Blocks and Their Functions
S5-95F
Example for the Use of the PID Controller Algorithm:
A PID controller is supposed to keep an annealing furnace at a constant temperature.
The temperature setpoint is entered via a potentiometer.
The setpoints and actual values are acquired via analog channels 0 (IW 40) and 1 (IW 42) and
forwarded to the controller. The computed manipulated variable is then output via the analog output
channel (QW10).
The controller mode is set in input byte 32 (see control word DW 11 in the controller DB).
You must use the well-known controller design procedure to determine how to tune the controller
for each controlled system.
Temperature sensor
Manipulated
variable
Transducer
Actual value
Setpoint adjuster
Analog input
module
OB251 with controller
DB (call in OB13)
Y
Analog output
module
=
=
W
X
+
Annealing furnace
Channel1
Channel0
Control byte (DR11)
IB32
PID
control
algorithm
Channel 0
Final control
element
Fuel gas flow
Controlled
system
S5-95F
Figure 9-4. Process Schematic
The analog signals of the setpoint and actual values are converted into corresponding digital values
in each sampling interval (set in OB13). OB251 uses these values to compute the new digital
manipulated variable, from which, in turn, the analog output module generates a corresponding
analog signal. This signal is then forwarded to the controlled system.
9-10
EWA 4NEB 812 6210-02
