Zero⁃order fringe automatic positioning and performance test for optical interference methane detector

In order to overcome the shortcoming that the eyepiece ruler position of the zero⁃order fringe distinguished by the naked eye is easy to cause errors，and study the influence of temperature and non⁃methane gas factors on the performance of the traditional optical interference methane detector. The photoelectric conversion device CCD is cho⁃ sen to replace the original eyepiece ruler structure. The peak extraction combined with Gaussian fitting is used to accurately locate zero⁃order fringes on the basis of the gray information of interference fringe obtained by CCD. Also，the re⁃ lationship between the zero⁃order fringe displacement and the methane concentration is linearly fitted when the meth⁃ ane concentration is 1%，4%，7% and 10%. Methane calibration gases of 0. 494%，0. 994%，1. 49% and 3. 94% are selected for the measurement accuracy and measurement stability experiments. The temperature drift experiment is set up，and the quadratic term temperature compensation is carried out according to the zero⁃drift curve. The measurement value of the common coal mine non⁃methane gas such as carbon dioxide is theoretically deduced， and the standard gas test experiment is carried out. The research results show that the coefficient of determination R2 of the concentration calculation relationship obtained by the fitting is 0. 998 7，and the linearity is basically consistent with the theoretical formula. The displacement caused by the unknown methane concentration can be used to automati⁃ cally calculate the methane concentration value. The experimental results prove that the improved optical interfer⁃ ence methane detector has high measurement accuracy and good measurement stability，which is better than the coal industry standard requirements. After the quadratic term temperature compensation，the zero value is less affected by temperature， and the drift value is basically concentrated at ± 0. 05%. Each increase of 1% carbon dioxide in the test gas will increase the measurement value of methane by 1.033%，and each decrease of 1% oxygen in the standard air will increase the measurement value of methane by 0.18%. Compared with the traditional detector，the im⁃ proved optical interference methane detector realizes the automatic positioning and digital processing of the zero⁃order fringe， overcomes the shortcomings of large subjective influence， improves the measurement accuracy， and reduces the measurement error caused by temperature drift.