Technical Specifications

635
Calibrate Tab
P Proportional gain P (%) is the ratio of proportional action (part of
controller output) to error. Common values for the positioner are 50
for small valves up to 4000 for large valves.
I Integral time or reset time (0.1 sec), is the time constant of integral
control. Higher values of I cause less integral action, however a
value of 0 gives no integral action. Common values are 10 to 200.
D Derivative time or rate time (msec) is the time constant of deriva-
tive control. Common values are 10 to 100.
P
Adj
Valves often have significantly different response when filling
verses exhausting. The proportional gain is adjusted by adding
Padj (%) to P when the valve is exhausting.
DeadZone 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 the stick/slip
action of the valve. In these cases the dead zone chosen might be
0.5% to 1%.
Beta Beta is nonlinear gain factor, ranging from -9 to 9. When beta is 0,
the controller gain is linear. Otherwise the gain is the function of
error. The larger the beta, the smaller the gain for small error. Typi-
cal beta values fer a valve position controller is 7 or 8.
Position
Compensation
Coefficient
The response of the valve is different when the valve is nearly
closed than when the valve is nearly open. The position compensa-
tion coefficient, which is a number between 0 and 9, allows you to
make adjustments to try to equalize the valve response. The nor-
mal value is 6.
Damping Coefficient The valve response may be made slower for some applications.
In SVI2 version 1.1.4 and earlier, a value of 0 gives no damping, and
a value of 9 gives maximum damping of valve motion.
For SVI2 version 1.2.1 and later, the damping is specified as the
maximum valve movement in %/second. A value of 0 indicates no
damping. Allowed values are 1 to 200 %/s. The damping can be
applied in both directions or only in one direction.
Apply Clicking Apply causes any changes made in the“Configure Tab” on
page 626 or “Calibrate Tab” on page 634 tabs to be witten immedi-
ately to the SVI2.
Change Mode When selected, you can change the SVI2 mode.The SVI2 can be in
any of three operating modes:
 Operating- In this mode the SVI2 responds to the input
signal and positions the valve appropriately (indicator
green).