Total Calibration-Free Gas Sensing and Its Optimization Based on ln-LC-WMS

Online detection of CO2 emissions can provide important data support for low-carbon operation of process industries. However, the cumbersome calibration process often limits the applications of gas sensors in field measurement. This article develops a total calibration-free gas detection method based on natural logarithm and linear convolution algorithms in TDLAS-WMS (ln-LC-WMS) and investigates its optimization in applications. Logarithm processing effectively eliminates the influence of light intensity on the harmonic, while linear convolution accurately quantifies the amplitude gain, which overcomes the problem of inaccurate filtering gain in the traditional demodulation method. Thereby, the harmonic is obtained with an accurate absolute amplitude that is positively correlated with gas concentration, and the gas concentration can be obtained without calibration. Meanwhile, to deal with the detection error caused by the mismatch between the preset and actual concentrations in the concentration inversion, an iterative process is generated to calculate the accurate gas concentration. To test the feasibility of the proposed method, three CO2 absorption lines near 2004 nm are applied for experimental verification. The experimental results indicate that to overcome the inaccurate preset concentration, within CO2 concentration of 5%, two iterations are sufficient to obtain the accurate result. Continuous measurements of a fixed CO2 concentration at different temperatures show high precision and stability, demonstrating that the proposed method is reliable and can obtain the gas concentration without additional calibration. The proposed method is expected to simplify the detection equipment and avoid calibration operations, which has good industrial application prospects.