User's Manual

Page 122 SITRANS LR560 (mA/HART) – INSTRUCTION MANUAL 7ML19985KB01
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D: Technical Reference
Appendix D: Technical 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 in vessels to a range of 100 m
(329 ft)
1)
. Radar level measurement uses the time of flight 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 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
2)
to the material surface. This value (sensor value) is used as a
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).
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 on page 76 for a complete list of parameters.
1)
The microwave output level is significantly less than that emitted from cellular phones.
2)
See Dimensions on page 11.