Multichannel Raman Gas Analyzer: The Data Acquisition and Control System. Measurement Improvement With Blue Laser Light

Abstract—In this paper, the data acquisition and control system of a multichannel Raman effect-based gas analysis device is presented, together with the improvements achieved in measurement of gas concentration sensitivities as a result of the operation of the system with a new blue laser-light source. The multichannel Raman gas sensor (MRGS) is based on the linear Raman scattering effect and uses photo multiplier tubes (PMTs) in the photon-counting mode of operation. An embedded microcontroller-based data acquisition and control (MDAC) system collects, digitizes, processes, and stores in real time the data from six photon-counting modules and the accompanying sensors, along with an overall system control through appropriate actuators. Furthermore, the MDAC system supports the remote operation of the MRGS device from a host computer through a serial link for the modification of the operating parameters, the downloading of new software versions, and the uploading of the collected data for further analysis. The overall device is controlled by the MDAC system and can operate daily, either manually or in a completely automated mode. Many software and hardware features of the MDAC system described in this article can be adapted to other microcontroller-based acquisition and control systems. Recent advances in the development of solid-state laser sources have enabled the use of a new, state-of-the-art, blue laser for the excitation of the Raman effect. Using this blue laser source, improvements in the sensitivities in measurements of concentration for all tested gases (SO2, CO2, CO, NO2, C6H6, and N2) have been substantiated, compared with the green laser source previously used and reported in a related article. Index Terms—Air-pollution, data acquisition, gas analysis, microcontroller, photon counting, Raman spectroscopy, real-time processing. I