Siemens SITRANS LG270 Operating Instructions Manual page 61

Treatment of measure-
ment errors
Measurement error with constant level
Fault description
Measured value shows a
too low or too high level
0 time
Measured value jumps to-
wards 100 %
0 time
PBD-51041506
Further comprehensive diagnostics options are available with a PC/
notebook with PACTware and the suitable DTM. In many cases, the
reasons can be determined in this way and faults rectified.
The below tables show typical examples for application-relevant
measurement errors. There are two measurement errors:
•
Constant level
•
Filling
•
Emptying
The images in column "Error pattern" show the real level as a broken
line and the level displayed by the sensor as a continuous line.
Fig. 27: The broken line 1 shows the real level, the continuous line 2 shows the
level displayed by the sensor
Note:
If the output level is constant, the cause could also be the fault setting
of the current output to "Hold value".
If the level is too low, the reason could be a line resistance that is too
high
Cause
Min./max. adjustment not correct
Incorrect linearisation curve
Running time error (small measurement
error close to 100 %/serious error close
to 0 %)
Due to the process, the amplitude of the
product echo decreases
A false signal suppression was not car-
ried out
Amplitude or position of a false signal
has changed (e.g. buildup); false signal
suppression no longer matches
SITRANS LG270 - Operating Instructions
0
Rectification
Adapt min./max. adjustment
Adapt linearisation curve
Repeat setup
Carry out a false signal suppression
Determine the reason for the changed
false signals, carry out false signal sup-
pression, e.g. with buildup
1
2
time
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