The difference between EMC design for commercial PCs and EMC design for industrial PCs - Advantech

As mentioned in the previous article, we know that the EMC design of the commercial PC is internal, while the EMC design of the industrial computer is bidirectional.

Let's compare it with a commercial PC to illustrate the difference between internal and bidirectional:

1. EMC design of heat dissipation port

First of all, we have a clear concept, whether internal or external, the best way to deal with electromagnetic radiation is to use a fully sealed metal box to shield the electromagnetic radiator, and the thicker the metal layer used for shielding, the better. In this way, the effect of electromagnetic shielding is the best, both internally and externally. However, due to the factors of heat dissipation and external expansion equipment. Neither commercial PCs nor industrial computers can be tightly sealed. One of the most important points in the design of the chassis to prevent electromagnetic leakage is the design of a good balance between heat dissipation and electromagnetic leakage, which requires both sufficient heat dissipation and electromagnetic compatibility design.

However, in fact, the design standard of electromagnetic leakage prevention has many restrictions on the size and shape of the heat dissipation aperture, and research experiments have shown that the square aperture has a better effect on preventing electromagnetic leakage than the circular aperture.

2. EMC design at the seams of the chassis

According to the theory, when the distance between two contact points on the chassis is greater than 0.25xλ (wavelength symbol), harmful electromagnetic radiation can easily leak between the two points. Therefore, the design at the seams of the chassis is also an important indicator to examine the EMC design foundation.

Now the thickness of the steel plate of the chassis of the commercial PC is only 0.6mm, the strength of the steel plate is limited, it is difficult to ensure that the chassis itself does not produce deformation after being stressed, and because the commercial PC is basically a vertical chassis now, it is difficult to ensure the close combination of the seams of the side opening panel, in order to overcome these phenomena, some high-end commercial PCs leave EMI shrapnel design at the joints of the chassis.

However, the use environment of industrial computer is complex and changeable, and some environments have strong vibration, and the EMI shrapnel design is easy to lose the elasticity of shrapnel in a vibrating environment. The chassis material used in the industrial computer is 1.2mm high-quality steel plate, which itself has excellent deformation resistance, because the industrial computer chassis is mostly horizontal, the weight of the top steel plate itself and the steel characteristics have been able to ensure the close contact between the chassis walls. Excellent industrial computer chassis can also pass CE, FCC and other EMC certifications when EMI shrapnel is not used. In some environments where EMC is extremely critical, such as in the military industry, we recommend that the customer use a more reliable metal conductive cloth at the seams of the chassis.

At the seam between the board and the chassis, this place is also extremely prone to electromagnetic leakage, and few brands in commercial PCs adopt EMI shrapnel designs in this place due to the fewer expansion cards. The industrial computer will insert multiple boards inside, and the close contact between the board and the chassis is an important indicator of whether the electromagnetic compatibility is excellent, so the industrial computer with excellent workmanship will use EMI shrapnel to ensure that the seam between the board and the chassis is tight and reliable.

3. Special design on the surface of the chassis

The material of the commercial PC chassis is mostly galvanized steel, and considering the effectiveness of absorbing the radiation in the chassis, there is no painting treatment inside the chassis, so the galvanized steel plate on the inner wall of the chassis can be conductive, and it is easier to absorb electromagnetic radiation, which also makes the commercial PC have inherent advantages in electrostatic protection and electromagnetic shielding. This kind of chassis for commercial PCs is not a problem under ordinary use, but it is very inappropriate if it is used in an industrial control environment.

First of all, industrial computers are used in strong corrosive environments at some times, such as sea salt at sea, car exhaust from highways, and gases from chemical plants. Therefore, the inner and outer surfaces of the chassis must be treated with anti-corrosion. The picture below shows Advantech's chassis after the outer surface of the case and the inner wall of the case have been treated with anti-corrosion baking paint.

Secondly, sometimes the computer will work in a vibrating environment, and in some special cases, vibration will cause some electrical components in the chassis to contact the internal surface of the chassis, because the inner wall of the chassis is conductive, so it is easy to cause a short circuit and burn the equipment.

The internal painting treatment of the industrial computer makes the inner wall of the chassis non-conductive, which can prevent the occurrence of this kind of phenomenon. However, it is precisely because these non-conductive chassis walls have higher challenges to the EMC design of industrial computers. Due to the paint treatment on the inner wall of the industrial computer, the surface of the chassis is not conductive and cannot be formed like a commercial PC, so the contact surface without painting is left in some positions to form a conductive body, forming an equipotential body on the surface of the entire chassis, and the treatment process is more complicated.

The difference between EMC design for commercial PCs and EMC design for industrial PCs - Advantech

The difference between EMC design for commercial PCs and EMC design for industrial PCs - Advantech

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