Chapter 6 Applied Instructions Additional remarks 1. The instruction can be used several times, but the registers specified by I_MV – I_MV +14 cannot be the same. 2. I_MV occupies 30 registers. 3. You can only use the 32-bit instruction in cyclic tasks and interval interrupt tasks. When using the 32-bit instruction in an interval interrupt task, the sampling time (Cycle) is the same as the interval between the timed interrupt tasks. 4. When the instruction is scanned, the 32-bit PID algorithm is applied according to the sampling time (Cycle), and it refreshes MV.
When you use the instruction in an interrupt task, the sampling time (Cycle) is the same as the interval between the timed interrupt tasks. The PID algorithm is applied according to the interval between the timed interrupt tasks. 5. Before the 32-bit PID algorithm is applied, the process value used in the PID instruction has to be a stable value. When you need the input value in the module to implement the DPID algorithm, must note the time it takes for the analog input to be converted into the digital input. 6.
When the PV (process value) is in the range of ERR_DBW , at the beginning, the present error is brought into the PID algorithm according to the normal processing, and then the CPU module checks whether the present error meets the cross status condition: PV (process value) goes beyond the SV (target value). Once the condition is met, the present error is counted as 0 when applying the PID algorithm. After the PV (process value) is out of the ERR_DBW range, the present error is brought into the PID algorithm again.
If PID_DE is true, that means it uses the variations in the PV to calculate the control value of the derivative, and after the cross status condition is met, 6_ the PLC treats Δ PV as 0 to apply the PID algorithm. (Δ PV = current PV – previous PV ). In the following example, the present error is brought into the PID algorithm according to the normal processing in section A ,and the present error or Δ PV is counted as 0 to apply the PID algorithm in the section B. 6-207