings are used to support
the FOM value.
Example:
FOM greater than 75% = good quality,
FOM less than 50% = poor quality.
Various things contribute to the FOM:
● success of the tracking (how closely can the next level vs. the actual next level be
predicted)
● level of noise
● confidence of the last echo
● time interval since last valid echo
● speed at which the process is moving
● quality of the echo shape and how it helps the calculation of the echo position
If FOM is low, reduce the noise in the process, or check the installation to increase signal
quality.
Shaper Mode and Auto False Echo Suppression
Note
• For detailed instructions on using this feature via PDM, see Auto False Echo Suppression
in LUT400 Communications manual
• For detailed instructions on using this feature via the local push buttons, see Shaper
Mode (2.12.3.4.) (Page 223).
Communications for SITRANS LUT400 (HART) Manual (7ML19985NE01)
1)
False echoes can be caused by an obstruction in the transducer shot path (such as pipes,
ladders, chains). Such false echoes may rise above the default TVT curve.
SITRANS LUT400
Operating Instructions, 07/2019, A5E33329501-AC
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