PROFIBUS is a manufacturer-independent Field bus standard for applications in manufacturing, process and building automation. Profibus technology is described in fixed terms in DIN 19245 as a German standard and in EN 50170 / IEC 61158 as an international standard.

It specifies the technical and functional properties of a serial bus system. The PROFIBUS standard is thus available to every provider of automation product. PROFIBUS distinguishes between master and slave. The masters determine the data communication on the bus.

A master can send messages without an external request if it has access rights to the bus (token). The slaves are peripheral devices. Typical slaves are I/O devices, valves, motors and transmitters.

They have no bus access rights. They can only confirm received messages or send a message on the request of the master. Slaves are passive devices on the PROFIBUS. PROFIBUS is composed of three types of protocol, each of which is used for different tasks. Of course, devices with all three protocols can communicate with each other in a complex system by means of a PROFIBUS network.

The three types of protocols are: PROFIBUS FMS, DP, PA.

Only the two protocol types DP and PA today are important for process automation and are supported within the 800xA System.

For this Project we will only be concentrating on Profibus DP (with a brief description of Profibus PA only to the extent of documentation).

PROFIBUS PA is an all-digital, serial, two-way communication protocol that connects field devices (instruments), such as sensors, actuators, and controllers.

PROFIBUS PA enables advanced diagnostics from all Field Bus components including the physical layer. This allows higher plant availability. A typical Field bus installation provides connection from a network of field devices via a segment coupler to a host system via a two way, serial communication link. The cabling and connections are arranged in a multi-drop fashion, requiring only a single pair cable with parallel connections to field devices.

PROFIBUS PA is different from the traditional approach of connecting 4 to 20mA devices to a DCS/PLC system using dedicated pairs of wires for each device.

Each Field bus running from the segment coupler to the field is known as a segment.

Each segment consists of a trunk or home-run, running from the segment coupler to the processing plant with parallel connected spurs linking to field devices such as transmitters and control valves.

Smart wiring blocks with integrated short circuit protection, such as Segment Protectors or Field Barriers, protect the trunk against short circuit on a spur.

Such protectors are preferred to connect the individual instruments to the trunk.

The interconnection from a PROFIBUS PA trunk to PROFIBUS DP is realized with a segment coupler.