Understanding the Correct Wiring of PROFIBUS-DP

PROFIBUS is an open digital communication system with a wide range of applications, representing a significant breakthrough in the transition from centralized automation systems to decentralized automation systems.

Since its inception, PROFIBUS has focused on system integration and engineering, particularly in the research and development of application protocols, making it suitable for fast, time-critical applications and complex communication tasks. It has become the only fieldbus capable of comprehensively covering both factory automation and process automation applications, especially in these fields. Thus, PROFIBUS has remained a leader in the field of fieldbus technology in the international market.

With the extensive application of PROFIBUS, many users have started to engage with and utilize fieldbus technology. However, due to varying levels of understanding of fieldbus technology among users, combined with the complexity of on-site construction, there may be hidden dangers in many projects’ fieldbus communication. If not detected and addressed promptly, this could lead to communication failures in the system, affecting the normal operation of the entire system.

The essence of PROFIBUS network communication is RS485 serial communication. Depending on different industry applications, there are mainly three communication protocols: DP (Decentralized Peripherals), FMS (Field Message Specification), and PA (Process Automation).

1. Popularizing the Correct Wiring of PROFIBUS-DP

The correct wiring is shown in the figure below; it is self-explanatory. The PROFIBUS cable is very simple, consisting of only two wires inside: one red and one green, with a shielding layer outside. When wiring, ensure the shielding layer is properly connected and does not touch the internal wires. It is essential to distinguish between the incoming and outgoing wires. If it is a daisy chain, it means one main bus runs down with several sub-stations connected in between, which is a common method. At both ends of the bus, the wires must be connected to the incoming holes, not the outgoing ones. These two ends’ connectors should have their switches set to ON, meaning only the incoming connection is active while the outgoing connection is inactive. All other intermediate connectors should be set to OFF, allowing both incoming and outgoing connections (memory tip: ON indicates connecting terminal resistance, so the end connectors are set to ON; OFF indicates disconnecting terminal resistance, so the intermediate connectors must be set to OFF).

2. A Step-by-Step Guide on How to Connect and Purchase

Whether forming an MPI or PROFIBUS-DP network, the main components used are the same:

For specific cable and connector order numbers, please refer to: Common Accessories Order Numbers

A. Cables and Strippers. Using FC technology does not require stripping the exposed copper wire.

Figure 1. PROFIBUS cable stripped at one end with a quick stripper (FCS, order number 6GK1905-6AA00).

B. Opening the PROFIBUS Network Connector. First, release the cable tension clamp, then lift the core wire lock.

Figure 2. Opened PROFIBUS Connector

C. Remove the protective layer from the PROFIBUS cable core wire, insert the core wire according to the corresponding color markings into the core wire lock, and then press the lock block down firmly to ensure contact with the internal conductors. Note that the stripped shielding layer of the cable must be in contact with the shielding connection clamp.

Figure 3. Inserting the Cable

Because of the high communication frequency, the communication cable is grounded at both ends. The shielding layer must be connected at both ends of the cable.

D. Reset the cable clamp, tighten the screws, and eliminate external tension affecting the internal connection.

The network connectors are mainly divided into two types: with and without programming ports. The connectors without programming ports are used for general networking, while those with programming ports can still provide a programming connection while being networked, suitable for programming or connecting HMI, etc.

Figure 4. Left: Network connector without programming port (order number: 6ES7 972-0BA52-0XA0); Right: with programming port

By connecting the PROFIBUS cable to the network plug, a bus-type network structure is formed.

Figure 5. Bus-type Network Connection

In the above figure, network connectors A, B, and C are inserted into the communication ports of three communication stations; cable a connects plug A and B, while cable b connects plug B and C. The linear structure can be extended accordingly.

Note the settings of the “terminal resistance” switch within the circles. The terminal resistance switch of the network terminal plug must be set to the “ON” position; the terminal resistance switch of the intermediate station plugs should be set to the “OFF” position.

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