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Statistical information
4.6.1 Analysis and monitoring
Analysis of the drive signal for control
valves starts one hour after the observation
period begins. No analysis is performed for
on/off valves.
The following effects can be read by com-
paring the correlation between the drive sig-
nal and valve position measured during op-
eration and in the reference graph:
−
The drive signal runs below the reference
as the gradient rises.
−
The drive signal starts to rise steadily at a
certain valve opening compared to the
reference graph. This pinpoints to signifi
-
cant leakage in the pneumatics arising
due to screw fittings that are not tight
-
ened properly or due to a tear in the di-
aphragm. The positioner generates the
'Leakage pneumatics' message with the
selected status classification.
−
The drive signal initially follows the
course plotted in the reference graph and
then starts to rise almost steadily. This
pinpoints to a supply pressure that is in-
sufficient for the valve to move through
its entire working range. The positioner
generates the 'Air supply' message with
the selected status classification.
−
The drive signal shifts downwards with a
smaller gradient than in the reference
graph, pinpointing to a reduced spring
force in a fail-close control valve. The po-
sitioner generates the 'Actuator springs'
message with the selected status classifi
-
cation.
Diagnosis > Status messages > Extended
−
Air supply
−
Leakage pneumatics
−
Actuator springs
The results from the Statistical information
test can be checked by performing a test
from Tests (out-of-service diagnostics) if the
process allows it. See section 5.1.
4.6.2 Resetting single status
messages
The messages 'Air supply', 'Leakage pneu-
matics' and 'Actuator springs' are reset by
the command "Reset 'Drive signal diagram
steady-state'" or "Reset 'Drive signal dia-
gram steady-state - short-term'".
By selecting and executing the command
"Reset 'Drive signal diagram steady-state'",
all the measured data of the diagram, in-
cluding the short-term monitoring, are reset.
By selecting and executing the command
"Reset 'Drive signal diagram steady-state -
short-term'", the measured data in the
'Short-term' folder are reset.
Operation > Reset
−
Reset 'Drive signal diagram steady-state'
−
Reset 'Drive signal diagram steady-state -
short-term'
Note
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