Technical data

Inverted control direction If you require an inverted control direction, preset a negative K value.
Limiting the control
information
If the control information (dY or Y) reaches a limit, the I action is
automatically disabled in order to prevent deterioration of the
controller response.
You can supply the control program with preset fixed values or with
adaptive (dynamic) parameters (K, R, TI, TD). These are input via the
memory cells assigned to the individual parameters.
6.32.2
PID Algorithm
The PID controller is based on a velocity algorithm according to
which the control increment dY
k
is calculated at time t = k * TA,
according to the following formula:
dY
k
=K
[
(XW
k
− XW
k−1
) R +
TA
2TN
(XW
k
+ XW
k−1
) +
1
2



TV
TA
(XU
k
− 2XU
k−1
+ XU
k−2
) + dD
k−1



]
=K ( dPW
k
R + dI
k
+ dD
k
)
dXXX
k
: change in variable XXX at time t.
U can be either W or Z, depending on whether XW or XZ is supplied
to the derivative unit. The following applies:
If XW
k
is supplied: If XZ is supplied:
PW
k
= W
k
- X
k
PW
k
= XW
k
- XW
k-1
PZ
k
= XZ
k
- XZ
k-1
QW
k
= PW
k
- PW
k-1
QZ
k
= PZ
k
- PZ
k-1
QW
k
= XW
k
- 2XW
k-1
+ XW
k-2
QZ
k
= XZ
k
- 2XZ
k-1
+ XZ
k-2
OB 250/251: Closed-Loop Control/ PID Algorithm
CPU 928B Programming Guide
6 - 112 C79000-B8576-C898-01