Technical Reference; Principles Of Operation; Process Variables; A.1 Principles Of Operation - Siemens SITRANS LR560 Operating Instructions Manual

Technical reference

A.1

Principles of operation

SITRANS LR560 is a 2-wire, 78 GHz FMCW (Frequency Modulated Continuous Wave) radar
level transmitter for continuous monitoring of solids and liquids in vessels to a range of 100 m
(329 ft)
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 LR560 consists of an enclosed electronic circuit coupled to an antenna and process
connection. The electronic circuit generates a radar signal (78 GHz) that is directed to the lens
antenna.
The signal is emitted from the lens 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 169)
2)
A.2

Process variables

The Process Variables are sensor value and measured value. Sensor value is the distance from
the sensor reference point (flange face) to the material surface. The measured value can be
either Level (distance from low calibration point to material surface), Distance (distance from
sensor reference point to the material surface), or Space (distance from high calibration point to
the material surface).
SITRANS LR560 (mA/HART)
Operating Instructions, 06/2017, A5E34647946-AD
. Radar level measurement uses the time of flight principle to determine distance to a
1)
to the material surface. This value (sensor value) is used as a basis for calculating the
2)
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