Endress+Hauser Fieldbus Levelflex M FMP41C Operating Instructions Manual page 58

Commissioning
!
58
Check that the following conditions are fulfilled:
• The echo quality at the end of measuring range should be at least 10dB.
• There should be practically no interference echoes in front of the level signal.
Note!
If the cyclical envelope curve display is still active on the display, the measured value is updated at
a slower cycle time. We therefore advise you to exit the envelope curve display after optimising the
measuring point. To do this, press F. (The instrument does not leave the envelope curve display
automatically.)
6.7.4 Envelope curve
The Levelflex emits individual pulses in quick succession and scans their reflection with a slightly
variable delay. The energy values received are ordered by their time-of-flight. The graphic
representation of this sequence is known as an "envelope curve".
6.7.5 Mapping (empty curve) and difference curve
To suppress interference signals, the envelope curve is not directly evaluated in the Levelflex. The
mapping (empty curve) is first subtracted from the envelope curve.
The system looks for level echoes in the resulting difference curve.
Difference curve = envelope curve - mapping (empty curve)
The mapping (empty curve) should be a good representation of the probe and the empty tank or
silo. Ideally, only the signals from the medium being measured remain in the difference curve.
6.7.6 Mapping
• Factory mapping
Mapping (empty curve) is already available in the instrument when the instrument is delivered.
• Customer mapping
In a partially filled state, the distance up to 10 cm before the actual total level can be mapped
(range of mapping = actual distance from total level - 10 cm), or values > LN can be mapped in
the case of empty tanks.
• Dynamic mapping
It is not static like factory and customer-specific interference echo suppression. Instead, it follows
directly from static mapping and constantly adapts to the changing features of the probe
environment during ongoing operation. Thus, dynamic mapping does not have to be recorded
explicitly.
6.7.7 Echo threshold
Maximum points in the difference curve are only accepted as reflection signals if they are above a
specified threshold.
This threshold depends on the location and is automatically calculated from the ideal echo curve of
the probe used.
The calculation of the threshold in question depends on the "Installation" customer parameter in the
extended calibration function.
Levelflex M FMP41C with FOUNDATION Fieldbus
Endress + Hauser