Kerstin Wiesner

Working mechanism of an ethanol filter for selective high-temperature methane gas sensors

Semiconducting metal-oxide gas sensors are generally nonselective, which limits their use as natural gas detectors in domestic environments when ethanol is present in high background concentrations. Using a thin-film Ga/sub 2/O/sub 3/ sensor with a thick-film catalyst filter of Ga/sub 2/O/sub 3/ and an operating temperature of 800/spl deg/C, the cross-sensitivity to ethanol is strongly reduced and the sensor response to methane is enhanced. Detection of natural gas is made reliable and the rate of false alarms is reduced. Oxidation of ethanol and methane over gallium oxide is studied using GC product analysis. These measurements of catalytic activity help to clarify the reactions involved in the filtering mechanism. Elimination of the ethanol cross-sensitivity is attributed to the thermal combustion of ethanol as it passes over the hot filter. The sensor response to methane is enhanced as methane is activated by the active catalytic Ga/sub 2/O/sub 3/ thick-film.

Platform for a hydrocarbon exhaust gas sensor utilizing a pumping cell and a conductometric sensor

Very often, high-temperature operated gas sensors are cross-sensitive to oxygen and/or they cannot be operated in oxygen-deficient (rich) atmospheres. For instance, some metal oxides like Ga2O3 or doped SrTiO3 are excellent materials for conductometric hydrocarbon detection in the rough atmosphere of automotive exhausts, but have to be operated preferably at a constant oxygen concentration. We propose a modular sensor platform that combines a conductometric two-sensor-setup with an electrochemical pumping cell made of YSZ to establish a constant oxygen concentration in the ambient of the conductometric sensor film. In this paper, the platform is introduced, the two-sensor-setup is integrated into this new design, and sensing performance is characterized. Such a platform can be used for other sensor principles as well.

P5.6 - Selective mixed potential ammonia exhaust gas sensor for harsh environments

An ammonia exhaust gas sensor for harsh environments enables to control the NH3 emission downstream an SCR (selective catalytic reduction) catalyst, which is used to reduce the NOx emissions of diesel engines and industrial plants. A novel mixed potential NH3 exhaust gas sensor for selective NH3 detection showed in synthetic exhaust a very good correlation between sensor voltage and NH3 concentration with a marginal NOx cross interference. First tests in real exhaust gas to proof the applicability showed promising results.

Dual-detector optical MEMS spectrum analyzer: advances, applications, and prospects

The spectroscopy market is enduring and growing one, in which the near infrared spectroscopy by means of the advances plays an important and indispensable role. Some nameable advances are the noninvasive character, the rapidity, which allows real-time measurements or the flexible sampling and sample presentation. To establish near infrared spectroscopic methods and tests at a wide variety of applications new technological innovations are necessary. One of these technological innovations is a modern scanning micro mirror spectrometers. We have developed a small sized, light weight MOEMS-spectrometers for different spectral regions which are due to the optical parameters less expensive, more flexible and offer better performance than traditional spectrometers even yet. The central component of the optical set-up is a large area scanning micro mirror, which oscillates in resonance with 250Hz. Thus, to record a single spectrum only 4 milliseconds are necessary. One of the important factors of NIR spectroscopy, which affects qualitative and quantitative determination, is the sample presentation. For optimal signal processing different sample presentation techniques such as transmission and flow cells, integrating spheres and attenuated total reflection (ATR) probes were realized. Consequently in combination with chemometric methods e.g. partial least square or principal component analysis several applications could be performed and investigated. This article describes the principles and the advances of the promising technology as well as some realized applications. Furthermore influences of the sample presentation and calibration procedures will be discussed closer.