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Integrated 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 using an analog input module and forwarded to the
controller. The computed manipulated variable is then output via an analog output module.
The controller mode is set in input byte 0 (see control word DW11 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
(e.g. 6ES5 460)
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.
9-22
Control byte (DR11)
W
PID
control
X
algorithm
OB251 with
controller DB
(call in OB13)
Temperature sensor
=
Annealing furnace
Figure 9-9. Process Schematic
Manipulated
variable
Y
Channel 0
Analog output module
(e.g. 6ES5 470)
Fuel gas flow
S5-100U
S5-100U
Controlled
system
Final control
element
EWA 4NEB 812 6120-02
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