Research On Approaches And System For In-Car Alcohol Concentration Detection With Laser

A detection system based on Tunable Diode Laser Absorption Spectroscopy (TDLAS) for in-car alcohol was developed to cope with the issue of drinking and driving. WMS was adopted in the system for remote and fast sensing.The primary principles of TDLAS was introduced with the fact that the second harmonic is in direct ratio with the concentration of the target gas and the ratio between the second harmonic and the first harmonic is not affected by the fluctuation of the laser intensity. The topper structure of the system was designed on the basis of application, choosing alcohol absorption peak at1.3928μm as the scanning area of the tuned laser. Driving and temperature-control circuits for laser were discussed. A cone concentrator was introduced to improve the collective efficient and SNR of the system. Great attention was given to the two-phase lock-in amplifier in the signal processing section with simulations for the whole signal processing unit. A MSP430fl49MCU was chosen as the computing unit of the LIA. The controlling unit was also configured with a MSP430MCU, forming a master-slave structure with the former one. The interface circuits and the software were designed under the request from applications.Tests in lab conditions proved that:the system collective efficient was significantly improved by the cone concentrator, the signal processing circuits were able to recover the tiny second harmonic and first harmonic from mixed output signal of the photo detector and the system could detect the alcohol concentration higher than1000ppm in an effective way.