Long-term monitoring
The measured results
∆
y are classified ac-
cording to the valve position x in the valve
position classes. The average value
∆
y per
valve position class is determined from all
the measured data.
The
Long-term
folder contains a table of the
results.
Short-term monitoring
To provide a short-term trend, the last ten
valve positions x and the associated
∆
y val-
ues are saved in the
Short-term
folder
(>
Valve position
and
Difference signal
drive
).
Graphs
The
Hysteresis
folder contains a graph with
two curves plotted. The
Measurement
curve
shows the measured data recorded for
long-term monitoring and the
Reference
curve shows the reference data recorded af-
ter initialization.
The graph plotted using the reference data
covers the full range of the valve.
The data for long-term monitoring are re-
corded online while the process is running,
and therefore, the graphs do not necessarily
cover the full range of the valve.
Reference values are used in cases where no
data could be compiled for valve classes.
If the test has not yet been activated, the
graph for the reference data is represented
by a straight line.
The diagram allows changes in
∆
y with the
corresponding valve positions to be
recognized.
Changes in friction are highlighted as
∆
y is
proportional to the actuator pressure which,
in turn, is a measurement for friction. A
change in friction leads to an alarm being
issued.
Test requirements:
The test is possible in relation to the travel
range between 2 and 98 %.
4
A successfully plotted reference graph is
necessary in order to analyze the fric-
tion.
4
The test can only be started when the tol-
erance band (Code 19) or
Positioner
folder (>
Error control
>
Tolerance band
)
is greater than 1 %.
4
The characteristic type (Code
20
) must
be set to
Linear
in order to record the
data.
4
Refer to section 1.6 in case a double-act-
ing actuator with reversing amplifier or a
booster is used or the SUb initialization
mode is set.
Note!
The valve can be moved through its travel
range in manual mode, during plant
shutdown or when the process allows it by
selecting
Drive signal diagram hysteresis
in
Test MAN
to check the results or statements
determined in automatic mode in the Status
message folder (> Extended).
18
EB 8388 EN
Statistical information AUTO
