Appendix D: Technical Reference; Principles Of Operation; Process Variables - Siemens SITRANS LR560 Operating Instructions Manual

Appendix D: Technical Reference

Note: Where a number follows the parameter name (for example, Device (2.1.) this is
the parameter access number via the local push buttons or handheld programmer. See
Parameter Reference

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)
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 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
basis for calculating the display of material level and mA output.

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).
1)
The microwave output level is significantly less than that emitted from cellular phones.
2)
Dimensions
See
A5E34647946 SITRANS LR560 (mA/HART) – OPERATING INSTRUCTIONS
on page 83 for a complete list of parameters.
1)
. Radar level measurement uses the time of flight principle to
2)
to the material surface. This value (sensor value) is used as a
on page 13.
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