Siemens SITRANS LG250 Operating Instructions Manual page 67

Guided wave radar 4...20 ma/hart - two-wire rod and cable probe with sil qualification
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Treatment of measure-
ment errors
Measurement error with constant level
Fault description
1. Measured value
shows a too low or too
high level
2. Measured value
jumps towards 100 %
PBD-51041388
Error
Current sig-
nal greater than
22 mA or less
than 3.6 mA
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 with a bro-
ken 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:
Wherever the sensor displays a constant value, the reason could
also be the fault setting of the current output to "Hold value"
If the level indication is too low, the reason could be a line resist-
ance that is too high
Error pattern
Cause
– Min./max. adjustment not
correct
– Incorrect linearization curve
0
time
– 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
0
time
not carried out
– Amplitude or position of a
false signal has changed (e.g.
buildup); false signal suppres-
sion no longer matches
SITRANS LG250 - Operating Instructions
Cause
Rectification
Electronics mod-
Exchange the instrument or send it in
ule in the sensor
for repair
defective
0
1
2
time
Rectification
– Adapt min./max. adjustment
– Adapt linearization curve
– Repeat setup
– Carry out a false signal sup-
pression
– Determine the reason for the
changed false signals, carry out
false signal suppression, e.g.
with buildup
67

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