Siemens SITRANS LG240 Operating Instructions Manual page 56

4 ... 20 mA signal
Error
4 ... 20 mA signal not stable
4 ... 20 mA signal missing
Current signal greater than
22 mA, less than 3.6 mA
Treatment of measure-
ment errors
56
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.
Connect a multimeter in the suitable measuring range according to
the wiring plan. The following table describes possible errors in the
current signal and helps to eliminate them:
Cause
Fluctuating measured value
Electrical connection faulty
Voltage supply missing
Operating voltage too low, load resist-
ance too high
Sensor electronics defective
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. 25: 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
SITRANS LG240 - Operating Instructions
Rectification
Set damping
Check connection, correct, if necessary
Check cables for breaks; repair if nec-
essary
Check, adapt if necessary
Replace device or send in for repair de-
pending on device version
0
1
2
time
PBD-51041037