Technical reference
A.5 Range extension
SITRANS Probe LR with mA/HART
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Operating Instructions, 05/2019, A5E32337711-AC
A.5
Range extension
In applications where the base of the vessel is conical or parabolic, a reliable echo may be
available below the vessel empty distance, due to an indirect reflection path. Increasing the
range extension to 30% or 40% can provide stable empty vessel readings. Range extension
is entered as a percentage of P006 (process empty level).
A.6
False-echo suppression
False echoes can appear during the receive cycle. They are often created by internal
impediments like a ladder rung, and are usually indicated by an incorrect high level reading.
A.7
TVT (Time varying threshold) curves
A TVT curve defines a threshold below which any echoes will be ignored. The default TVT
curve 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 curve. You can use Auto False-Echo Suppression to filter it out.
The default TVT curve is used until P837 and P838 are used to create a new "learned TVT
curve".
A.8
Auto false-echo suppression
The TVT adjustment parameters allow you to adjust the TVT (Time Varying Threshold)
curve, so that SITRANS Probe LR will ignore false echoes in your application.
P838 allows you to set a distance, and P837 then instructs SITRANS Probe LR to "learn"
where the obstructions/false echoes are within that distance. If possible, rotate the
instrument before using Auto False-Echo Suppression, to lower the amplitude of false
echoes.
When you set P837 to "Learn", the instrument learns the echo profile at that moment
1)
. Then
it uses the learned profile instead of the default TVT curve, for the distance set in P838. The
learned profile (learned TVT curve) follows the echo profile, so that no large false echoes
rise above the learned TVT curve. From the end of the Auto False-Echo Suppression
Distance, the default TVT curve is used. The material level echo rises above this, and is
selected as the true echo.
1)
Set P837 to "Learn" when the material level is substantially lower than process full level
(ideally when the tank is empty or almost empty).