Tunable diode laser absorption spectroscopy (TDLAS), as a branch of gas spectrum detection technology, has the merits of high resolution, high sensitivity, low detection limit, less environmental impact and suitable for various complex environments. It plays an important role in the field of air pollution monitoring, aeromechanics, mine development, industrial manufacturing, biomedicine and other fields. With technology accumulation over the past few years, TDLAS has become the most widely used and representative gas detection technology. The influence of the residual amplitude modulation brought by the phase difference on the harmonic signals is analyzed. The relation formula of gas concentration after the phase difference added is derived from the theoretical formula. Then the influence of the factors such as the modulation amplitude and the modulation frequency is further investigated. A set of BRD circuits is designed to make the reference beam and the detected beam normalization at the current level, which improves the signal to noise ratio and eliminates the asymmetry of the left and right peaks of the harmonic signals caused by the residual amplitude modulation, and improves the measurement accuracy. The experiment shows that the spectral line distortion is proposed by using a BRD circuit to eliminate spectral line distortion caused by the phase difference. After using the BRD circuit, the resolution of the direct concentration signal is increased by nearly 3 times.
For instantly monitoring the safety status of lithium-ion batteries, this letter provides a scheme of insitu monitoring system of lithium-ion battery based on multifunctional fibers and constructs the corresponding test system. In this scheme the distributed temperature sensing system(DTS) is employed for testing the temperature of lithium-ion batteries and the distributed gas detection system combined with trace gas sensors based on TDLAS technique and optical switch control is utilized for monitoring the leakage of lithium-ion batteries. Aiming at the character of the large deformation of lithium-ion batteries especially in soft packed batteries, a wide-range deformation test scheme is designed. The preliminary test results of the in-situ monitor system of lithium-ion battery indicate that the temperature accuracy of this system is ±1 degrees centigrade and the spatial resolution is 1 meter. The resolution of gas detection of CH4, CO, CO2 and HF gas meets the design. The strain range of the system is 10000με and the accuracy is 100με . The system meets the demand of insitu monitoring of lithium-ion battery.