Siemens SITRANS L Operating Instructions Manual page 234

Appendix A: Technical reference
A.2 Echo processing
Process Intelligence is able to differentiate between the true microwave reflections from the
surface of the material and unwanted reflections being returned from obstructions such as
seam welds or supports within a vessel. The result is repeatable, fast and reliable
measurement. This technology was developed as result of field data gained over some
twenty years from more than 1,000,000 installations in many industries around the world.
Higher order mathematical techniques and algorithms are used to provide intelligent
processing of microwave reflection profiles. This "knowledge based" technique produces
superior performance and reliability.
A.2.2 Echo Selection
Time Varying Threshold (TVT)
A Time Varying Threshold (TVT) hovers above the echo profile to screen out unwanted
reflections (false echoes).
In most cases the material echo is the only one which rises above the default TVT.
In a vessel with obstructions, a false echo may occur. See Auto False Echo Suppression
(Page 238) for more details.
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default TVT
echo profile
material level
echo marker
SITRANS LR250 with FOUNDATION FIELDBUS
Operating Instructions, 09/2021, A5E32221411-AH