Tunin
the 640B Series Pressure Controlle
Chapter Three: Overview
34
Tuning the 640B Series Pressure Controller
Tuning optimizes the way the 640B Series unit controls your system. The Proportional (P) and
Integral (I) terms adjust the response of the 640B Series controller. The controller responds to
changes in either the pressure of the system or the value of the set point.
Proportional Term
The Proportional (P), or gain, term is used as a constant to create a valve drive signal that is
proportional to the error signal. The error signal is multiplied by the proportional control setting,
thus creating a proportional valve drive signal. The higher the proportional control, the greater
the change in valve drive signal. Typically, a higher proportional control setting yields a faster
response. However, too high a proportional control setting will cause the pressure to oscillate
around the set point. Too low a proportional control setting will result in a slow response from
the controller. Figure Error! Bookmark not defined. shows the effects of the Proportional term.
Figure 14: Effects of the Proportional Control
Adjusting the Proportional Control
The Proportional (P) term adjustment is located on the top of the 640B Series unit, as shown in
Figure 11, page 31. The control is a 10-position dial, though it uses only 8 values. The last
positions, 8 and 9, repeat the values of positions 0 and 1. The initial setting is 0. As you increase
the setting number, the value of the term increases by a factor of approximately 2.8.
Set Point Signal
Pressure Signal
Time
Pressure
Gain (Proportional term) set too low,
causing a slow response
Pressure Signal
Set Point Signal
Time
Pressure
Gain (Proportional term) set too high,
causing oscillation
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