INSTALLATION
Series 642
52/113
Edition 2017-11-24
605593EC
4.7.2
Tuning of control performance with fixed PI algorithm
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.
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.
Local operation:
(‘Control View’ resp. ‘Control Performance
Analyzer’)
Remote operation:
Go to ‘Tools / Terminal’ menu and do the:
Pressure control cofiguration
Controller
mode + PI-Parameters
Refer to chapter «Pressure control configuration»
for details.
It’s not possible to optimize P-gain and I-Gain via
DeviceNet
®
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. 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:
4 – 10 Torr
Flow range:
2 – 4 slm
Pressure set points and gas flow for optimization:
SP1
=
7 Torr
SP2
=
6 Torr
Gas flow
=
4slm
