Interbus - the Network for Enterprises

What is a Bus?

Interbus is a system for serial data transmission which transfers data between different systems/ computers and controllers and which is connected with actuators and sensors, e.g. for temperature control on a machine.
Entire production equipment and higher-level systems can be connected with each other quickly, safe, and easily. All subscribers are connected actively by the ring system.
The Interbus system was developed by Phoenix Contact and has been available since 1987. Since its introduction at the Hanover Messe, it is one of the leading fieldbus systems that meets the European standard. It is an open network system and as such, it is distributed by several manufacturers.

How does Interbus work?

The serial Interbus technology was revolutionary and has facilitated the networking of enterprises considerably. It offers fast, easy handled communication and is characterised by low susceptibility. 512 subscribers (max.) can participate, and the last subscriber closes the ring. This way, the ring structure is always assured. This always remains user-friendly, as subscribers can be added or removed at any time. Closing of the loop is assured by the loop-back bit combination, which passes once through the loop and signals to the master that the circle is closed and that everything functions correctly. As each participant is connected by two bus terminals, a tree structure physically results. This permits incoming and outgoing signals that are processed by the master. Actuators and sensors are networked per loop, so that flexible, stable, and efficient networks are possible.
Today, 17 million devices are installed worldwide and as such, the technology has been accepted widely. Currently over 600 enterprises participate in converting Interbus to control systems in order to keep it up to date.
Furthermore, fieldbus technologies are changing, and the tendency is towards Ethernet technology. For this reason, work has been done and is being done to connect the two technologies with each other in order to permit optimum modern networking.

Advantages of the Interbus

Interbus runs on a transmission rate of 500 kbps. Branch bus terminals enable a sub-network, and coupling elements prevent faults from spreading from one network to another. This contributes to the stability of the system. The local buses branch from the bus terminal which is connected to the remote bus, and in doing so they divide the network. These sections then can be switched on and off independently of each other. Addressing is done automatically, so that time-consuming calibration is not required. This also facilitates maintenance and promotes smooth switching to the serial bus system. Errors during installation are a main cause of the trouble that occurs in networks. This is prevented through automatic installation and immediate diagnosis of the system.

Elements of the Interbus

The secret of a functioning network is the communication of its components. For this purpose, the remote bus, which assures the power supply and permits a distance of 400 m between two participants, is an important element of the Interbus. Bus terminals connecting a branch network with the main network are connected to the local bus. It can be switched off separately, but does not permit any further branching. The Interbus loop, which integrates actuators and sensors into the network, allows a distance of up to 20 m between two participants. At this point, the ring structure now also becomes physical. All of these elements function as slaves with regard to a master connected to a remote bus (this is also known as a connection group).

Diagnosis with CDM

CMD was developed for control and diagnosis (and stands for Configuration Monitoring Diagnostic). It is useful in all areas of Interbus operation: In the process planning phase, CMD can be used to configure the equipment with all program addresses. During operation, the connection group can be maintained and operated using the CMD. In addition, the sub-installations can be checked. The data gathered by the CMD are stored centrally and in doing so, they are available to all participants. As such, CMD clearly facilitates the work with the Interbus and makes smooth operation possible.
In the case of a fault with a subscriber or a short-circuit, the network functions up to the fault location. This makes it easy to locate the fault, and makes quick elimination of the problem possible. In the case of transmission pauses, the subscribers are placed into a safe “idle state” condition. This way, that the subscribers are also placed into this safe “idle state” condition in the case of a fault, so that a fault does not cause permanent damage. However, the master can maintain the ring so that the network continues normally, whilst the problem of the failed subscriber is removed. Furthermore, Interbus offers the statistical evaluation of faults and problems. These can be used to recognize and eliminate wear and tear phenomena before a larger problem occurs. A diagnosis display is installed on the remote bus and on the computer. The system can be checked with CMD. All of these elements make system maintenance easy and a long service life possible.