As a newcomer to industrial control, many people, like me, probably found it difficult to understand what fieldbus was at first. So I consulted a lot of materials and asked many experienced people for advice. After a period of learning, I now have a general understanding of fieldbus, and I will share my learning experience with you below.
While fieldbus technology may not be the most widely discussed topic in the automation field in the past two years, it is certainly a key area of competition among automation manufacturers vying for market share. In reality, automation manufacturers are well aware that whoever controls the fieldbus controls the standard; whoever controls the standard controls the market; and whoever is the technology leader. So, what exactly is fieldbus?
Fieldbus technology is an industrial control technology that emerged internationally in the mid-1980s. Simply put, fieldbus is a bus technology used in the field, similar to the bus concept inside a computer. However, due to the special environment of the field (such as temperature, installation conditions, interference, etc.), it differs from the indoor environments typically used by computers. To distinguish it, we call this type of bus a fieldbus.
Anyone who has worked with PLCs knows that if there are 100 I/O points in the field, we need to run more than 100 wires from the PLC cabinet to the field. What if there are 1000? So some people wonder if it is possible to connect all these points with a single cable. That's right, fieldbus achieves this function, greatly simplifying wiring.
A fieldbus mainly consists of three parts: physical communication method, communication protocol, and network scheduling mechanism.
Physical communication methods essentially include RS485, RS232, RS422, and TCP/IP. Wireless communication is also an option, but currently, the stability of wireless technology and industry/national standards are lacking, so it's unlikely to be widely used as a fieldbus in the next few years.
Communication protocols are not unfamiliar to automation engineers, but few people have a deep understanding and mastery of them. The main concept of fieldbus protocols is how each fieldbus station needs to transmit communication data.
The network scheduling mechanism might seem like the same thing as the communication protocol, but it's not. It's a characteristic of field communication. Ordinary buses only handle key communication data, while fieldbuses need to support time stamps and priorities. In other words, this scheduling mechanism mainly ensures the real-time and timely nature of communication data.
Fieldbus is equivalent to the transportation system in life; the communication method is equivalent to transportation by land, sea, and air; the communication protocol is equivalent to traffic rules; and the network dispatch is equivalent to the traffic police command system.
In daily life, people travel by land, water, or air, regardless of the mode of transportation. And regardless of the mode of transport, traffic rules must be followed. Only by obeying traffic rules can one travel normally and reach their destination. The work of traffic police is to resolve traffic congestion caused by disruptions during normal operations. Traffic police primarily focus on resolving congestion, ensuring the smooth flow of traffic on key roads, and effectively implementing traffic priorities.
Fieldbus technology has indeed changed the traditional bus control mindset. Conventional bus control involves a master CPU retrieving data from substations via the bus, performing calculations, and then sending control requests to other substations based on the results. This wastes bus bandwidth. Fieldbus technology distributes control across various substations, each with its own data acquisition terminal and executor. This effectively reduces the burden on the central CPU and changes the conventional control model. (Today's forwarding code is: Yiwei, focusing on core control.) Many people used to say that fieldbus could save a lot on cabling costs. While cabling costs do exist, they are not the reason for fieldbus technology's existence. It's a revolutionary technology that changes conventional control by decentralizing the core of control to each station. The communication stations on the bus are no longer just data acquisition and control execution terminals, but rather the brains with control logic.
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