Siemens SITRANS LUT400, Operating Instructions Manual

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Page 260 SITRANS LUT400 (HART) – OPERATING INSTRUCTIONS A5E33329501
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Figure of Merit
Figure of Merit (3.2.9.1.) 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
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.
Auto False Echo Suppression Range (2.12.3.2.) specifies the range within which the
learned TVT is applied. Default TVT is applied over the remainder of the range.
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.
The device learns the echo profile over the whole measurement range and the TVT is
shaped around all echoes present at that moment.
Notes:
• For detailed instructions on using this feature via PDM, see Auto False Echo
Suppression in LUT400 Communications manual
a
.
• For detailed instructions on using this feature via the local push buttons, see Shaper
Mode (2.12.3.4.) on page 185.
a.
Communications for SITRANS LUT400 (HART) Manual (7ML19985NE01)