Siemens LR 460 User Manual
7ML19985JM01
SITRANS LR 460 – INSTRUCTION MANUAL
Page A-73
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False Echoes
False echoes can appear during the receive cycle. They can be caused by interference
with the emission cone, or by internal impediments like a ladder rung, and are usually
indicated by an incorrect high level reading.
with the emission cone, or by internal impediments like a ladder rung, and are usually
indicated by an incorrect high level reading.
Beam angle at –3dB reference
Make allowance for the beam
spreading, to avoid interference
with the emission cone.
spreading, to avoid interference
with the emission cone.
Polarization reference point
You can rotate the device to minimize false echoes. See
page 14 for details.
Auto False-Echo Suppression
The TVT adjustment parameters allow you to manipulate the TVT (Time Varying
Threshold), so that SITRANS LR 460 will ignore false echoes.
Threshold), so that SITRANS LR 460 will ignore false echoes.
The default TVT hovers above the echo profile, and effectively screens out small false
echoes. But if an obstruction is causing a large echo before the material level echo, that
echo will rise above the default TVT.
echoes. But if an obstruction is causing a large echo before the material level echo, that
echo will rise above the default TVT.
1.
Set Auto False-Echo Suppression to Learn. The instrument learns the echo profile at
that moment
that moment
1
. The new TVT follows the echo profile, so that nothing rises above it.
2.
Set Auto False Echo Suppression Distance so that the learned TVT will be used in
the area of the false echoes, which will not rise above it. From that point on the
default TVT will be used. The material level echo rises above this, and is selected as
the true echo.
default TVT will be used. The material level echo rises above this, and is selected as
the true echo.
See page 58 for examples of the echo profile before and after using Auto False-Echo
Suppression.
Suppression.
Note:
If possible, rotate the instrument before using Auto False-Echo Suppression, to
lower the amplitude of false echoes.
1.
Set Auto False-Echo Suppression to Learn when the material level is substantially lower than
process full level (ideally when the vessel is empty or almost empty).
process full level (ideally when the vessel is empty or almost empty).
3" horn
4" horn
11°
emission
cone
reference
point
8°
distance to
target