AH500 Programming Manual Temperature command (SV) Example 4: The steps of tuning the parameters used with the instruction PID Suppose that the transfer function of the plant is the first-order function ( ) a + s b = s G , the SV is 1, the sampling time Ts is 10 milliseconds. It is suggested that the steps of tuning the parameters are as follows. Step 1: First, set the K I and the K D to 0. Next, set the K P to 5, 10, 20 and 40 successively, and record the target values and the process values. The results are shown in the diagram below. 1.5 K =40 P K =20 P K =10 P SV=1 1 K =5 P 0.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Time (sec) Step 2 : When the K P is 40, there is overreaction.
Thus, the K P is not chosen. When the K P is 20, the reaction curve of the PV is close to the SV, and there is no overreaction. However, due to the fast start-up, the transient output value (MV) is big. The K P is not chosen, either. When the K P is 10, the reaction curve of the PV approaches the SV smoothly. Therefore, the K P is chosen. When the K P is 5, the reaction is slow. Thus, the K P is not chosen. Step 3 : After the K P is set to 10, increase the K I . For example, the K I is set to 1, 2, 4, and 8 successively. The K I should not be larger than the K P . Then, increase the K D . For example, the K D is set to 0.01, 0.05, 0.1, and 0.2 successively.
The K D should not be larger than ten percent of the K P . Finally, the relation between the PV and the SV is present in the following diagram. 1.5 PV=SV 1 0.5 K =10,K =8,K =0.2 P I D 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Time (sec) 6-173 Heating (MV) PID Heater Temperature detector Actual temperature (PV) PID Heating (MV) Heater Temperature detector