MKS 640B - Tuning the 640 B Controller; Figure 16: Controller Response with Initial P Term and I Term Values

Tunin
g
the 640B Series Pressure Controlle
r
Chapter Three: Overview
36
Tuning the 640B Controller
Tuning the 640B controller involves adjusting the Proportional and Integral terms to optimize the
response of the controller in your system. Since every system is different, the optimum settings
for the P term and I term will vary. Also, the response of the system to increasing and decreasing
pressures may vary. Tune the system to provide the best response in the direction of pressure
change that you anticipate.
The following graphs show the response of the 640B controller to changes in the set point. The
set point changed from 4 Torr (2 Volts) to 6 Torr (3 Volts), and back again. The pressure
response was tracked using a digital storage oscilloscope.
Note
The following three graphs were generated on a system consisting of a
640B controller positioned for downstream control, with a 10 Torr
transducer, 1000 sccm flow of nitrogen gas, 30 psia inlet pressure, and 1
liter system volume. Tuning with nitrogen may not offer maximum
p
erformance if another gas is used for processing.
The same P and I term values may not create the same effect in your
system.
Controller Response with the Initial Values
The initial values (P = 0; I = 0) yield:
Figure 16: Controller Response with Initial P Term and I Term Values
The controller response is slow to reach the set point, however, there is no pressure overshoot and
no oscillation. Increase the P term to create a faster response.
P = 0
I = 0
Settling Time
Settling Time
Set Point
Signal
4
2
6
8
Pressure, (Torr)
Time