1.3Methods of decentralisation

By using the coupler or the controller it is possible to realise various methods for the decentralisation of control tasks.

Fig. 1.9: Decentralisation methods

Central control using a coupler or a controller (1)

The process methods common to date: All input sensor signals are joined in the coupler (Slave) and led to the higher ranking controls (Master) via a bus system. The data generated for signal output in the higher ranking controls reaches the actuators via bus and nodes. The reaction time of the controls is dependent upon the fieldbus.

This principle can be performed in the same manner using the controller.

Signal pre-processing using controller (2)

Certain control tasks, e.g. impulse generation, delays and counts (e.g. quantity), are taken care of on site. The logic operations required are processed in the controller. The bus system only transmits the results of the logic operations as process data to the higher ranking controls. For signal pre-processing the amount of fieldbus data required is less than that required for a central connection.

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Decentral control with controller (3)

The on site controller controls an assigned function area, e.g. a machine unit or components of a transport system. The unit test can be made independently, i.e. without higher ranking controls.

The higher ranking controls transmit data to the controller via the bus system, e.g. the operating mode, set point values or the current production program (recipe). The controller transmits local operating data to the higher ranking controls, such as operating and control messages, actual values, counter readings etc. The complete linking for actuator triggering is made in the controller, in other words directly on site. This permits a fieldbus independent reaction of the controls.

In the case of a fieldbus failure the control program can be independently further processed and the node put into a defined status.

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