Schneider Electric Modicon M262 PLC Internal Disassembly Analysis

Introduction >>

PLC, programmable logic controller, is the most commonly used controller in industrial automation and the most familiar automation product for electrical automation engineers. Nowadays, with the rise of edge computing, local control devices such as PLC are becoming more important.

Since PLC is common, reliable and indispensable in the field of industrial automation, people in both IT and OT are now curious about PLC. Why is it so powerful and irreplaceable in many occasions?

Today, in order to unveil the mystery of PLC, we specifically disassembled the Schneider Electric Modicon M262 to see what special designs this PLC, which represents the most advanced technology, has and why it can achieve both excellent performance and be super stable and reliable.

Let's talk about the Modicon M262 PLC first:

When it comes to PLC, some people may ask who invented it.

In fact, PLC was invented by Modicon more than 50 years ago. Later, Modicon was acquired by Schneider Electric and became Schneider Electric's PLC brand.

Modicon M262 is a PLC that integrates logic control and motion control, released by Schneider Electric following the M580, M340, M241 and other large, medium and small PLCs. It not only has excellent performance, but also has IoT functions such as direct access to the cloud. It can be said to be a representative work of the current new generation of PLCs.

Therefore, taking a look at the internal design of such a PLC can also give you the latest understanding of PLC.

This is Schneider Electric's latest PLC that we are going to dissect this time - Modicon M262. It is similar in size to an iPhone, has both logic control and motion control functions, and also has IoT features such as direct access to the cloud.

Let's take a look at the basic components of PLC:

Before we start the dissection, let's review the basic components of PLC. Usually PLC consists of six parts: CPU, power supply, input circuit, output circuit, memory and communication interface circuit. The schematic diagram is as follows:

Simply put, PLC is like a small computer. The CPU is responsible for processing data, including logical operations, timing, counting, arithmetic operations and transmission, communication networking, compiling the compiled program, executing commands, and transmitting the results to the output end.

The memory (storage) of PLC consists of two parts. One is the ROM that stores the system program. The content of this read-only memory has been solidified before the PLC leaves the factory and cannot be changed by the user. The other is the read-write RAM memory that stores the user program and working status data.

Then there are input and output units and I/O expansion interfaces, which are responsible for connecting to external devices. Finally, there is a power module, which processes the external input power and converts it into the DC power required for the PLC's CPU, memory, input and output interfaces and other internal circuits, such as 24V.

Now, here comes the key point.

What designs are inside the PLC?

What makes it so popular among control engineers since its birth?

Compared with other control devices, the biggest features of PLC are that it is sturdy, simple, reliable and durable, so PLC must comply with these characteristics in the selection of processor and memory, PCB circuit layout, power supply unit and communication circuit design, and structural design.

It can be said that whether a PLC can operate stably and reliably for a long time determines its quality. Therefore, we mainly look at how the reliability of the PLC is designed.

First, we turned the M262 over and saw that there were four screws at the bottom, but they were hexagonal and could not be unscrewed by common flat-head and cross screwdrivers. This can also prevent some people from opening the PLC at will. We easily unscrewed the four screws with a special hexagonal screwdriver.

However, even though all four screws were removed, the bottom cover and top cover of the M262 were still tightly fixed together by a circle of buckles. You can only use a flat-blade screwdriver to push in one by one and then forcefully pry open the bottom cover.

After loosening all the clips in a circle, the bottom cover and the top cover can be separated smoothly.

After opening the back cover, you can see the back of the M262 motherboard. The green PCB board is well made, with uniform color, smooth and flat surface, and no odor. The densely packed solder joints are neatly arranged and specially fixed. Unlike ordinary commercial computer motherboards, which have burrs, it is not prickly at all.

It is particularly worth mentioning that there is a stainless steel thin plate attached to the inside of the upper cover, with two clips on it for use when installing the track. This entire stainless steel plate can not only prevent dust and other substances from entering the PLC, but also can effectively shield EMI electromagnetic interference, which is very important for the stability of the PLC. You will see the same design when you open the upper cover.

After opening the bottom cover, you can directly remove the top cover. After removing it, you can see that the top and two sides of the PLC are also wrapped with a thin steel plate. In this way, except for the two sides for heat dissipation, the four sides of the PLC have EMI shielding design.

Next, remove the shielding steel plate on the M262. This steel plate is fixed by two hexagonal studs on the side of the encoder interface and two hexagonal screws on both sides of the middle. You need to use a hexagonal screwdriver or needle-nosed pliers to unscrew it. After unscrewing these four screws, you can remove the shielding cover, and the true face of the M262 is fully exposed before our eyes.

We can see that the entire M262 is very compact and neatly designed. It adopts a modular structure, which is easy to implement distributed configuration. It consists of a main board and four vertical expansion boards.

The five panels are fixed by a metal frame, which has a solid structure and is highly resistant to vibration and shock.

The four expansion boards are the network communication module, input and SD memory card module, power module and input module.

We can directly pull out the M262 motherboard from the bottom. A large aluminum heat sink can be seen on the motherboard, and below it is the CPU of this PLC. Of course, fans are never used to dissipate heat in PLC. There is gold immersion around the board, which can not only enhance the flatness of the board, but also ensure good grounding of the board. The thickness of the board reaches 2mm, and the rigidity is very good. There is no deformation even if you bend it with both hands.

This is the input and output module circuit board of M262, which has I/O input and output, encoder interface and expansion interface. The whole board is the same as the main board, with very neat design and exquisite workmanship.

This is the power module. It supports 24V DC power supply and has a normally open watchdog signal. The most obvious thing on this board is that there are two large capacitors, and multiple pieces of foam glue are used for earthquake resistance reinforcement. This is an aluminum electrolytic capacitor used for power supply filtering, with a specification of 35V and 1500μf.

This is the stop switch and the SD card and mini USB interface module. The most obvious thing here is a blue supercapacitor, which is used to supply power to the PLC to prevent data loss and maintain the clock when the PLC suddenly loses power. In the past, batteries were often used as backup power, but now supercapacitors are more robust and reliable.

This is the communication network circuit board, with a total of 3 Ethernet ports, the rightmost of which also supports the Sercos real-time motion control bus. In the small right corner there is also a black PULSE HX5008 Gigabit industrial-grade network filter, and on the back is a Gigabit network expansion port.

Finally, let’s summarize:

From the internal dissection of Schneider Electric's Modicon M262, we can see that PLC, as an important control device in the field of industrial automation, follows the controller stability and reliability as the most important principle in terms of internal structure design, circuit board workmanship, and selection of electronic components.

Coupled with the fact that PLC can be repeatedly programmed and does not require manual rewiring or reconnection of hardware, PLC has become the first choice for discrete control since its inception.

Of course, back to the Modicon M262 controller itself that was disassembled this time, whether it is workmanship or the selection of components such as CPU and memory, it is very high-end and leading. High-performance processor, large memory, high-bandwidth communication network, low power consumption, all of which represent the current development trend of PLC.