Siemens SITRANS LG270 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
A PC with the software PACTware and the suitable DTM or the soft-
ware PDM with a suitable DD offer further comprehensive diagnostics
options. In many cases, the reasons can be determined in this way
and faults can be 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. 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
SITRANS LG270 - 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-51041064