Installation, Operating & Maintenance Instructions
Series 615 DN 40 (I.D. 1½”), DeviceNet
VAT Vakuumventile AG, CH-9469 Haag, Switzerland
Tel +41 81 771 61 61 Fax +41 81 771 48 30 CH@vatvalve.com www.vatvalve.com
3.11.2 Tuning of pressure control performance with Fixed algorithm
1. Introduction
Fixed algorithm is used if for any reason (e.g. too long system time constant) the adaptive control mode does not provide
satisfying control performance.
In Fixed algorithm 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.
For the fixed algorithm it is possible to set 2 parameter sets. To use fixed algorithm set Pressure control algorithm to «Fixed
PI downstream » or « Fixed PI upstream». Refer to chapter: «Pressure control algorithm» for details.
Normally the default settings will result in good pressure control performance. For some applications tuning may be
required to improve performance.
Note: In downstream control direction valve will move towards open when current pressure is higher then set point.
In upstream control direction valve will move towards close when current pressure is higher then set point.
2. Pressure and gas flow for optimization
The Fixed algorithm 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
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