Vega VEGAPULS 67 Operating Instructions Manual page 63

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 with bulk
solids
VEGAPULS 67 • 4 ... 20 mA/HART - four-wire
•
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 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 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
9 Diagnosis, asset management and service
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
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