Interbus

Interbus is a field bus system for a wide range of applications in an enterprise. Interbus covers various application areas off of the sensor / actuator level in process automation, to monitoring PC.

History

In 1983 the company Phoenix Contact developed a specification for an industry-standard fieldbus. This was introduced in 1987 at the Hannover Fair under the name Interbus -S.

Benefits of fieldbus and the INTERBUS

The requirements for data exchange in a manufacturing company are steadily increasing. However, to keep the cost of the wiring of the equipment in relation to relatively low field buses were introduced. In the conventional technique, namely, the parallel wiring, the overhead due to the greater number of input and output points is higher.

A serial networking, however, is more flexible and cheaper. The fieldbus line replaces the bundle of parallel wires by a single Fieldbus, through which all data to be exchanged, independent of the type of the data or of the programmable controllers.

Increasingly significant is the possibility for intelligent field devices is also to transfer parameters for the configuration in addition to process information.

INTERBUS is widely used in production of the automotive industry, because it has the following advantages over other field bus systems:

• Quick and easy commissioning
• Good and simple diagnostic capability through the active participants coupling
• Diagnosis of fiber optic transmissions by diagnosing the track, readjustment of the transmitter in case of excessive path attenuation and error message to the bus master before the route turns
• Through integrated Coupler with fiber optic (fiber optic ) low cost, while electrical isolation of system components as well as insensitivity of the route towards EMV-Störungen/Einkopplungen

Using the " INTERBUS SAFETY " profile, it is possible to transmit safety-related data with non-secure data on the INTERBUS.

Technology

An Interbus network is topologically an active ring structure dar. Since return channel but are combined in one cable and the participants have at least two terminals ( inbound / outbound ), the result is a tree-like, physical cabling structure. To close the ring all nodes can bridge their outputs internally, should follow no other node. In branches of so-called Bus Terminal, the new branch is involved in the forward channel and the ring expands so. Should a participant fail due to failure of previous participants bridged its output to close the ring and to keep the system run until the faulty participants.

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

• The remote bus up to 400 m between two stations when using copper lines, max 13 km total length
• Power locally at the subscriber
• Electrically specified as RS -485 interface

• Installation remote as remote bus, but with central power supply

• The local bus branches via a transceiver ( Bus Terminal ) from the remote bus from
• No further branching is possible
• Central power supply
• Can be separated one from the remote bus ( off)

• Interbus-Loop 20 cm - 20 m between two devices, a maximum of 200 m total length
• Two-wire interface for centralized energy supply and modulated bus data
• Resolution in now physical ring structure

All participants will act as a repeater. For wiring of remote and local bus both electrical and optical waveguides can be used. All participants will act as a slave under a master connected to the remote bus (interface ).

Protocol

In the physical layer (layer 1) is a NRZ coding (non- return to zero ) is used. By default the data is transmitted with 500 kbit / s Be used telegrams with 13 bits in length (5 bit header, 8-bit data ). For status determination in transmission pauses special headers are transmitted without data bits.

In the data link layer (layer 2) of the Interbus a summation frame method is employed. A frame with data slots for each bus user is created and pushed like a shift register by the participants. Participants read a case, the input data in "their " slot and save for their output data. By a marker at the end of the frame ( loop-back word ) of the master detects the arrival at the other end of the ring and thus the end of a cycle.

The summation frame procedure here is similar to the functional principle of EtherCAT. To create the frame during the initialization or for errors of the master polls all nodes into one or more identification cycles. This answer identification and configuration data. This is followed by data cycles for user data transmission. The length of the data frame is derived from the number of bus nodes and the width of the respective user data. In addition, a 16 -bit long word loopback by which the master recognizes the end of a cycle. On the frame end a 32-bit checksum is appended to detect data errors.

The individual nodes are not directly addressed, but addressed indirectly by their position in the ring. An implementation of logical addresses is done only in layer 7

By the summation frame procedure results in a deterministic runtime of the data. The bus can thus be used to control time critical systems. The reading and writing of data is also always by all participants at the same time, so there are no inconsistencies.

In addition to these cyclical data (process data) and acyclic data occurring greater quantity ( parameter data) can be transmitted. To this end, each participant has in its slot in addition a range of such acyclic data, which remains empty in most cases. The transmission of process data and the deterministic time behavior are not affected by this. In layer 7, these two paths are referred to as process data channel and parameter channel. A separate protocol (PCP - Peripherals Communication Protocol ) handles the allocation of often extensive parameter data into individual packets transferred in several cycles in the free areas of the slots and then reassembled.

Organization

In parallel with the technical development and functional expansion of INTERBUS created a number of supporting activities of manufacturers and users. These include, inter alia, 1992 eV the establishment of user association INTERBUS Club and the development of application profiles (starting in 1992 with the DRIVECOM profile for Electric Drives ) by working groups of the INTERBUS Club.

As of 1993, the INTERBUS Club awards a certification symbol for INTERBUS devices based on a passed conformance and interoperability testing.

2012, the INTERBUS Club decides to dissolve the association and to organize the care of the INTERBUS technology together with the successor system PROFINET in the PNO.

After a positive development until about 2003, it is observed that a variety of sensor and actuator manufacturers slowly from the segment " interbusfähige devices" withdraws.