Technical Reference; Principles Of Operation; Echo Processing - Siemens SITRANS LR500 Series Operating Instructions Manual

Technical reference

B.1

Principles of operation

SITRANS LR500 series is a 2-wire, 80 GHz FMCW (Frequency Modulated Continuous Wave) radar
level transmitter for continuous monitoring of liquids, solids and slurries in vessels to a range of
100 m (329 ft)
to a material surface.
FMCW radar transmits a continuous wave. The frequency of the wave is constantly
increasing: this is known as the sweep. By the time the first part of the wave has been
reflected off the target and returned to the device, the part of the wave that is just being
emitted is at a higher frequency. The difference in frequency between the transmitted and
received signals is proportional to time of flight.
Electromagnetic wave propagation is virtually unaffected by temperature or pressure
changes, or by changes in the vapor levels inside a vessel. Electromagnetic waves are not
attenuated by dust.
SITRANS LR500 series consists of an enclosed electronic circuit coupled to an antenna and
process connection. The electronic circuit generates a radar signal (80 GHz) that is directed to
the antenna.
The signal is emitted from the antenna, and the reflected echoes are digitally converted to
an echo profile. The profile is analyzed to determine the distance from the sensor reference
point
display of material level and mA output.
The microwave output level is significantly less than that emitted from cellular phones.
1)
See Dimension drawings (Page 187)
2)
B.2

Echo processing

B.2.1 Echo processing
Echo processing consists of echo enhancement, true echo selection, and selected echo
verification.
Echo enhancement is achieved by filtering
(echo reflected by the intended target) is selected when that portion of the echo profile
meets the evaluation criteria of Process Intelligence. Insignificant portions of the echo profile
outside of the measurement range
threshold
evaluated using the selected algorithm
confidence
Echo verification is automatic. The position (relation in time after transmit) of the new echo
is compared to that of the previously accepted echo. When the new echo is within the echo
SITRANS LR500 series with mA/HART
Operating Instructions, 03/2024, A5E51099898-AA
. Radar level measurement uses the time of flight principle to determine distance
1)
to the material surface. This value (sensor value) is used as a basis for calculating the
2)
, are automatically disregarded. The remaining portions of the echo profile are
5)
is selected.
7)
and reforming
1)
, below the TVT curve
3)
. The echo profile portion providing the best echo
6)
the echo profile. The true echo
2)
, and less than the confidence
4)
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