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Tuning the MFC for Optional PC Chapter Six: Embedded Web-Based GUI and Diagnostics
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The Optional PID parameters are always settable on the plot page, but they will have no effect unless the
Optional Input is enabled. The following section discusses tuning the PID values.
Note
A MFC is typically used as a PI controller only. If the derivative term (Kd) is going to be used, it
is recommended that you increase the value in increments of 0.001.
Tuning the MFC for Optional PC
Tuning optimizes the way the MFC unit controls your optional input system. As noted in the previous section,
How the MFC Controller Works
, the controller functions as a PID (Proportional-Integral-Derivative)
controller, but the recommended use is with the Derivative term off, i.e. set to zero. Thus, in this manual, only
the Proportional and the Integral term will be discussed. These values can be adjusted through the Embedded
GUI on the Plot Page in Setup Mode. Each method is discussed in the
Adjusting the Proportional and
Integral Control
section on page 75.
Proportional Term (Kp)
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 (Kp), thus creating a
proportional valve drive signal. The higher the proportional control, the greater the change in the 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. The following figure shows the effects of the
Proportional term.
Figure 29: Effects of the Proportional Control