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9 Diagnosis, asset management and service
VEGAPULS SR 68 • 4 … 20 mA/HART - two-wire
38294-EN-160707
•
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:
Error
Cause
Rectification
4 … 20 mA signal not sta-
ble
– Fluctuations of the
measured variable
– Set damping appropriate to the instrument via the
display and adjustment module or PACTware/DTM
4 … 20 mA signal missing
– Electrical connection
faulty
– Check connection according to chapter "
Connection
steps
" and if necessary, correct according to chapter
"
Wiring plan
"
– Voltage supply missing
– Check cables for breaks; repair if necessary
– Operating voltage too
low or load resistance
too high
– Check, adapt if necessary
Current signal greater than
22 mA or less than 3.6 mA
– Electronics module in
the sensor defective
– Exchange the instrument or send it in for repair
The below tables show typical examples of application-related
measurement errors with bulk solids. A distinction is made between
measurement errors during:
•
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.
1
2
Level
time
0
1 Real level
2 Level displayed by the sensor
Notes:
•
Whenever the sensor displays a constant value, the reason could
also be that the fault setting of the current output is set to "Hold
value"
•
If the level indication is too low, the reason could be a line resist-
ance that is too high
Check the 4 … 20 mA
signal
Treatment of measure-
ment errors with bulk
solids