Tuning Of Control Performance With Fixed Pi Pressure Controller; Optimizing P Gain And I Gain - VAT 590 Series Installation, Operating, & Maintenance Instructions

4.6.1

Tuning of control performance with fixed PI pressure controller

4.6.1.1

Optimizing P gain and I gain

This valve may be used for downstream or upstream pressure control depending on configuration.
The PI parameters of the pressure controller require correct adjustment. These parameters must be
set once during system setup and are stored in the device memory which is power fail save. Based on
the PI controller configuration, the valve is able to run fast and accurate pressure control cycles. The
PI parameters can be evaluated using below instruction.
Local operation:
('Control Performance Analyzer')
With CPA:
Do the 'fixed 1' adjustment in menu 'Pressure
Control' / 'Setup' / 'fixed 1'.
(Default: P-Gain: 0.0056 / I-Gain: 0.0320)
Introduction
PI controller mode is used if for any reason (e.g. too long system time constant) the adaptive control
mode does not provide satisfying control performance.
In PI controller mode the parameters P gain and I gain have to be set according to the systems
characteristics. The best set of parameters can be found by using the empiric method below.
1. Optimizing P gain and I gain.
1.1 Pressure and gas flow for optimization
A PI controller delivers the best results for a certain working point (pressure/gas flow). If there is only
one working point, this pressure and gas flow has to be used for optimizing P and I gain. If there are
several working points that have to be covered, the pressure for optimizing is the medium pressure
between highest and lowest pressure to be controlled, the gas flow for optimizing is the highest flow
out of all working points.
Two different pressure set points are necessary for optimization. Set point 1 (SP1) is the pressure for
optimizing as determined above. Set point 2 (SP2) is about 10 - 20% lower than SP1.
Example: pressure range:
Pressure set points and gas flow for optimization:
34/77
INSTALLATION
•
In downstream control mode valve will move towards open when current pressure
is higher than set point.
•
In upstream control mode valve will move towards close when current pressure is
higher than set point.
Flow range:
SP1 =
SP2 =
Gas flow =
Edition 2015-12-02
Remote operation:
(Refer to chapter «Pressure control
algorithm» > «Fixed 1 control algorithm » for
details)
Send 'Fixed 1 control algorithm parameter'.
4 – 10 Torr
2 – 4 slm
7 Torr
6 Torr
4slm
Series 590
820655EA