0 Preface This paper analyzes the main types of electromagnetic interference and its hazards in medical electrical equipment, focusing on the application of power filters in medical electrical equipment to solve the phenomenon of electromagnetic interference in medical electrical equipment. In hospital outpatient rooms, operating rooms and wards, the electromagnetic interference generated by a medical electrical equipment with strong electromagnetic radiation will destroy or reduce the working performance of other medical electrical equipment; and produce harmful effects through the physical and chemical effects on human tissues and organs Physiological effects cause damage to human tissues and organs, endangering human health. Therefore, many countries in the world have begun to pay attention to the electromagnetic radiation of medical electrical equipment, and have formulated corresponding standards and documents, and proposed mandatory requirements for the radiation and anti-interference of medical electrical equipment. Therefore, various medical electrical equipment manufacturers are increasingly concerned about electromagnetic interference. 1 Types of electromagnetic interference Electromagnetic compatibility refers to the ability of a product and other products to coexist in a specific electromagnetic environment without causing degradation or damage to other products or its own performance. It mainly includes two fields of radiation and immunity. There are two main types of electromagnetic interference: 1.1 Radiated interference Radiated interference refers to a way in which electromagnetic waves generated by a device propagate through space and cause useless voltage / current to other device circuits. When the distance between the two devices is longer than the wavelength, the interference propagates in the form of electromagnetic waves. For example, when a doctor uses a mobile phone, the image of the computer display of the medical device next to it will jitter, because the signal emitted by the mobile phone when it is working is transmitted to the interior of the display through the space in the form of an electromagnetic field. 1.2 Conducted interference Conducted interference refers to a type of interference in which voltage / current changes generated by one device are conducted through power lines and signal lines and affect other devices. When the length of the device and the conductor is shorter than the wavelength, the conducted interference is mainly the common mode interference and differential mode interference transmitted through the power line, control line, and signal line, as well as the common impedance generated by different devices using a common power supply or a common ground line. interference. In modern hospitals, due to the need for diagnosis and surgery, outpatient rooms and operating rooms are often no longer a single medical device, but multiple devices are placed centrally, which inevitably makes multiple medical electrical equipment share a power supply . Originally, the power cord was only used to transmit 50Hz AC power, but due to the electromagnetic interference of the connected equipment, the current on the power cord was very impure. Conducted interference can easily enter the medical equipment through the power cord, making the equipment wrong or even damaged, thereby affecting the accuracy of the diagnosis results. If such conduction interference occurs during the operation, it will endanger the patient's life safety in severe cases. Therefore, it is very important to suppress conducted interference of power cords in medical electrical equipment. Usually, the main and effective method we adopt is to install power filter on the power line of the interfered equipment. 2 The specific application of power filter in medical equipment Medical operating microscopes need to be exported to the EU, and they are tested for electromagnetic compatibility in accordance with IEC 60601-1-2. It is found that the conducted interference test results of the AC power port of this product are shown in Figure 1. It can be seen from the figure that the conducted interference of the power port of this product does not pass the requirements of Class B limits. After analysis and discussion, it was decided to install a power filter on the power input of the product. 2. 1 choice of power filter A filter is a two-port network that has the characteristic of selecting frequencies. It allows certain frequencies to pass smoothly while blocking others. The power filter belongs to the interference suppression filter. From the perspective of frequency selection, it is also a low-pass filter. It can transmit the power of the DC power supply and the AC power supply to the device without attenuation, and at the same time, it can make high-frequency interference. The signal is greatly attenuated to protect the device from damage. When choosing a specific model, in order to achieve the maximum possible mismatch within the frequency range of the suppressed electromagnetic interference signal, so that the electromagnetic interference signal that needs to be suppressed is subject to the maximum possible attenuation, it must be based on the power supply impedance and The network structure and parameters of the power filter can be selected by the load impedance in order to obtain a satisfactory interference suppression effect. After selection, we chose a power filter with a passive low-pass network (model 6EHG1-2 produced by TYCO). Connect one end of the filter to the interference source, and the load is connected to the interfered device, which can suppress the common mode EMI signal existing on the power line, make it attenuated, and control to a very low level. 