Distributed I/O systems create islands of automation

To meet the needs of machine designers and end users, many automation input/output architectures have been decentralized while still delivering performance similar to that of centralized systems. Installed as close to a machine as possible, these newer “island” architectures reduce the time and cost of wiring for sensors and actuators and increase system availability.

The latest distributed I/O systems are open, modular systems that make it possible to design automation islands managed by a master controller via a bus or communication network. Distributed I/O systems can be used to connect motor starters, variable speed drives, operator interface terminals, encoders and other third-party products across networks and fieldbuses using protocols such as the CANopen bus.

An advanced distributed I/O platform provides a wiring solution, power management and device integration all in one compact system. Open and modular, distributed I/O is a cost-effective and feature-rich solution for centralized communications. It puts I/O capabilities at the point of control, which can provide up to a 60% cost savings in wiring and installation, while also improving reliability by incorporating all capabilities in one system.

The most sophisticated I/O software supports the user with a reliable system from the design phase to start-up and maintenance. The island components are in the form of electronic modules mounted on DIN rails in which the power supplies – controlling logic, sensors and actuators – are distributed automatically.

Distributed I/O islands are made up of one or more segments comprising power distribution modules and input/output modules. An island can be made up of a single segment or a primary segment, and up to six extension segments connected by extension modules.

On each segment, the power distribution modules typically are placed to the right of the network interface modules or extension modules, and the I/O modules typically are placed to the right of the power distribution modules that supply them with power. Every module is held in a fixed base on the DIN rail.

The bases ensure the continuity of the internal bus, the auto-addressing of the modules and the separated and isolated distribution of the internal power supplies, actuators and sensors. This configuration – which is compatible with distributed I/O debugging software – allows the output power supply to be independent of inputs (e.g., if a power contactor is closed, the analog input measurements will not be disturbed).

Today’s distributed I/O systems feature two groups of modules that result in a more feature-rich system at a lower cost. The two groups include:

• Basic modules – A full set of economical network modules and interfaces, with simplified operating modes
• Standard modules – An extended range of I/O modules with additional functions, including configurable parameters and extended operating modes.

Users can combine their I/O systems to perform a wide range of functions with several key time savings and cost advantages – such as reduced engineering, less wiring and lower connectivity costs – by using the best features from the two groups of modules to fit their application.

In addition to price optimization, there are other important benefits with today’s I/O systems. For example, solutions can be customized to mix and match low-feature and high-feature components. This allows the user to create a more scalable and extendable distributed I/O system. Most new modules are designed for applications that do not require advanced capabilities, such as software configuration, local reflex action, local HMI connectivity or advanced diagnostics.

New distributed I/O systems also feature new network interfaces, power distribution and I/O modules. This means broader coverage and a more cost-effective solution.

Using local reflex functions, the distributed I/O platform enables high-speed logic solving – from one to three milliseconds – for time-critical applications. This reduces the logic load on the PLC, freeing it up to perform more essential operations.

The hot swap capability – unplugging a module under power – of distributed I/O maximizes productivity and minimizes downtime by allowing failed I/O modules to be changed at the local level without shutting down the machine. Application-specific modules offer direct connections to third-party devices, resulting in fast and easy integration of special functions critical to the application, such as motor starters, drives or valves.

During the planning, installation and commissioning steps for a distributed I/O platform, a number of factors are critical to saving time and money in the process. These critical factors include:

• Using comprehensive and simple-to-use configuration software enhances the functionality of the distributed I/O with advanced diagnostics, including configuration of reflex functions, test mode, resource analysis and other capabilities
• Specifying advanced power distribution capabilities provides separate power for input and output devices. It also eliminates the need for extra terminals and protection devices
• Using a removable wiring connector saves time and speeds up commissioning through pre-wired connectors
• Selecting a removable memory card facilitates backup procedures and reproduction of custom configurations on multiple machines
• Connecting to the major fieldbus protocols simplifies integration with the master controller. This allows systems to be remotely monitored through an embedded Web page, or locally monitored at the I/O level via an embedded serial port that can provide a direct connection to a standard fieldbus HMI.

Machine manufacturers increasingly design their automation systems using modular architectures. This, in turn, makes the use of distributed I/O more and more commonplace, making it the system of choice when connecting motor starters, variable speed drives and operator interface terminals. Distributed I/O provides the right technical/economical balance to meet machine designers’ needs when considering size, ease of cabling, set-up and operational costs.