PIDControlPro app for iPhone and iPad

This app allows straightforward design of PID controllers based on two types of identification experiments: Relay Tuning or Step Response–also known as Process Reaction Curve. A convenient input form allows entry of experiment parameters and results. For the relay tuning method, Ziegler Nichols tuning rules are available, for the step response method, Ziegler Nichols, Cohen-Coon, or Minimum ITAE can be selected.

This is the paid upgrade from PIDControl. In addition the the features of the free version, you can:

1) Design PI & PID controllers when using step response method
1) Export tuning results via e-mail
2) Set the number of significant digits
3) Save entered values even if the App is quit or the phone rebooted
5) Save last used tab

RELAY TUNING
When put under closed loop control with a relay, i.e., an on/off controller, a process is put into sustained oscillations. From the amplitude of input and output the ultimate process gain can be computed. The period of oscillation is the ultimate process period. These two parameters are traditionally obtained from open loop experiments which can be time consuming and unsafe because the process can become unstable. Using a relay controller these values can be obtained quickly and safely.

STEP RESPONSE METHOD
A traditional method of identifying a process model is through a step response experiment. The process is put under open-loop control and allowed to steady out. Then a step change in the input is implemented and the process response is observed. This experiment allows identification of process gain, time delay, and time constant assuming a first-order-plus-time-delay process model. Various tuning rules exist based on these three process parameters.