If you are an old PC user, you may have heard of the RS-232C standard. So what about the word PLC? In fact, these are the standards and words used in the field of industrial networks, which are very important in the industrial field. Here’s a quick introduction to industrial networks.
What is an industrial network?
An industrial network is a network that controls sensors and devices installed in a device or production line and transmits information from it to a higher system, such as a manufacturing execution system. Also known as field network, FA network, and Fieldbus.
Typically, a factory’s network system consists of the following four-layer structure:
- Layer 1: Information Systems Network
- Layer 2: Controller Network
- Tier 3: Field Network
- Layer 4: Wiring-saving network
Information system networks include manufacturing execution systems (MESs) and controller networks include programmable logic controllers (PLCs). In addition, field networks include controllers that communicate with sensors and motors, and the lowest layer is a wiring-saving network that simplifies the communication wiring between sensors and controllers.
This article covers a third-tier field network. The rs-232C interface attached to old PCs is originally an old standard for this third-layer network.
In factory equipment and production lines, the components of a network, such as physical devices and sensors, do not fluctuate much, and the same is often connected at all times. On the other hand, there are no problems such as data transmission errors or stops, and it is required to always operate stably and reliably at the same speed regardless of the change in the amount of data transmission (this is called “ensuring real-time performance”).
Therefore, instead of Ethernet, which is a standard for networks such as the Internet and LAN used in offices, the standard of the original network has developed. However, as a result of the fact that high-ranking systems such as manufacturing execution systems, which have been popular in recent years, have been built on an Ethernet basis, and real-time improvements, which were weak points of Ethernet systems, field networks have been increasing in Ethernet-based standards recently.
History and Criteria of Field Network
The idea of connecting factory equipment with a network, collecting data, or connecting a controller for controlling motors, robots, etc. with a network and integrated management is close to the IoT today in 1970. It is said that it was in the 1990s. Experimental research had already been made. However, at that time, in the era of analog technology, digital hardware and software were still poor, so it was thought that the realization of such a practical digital network was a thing for the time being.
Subsequent advances in digital technology have led to the practical application of field networks in the 1990s. At that time, various standards were born, and there was a time when about 40 kinds of standards were crowded. Since then, the organization has progressed, and now it is narrowed down to more than 10 types of major standards.
There are three field networks: an rs-485 system developed from RS-232C, an Ethernet system, and a wireless system. As mentioned earlier, ethernet standards have dominated in recent years. In addition, wireless systems are gradually increasing.
Features for RS-485 field networks
It can be said that the advantage of the RS-485 system is that it has a long history and has been used in many sites. In addition, the operation is relatively stable and has excellent real-time performance. In addition, it is also characterized by being resistant to noise. These “high reliability” and “achievements” are the major reasons why rs-485 field networks have been in use for more than 30 years, and even now that Ethernet systems are dominant, they are quite a “hard to throw away” standard.
The disadvantage is that the transmission speed is slower than that of ethernet systems. In addition, the price of equipment tends to be slightly higher than that of Ethernet systems.
Features for Ethernet field networks
The advantage of Ethernet systems is that they still have relatively fast best-effort transmission speeds. Since the protocols and hardware are common to the top information systems, they can be easily introduced. In addition, hardware such as cables and network adapters are common to LANs that are already widely used, so the price of equipment can be kept low.
On the other hand, ethernet has a slower transmission speed as network traffic increases. In other words, the scale of the production system increases, and if you try to increase the time, the transmission speed will decrease and the real-time nature of the data transmission will be lost. Therefore, some ingenuity is required to ensure real-time performance.
Characteristics of wireless field networks
The biggest advantage of wireless systems is that wired wiring is not required. This is very advantageous when you are installing a field network later, or when there is no space under the floor or ceiling of the factory for wired wiring. In addition, for the same reason, we can flexibly respond to cases such as factory layout changes. In addition, the initial cost of the entire system tends to be low because there is no cost only for installing cables.
On the other hand, wireless uses radio waves to communicate, so transmission may not be successful depending on the propagation status of radio waves such as diffraction and reflection, which is a disadvantage unique to wireless. Therefore, as a general rule, antennas of equipment will need to be placed in a position that can see each other.
Typical standards for each lineage and their special
RS-485 standard and its specials
The main ones include CC-Link and PROFIBUS DP.
“CC-Link” is a leading standard developed by Mitsubishi Electric in Japan and Asia. Features include a transfer speed of up to 10 Mbps and a transmission distance of 1.2 km, which are relatively high speeds and have a long transmission distance. It can also connect 64 devices per network. In Japan, this standard has almost become the factory standard. Cc-Link is originally an RS-485 standard, but ethernet-based CC-Link IE has also appeared in recent years. Controllers with Ethernet and RS-485 conversion are also available.
“PROFIBUS DP” is a powerful standard mainly in Europe. It has the largest share worldwide. As a feature, 126 devices per network can be connected. It is also compatible with fiber optic cables.
Ethernet Standards and Their Specials
The main ones are “EtherNet/IP” and “EtherCAT”.
“Ethernet/IP” is a communication standard that supports cyclic communication in order to overcome the weaknesses of Ethernet. It stands for Cyclic communication. Communication control is unique to this standard by communicating at a certain period of time. This ensures apparent real-time. It is also known for its adoption by automaker GM, which has gained a large share in the U.S.
“Ether CAT” is a standard that, in principle, confines the network topology (the physical connection form of the network) from tree to ring in order to overcome the weaknesses of Ethernet. This is known for the adoption of Toyota Motor Corporation. In a normal network, it branches in a tree shape using a hub or router, but EtherCAT connects the equipment in a daisy chain shape. This results in a constant amount of traffic in the ring, ensuring real-time.
Wireless standards and their specialties
Wireless standards include “local 5G” and “LPWA”.
“Local 5G” is a limited-space use of 5G, the standard for next-generation mobile phones. It is expected that 5G high speed can be used for field networks.
“LPWA” is the mainstream method currently used in wireless field networks, and it is popular as being able to cover a large area with low power. There is a disadvantage that the transmission speed is slow, but the cost is low and it helps spread.
The number of standards is that the range of selection is wide
Above, we have briefly introduced the standards for industrial networks. There are many different standards for industrial networks. At present, ethernet standards are somewhat dominant, but rs-485-based standards, which have been used in many sites over the years, are also difficult to throw away. In addition, in some cases, wireless systems can be said to be a little more considerable. In any case, it is important to understand the characteristics of each standard and choose the most suitable standard for the production system you are trying to build. Let’s make use of the wide range of selections because there are various standards.
