Delta AS Series Programming Manual page 763

AS Ser ies Pro gra mm in g M anu al
ERR_DBW
When the PV (present 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 (present 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 (present 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, 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
α, β Value
To reduce overshoot, you can use parameters of ALPHA or BETA in the beginning of the PID operation or while SV
(target value) varies to compensate initial value of integral calculus (for heating up or cooling down). See the images
below. Use ALPHA parameter to reduce overshoot while the temperature is climbing up. Use BETA parameter to
reduce overshoot while the temperature is dropping.
Tem perature ( C)
6-484
0 0
Temperature ( C)
Tim e
Time