User's Manual

7ML19985LT01 SITRANS LR560 (PROFIBUS PA) – OPERATING INSTRUCTIONS Page 115
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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
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.
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).
Echo Processing
Process Intelligence
The signal processing technology embedded in Siemens radar level devices is known as
Process Intelligence.
Process intelligence provides high measurement reliability regardless of the dynamically
changing conditions within the vessel being monitored. The embedded Process
Intelligence dynamically adjusts to the constantly changing material surfaces within
these vessels.
Note: Where a number follows the parameter name (for example, Algorithm (2.4.5.1.)
this is the parameter access number via the local control buttons or the handheld
programmer. See Parameter Reference on page 62 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 12.