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Tuning the 640 Series Pressure Controller Chapter Three: Overview
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Tuning the 640 Controller
Tuning the 640 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 640 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
640 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
performance 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:
P = 0
I = 0
Settling Time
Settling Time
Set Point
Signal
4
2
6
8
Pr
e
s
su
re
, (T
o
rr)
Time
Figure 17: 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.