Siemens S5-100U - Page 252

Integrated Blocks and Their Functions S5-100U
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.
Y
Temperature sensor
Manipulated
variable
Transducer
Actual
value
Setpoint
adjuster
Analog input module
(e.g. 6ES5 460)
OB251 with
controller DB
(call in OB13)
Analog output module
(e.g. 6ES5 470)
=
=
W
X
+
Annealing furnace
Channel1
Channel0
Control byte (DR11)
IB32
Channel 0
Final control
element
Fuel gas flow
Controlled
system
S5-100U
PID
control
algorithm
Figure 9-9. 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.
9-22 EWA 4NEB 812 6120-02