Function PrincipleΒΆ
Function principle of Auto Tuning
The auto tuning process serves to determine optimized controller parameters for the PID controller. The auto tuning identifies the parameters of one temperature zone (controlled system) and calculates the optimized controller parameters for that zone. The dynamic behaviour of these thermal processes can be approximately acquired by means of the following characteristic quantities, which can be defined on the basis of the transfer function:
- Tu: Delay time
- Tg: Stabilization time
- Ks: Transfer factor (controlled system gain)
At the end of the auto tuning process, the actual progression of the transfer function is replaced by the linear-progressing reversing tangent placed at its turning point.
Function principle of Auto Tuning
The figure above represents the transfer function, the reversing tangent and the resulting characteristic quantities for a temperature control process. As long as Tu, Tg, Ks are acquired, PID controller parameters like KP, TI, TD and T1 will be calculated.
Auto tuning is only allowed when the actual temperature has reached its steady state. The auto tuning can be executed both during process start-up (initial settings) and when the value of the desired set point changes. This allows auto tuning of the control parameters in case of a process which must be operated at different set points and where the initially fixed control parameters may lead to undesired control response due to set point change. In both cases, the relative change should be as large as possible to ensure a precise measurement during the auto tuning, thus a good result of PID parameters.
Continuous auto retuning of the controller parameters is not built in.