| Along with the rapid development of digital electronic products, strong electromagnetic interference is generated because a large of electronic devices work in the same space and time, which affects the reliability of electronic products and system seriously. More and more consumers concern not only the price and function of products but also the reliable operation now. Due to special working environment and strict requirement, the reliability of combustible gas alarm has been the necessary question. Many products are designed mainly on function but few on EMC. When failing in the EMC test, the produce must be improved and even redesigned, which will lose the best chance for the market. Some companies pass the test by illegal means, which makes the consumer in danger. So the design on reliability is significant.Firstly, the origin and background of the subject are introduced. The purpose and significance of EMC design on products are analyzed.Secondly, the working principle, functional requirements of combustible gas system are described briefly and the design based on the requirements is proposed. CAN bus and RS485 bus are combined in communication. Master controlled, CAN/485 converter, detector and linkage module are combined in structure of network. CAN bus is the top network used between the master controller and CAN/485 converters. RS485 bus is the lower layer network used between CAN/485 converter and detector. The effect of this structure is better in monitoring combustible gas.Thirdly, the principles and the development of EMC and the EMC standards of product are discussed. Due to the non-stationary of interference signals, wavelet is used to analyze the signal because it can restrain noise well and analyze signal from time-frequency of local. Db4 wavelet is used in analyzing power signals. The frequency and time characteristics are obtained. The EMI filter is selected according to the result of analysis to restrain the noise. Then db6 wavelet is used to diagnose the communicational signal and the electrostatic discharge signal is found. The theoretical guidance is provided for the design of circuit. Fourthly, the reliability design of product is carried on according to the result of signal analysis. In the design of hardware, the advanced devices are used for the design of circuit such as filter circuit , isolation circuit and thunder-prevent circuit. Then the PCB and the choice of enclosures and communication line are designed. The measures adopted in the software include digital filter and avoiding interference.In the end, the contents and methods of EMC test are introduced in detail and the results of test are analyzed and summarized.As a lot of effective work has been done in the process of EMC design, combustible gas system pass the national EMC test successfully and production license is obtained. Now, a few products have entered the market and been praised by consumers. |
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