Various types of I/O systems are used in automation today. These include centralized systems, in which all I/O hardware is housed in a single hardware unit, and distributed systems, where the I/O hardware is distributed across several control cabinets in the field. This architecture has established as the more popular variant in industrial environments due to their simpler and more efficient cabling.
I/O systems are usually located close to a central or decentralized control unit and bundle all cables and signals from the connected field devices in order to ultimately forward them to the controller. This results in the basic structure of an I/O system, which has a fieldbus or RTE interface which is called Bus Terminal on the control side and towards the field level the so-called field or bus couplers. This is the name for the various input and output modules that are required to connect countless different field devices to the I/O system.
The variety of different I/O modules is just as diverse as the different types of field devices. In a simplified representation, these can be divided into three categories:
- Simple modules are connected to the field and switching devices via singular wiring and only have basic functions such as analog-to-digital conversion.
- Intelligent modules also have prefabricated but unchangeable additional functions that can be set via parameters. By outsourcing the pre- or post-processing of data, they reduce the load on the CPU. I/O modules with counting and evaluation functions should be mentioned here as an example.
- Programmable modules are modifiable intelligent modules that can be used to implement complex sensor or actuator-related functions independently of the component manufacturer.
