VAT 642 Series User Manual

Series 642 INSTALLATION
742280ED Edition 2017-11-24 51/
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4.7.2 Tuning of control performance with fixed PI pressure controller
4.7.2.1 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.
• 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 Performance Analyzer’)
Remote operation
:
(Refer to chapter «Pressure control
algorithm» > «Fixed 1 or Fixed 2 control
algorithm» for details)
With CPA:
Do the ‘Fixed 1’ or ‘Fixed 2’ adjustment in menu
‘Pressure Control’ / ‘Setup’ / ‘fixed 1’ / ‘fixed 2’.
Send ‘Fixed 1 or 2 control algorithm
parameter‘.
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.
5. 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: 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

VAT 642 Series Specifications

General

Brand	VAT
Model	642 Series
Category	Control Unit
Language	English