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Blocks and Their Functions
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.
IB32
+
Channel0
Channel1
Setpoint adjuster
Analog input
module
Actual value
=
Transducer
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
Control byte (DR11)
W
PID
control
X
algorithm
OB251 with controller
DB (call in OB13)
Temperature sensor
=
Annealing furnace
Figure 9-4. Process Schematic
Manipulated
variable
Y
Channel 0
Analog output
module
Fuel gas flow
S5-95F
S5-95F
Controlled
system
Final control
element
EWA 4NEB 812 6210-02
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