GE Masoneilan SVI II ESD Installation And Maintenance Manual page 208

Positioner Tuning Parame-
ters
Tuning Parameters
P
I (0.1 sec)
D (msec)
Beta
Padj (%)
Position Compensation
Coefficient
Damping Coefficient
Dead Zone(%)
Quick Opening
Relay, Pneumatic
Safe Area
208 |
=GE Oil & Gas
The positioner requires six integer parameters to determine its
response for a setpoint change. Internally, the positioner uses an
improved PID control algorithm to control valve position.
P is a dimensionless gain factor related to proportioning action of the
algorithm. It ranges from 0 to 5000. Common values for positioner
are 50 for small valves up to 4000 for large valves.
Integral time or reset time, is the time constant of integral control.
Higher values of I cause slower integral action. Common values are
10 (1 second) to 200 (20 seconds). A zero value disables integral
action.
Derivative time or rate time is the time constant of derivative control
expressed in milliseconds. It ranges from 0 to 200 msec. Common
values are 0 to 100. A zero value disables derivative action.
Beta is a nonlinear dimensionless gain factor, ranging from -9 to 9.
When beta is 0, controller gain is linear. Otherwise gain is the error
function. The larger the beta, the smaller the gain for small error. Typ-
ical beta values for a valve position controller are between –9 and 0.
Valves often have significantly different response when filling versus
exhausting. The proportional gain is adjusted by adding Padj to P
when the valve is exhausting. Padj is normally less than P.
The valve response is different when the valve is nearly closed than
when it is nearly open. The position compensation coefficient, a
number between 0 and 9, allows the control algorithm to optimize
valve response.
The valve response can be made slower for some applications. A
value of 0 gives no damping, and a value of 9 gives maximum damp-
ing of valve motion.
When the valve position is within the setpoint +⁄- the dead zone, no
additional position control is performed. This value is normally 0%,
however for high friction valves (e.g. valves with graphite packing), a
higher dead zone helps avoid limit cycling due to stick⁄slip action of
the valve. In these cases the chosen dead zone might be 0.2% to 1%.
See Characteristic.
The component that amplifies pneumatic control signals to provide a
wide range of actuation pressure and to supply and vent at high flow
rates for responsive control.
The plant area where there is no explosion hazard, such as a control
room or a marshalling cabinets area.
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