Endress+Hauser FMR 231 - Aligning the Micropilot

7.5 Echo quality
The echo quality of the measurement is displayed in dB in V3H2 and via the bargraph in
V0H8 and V0H9. In this case, each segment represents 5 dB. For devices without
communication (operating and display module VU 330, DXR 275 or Commuwin II), the
echo quality cannot be checked.
For reliable measurement the echo quality should be:
•
at least 10 dB or 3 segments,
•
better is 20 dB or 4 segments.
The probability that the echo will be lost when measuring conditions change (E641), e.g.
waves or large measuring ranges, increases with decreasing quality.
Better quality can be attained by exact alignment (turning the process connection) during
installation or a change of mounting position.
Aligning the Micropilot An alignment point is to be found on the flange or threaded connection of the Micropilot.
During installation, this should be aligned as follows:
•
for tanks: towards the tank wall,
•
for stilling wells: towards the slots.
After the Micropilot has been commissioned, the echo quality can be used to determine
the signal strength. If necessary, this can be maximised by optimising the alignment. On
the other hand, optimum alignment using echo quality can also be used minimise the
effect of an interference echo. The advantage here is that a subsequent echo
suppression map will use a lower threshold, causing an overall increase in signal
strength. Proceed as follows:
Warning
•
Danger of injury when re-aligning the Micropilot. Before the process connection is
unscrewed or loosened, check that the tank is not pressurised and does not contain
substances which are hazardous to health.
1) Empty tank as far as possible.
2) Check whether the distance displayed in V0H8 corresponds to the distance to the
product surface:
– If yes: the echo is a level echo. The echo quality must be maximised.
– If no: the echo is a false echo. The echo quality must be minimised.
3) Unscrew flange or loosen threaded connection by half a turn.
4) Turn flange by one hole or tighten threaded connection by an eighth of a turn. Note
the echo quality.
5) Turn stepwise through 360°, noting the echo quality at each turn.
6) Determine the optimal alignment from the noted echo qualities:
– level echo: maximum value
– interference echo: minimum value.
7) Mount flange or threaded connection in this position.
If necessary renew seal.
8) Record echo suppression map, see Chapter 6.3.
Warning!
Chapter 7 Trouble-Shooting Micropilot FMR 231
40 Endress+Hauser