PROFIBUS is an open digital communication system with a wide range of applications, representing a major breakthrough in the transition from centralized to decentralized automation systems.
Because PROFIBUS has always focused on system integration and systems engineering, especially on application-specific research and development, it is well-suited for fast, time-critical applications and complex communication tasks. This makes it the only fieldbus capable of comprehensively covering factory automation and process automation applications, making it particularly suitable for these fields. Therefore, since its inception, PROFIBUS has been a leader in the international fieldbus technology market.
With the widespread adoption of PROFIBUS, many users have begun to use fieldbus. However, due to varying levels of understanding of fieldbus technology among users, coupled with the complexity of on-site construction conditions, potential problems may exist in fieldbus communication in many projects. If these problems are not detected and addressed in a timely manner, they could lead to communication failures, thereby affecting the normal operation of the entire system.
The essence of PROFIBUS network communication is RS485 serial communication. According to different industry applications, there are three main communication standards: DP (Decentralized Peripherals), FMS (Field Message Specification), and PA (Process Automation).
I. Basic Knowledge of Correct PROFIBUS-DP Cable Connection
The correct wiring method is shown in the diagram below. No explanation is needed; the diagram is self-explanatory. PROFIBUS cables are very simple, with only two wires inside, one red and one green, and an outer shielding layer. When wiring, ensure the shielding layer is properly connected and does not come into contact with the internal wires. Distinguish between the incoming and outgoing wires. If it's a series connection, it's a common method where a single bus connects to multiple substations. At both ends of the bus, the wires must be connected to the incoming terminal, not the outgoing terminal. These two end terminals must be switched to the ON position. At this point, only the incoming wire is connected, while the outgoing wire is disconnected. All other intermediate terminals should be switched to OFF, meaning both their incoming and outgoing wires are connected. (Remember: ON indicates a terminating resistor is connected, so both ends should be switched to ON; OFF indicates the terminating resistor is disconnected, so intermediate terminals should be switched to OFF.)
II. Step-by-step guide on how to receive and purchase.
Whether building an MPI or RPOFIBUS-DP network, the main components used are the same:
For specific cable and connector order numbers, please refer to: Common Accessory Order Numbers
A. Cables and wire strippers. FC technology eliminates the need to strip the bare copper wires.
Figure 1. PROFIBUS cable stripped at one end with a quick wire stripper (FCS, order number 6GK1905-6AA00).
B. Open the PROFIBUS network connector. First, open the cable tension release block, then lift the core wire lock.
Figure 2. Open PROFIBUS connector
C. Remove the protective layer from the PROFIBUS cable cores, insert the cores into the core lock according to the corresponding color markings, and then press the lock block down firmly to make the internal conductors contact. Ensure that the stripped shielding layer of the cable contacts the shielding connection plate.
Figure 3. Inserting the cable
Because the communication frequency is relatively high, the communication cable is grounded at both ends. Shielding layers must be connected to both ends of the cable.
D. Reset the cable clamp, tighten the screws, and eliminate the influence of external tension on the internal connection.
Network connectors are mainly divided into two types: those with and without programming ports. Plugs without programming ports are used for general networking, while plugs with programming ports can still provide a programming connection port while networking, for programming or connecting HMIs, etc.
Figure 4. The left side shows a network connector without a programming port (order number: 6ES7972-0BA52-0XA0), and the right side shows one with a programming port.
A bus-type network structure is formed by connecting the network plug via a PROFIBUS cable.
Figure 5. Bus-type network connection
In the diagram above, network connectors A, B, and C are plugged into the communication ports of the three communication stations, respectively; cable a connects plugs A and B, and cable b connects plugs B and C. The linear structure can be extended accordingly.
Note the "termination resistor" switch setting within the circle. For network terminal plugs, the termination resistor switch must be in the "ON" position; for intermediate station plugs, the termination resistor switch should be in the "OFF" position.
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