Siemens SITRANS LG250 Operating Instructions Manual page 62

Check the 4 ... 20 mA
signal
Error
4 ... 20 mA signal not sta-
ble
4 ... 20 mA signal missing
Current signal greater than
22 mA or less than 3.6 mA
Treatment of measure-
ment errors
62
•
Evaluation of fault messages, for example via the display and
adjustment module
•
Checking the output signal
•
Treatment of measurement errors
Further comprehensive diagnostics options are available with a PC
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
– Fluctuations of the
measured variable
– Electrical connection
faulty
– Voltage supply missing
– Operating voltage too
low or load resistance
too high
– Electronics module in
the sensor 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. 26: 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
SITRANS LG250 - Operating Instructions
Rectification
– Set damping appropriate to the instrument via the
display and adjustment module or PACTware/DTM
– Check connection according to chapter "Connection
steps" and if necessary, correct according to chapter
"Wiring plan"
– Check cables for breaks; repair if necessary
– Check, adapt if necessary
– Exchange the instrument or send it in for repair
0
1
2
time
PBD-51041387