Low-Power Architecture for an Optical Life Gas Analyzer

A simple camcorder battery can be used for as long as eight hours.

Analog and digital electronic control architecture has been combined with an operating methodology for an optical trace gas sensor platform that allows very low power consumption while providing four independent gas measurements in essentially real time, as well as a user interface and digital data storage and output. The implemented design eliminates the cross-talk between the measurement channels while maximizing the sensitivity, selectivity, and dynamic range for each measured gas. The combination provides for battery operation on a simple camcorder battery for as long as eight hours. The custom, compact, rugged, self-contained design specifically targets applications of optical major constituent and trace gas detection for multiple gases using multiple lasers and photodetectors in an integrated package.

Commercial off-the-shelf digital electronics including data acquisition cards (DAQs), complex programmable logic devices (CPLDs), field programmable gate arrays (FPGAs), and microcontrollers have been used to achieve the desired outcome. The lowest-power integrated architecture achieved during the project was realized in the prototype that utilized a custom FPGA digital board (in combination with a custom-built, lowpower analog electronics board) and a low-performance commercial microcontroller. The FPGA generated all the necessary control signals for the analog board, and performed data acquisition and low-level, time-critical data processing. The microcontroller was used to implement high-level data analysis, the user interface, and data storage and output. Further power savings were realized by operating the four lasers sequentially, rather than operating them in parallel. A several-Hz update rate was achieved even with sequential operation, much faster than required for gas measurement on the International Space Station.

A rugged and flexible multiple gas sensor platform was developed, which involves laser diode-based optical absorption spectroscopy coupled to an elegant optical path length enhancement solution and advanced digital and analog electronic design. The optical absorption cell is shared by multiple lasers and detectors, which minimizes the footprint of the device. On the other hand, the optical layout is simple and flexible: no precise alignment is required. The laser diodes are easily interchangeable, which, in principle, allows reconfiguring the sensor to measure different sets of trace gases. Custom power-efficient analog and digital electronic boards are designed to minimize the power consumption of the sensor. Further power savings are realized by fast time-multiplexing the measurements of different gases, rather than implementing them in parallel. This development allows a fully integrated multiple gas monitor to operate on simple camcorder batteries for a period of several hours.

This work was done by Jeffrey Pilgrim and Andrei Vakhtin of Vista Photonics, Inc. for Glenn Research Center.

Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steven Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. LEW-18894-1

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