Yokogawa YVP20S - Manual (Page 105)

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<Toc> <Ind> <10. CALIBRATION SERVICES>
10.2.4 Manual parameter adjustment
After auto tuning is complete, or as an alternative to auto tuning, the parameters may be
manually entered in the text boxes (Now).
● Positioner Tuning Parameters
The position controller is a type of non-linear PID control algorithm with 5 standard param-
eters listed below. See Table 10.1 Servo Tuning Parameter Ranges for the allowed and
default parameter ranges. There an additional 16 advanced servo tuning parameters. See
Section 10.4.
P (dimensionless)
Proportional gain P is the ratio of change of output due to proportional control action to the
change in position error. Common values for the positioner are 50 for small actuators and
up to 5000 for large actuators. The larger this gain, the faster the valve will respond with
increasing tendency to overshoot. If the gain is too low friction may cause limit cycles. Air
supply pressure affects this value. Therefore, the position controller should be re-tuned in
case of air supply pressure changes. The default value of 120 is normally changed by Auto
Tune.
I (s)
Integral time or reset time is the time constant of integral control. Higher values of “I” cause
less integral control action and increase loop stability. However, higher values of “I” will also
increase the time to eliminate a steady-state position error. The special value of “0” turns
off integral action and will result in a steady-state position error. Sustained deviation may
result in failsafe action if T2 is set. Therefore, “0” should be avoided for use in most real
applications. The default value of 15 seconds is normally changed by Auto Tune.
D (s)
Derivative time or rate time is the time constant of derivative control. Larger derivative time
causes more derivative control action. The special value of “0” disables derivative action.
Derivative Gain (dimensionless)
Derivative gain controls the maximum response to rapid position change. The default value
of 5 is normally adequate.
Dead Zone (%)
When the valve position is within its 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 will help avoid limit cycling due to the stick/slip
action of the valve. In these cases the dead zone may be set at 0.1% to 5%.
Table 10.1 Servo Tuning Parameter Ranges
Parameter Defaults Range Units
Proportional Gain
Integral Time
120
15
0.5 to 1300
0 (disables);
2 to 50
(Dimensionless)
Seconds
Derivative 0.22 0 (disables);
0.05 to 1.0 Seconds
Derivative Gain 5 2 to 20 (Dimensionless)
Dead Zone 0 0 to 50 %
T1001.EPS