The Design And Implementation For Real-time Online Monitoring Unit Of Insulation Resistance In Airfield Lighting Circuit

Airfield navigational lights is necessary to ensure the safety of the plane during take-off and landing under the special environment. Keeping insulation in good condition is in order to ensure the normal operation of the airport navigation lights. So, it is crucial to researching and designing the real-time online monitoring unit of insulation resistance in airfield lighting circuit. But there are some defects in the existing insulation online monitoring methods.The thesis, firstly, introduces the research status and the existing methods domestic and overseas of insulation resistance online monitoring, and demonstrates the limitations and defects theoretically. A new kind of design scheme has been proposed. There are three main points in it. The low voltage, 24 V.DC excitation power supply, is used in the new scheme, instead of high voltage, which can reduce the high pressure of lighting cable. The switch method is adopted in the new scheme which can sample the currents generated by only AC voltage and AC DC voltage together. So the interference caused by AC high voltage can be counteracted. Magnetic separation method is used in the new scheme, which can improve the isolation level, and ensure the safety of circuit.The thesis proves the feasibility of new method in detail, theoretically. Firstly, the equivalent physical mode of the insulation resistance is built. Secondly, compared with the defects in the existing methods, the thesis analyses the advantages and feasibility of new project. Finally, the measured results are listed proving that the new scheme is reliable.In the hardware circuit design, the push-pull converter is selected to provide magnetic isolation protection for the whole circuit. The thesis introduces the working principle of the push-pull transformer and its design process. AT89C51 single chip microcomputer is used as intelligent data processing control chip. Series of supporting circuits, such as data acquisition, conversion, processing and communication transmission, are designed based on AT89C51. The whole hardware circuit can achieve the goal that the insulation resistance in airfield lighting circuit could be monitored accurately and timely. In software, initialization subroutine, timing subroutine, calculation of insulation resistance subroutine and communication interrupt subroutine based on MODBUS are designed.The unit picks current signals in the circuit, transfers them to CPU where the signals can be processed, and the real-time insulation resistance can be calculated. The results are sent by MODBUS to the upper computer, where the results can be recorded in order to find defects of lighting cables.