2.2 Installation of power filter After the correct selection of the filter, the power filter was installed on the power input of the surgical microscope, but the product still failed the conducted interference test. Analyze the reason: first suspect that the poor grounding of the filter causes the filter effect to deteriorate. So put the chassis on the ground plane, the power supply of the filter is directly grounded with a short wire, and the result is still not improved. After observation and experiment, it is found that the installation position of the power filter in the product is different, and the conducted interference test results are different. When the power filter is installed as shown in Figure 2 (a), the conducted interference test results are not significantly improved; when the power filter is installed as shown in Figure 2 (b) and the filter is filtered with metal screws and star spring washers When the shield of the device is firmly fixed on the machine metal casing of the equipment power inlet, the conducted interference test data is significantly reduced. After analysis, we found that the installation in the mode of Figure 2 (a) will cause an electromagnetic coupling path between the input wire of the filter and the output wire, thereby forming crosstalk in the wire. If the cable between the input and output of the filter is then connected Bundled together, it will aggravate the electromagnetic coupling between the input and output ends of the filter, and severely damage the suppression ability of the filter and the equipment shielding to the interference signal, so that the EMI signal at the end of the filter will escape the limitation of the filter without going through The attenuation of the filter is directly coupled to the other end of the filter. The installation in the mode of Fig. 2 (b) is to effectively isolate the input end and the output end of the power filter through the shielding of the equipment, and to control the electromagnetic coupling (ie crosstalk) that may exist between the two ends to a minimum. And the filter is installed on the equipment shell of the power inlet line, the shielding shell of the filter is in good contact with the equipment shell (the equipment shell is grounded), so that the filter is well grounded. It can be seen that the correct installation of the filter is also a very important part of preventing electromagnetic interference. The purpose of the power filter is to prevent conducted interference from the power supply from directly entering the medical electrical equipment. If the filter is improperly installed, even in the shielded cabinet, the interference of the power cord will affect the medical electrical equipment through radiation or induction, so the correct installation method is very important. 2.3 Improvement measures According to the above theoretical analysis, install a power filter on the power input end of the surgical microscope, and ensure good isolation between the filter input and output, and at the same time assist some internal circuit changes, and test again. The test results are shown in Figure 3. . The conducted interference of the power port of this product passes the requirements of ClassB limits. According to the modified plan, the surgical microscope was mass produced, and the electromagnetic compatibility test results of each product all met the standard requirements. 3 Conclusion The power filter is a device commonly used to meet the electromagnetic compatibility requirements of the product. When it is connected to the entrance of the power line of the device, it can effectively suppress the interference signal from the power grid from entering the device and the interference signal generated by the internal circuit of the device. Pass the power line to the power grid. In the production process of medical electrical equipment, in order to enable the electromagnetic compatibility design to meet the requirements, not only need to select a power filter with good filtering effect, but also to correctly install the filter for electromagnetic compatibility requirements.
we offer 38kv Power Pole and 30m High Mast.
Yixing Futao Metal Structural Unit Co. Ltd. is com manded of Jiangsu Futao Group.
Power Tower, Power Pole, Electric Power Pole, Power Transmission Line Pole,35ft Power Pole,38kv Power Pole YIXING FUTAO METAL STRUCTURAL UNIT CO.,LTD( YIXING HONGSHENGYUAN ELECTRIC POWER FACILITIES CO.,LTD.) , https://www.chinasteelpole.com
It is located in the beach of scenic and rich Taihu Yixing with good transport service.
The company is well equipped with advanced manufacturing facilities.
We own a large-sized numerical control hydraulic pressure folding machine with once folding length 16,000mm and the thickness 2-25mm.
We also equipped with a series of numerical control conveyor systems of flattening, cutting, folding and auto-welding, we could manufacture all kinds of steel poles and steel towers.
Our main products: high & medium mast lighting, road lighting, power poles, sight lamps, courtyard lamps, lawn lamps, traffic signal poles, monitor poles, microwave communication poles, etc. Our manufacturing process has been ISO9001 certified and we were honored with the title of the AAA grade certificate of goodwill"
Presently 95% of our products are far exported to Europe, America, Middle East, and Southeast Asia, and have enjoyed great reputation from our customers,
So we know the demand of different countries and different customers.
We are greatly honored to invite you to visit our factory and cheerfully look forward to cooperating with you.