Page 112 SITRANS LR250 (PROFIBUS PA) – INSTRUCTION MANUAL 7ML19985JF02
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D: Technical Reference
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 750,000 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.
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 (2.2.4.2.)
on page 114 for
more details.
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, and
reliability, amongst other characteristics.
Algorithm (2.2.3.1.1.)
The true echo is selected based on the setting for the Echo selection algorithm. Options
are true First Echo, Largest Echo, or best of Largest or First.
default TVT
material
level
echo marker
echo profile
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