CAN BUS

Communication is a key factor in industrial production systems. The performance required in terms of information flow is just as important (if not more so) than the flow of materials and energy. The main purpose of the network is to exchange information.

Decentralized architecture has rapidly become the preferred choice for process control. Distributed systems are generally better suited to the location of the sensors and actuators that provide the information. This requires reliable, robust communication, combined with low-cost, "intelligent" electronics.

In industry, network communications are classified into four levels, often represented by a pyramid. The concept of computer-aided production or CIM (computer integrated manufacturing) comprises a field level, a cell level, a factory or workshop level and a design and management level.

• The design and production level centralizes design-related information such as CAD tool files.

• The factory level concerns production and order management.

• The cell level will enable supervision, stock monitoring and production control.

• The field level is closest to production; it corresponds to the various machines involved in the manufacture, transformation and assembly of an object or assembly. It links numerically controlled machines, robots, PLCs, controllers, conveyors, sensors and actuators.

The fieldbus network is also known as an "industrial local area network". It's called industrial because it's production-oriented, and local because it's set up in a part of the production site that makes up a company. It enables communication between sensors, actuators, PLCs, CNC machines, robots, industrial controllers and simple command and control systems. In field networks, the size of messages exchanged is relatively small compared with other types of network, whether local or long-distance. Information flows tend to be periodic, and time is of the essence (real-time applications).

Since field networks operate in electromagnetically disturbed environments, the support is generally a shielded coaxial cable or a twisted pair working in differential mode, or an optical fiber for greater noise immunity. Communication distances are relatively short compared with other types of network, often less than a few dozen meters.

A bus topology is generally adopted for its ease of implementation, evolution (addition or removal of systems) and extension (repeaters).

To refer to the ISO network architecture standardization OSI (open system interconnection), three of the seven layers are covered: the physical...