Technical Specifications

223
Setup Wizard Selections
Monitor
Pos Comp (Position Com-
pensation 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 20, makes
adjustments to try to equalize the valve response. The normal
value is 6. For springless actuators the value is 15.
Beta Beta is a 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 a small error
( Beta Response).
Figure 27 Beta Response
Dead Zone 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 pack-
ing) 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%.
Boost This field controls a supplemental pressure or boost to speed up
initial valve response from setpoint from 0 to 100%.
The values determined above provide sufficient response for most applications. However
these values are determined by a target set of performance criteria built into the SVi1000.
You may want performance different than this set and may therefore want to set the PID
values differently than determined by Autotune. You can individually set tuning values from
the Calibrate tab.
Positive Beta Negative Beta