Siemens LR 460 False Echoes, Auto False-Echo Suppression, Beam angle at -3dB reference, Technical

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.

Beam angle at –3dB reference

A: Technical

Make allowance for the beam spreading, to avoid interference with the emission cone.

3" horn	4" horn
	reference
	point
	emission
	cone

distance to

target

Reference

11° 8°

Polarization reference point

You can rotate the device to minimize false echoes. See Polarization Reference Point on page 14 for details.

Auto False-Echo Suppression

Note: If possible, rotate the instrument before using Auto False-Echo Suppression, to lower the amplitude of false echoes.

The TVT adjustment parameters allow you to manipulate the TVT (Time Varying 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.

1.Set Auto False-Echo Suppression to Learn. The instrument learns the echo profile at that moment1. 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.

See page 58 for examples of the echo profile before and after using Auto False-Echo Suppression.

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).

7ML19985JM01 SITRANS LR 460 – INSTRUCTION MANUAL Page A-73