Siemens SITRANS LR500 Series - Technical Reference; Principles of Operation; Echo Processing Overview; Detailed Echo Processing Steps

Technical reference
B
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)
1)
. Radar level measurement uses the time of 󹪞ight principle to determine distance
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 󹪝rst part of the wave has been
re󹪞ected o󹪜 the target and returned to the device, the part of the wave that is just being
emitted is at a higher frequency. The di󹪜erence in frequency between the transmitted and
received signals is proportional to time of 󹪞ight.
Electromagnetic wave propagation is virtually una󹪜ected 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 re󹪞ected echoes are digitally converted to
an echo pro󹪝le. The pro󹪝le is analyzed to determine the distance from the sensor reference
point
2)
to the material surface. This value (sensor value) is used as a basis for calculating the
display of material level and mA output.
1)
The microwave output level is signi󹪝cantly less than that emitted from cellular phones.
2)
See Dimension drawings (Page187)
B.2 Echo processing
B.2.1 Echo processing
Echo processing consists of echo enhancement, true echo selection, and selected echo
veri󹪝cation.
Echo enhancement is achieved by 󹪝ltering
1)
and reforming
2)
the echo pro󹪝le. The true echo
(echo re󹪞ected by the intended target) is selected when that portion of the echo pro󹪝le
meets the evaluation criteria of Process Intelligence. Insigni󹪝cant portions of the echo pro󹪝le
outside of the measurement range
3)
, below the TVT curve
4)
, and less than the con󹪝dence
threshold
5)
, are automatically disregarded. The remaining portions of the echo pro󹪝le are
evaluated using the selected algorithm
6)
. The echo pro󹪝le portion providing the best echo
con󹪝dence
7)
is selected.
Echo veri󹪝cation 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 201