AH500 Programming Manual N ETWORK 1 Additional remark: 1. The instruction can be used several times, but the registers specified by I_MV~I_MV+9 cannot be the same. 2. I_MV occupies 20 word registers. I_MV used in the instruction DPIDE in the example above occupies D126~D145. 3. The instruction DPIDE can only be used in the cyclic task and the time interrupt. When the instruction DPIDE is used in the time interrupt, the sampling time is the same as the interval between the time interrupts. 4. When the instruction DPIDE is scanned, the PID algorithm is implmented according to the sampling time, and the MV is directly refreshed.
Whether the scan time reaches the sampling time is not calculated automatically. When the instruction is used in the time interrupt, the sampling time is the same as the interval between the time interrupts. The PID algorithm is implemented according to the interval between the time interrupts. 5. Before the PID algorithm is implemented, the present value used in the instruction DPIDE has to be a stable value. When users need the input value in the module to implement the PID algorithm, they have to notice the time it takes for the analog input to be converted into the digital input. 6.
If the PV is in the range indicated by ERR_DBW, the CPU module will bring the error into the PID algorithm until the PV reaches the SV. The cross status condition will not be met until the PV crosses the zero cross point indicated by the SV. If the cross status condition is met, the error will be count as 0 until the PV is out of the range indicated by ERR_DBW. If PID_DE is set to true, the variations in the PV will be used to calculate the control value of the derivative, and the CPU module will count the Delta PV as 0 after the cross status condition is met.
(Delta PV=Current PV-Previous PV) In the PV trend chart shown below, the CPU module implements the PID algorithm normally in the A sections A. In the B sections, the CPU module counts the error or the Delta PV as 0 when it implements the PID algorithm. 6-188