Range Extension; False-Echo Suppression; Tvt (Time Varying Threshold) Curves; Auto False-Echo Suppression - Siemens Sitrans Probe LR Operating Instructions Manual

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).

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.

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".

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
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.
See page 95 for examples of the echo profile before and after using Auto False-Echo
Suppression.
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).
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