leaks in the pneumatics before they have an
impact on the process.
The measured data allows the following
problems to be detected and the associated
alarms to be issued:
4
Air leakage in the pneumatics
4
Spring force reduced
4
Changes in supply pressure
The valve position and its associated drive
signal y are measured after the pressure
conditions have settled (steady-state). Each
pair of measured data points recorded is
assigned to a valve position class. The
average drive signal y is calculated for each
class. The stored data can be read.
The reference data required are plotted and
stored after initialization.
Long-term monitoring
The long-term monitoring involves the aver-
age drive signal y for each valve position
class being determined from all measured
data points per valve position class.
The
Long-term
folder contains a table of the
valve position classes with the associated
average drive signal y.
Short-term monitoring
The short-term monitoring involves the aver
-
age drive signal y determined from the last
measured data points per valve position
class. This allows short-term changes in ac
-
tuator pressure to be pinpointed at various
valve positions.
The
Differential drive signal
and
Valve posi
-
tion
s folders contain a table of the last ten
measured data points.
Graphs
The
Steady-state
folder contains a common
graph for long-term, short-term and refer
-
ence data. The graph plotted using the ref
-
erence data covers the full range of the
valve.
The data for long-term and short-term moni
-
toring are recorded 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 positions x
as the valve did not move to those positions
or a steady-state could not be reached.
The diagram allows changes in drive signal
y at the corresponding valve positions to be
easily recognized. Changes in pressure are
also evident as the drive signal y is propor-
tional to the actuator pressure.
Data can be reset in the
Status messages
folder.
Test requirements:
A successfully plotted reference graph is
necessary to record and analyze the data.
Refer to section 1.6 in case a double-acting
actuator with reversing amplifier or a
booster is used or SUb initialization mode is
set.
Note!
The valve can be moved through its travel
range in manual mode, during plant shut
-
down or when the process allows it by se
-
lecting
Drive signal diagram steady
in
Test
MAN
to check the results or statements de
-
termined in automatic mode in the
Status
message
folder (> Extended).
16 EB 8388 EN
Statistical information AUTO
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