What is the topology structure underlying the INTERBUS bus system? What are its key characteristics?
INTERBUS is a bus system introduced by the German company Phoenix Contact in 1987 at the Hannover Industrial Fair, initially named "INTERBUS-S" and later changed to "INTERBUS."
INTERBUS is a serial bus utilizing a ring topology for signal transmission between control systems (such as PLCs and industrial computers) and distributed modules.
In the circular topology of INTERBUS, all devices (modules) are connected to a closed transmission path. Each device (module) can receive signals from the preceding level, amplify the signals, and then transmit them to the subsequent level. Unlike typical ring networks, INTERBUS's ring bus employs full-duplex communication, featuring both sending and receiving lines, allowing simultaneous transmission and reception of information.
Devices within the INTERBUS system include: Controller Board, BUS Terminal Module, Remote BUS, and Local BUS. The Controller Board functions as the master device, while other devices (modules) operate as slaves. The bus connecting the Controller Board and the BUS Terminal Module is referred to as the Remote BUS, and the bus connecting the BUS Terminal Module and local modules is known as the Local BUS. Please refer to the diagram below:
The Controller Board, serving as the master device in the INTERBUS system, is tasked with controlling and diagnosing the entire INTERBUS network. It houses an internal input/output data stack, where data exchanged with each subordinate station during bus operation is stored. INTERBUS employs a master-slave communication model, necessitating a Controller Board as the master station in every INTERBUS system. The master station, via a loop connection, is linked to each subordinate station. Additionally, the Controller Board features interfaces for communication with control systems (such as PLCs and PCs), facilitating the transfer of bus data into the control system. The diagram below illustrates the connection of the Controller Board IBS S7 300 DSC-T to the S7 300:
The Remote BUS is employed to establish a connection between the Controller Board and remote bus devices. The physical layer transmission media for the Remote BUS can include copper conductors (following the RS-485 standard), optical fibers, or infrared technology. When utilizing copper conductors, the maximum length of the Remote BUS (from the Controller Board to the last terminal module) is 12.8 kilometers; whereas, with optical fibers, the maximum length can extend up to 80 kilometers. Remote bus devices encompass BUS Terminal Modules, specialized I/O modules, remote robots, or drives, with BUS Terminal Modules being the most commonly utilized. The diagram below illustrates the conceptual representation of Remote BUS distances:
The BUS Terminal Module (BK Module) plays a pivotal role in the INTERBUS system, serving as a link between the past and the future. On one hand, it connects to the Controller Board through the Remote BUS, while on the other hand, it interfaces with distributed sensors via the Local BUS. Signals from various sensors are transmitted through the Local BUS to the BUS Terminal Module, and then forwarded to the Controller Board through the Remote BUS. INTERBUS supports a maximum of 254 BUS Terminal Modules, with the maximum distance between two modules being 400 meters (using copper conductors). The maximum distance from the Controller Board to the first BUS Terminal Module is also 400 meters (using copper conductors). The power supply for the BUS Terminal Module is non-disruptive, meaning that the power cannot be cut off during bus operation due to bus faults or other reasons. As INTERBUS operates in a ring topology, the communication of the entire bus will be affected if a BUS Terminal Module loses power. The BUS Terminal Module also provides power for communication on the Local BUS. The diagram below illustrates the schematic representation of an optical fiber-type BUS Terminal Module (BS ST BKM-LK):
The Local BUS is interconnected with the BUS Terminal Module, and on-site distributed sensors (I/O) connect to modules on the Local BUS, which are then transmitted to the Remote BUS through the BUS Terminal Module. Unlike the Remote BUS, the Local BUS employs TTL-level signals, with a maximum permissible length of 10 meters. The maximum length between two Local BUS modules cannot exceed 1.5 meters. The Local BUS can be classified into two types: ST BUS and INLINE BUS. ST stands for "Smart Terminal," and ST modules include digital inputs, outputs, analog inputs, outputs, and intelligent modules, facilitating the connection of various on-site digital and analog signals. ST modules are interconnected through ST cables and connected to the BUS Terminal Module.
The INLINE Local BUS is an open bus system, allowing connectivity with other bus systems through various couplers (such as Profibus couplers, Profinet couplers, DeviceNet couplers, and CANOpen couplers). The INLINE BUS itself supports digital input/output, analog input/output, intelligent module functionalities, providing convenient usability.
There is also a circular segment within the Local BUS, known as the LOOP segment. It is an IP65-rated segment directly used for on-site Local BUS applications. The transmission medium for the LOOP segment is an unshielded two-core wire, using a current loop for signal transmission. Each LOOP segment can install a maximum of 63 modules, with a maximum distance of 20 meters between two modules. The LOOP segment supports a maximum length of 200 meters, with a maximum current of 1.8 amperes in the loop. Compared to voltage signals, current loops exhibit stronger interference resistance and can be applied in places with higher interference.
INTERBUS adopts a ring topology where each node performs data transmission and reception through shift registers, eliminating the need to set node addresses. In case of module failure, quick replacement is possible, simplifying system installation and maintenance. However, it is worth noting that a ring network demands stability and reliability from each node, as a failure in any node can impact the entire system. This is in contrast to a tree topology where a failure in a branch node does not affect the communication of other nodes.
In 1994, INTERBUS became the German national standard (DIN 19825), followed by its recognition as the European standard (EN 50254) in 1997 and achieving international standard status (IEC 61158) in 2000. Over the years, INTERBUS technology has experienced significant development, resulting in thousands of products in the market. To ensure the consistency and continuity of INTERBUS products, the INTERBUS Club was established as early as 1992.
The INTERBUS Club is responsible for certifying INTERBUS products, granting a certification mark and issuing a certificate to products that comply with the standards. The diagram below shows the INTERBUS certification mark released by the INTERBUS Club:
In summary, the INTERBUS bus system boasts excellent reliability, high flexibility, and significant openness, making it one of the widely adopted bus systems in modern industrial environments. Masterofplc will continue to introduce more knowledge about INTERBUS in upcoming articles. We welcome your continued interest and attention.