User's Manual

7ML19985JE03 SITRANS LR250 (HART) – INSTRUCTION MANUAL Page 127
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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 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.
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 (2.8.7.1.)
on page 130 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 (2.8.4.1.)
The true echo is selected based on the setting for the Echo selection algorithm. Options
are true First Echo, Largest Echo, or best of First and Largest.
Position Detect (2.8.4.2.)
The echo position detection algorithm determines which point on the echo will be used to
calculate the precise time of flight, and calculates the range using the calibrated
propagation velocity (see Propagation Factor (2.8.3.) for values). There are three options:
•Center
• CLEF (Constrained Leading Edge Fit)
• Hybrid
default TVT
material
level
echo marker
echo profile