Tightness Detecting Technique for the Valves of Diaphragm Gas Meter Based on Chromatic Confocal Method

Abstract

Diaphragm gas meter is a specialized flow meter that measures the volume of fuel gas such as natural gas and coal gas. Valve bonnet and valve seat are the key parts of diaphragm gas meter, which compose the main factors of its metering error. The widely detecting ways are direct observational method and pneumatic pressure method. Direct observational method only realizes the qualitative detection with lacking science. Pneumatic pressure method can realize the quantitative detection, but with low accuracy and bad reliability. In order to evaluate the gas tightness of diaphragm gas meter valve accurately, surface texture method was adopted. Firstly, the surface roughness mathematical model of valve working face was established. A fast Gaussian filtering convolution algorithm was proposed based on the symmetry of Gaussian density function. Secondly, the working face of gas valve on the high-precision air floating stage was scanned by the chromatic confocal sensor. And the roughness profile of valve working face was got through the fast Gaussian filter when the cut-off wavelength was 0.8mm. Then the roughness parameters could be calculated with MATLAB by setting the sampling length and evaluation length. The results show that surface roughness has a difference of over 1μm between the qualified and unqualified valve. Besides, there is a little deviation of below 9% between the experimental value and the stylus profilometer measuring value, which has no influence on the judging result of qualified or unqualified about the measured workpiece. The gas tightness performance of gas valve can be judged by measuring surface roughness of its working face, which can provide a scientific basis for evaluating the quality of diaphragm gas meter valve in a quantitative way.