Teach you to solve EMC problems in medical equipment

This year, the EMC test of medical equipment that suddenly "smashed out" caused many medical equipment manufacturers and EMC rectification engineers to be caught off guard and even rushed to the hospital. As a senior EMC engineer who has been battling in the field of EMC, Hua 2 has experienced EMC rectification of nearly 20 medical products. In order to better serve the majority of medical equipment manufacturers, Hua 2 shares his own experience and how to solve it. The EMC problem of medical equipment is mainly the view of the second, and you are welcome to make a brick!

To do a good job in EMC design of medical equipment, we must require the concept of the system and control several key points, mainly as follows:

1, choose a switching power supply

The EMC problem of medical equipment is caused by 60% of the quality of the switching power supply. Customers must use high-quality switching power supply modules before sending inspections. The domestic switching power supply modules are uneven, and many have claimed 3C certification. Products, when used in medical equipment, can also cause problems, especially Class B-level RE, CE testing.

From experience, Japan's "TDK-Lamada", Taiwan's "all-Han", domestic "Lenovo" and other power adapters or switching power supplies, has not appeared RE, CE problems, even the genuine "Ming Wei" switching power supply, There may also be RE issues (CE issues have not been discovered).

Many domestic switching power supplies and power adapters claim that their products have passed 3C certification and there is no EMC risk (especially RE and CE issues). However, in the case of 3C certification, this type of switching power supply is generally connected to a resistive load test. Once connected to the "real load", EMC problems will be exposed. Moreover, the price war of domestic power supply modules is serious, and power supply suppliers may save EMC equipment in mass production.

Therefore, the second proposal, the sample should be sent, and the switching power supply must be selected. This is one of the key factors for whether medical equipment can pass EMC.

2, select the isolation transformer, power filter

For large medical equipment, there are generally isolation transformers and medical filters. They have very good isolation and filtering effects on surges, EFT and CE in EMC testing, which can improve the anti-jamming performance of the equipment. Choose isolation transformers, power filters, and choose a good brand.

It is recommended to use the isolation transformer and power filter of the "Maily" and "Zhuhai Hejia" medical product suppliers. An experienced EMC engineer can see at a glance whether the EMC performance of the isolation transformer, such as the structure of the isolation transformer, is conducive to reducing the parasitic capacitance of the primary/secondary coil (which has a great influence on high-frequency EFT, CE, RE) ? Does the isolation transformer have a shield?

A good power filter, even if the EMC performance of the switching power supply is not good, can at least allow the equipment to pass CE, EFT experiments, plus isolation transformers, isolation of the surge, a number of EMC tests of the product, can easily pass.

In addition, well-known power filter manufacturers, there will be a lot of senior EMC engineers and equipment, they have rich experience, for CE, EFT, Surge and other conventional EMC problems, it is almost a fatal, hand to disease. For example, Changzhou Duo, Zhongshi Weiye, Tai Paist, Lizheng Industry, Changzhou Jianli, etc.

3, do a good job of shielding, through RE

Large medical equipment, usually a plastic outer casing, has no inhibitory effect on the radiation disturbance generated inside the product. Therefore, the second customer is advised to spray “conductive paint” on the plastic casing. Conductive paint has a great attenuation of electromagnetic disturbance. From the experience of the second, it may be as high as 20~30db, and the worst can reach 15db or less.

4, to do board-level EMC design, is the fundamental

As a senior EMC engineer knows that board-level EMC design, component or module selection is the fundamental and the most efficient and lowest cost EMC method.

PCB design, mainly pay attention to suppress signal line loop, select DC/DC switching power supply module, I/O port trace, crystal oscillator trace.

If the PCB design is good, even the bare board can pass the ESD, RE, Surge, EFT test, and it is not good to increase the cost. If it is matched with the appropriate switching power supply, then there is no suspense in EMC.

5, calm and fight

If the medical equipment encounters EMC problems, customers should not panic. Many times, for module suppliers, it is a small problem. The main solutions are as follows:

(1) EMC problem of the power port, find a supplier to solve

Power supply port interference and harassment, such as EFT, Surge, CE problems, directly find switching power supply suppliers, power filter suppliers to solve, they are most familiar with their products, know that there is a problem, and more importantly, The problem can be solved quickly or at a low cost.

At this point, if the customer insists on their own opinions and continues to toss, the cost and time consumption is too large; looking for the so-called EMC expert rectification, they are often the test engineer, almost do not understand the power or hardware, will be a little spectrum analyzer, can be on the periphery Do some hands and feet (such as shielding, adding filters, etc.), and the cost of rectification is too high, which is not cost-effective for customers.

When looking for EMC experts to rectify, be sure to understand whether they understand the hardware, because hardware or power is the basis of EMC.

(2) Pay attention to attitude, find a laboratory or network to recommend EMC rectification plan

Laboratory inspectors, especially those who are older, they are well-informed and old-fashioned. If customers are humble, they will teach customers some methods of rectification.

Even if it is the EMC field, the more conceited "two for one", I have to admire and admire: once a high-powered motor RE101 (low-frequency magnetic field harassment), more than three months, the second and the customer tried not Less programs have already exhausted us, and even have the idea of ​​giving up. Later, they were invigorated by the ideas provided by a laboratory netizen, that is, they bought a professional power cord.

Of course, the EMC of some medical devices, such as ESD, EFT, RE, RS, CS, may be tricky.

You can find a senior EMC engineer to assist in positioning and processing.

In the market, the current situation is mixed, the quality is difficult to distinguish, how can we find the right EMC engineer to solve the EMC problem of their own products?

Looking for EMC experts, don't want EMC "special" home

Experts are engineers who are deeply involved in a certain field of EMC. They are often “special” or “deep” hardware engineers in a certain field or product. For example, there are senior switching power supply engineers who know the EMC problem of switching power supply. Solve the EMC problem of switching power supplies with the simplest, lowest cost, and fastest method.

The so-called EMC experts, due to their limitations (such as experts are testing engineers, he does not understand the product or hardware), it is impossible to solve all problems in the EMC field. Including the second person, despite nearly 8 years of hardware and EMC design, but also unfamiliar with the testing standards and experimental methods.

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