Siemens SIMATIC S5 Manual page 217

Blocks
The individual proportional-action, integral-action, and derivative-action components can be
deactivated via their particular parameters (R, TI, and TD) by presetting the pertinent data words
with zero. This enables you to implement all desired controller structures easily, e.g. PI, PD, or PID
controllers.
You can apply the control deviation XW or, using the XZ input, any disturbance variable or the
inverted actual value X to the differentiator. Specify a negative K value for an inverted control
direction.
When the correction information (dY or Y) is at a limit, the integral-action component is
automatically deactivated in order not to impair the dynamic response of the controller.
The switch settings in the block diagram are implemented when programming the PID controller.
This is done by setting the appropriate bits in the "STEU" control word ( Table 6-2).
Table 6-2. Meaning of the Control Bits in Control Word STEU
Control Name
Bit
0 AUTO
1 XZ EIN
2 REG AUS
3
GESCHW
4 HAND-
ART
5
NO Z
6 to 15 -
The control program can be initialized with fixed values or parameters. Parameters are input via
the assigned data words. The controller is based on a PID algorithm. Its output signal can be either
a manipulated variable (correction algorithm) or a manipulated variable change (correction rate
algorithm).
6-16
Signal
State
0
Manual mode
1
Automatic mode
0
XW is applied to the differentiator. No account is taken of the XZ input.
k
1
A variable other than XW
0
Normal control operation
1
When the controller is called (OB 251), all other variables (DW 18 to DW 48)
are erased with the exception of D, R, TI, TD, BGOG, BGUG, YH
The controller is deactivated.
0
Correction algorithm
1
Correction rate algorithm
0
For GESCHW=0:
The controller output signal YA is applied exponentially to the set manual
value in four sampling steps after switching over to manual mode. Other
manual values are then accepted immediately at the controller output.
For GESCHW=1:
The manual values are routed through to the controller output immediate-
ly. The limits are effective in manual mode.
The following variables are updated in manual mode:
1) X , XW and PW
K K-1
2) XZ , XZ
K K-1
3) Z and Z
K K-1
The variable dD
K-1
For GESCHW=0:
1
The last manipulated variable output is retained.
For GESCHW=1:
The correcting increment dY
0
With feedforward injection of disturbance variable
1
No feedforward injection of disturbance variable
These bits are used by the PID algorithm as flag bits.
Meaning
is applied to the differentiator via the XZ input.
k
K-1
and PZ , if STEU bit 1=1
K-1
, if STEU bit 5=0
is set to = 0. The algorithm is not computed.
is set to zero.
K
S5-115F Manual
and W .
k k
EWA 4NEB 811 6149-02