A method of compensating for the effects of humidity on the readouts of electronic noses has been devised and tested. The method is especially appropriate for use in environments in which humidity is not or cannot be controlled — for example, in the vicinity of a chemical spill, which can be accompanied by large local changes in humidity.
Heretofore, it has been common practice to treat water vapor as merely another analyte, the concentration of which is determined, along with that of the other analytes, in a computational process based on deconvolution. This practice works well, but leaves room for improvement: changes in humidity can give rise to large changes in electronicnose responses. If corrections for humidity are not made, the large humidityinduced responses may swamp smaller responses associated with low concentrations of analytes.
The present method offers an improvement. The underlying concept is simple: One augments an electronic nose with a separate humidity and a separate temperature sensor. The outputs of the humidity and temperature sensors are used to generate values that are subtracted from the readings of the other sensors in an electronic nose to correct for the temperature-dependent contributions of humidity to those readings. Hence, in principle, what remains after corrections are the contributions of the analytes only. Laboratory experiments on a first-generation electronic nose have shown that this method is effective and improves the success rate of identification of analyte/water mixtures. Work on a second-generation device was in progress at the time of reporting the information for this article.
This work was done by Margie Homer, Margaret A. Ryan, Kenneth Manatt, Hanying Zhou, and Allison Manfreda of Caltech for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Physical Sciences category.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Innovative Technology Assets Management
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Refer to NPO-30615, volume and number of this NASA Tech Briefs issue, and the page number.
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Compensating for Effects of Humidity on Electronic Noses
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Overview
The document titled "Compensating for Effects of Humidity on Electronic Noses" from NASA's Jet Propulsion Laboratory (JPL) addresses the challenges posed by humidity on the performance of electronic noses (ENoses) used in space missions. The context of the study is based on a demonstration experiment conducted aboard the Space Shuttle STS-95 in October-November 1998, where the ENose was operated continuously for six days. During this period, the cabin air's relative humidity (RH) fluctuated between 30-55%, with localized changes of 10% or more occurring within short time frames of 10-20 minutes.
The primary concern highlighted in the document is that small responses from analytes (substances being detected) could be overshadowed by significant humidity variations, particularly in scenarios involving spills or contaminants present in low concentrations. This could lead to difficulties in accurately identifying and quantifying the presence of specific analytes in the air.
To address these challenges, the document proposes a solution that involves the integration of an independent humidity sensor into the JPL ENose system. This addition allows for the implementation of humidity background subtraction during the preprocessing of sensor data, thereby enhancing the accuracy of analyte detection. The latest design of the system allocates signal channels specifically for independent measurements of vapor temperature and humidity.
A custom sensor was developed using commercial components, including a silicon temperature sensor, power conditioning, a humidity sensor, and a metal frit for optical darkness and sensor protection. This sensor is designed to be low power and provides robust voltage outputs for both temperature and humidity measurements.
The document emphasizes the importance of this technological advancement not only for space applications but also for potential wider technological, scientific, and commercial applications. It is part of NASA's Commercial Technology Program, which aims to disseminate aerospace-related developments that can benefit various sectors.
Overall, the document serves as a technical support package that outlines the innovative approaches taken by NASA to improve the functionality of electronic noses in challenging environments, ensuring reliable detection of analytes despite the complicating effects of humidity.
