User's Manual

Page 116 SITRANS LR560 (PROFIBUS PA) – OPERATING INSTRUCTIONS 7ML19985LT01
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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 (2.4.8.1.)
on page 118 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 (2.4.5.1.)
The true echo is selected based on the setting for the Echo selection algorithm. For a list
of options see Algorithm (2.4.5.1.) on page 71.
Position Detect (2.4.5.2.)
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. The following options are available:
• Rising
• Center
•Hybrid
• CLEF (Constrained Leading Edge Fit)
Rising
Uses rising edge of the echo.
Center
Uses center of the echo.
Hybrid
Uses the Center algorithm for the top part of the vessel, and the CLEF algorithm for the
part nearest the vessel bottom, according to the setting for CLEF range.
default TVT
material
level
echo marker
echo profile