7 Application Instructions API 50-99 Example 4: How to adjust PID parameters Assume that the transfer function of the controlled device G(S) in a control system is a first-order function b s G (most models of motors are first-order function), SV = 1, and sampling time (T S ) = 10ms, we a s suggest you to follow the steps below for adjusting the parameters. Step 1: Set K I and K D as 0 and K P as 5, 10, 20 and 40. Record the SV and PV respectively and the results are as the figure below. 1.5 K =40 P K =20 P K =10 P SV=1 1 0.5 K =5 P 00 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Time (sec) Step 2:
From the figure, we can see that when K P = 40, there will be over-reaction, so we will not select it. When K P = 20, the PV reaction curve will be close to SV and there will not be over-reaction, but due to its fast start-up with big transient MV, we will consider to put it aside. When K P = 10, the PV reaction curve will get close to SV value more smoothly, so we will use it. Finally when K P = 5, we will not consider it due to the slow reaction. Step 3: Select K P = 10 and adjust K I from small to big (e.g. 1, 2, 4 to 8). K I should not be bigger than K P . Adjust K D from small to big (e.g. 0.01, 0.05, 0.1 and 0.2). K D should not exceed 10% of K P .
Finally we obtain the figure of PV and SV below. 1.5 PV=SV 1 0.5 K =10,K =8,K =0.2 P I D 00 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Time (sec) Note: This example is only for your reference. Please adjust your parameters to proper ones according to your actual condition of the control system. DVP-PLC APPLICATION MANUAL 7-140