15. Handy Instruction Design Examples M1013 M0 Sample PV of the oven every 1s and store it in D11 Set the control direction as auto-tuning temperature RST M0 M1 Store PID operation result in D200 Program Description: z Format of PID instruction: S 1 → Set value (SV) S 2 → Present value (PV) S 3 → Parameter (Users need to set and adjust it. For the definition, refer to PID parameter table in the last part of this example) D → Output value (MV) (D has to be the data register area with latched function) z There are a lot of circumstances where PID instruction can be applied; therefore, please choose the control functions appropriately.
In this example, the parameter auto-tuning for temperature is only for the temperature control, users cannot use it in a speed or pressure control environment or errors could occur. z Generally, adjusting control parameters of PID requires experience and repetitive tests. (except the auto-tuning function in temperature control environment) The common parameter adjusting steps are as below: 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) DVP-PLC Application Examples 15-23 OM K0 K6 D11 K1 OV K3 D204 ID D10 D11 D200 D0 WM D0 D20 Y0 PID S 1 S 2 S 3 D