User's Manual

A5E32337685 SITRANS LR260 (PROFIBUS PA) – OPERATING INSTRUCTIONS Page 103
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D: Technical Reference
Appendix D: Technical Reference
Principles of Operation
SITRANS LR260 is a 2-wire 25 GHz pulse radar level transmitter for continuous monitoring
of solids and liquids
1)
. Radar level measurement uses the time of flight principle to
determine distance to a material surface. The device transmits a signal and waits for the
return echo. The transit time is directly proportional to the distance from the material.
Pulse radar uses polarized electromagnetic waves. Microwave pulses are emitted from
the antenna at a fixed repetition rate, and reflect off the interface between two materials
with different dielectric constants (the atmosphere and the material being monitored).
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 LR260 consists of an enclosed electronic circuit coupled to an antenna and
process connection. The electronic circuit generates a radar signal (25 GHz) that is
directed to the horn.
The signal is emitted from the horn, and the reflected echoes are digitally converted to an
echo profile. The profile is analyzed to determine the distance from the material surface
to the reference point on the instrument. This distance is used as a basis for the display of
material level.
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.
Process Intelligence is able to differentiate between the true microwave reflections from
the surface of the material and unwanted reflections being returned from obstructions
such as seam welds or supports within a vessel. The result is repeatable, fast and
reliable measurement. This technology was developed as result of field data gained over
some twenty years from more than 1,000,000 installations in many industries around the
world.
1)
The microwave output level is significantly less than that emitted from cellular phones.