Technical Reference; Principles Of Operation; Measurement Response - Siemens SITRANS LR460 Operating Instructions Manual

Technical reference

A.1

Principles of operation

SITRANS LR460 is a long range FMCW (Frequency Modulated Continuous Wave) radar
transmitter. 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 or dust levels inside a vessel.
SITRANS LR460 consists of an enclosed electronic component coupled to an antenna and
process connection. The electronic component generates an electromagnetic signal from
24.2 GHz to 25.2 GHz that is directed to the antenna.
The signal is emitted from the antenna, 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 and output.
A.2

Measurement response

The measurement response (response rate) limits the maximum rate at which the display and
output respond to changes in the measurement. Once the real process fill/ empty rate (m/s) is
established, a response rate can be selected that is slightly higher than the application rate.
The response rate automatically adjusts the filters that affect the output response rate.
There are three preset options: slow, medium, and fast.
Related parame-
ters
Values
If none of the preset options is satisfactory, the filters can be adjusted individually.
SITRANS LR460
Operating Instructions, 10/2021, A5E42035355-AB
Response rate LOE Timer
(minutes)
* slow 100
medium 10
fast 1
Fill rate Empty rate
0.1 m/minute 0.1 m/minute
1 m/minute 1 m/minute
10 m/minute 10 m/minute
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