PIDTune 3.6

The PID Tuner employs the Internal Model Control (IMC) methodology to determine optimal PID tuning parameters. Having evaluated various tuning approaches over the years, I find this method to be among the most effective. The application is designed for the iPad, providing a consolidated view of all relevant information on a single screen.

The software calculates the following PID parameters:

• Controller Gain (Kc)
• Integral Time (Ti)
• Derivative Time (Td)

It supports different process models, including:

• First Order with Dead Time (FO)
• Second Order with Dead Time (SO)
• Integrating or Long Time Constant with Dead Time (I)

Regarding controller configurations, it accommodates:

• Parallel (non-interacting), represented by c(s) = Kc (1 + 1/(Ti s) + Td s)
• Series (interacting), described by c(s) = Kc (Ti s + 1)/(Ti s)(Td s + 1)

The controller modes available are PID and PI. Users can input the process gain (Kp) directly or specify changes in the controlled variable (CV) and manipulated variable (MV).

Control aggressiveness is modulated via a slider that adjusts the closed-loop time constant relative to the process time constant ratio (λ/Ƭ). The closed-loop time constant (λ) indicates the expected time for the process to reach set point, including dead time (ϴ). Setting λ/Ƭ to 1.0 causes the manipulated variable to reach its final value and allows the process to settle at the setpoint. Values greater than 1.0 delay response, resulting in a slower process, while values less than 1.0 produce an initial larger change in MV followed by adjustments towards the final value. For tight control, setting λ/ϴ—the dead time ratio—is recommended.

The tool supports tuning for integrating processes or those with long time constants by setting the process type accordingly (Ƭ = ∞). In these cases, maximum slope is used as the process gain. Control aggressiveness is then based on the ratio of λ to ϴ, with a closed-loop time constant set equal to dead time for optimal responsiveness.

This approach aligns with established literature, including Sigurd Skogestad's “Probably the simplest PID tuning rules in the world” (Journal of Process Control, July 2001) and Y. Lee et al.'s “Consider the generalized IMC-PID method for PID controller tuning of time-delay processes” (Hydrocarbon Processing, January 2006).