Interbus

from Wikipedia, the free encyclopedia

Interbus is a field bus system for wide use in a company. Interbus covers various application areas, from the sensor / actuator level in process automation to monitoring PCs .

history

In 1983, Phoenix Contact drew up a specification for an industry-standard fieldbus. This was presented in 1987 at the Hanover Fair under the name InterBus-S.

Use of field buses and the InterBus

The requirements for data exchange in a production company are constantly increasing. In order to keep the wiring of the equipment relatively low in relation to this, field buses were introduced. With conventional technology, namely parallel cabling, the effort is higher due to the larger number of input and output points.

In contrast, serial networking is more flexible and cheaper. The fieldbus replaces the bundle of parallel cables with a single fieldbus cable, over which all data is exchanged, regardless of the type of data or automation devices .

The possibility for intelligent field devices to transfer not only process information but also parameters for configuration is becoming increasingly important.

INTERBUS is widely used in production systems in the automotive industry because it has the following advantages over other fieldbus systems:

  • quick and easy commissioning
  • good and simple diagnosis option through the active participant coupling
  • Diagnosis of fiber optic transmissions through diagnosis of the line, readjustment of the transmitter if the line attenuation is too high and error messages to the bus master before the line fails
  • integrated bus coupler with fiber optic cable (fiber optic cable) low costs and galvanic separation of system parts as well as insensitivity of the line to EMC interference / coupling
  • high data throughput at low symbol rate (500 kBit / s or 2 MBit / s)

With the help of the "INTERBUS SAFETY" profile, it is possible to transfer safety-related data together with non-safe data via the INTERBUS.

technology

An Interbus network is topologically an active ring structure. However, since the outgoing and return channels are combined in one connection cable and the subscribers have at least 2 connection terminals (incoming / outgoing), a tree-like , physical cabling structure results . To close the ring, all bus participants can bypass their outputs internally, provided that no other participant follows. In the case of branches on so-called Bus Terminals, the new branch is integrated into the forward channel and the ring is thus expanded. If a participant fails due to a malfunction, the previous participant bridges its exit to close the ring and keep the system running until the faulty participant is reached.

There are four versions in three hierarchical levels in the tree-like cabling:

  • the long-distance bus
    • Max. 400 m between two participants when using copper cables, max. 13 km total length
    • Energy supply locally at the participant
    • Electrically specified as an RS-485 interface
  • Installation remote bus
    • like long-distance bus, but with central energy supply
  • the local bus
    • branches off from the remote bus via bus coupler ( bus terminals )
    • no further branching possible
    • central energy supply
    • can be separated (switched off) individually from the remote bus
  • Interbus loop
    • 20 cm - 20 m between two participants, maximum 200 m total length
    • Two-wire interface for central energy supply and modulated bus data
    • Dissolution into a now also physical ring structure

All participants act as repeaters . Both electrical and fiber optic cables can be used for cabling long-distance and local buses . All participants act as slaves under a master connected to the remote bus (interface module).

protocol

In the bit transmission layer (layer 1), NRZ ( Non Return to Zero ) coding is used. The standard data transfer is 500 kBit / s. Telegrams with a length of 13 bits (5-bit header, 8-bit data) are used. To determine the status, special headers without data bits are transmitted during transmission pauses.

A summation frame method is used in the data link layer (layer 2) of the Interbus. A frame with data slots for each bus participant is created and shifted through the participants like a shift register . The participants read the input data into "their" slot and save their output data for it. By marking the end of the frame (loopback word), the master recognizes the arrival at the other end of the ring and thus the end of a cycle.

To create the frame during initialization or after errors, the master queries all bus participants in one or more identification cycles. These respond with identification and configuration data. This is followed by data cycles for transferring user data. The length of the data frame results from the number of bus participants and the width of the respective user data. There is also a 16-bit loopback word that the master uses to recognize the end of a cycle. A 32-bit checksum is appended to the end of the frame to detect data errors.

The individual bus participants are not addressed directly, but addressed indirectly through their position in the ring. A conversion to logical addresses only takes place in layer 7.

The sum frame method results in a deterministic runtime of the data. The bus can thus be used to control time-critical regulations. Reading and writing of the data is also always done by all participants at the same time. This way there are no inconsistencies.

In addition to this cyclic data ( process data ), acyclically occurring data of larger amounts (parameter data ) can also be transmitted. For this purpose, each participant also has an area in its slot for such acyclic data, which usually remains empty. The transfer of the process data and the deterministic time behavior are not influenced by this. In layer 7, these two transmission paths are referred to as the process data channel and the parameter channel. A separate protocol (PCP - Peripherals Communication Protocol) takes care of the division of the often extensive parameter data into individual packets, which are transmitted in several cycles in the free areas of the slots and then reassembled.

organization

In parallel to the technical development and functional expansion of INTERBUS, a number of supporting activities by manufacturers and users have arisen. These include a. 1992 the establishment of the user association INTERBUS-Club eV and the development of application profiles (starting in 1992 with the DRIVECOM profile for electric drives) by working groups of the INTERBUS-Club.

The INTERBUS Club has been awarding a certification symbol for INTERBUS devices since 1993 on the basis of a passed conformity and interoperability test.

In 2012 the INTERBUS Club decided to dissolve the association and to organize the maintenance of INTERBUS technology together with the successor system Profinet in the PNO .

After a positive development up to around 2003 it can be observed that a large number of sensor and actuator manufacturers are gradually withdrawing from the "Interbus-compatible devices" segment.

Web links

Individual evidence

  1. ↑ INTERBUS Club , press release on the dissolution.