The following parameters are changed dur
-
ing hysteresis test/d5 correspondingly:
4
Lower x-range value (Code 8): 0 %
4
Upper x-range value (Code 9): 100 %
4
Lower/upper x-limit (Code 10/11): OFF
4
Setpoint cutoff w decrease/increase
(Code 14/15): OFF
4
Pressure limit (Code 16): Active pressure
limit is raised one stage higher
4
W-ramp OPEN/CLOSED (Code 21/22):
Variable
Data can be reset in the
Status messages
folder.
2.6 End position trend
The end position trend is used to detect a
creeping zero point shift due to seat and
plug wear or dirt between the seat and
plug. A fluctuating zero point also causes an
alarm to be issued.
To accomplish this function, the valve posi-
tion x and the drive signal y are automati
-
cally logged and time-stamped by the oper
-
ating hours counter in automatic mode
when the valve moves to the lower end posi
-
tion. The measured data are stored in an
FIFO memory that always stores 30 mea
-
sured data points.
The measured data are first stored in a ring
buffer if the valve position x differs by
±0.25 % from the measured value previ
-
ously recorded.
To allow the test to run automatically in the
background, activate the tight-closing func
-
tion (over Code 14 or in the
Positioner
folder (>
Reference variable
>
Setpoint cut
-
off decrease
) and make sure the positioner
is in AUTO operating mode.
When the valve moves to the zero point for
the first time in controlled operation, this
measured value serves as a reference. The
reference value is stored in a non-volatile
memory independent from the ring buffer.
EB 8388 EN 19
Statistical information AUTO
Fig. 9 · End position trend with zero point shift at measuring point 1
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