MKS 640A/641A - Integral Term; Figure 16: Effects of the Integral Control

Chapter Three: Overview Tunin
g
the 640 Series Pressure Controlle
r
37
Integral Term
The action of the Integral (I) term creates a valve drive signal that is proportional to the
magnitude and sign of the area under the error signal curve (error signal with respect to time).
Therefore, as time passes, the integral term acts to position the valve to reduce the error signal to
zero. An increase in the integration time increases the period of time over which the error signal
is generated, and the system response gets slower. Figure 16 shows the effects of the Integral
term.
Set Point Si
g
nal
Pressure Si
g
nal
Time
Pressure
Inte
g
ral term set too low, (inte
g
ration time
too lon
g
) system slow to reach set point
Pressure Si
g
nalSet Point Si
g
nal
Time
Pressure
Inte
g
ral term set too hi
g
h, (inte
g
ration time
too short) system overshoots the set point
Figure 16: Effects of the Integral Control
Adjusting the Integral Control
The Integral (I) term adjustment is located on the top of the 640 Series unit, as shown in
Figure 13, page 33. The control is a 10-position dial where the 0 setting has the
longest
integration time; the 9 position setting has the
shortest
integration time. The initial setting is 0.
Note
To
shorten
the integration time,
increase
the I term setting.