26
CAUTION: Before selecting valve “Open”mode check Instrument Inlet
Pressure! Make sure the differential pressure transient during valve
opening will not exceed sensor maximum differential pressure. Improper
usage may lead to damage of the instrument pressure sensors! Do not
activate valve “Open”mode if instrument has more than 10 PSIG applied
to the inlet and instrument output is connecting to the atmosphere!
NOTE: The Valve Mode menu selection only available from main PI screens 1 to
4 (see fi gure 10)
The
"Local & Digital Set Point Merge"
parameter if enabled allow change set point value
via digital interface even the
Set Point Source
is assigned to
"Local Interface"
. The
"Local
Set Point Auto Start"
parameter if enabled will automatically set valve mode in
"Auto"
after
power is applied and start last saved
Local Set Point
execution (if
Set Point Source
param-
eter is set to
"Local"
). Consult factory for more information.
CAUTION: DPC instrument Valve PID parameters were adjusted on the
factory according to your order and they allow to handle most applications.
Do not change PID parameters unless instructed by factory technical support
representative! It is recommended to contact factory technical support if DPC
instrument exhibit any problem with stability, response time or different PID
parameters are required for your application.
6.4.4 Controller PID Parameters
PID
Parameters determine the performance of proportional valve control algorithm.
P
refers
to the
Proportional
term of the
PID
loop,
I
refers to the
Integral
term of the
PID
loop and
D
refers to the
Differential
term of the
PID
loop. These values impact control speed, valve
stability, overshoot, undershoot and oscillation. DPC instruments shipped from the factory
with a generic
PID
values designed to handle most applications. If your application required
different settings (there are issues with valve stability, oscillation or speed), adjustment of
these parameters may resolve the problem.
DPC instruments support 3 different implementations of the
PID
control loop algorithm:
PD
,
PID
and
PIDD
.
The
PD
algorithm is the default algorithm used on most DPC controllers and usually works
fi ne for most generic applications with wide range of the differential pressure across the
valve. With this algorithm the
Integral
term is disabled (not used).
NOTE: If
PID
loop type is changed, the
PID
parameters may need to be adjusted
to work properly with different
PID
loop type.
The
PID
Loop Type can be selected from
“Valve PID Loop Type”
menu selection in the
“Valve Parameters”
menu.
Summary of Contents for DPC
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