VEGA VEGAFLEX 81 4 … 20 mA_HART - four-wire Coax probe - Manual (Page 60)

60
9 Diagnostics and service
VEGAFLEX 81 • 4 … 20 mA/HART - four-wire
42280-EN-130314
Error Cause Rectification
4 … 20 mA signal
missing
– Electrical con-
nection 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 volt-
age too low or
load resistance
too high
– Check, adapt if necessary
Current sig-
nal greater than
22 mA or less
than 3.6 mA
– Electronics
module in the
sensor defec-
tive
– Exchange the instrument or send it
in for repair
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 with a bro-
ken line and the level displayed by the sensor as a continuous line.
1
2
Level
time 0
Fig. 21: 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"
•
In case of a too low level indication, the reason could be a line
resistance that is too high
Measurement error with constant level
Fault description Error pattern Cause Rectification
1. Measured value
shows a too low or too
high level
Level
time 0
– Min./max. adjustment not
correct
– Adapt min./max. adjustment
– Wrong linearization curve – Adapt linearization curve
– Running time error (small
measurement error close to
100 %/serious error close to
0 %)
– Repeat setup
Treatment of measure-
ment errors