基于中红外LED的润滑油水分含量测量研究

Monitoring Water in Lubricating Oil with Min-Infrared LED

针对船舶机械润滑油中水分含量的测量问题,研究了基于中红外LED的油液水分含量测量方法。利用峰值发射波长为2 840nm,半高宽为400nm的中红外LED作为发射光源,发射的红外光进入油样,一部分被吸收,剩下的透过油样被红外探测器接收,根据油样对光能的吸光度确定油液中水分含量。实验设计了红外光发射、吸收和探测的装置,采用氟化钙晶片作为窗片,选择截面为圆形的硬质金属线圈作为垫圈以保证精确的油膜厚度,采用探测波长范围为2 500-4 800nm,响应时间为10-20ns的光电二极管作为光强探测器。开发了信号的前置放大和基于单片机的数据采集、储存和通讯系统。通过实验,获得了含水质量分数为0,0.062 5%,0.125%,0.25%,0.375%和0.5%六个油样的吸光度数据,利用最小二乘法对数据进行拟合,得到吸光度和含水量的线性回归方程。对误差进行量化分析,回归方程和数据点的决定系数为0.996。最后,为了检验该测量方法的精确性,用含水量为0.317 5%的油样进行验证,利用实验装置测量吸光度,代入回归方程计算含水量,结果显示通过该方法测得的含水量和实际含水量的相对误差为2.7%,满足工程实际需求,说明该方法能够准确测量油液中的含水量。

A method that could be used to quantify the water concentration in ship machinery lubricating oil based on Mid-infrared LED is discussed.A Mid-infrared LED with peak emission wavelength of 2 840 nm and FWHM of 400 nm is used as the light source,the emitting light is partly absorbed by the oil sample,the remaining is received by the infrared detector.The percentage of water is determined according to the absorbance.In the experiment,a optical configuration including the transmission,absorbing and receiving of infrared light is designed,calcium fluoride wafer is used as the window,a hard metal coil with circular section is selected as the washer to get the fixed thickness of oil film accurately,aphotoelectric diode with detection wavelength of 2 500-4 800 nm and response time of 10-20ns is used as the detector of light intensity.Matching with this,a system of signal preamplifier,microcontroller-based data acquisition,storage and communication is developed.Absorbance data of six oil samples with different water mass concentration：0,0.062 5%,0.125%,0.25%,0.375% and 0.5% is acquired through experiment.Fitting the data by the method of least squares,a linear equation in terms of absorbance and water concentration is obtained,and the determination coefficient is 0.996.Finally,in order to test the accuracy of this measurement method,using oil sample with water concentration of 0.317 5% to validate the equation,measuring the absorbance by the experimental device,the water content is calculated through the linear equation,the results show that the relative error is 2.7% between the percentage calculated and the real sample,indicating that this method can accurately measure the water concentration in the oil.