Release date: 2018-03-23 Conducted emission mainly assesses the conducted emission characteristics of the product network power supply in the frequency range of 150kHz~30MHz [3]. For medical laser equipment with excessive conduction disturbance, the following methods can generally be used for diagnosis: 1 Check whether the equipment uses a power supply filter or a filter circuit. 2 Check that the power filter or filter capacitor is installed in the correct position. 3 Check if the isolation between the cables is sufficient. 4 Check if the filter is suitable. When rectifying, if you do not use a power filter or filter capacitor, you can first consider adding a filter or filter. When adding filters or filter components, care should be taken to consider whether the position is appropriate, whether the grounding is reliable, and whether there is effective isolation between the input and output of the power supply. In addition, increasing the distance between the power line and the signal cable, such as physically isolating the two, using shielded cables, and adding a magnetic ring, is also a way to reduce conducted disturbances. If the conducted disturbance is still exceeded after using the above method, it is necessary to consider the selection of the filter or filter component, and optimize the parameters of the filter until the conducted disturbance test is qualified. 2.2 Radiation emission Radiation emission mainly assesses the electromagnetic wave energy transmitted by the device under test through radiation. According to the classification of the product, the GB 4824 standard gives the limit of the frequency range of 30MHz~1GHz. To form an effective radiation emission disturbance, it is necessary to have both the disturbance source and the radiation path. When performing diagnostic analysis of the cause of excessive radiation, you can gradually plug in the interface cables according to the working characteristics of the product, or turn off the power supply of the board to confirm the source of noise radiation. The noise source is generated by the product board itself or the circuit noise is radiated through the cable as an antenna. Medical laser equipment differs from other medical electrical equipment in that its light guiding system often causes problems, resulting in excessive emission of radiation, and special attention should be paid to diagnostic analysis [4]. For medical laser equipment with excessive radiation disturbance, the following five methods are usually used for rectification: 1 By analyzing and rectifying the signal characteristics of the PCB or the circuit itself: such as the definition of PCB stacking, whether each layer of the signal has a corresponding image plane layer; Whether the line crosstalk path conforms to the 3W rule; the filter processing of the signal port; the source of the high-speed signal, the terminal impedance matching; the near-field probe is used to simulate the receiving antenna, and the noise source is sought. 2Structure shielding: This method is often preferred. In the development of medical laser equipment, the design of metal shielding openings is often very important, but the processing of gaps is generally ignored. The gap processing is the key to shielding effectiveness. Noise, especially high-frequency noise, easily leaks from the gap, and the allowable length of the gap is generally judged by λ/20 of the highest frequency. 3 pairs of processing cable processing: if using shielded cable (note that the shield should be connected with the plug); add a magnetic ring (note that the magnetic ring needs to be wound 1.5 turns). 4 Shield the joints of the light guide arm. 5 software processing: The high frequency signal transmission frequency can be changed by software, or the spread spectrum can be used. Using this method is likely to affect the functionality of the product, so it is generally not recommended. In addition to the above methods, adding filters or filter components is also a way to reduce radiated disturbances. The use and selection of filters has been given in the method of rectification of conducted disturbances, and will not be repeated here. 3. Case analysis According to the relevant test requirements, when conducting the conducted disturbance and radiation disturbance test of the medical laser equipment, it should be carried out under the maximum emission state of the equipment, that is, the full power working state. A medical laser device is powered by 220V AC. When conducting conducted disturbances and radiated disturbances, it exceeds the limit of one group of Class A standards. For radiation disturbances exceeding the standard, the first consideration is due to excessive cable radiation. Unplug the signal cable and connect only the power supply to classify the cable. The test results are not significantly improved. After disassembling the product casing, it was found that the main control board was not shielded and its signal cable was shielded but not grounded. After shielding the product and grounding the signal cable, the test results have been greatly improved, as shown in Figure 1. For conducted disturbances, the first consideration is caused by poor filtering. Check the installation of the internal filter of the machine and find that the input and output lines are long, and tie the two wires together with a cable tie. The analysis may be that the interference signal generated inside the machine is disturbed to the output line of the filter power supply. Recoupled to the power line outside the product. By physically isolating the input and output lines of the filter and adding a magnetic ring on the input line, the final test result is shown in Figure 2. It is found that the conducted emission can be effectively solved. 4. Summary In this paper, the rectification suggestions for the electromagnetic interference exceeding the standard in the electromagnetic compatibility test of medical laser equipment are put forward, which can better guide the problem product to pass the electromagnetic compatibility test. For the problems that occur in the electromagnetic compatibility test after the product design is finalized, it is still only possible to adopt the method of “discovering what to solve and what to solve†to achieve the purpose of complying with the requirements of electromagnetic compatibility. In order to effectively solve the electromagnetic compatibility problem of products, it is also necessary for the R&D personnel to consider the electromagnetic compatibility of the products at the beginning of the product design, and reduce the possibility of electromagnetic compatibility problems at the source. Source: China Medical Device Information Magazine Medical Heat Sealer,Medical Sealing Machine,Medical Pouch Sealing Machine,Sterilization Pouch Sealing Machine ZHEJIANG FOMOS MEDICAL TECHNOLOGY CO.,LTD. , https://www.ifomos.com
