Loss Of Echo (Loe); Blanking Or Auto False Echo Suppression; Typical Receiver Signal - Siemens SITRANS LR 300 Instruction Manual

Loss of Echo (LOE)

A loss of echo (LOE) occurs when the calculated measurement is judged to be unreliable
because the confidence (P805) is less than the threshold (P804). Refer to Operation
Troubleshooting on page 92.
If the LOE condition persists beyond the time limit set by the Fail-Safe timer (P070), the
Confidence icon will change from full to partial:
The response to LOE is set by P072 and P219. They determine whether the reading and
mA output will be immediately forced to the Fail-Safe default (P071 and P219). Upon
receiving a reliable echo, the loss of echo condition is aborted, the Confidence icon
returns to full, and the reading and mA output return to the current level at the rate set by
P072.

Blanking or Auto False Echo Suppression

Near-blanking (P800) is set to ignore the zone in front of the antenna where 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. False echoes
can be overcome by increasing the near-blanking value from its factory setting.
Auto False Echo Suppression (P837) is recommended in preference to extending the
blanking distance from factory values.

Typical Receiver Signal

End of
Transmit
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.
Page 46
P800
Near-blanking
Empty distance to antenna
P006
SITRANS LR 300 – INSTRUCTION MANUAL
to
0
Range Extension
(P801) as % P006
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