Tuning Of Pressure Control Performance With Fixed Pi Control - VAT 612 Series Installation, Operating, & Maintenance Instructions

4.7.2

Tuning of pressure control performance with fixed PI control

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.
Local operation:
(„Control View‟ resp. „Control Performance
Analyzer‟)
Go to „Tools / Terminal‟ menu and do the:
Refer to chapter « Pressure control configuration»
for details.
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.
1.1
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:
1.2
While optimizing P gain, the gas flow determined above has to be constant all the time.
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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.
Control cofiguration  Control
mode + PI-Parameters
Optimizing P gain and I gain
Pressure and gas flow for optimization
Flow range:
SP1 =
SP2 =
Gas flow =
Optimizing P gain
Edition 2013-02-19
Remote operation:
(Refer to chapter «RS232 setup commands»
4 – 10 Torr
2 – 4 slm
7 Torr
6 Torr
4slm
Series 612
for details)
298317EB