INSTALLATION
Series 655
56/112
Edition 23.09.2019
979645EA
4.8.5.3
Tuning of control performance with soft pump pressure controller
Optimizing P gain
This valve may be used to control pressure ramps during pump down. The P parameter of the pressure
controller requires correct adjustment. This parameter must be set once during system setup and is
stored in the device memory which is power fail save. Based on the soft pump controller configuration, the
valve is able to run fast and accurate pressure control cycles. The P parameter can be evaluated using
below instruction.
Introduction
Pump down control mode allows a completely user-defined pressure profile, usually from atmosphere
down to some process pressure
1.
Optimizing P gain
The P gain value evaluated for soft pump control mode might be different than the P gain value evaluated
for PI controller mode. When switching to pump down control mode the P gain value evaluated for the PI
controller has to be send to the valve controller. When switching back into PI controller mode the
respective P gain value has to be send again.
Adaptive pressure control mode ignores any P gain value.
1.1
Basic settings
The pump down characteristic is determined by start pressure, end pressure and pump down time. This
straight line from start pressure to end pressure.
The VAT soft pump controller requires a pump down time shorter than 10 sec. for good control results. If
the required pump down time is longer than 10 sec., the pump down curve has to be partitioned into
sections shorter than 10 sec. with corresponding end pressure.
Example:
Start pressure:
760 Torr
End pressure:
10 Torr
Pump down time:
30 sec.
Here the pump down time and the corresponding pressure is being divided into three sections. The host
sends a new pressure set point every 10 sec.:
Time
Set point
0 sec.
760 Torr
10 sec.
510 Torr
20 sec.
260 Torr
30 sec.
10 Torr
