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Entry type: FAQ Entry ID: 2361324, Entry date: 06/06/2000
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Sample program: controlling two actuators

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QUESTION:
How can I control two actuators with one PID control loop?

ANSWER:
Use a demultiplexer and switch over the output using a BOOL variable.

Example:
In this example an air-conditioning controller has two redundantly chilled water supply systems. There is always only one chiller in operation (see figure).

A PID controller and two actuators are implemented in this example. The demultiplexer switches the control output of the control loop to one of the actuators.

Warning:
This sample program is not suitable for controlling different control loops with on PID controller. Furthermore, it must be ensured that the actuator not required at the time does not have any further influence on the controlled system (e.g. is still half open).
 

Parameter

Declaration

Data type

Description

Value

INPUT

WORD

The current control value

Select

INPUT

BOOL

Switching between actuators

output_0

OUTPUT

WORD

Output for the first actuator

output_1

OUTPUT

WORD

Output for the second actuator

STL code:

FB1.pdf ( 5 KB )

Sample project:
Copy the Regler.exe file into a separate directory and then start it with a double-click. The STEP7 project is now unpacked with all the associated subdirectories. You can then open and process the unpacked project with the SIMATIC Manager.

Regler.exe ( 52 KB )