Time Varying Threshold (Tvt) Curves - Siemens sitrans LR200 Instruction Manual

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.

Time Varying Threshold (TVT) Curves

A Time Varying Threshold (TVT) curve hovers above the echo profile to screen out
unwanted reflections (false echoes).
TVT
curve
0
In most cases the material echo is the only one which rises above the default TVT curve.
In a vessel with obstructions a large false echo may rise above the default TVT. The Auto
False Echo Suppression feature (see below) can be used to screen it out.
The device characterizes all echoes that rise above the TVT as potential good echoes.
Each peak is assigned a rating based on its strength, area, height above the TVT, amongst
other characteristics.
The true echo is selected based on the setting for the Echo selection algorithm: Algorithm
(2.2.3.1.1.). Options are true First Echo, Largest Echo, or best of Largest or First.
7ML19985JR01 SITRANS LR200 (PROFIBUS PA) – INSTRUCTION MANUAL
false
echo
1 2 3
Distance [M]
true
echo
sensor reference point
High Cal. Pt.
= 0
obstruction
at 1.2 m
material
level at
2.9 m
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