Erhard Magori

Thick film device for the detection of NO and oxygen in exhaust gases

Diffusion limited amperometric yttria stabilised zirconia sensors with two consecutive electrodes can be used as a combined broad band λ/NO sensor for the analysis of automotive exhausts. At an appropriately low pumping voltage, the first electrode removes all oxygen from the gas, but not the NO, which can only be pumped using higher cathodic potentials. The NO is then reduced at the second electrode. The pumping currents at the two electrodes are connected to the amounts of oxygen and NO. This paper reports on the fabrication and performance of a screen printed version of such a sensor. The sensors are self-heated with dimensions ready for use in real exhausts.

Fractional exhaled nitric oxide measurement with a handheld device.

A sensing system for fractional exhaled nitric oxide (FeNO) measurement is presented, which is characterized by a compact setup and a cost potential to be made available for the patient at home. The sensing is based on the work function measurement of a phthalocyanine-type sensing material, which is shown to be sufficiently sensitive for NO(2) in the ppb range. The transducer used to measure the work function is a field effect transistor with a suspended gate electrode. Selectivity is given with respect to other breath components including typically metabolic by-products. The measurement system includes breath treatments in a simple setup, which essentially are dehumidification and a quantitative conversion of NO to NO(2) with a conversion rate of approx. 95%, using a disposable oxidation catalyst. The accomplishment of the correct exhalation maneuver and feeding of the suited portion of exhaled air to the sensor is provided by breath sampling means. The sensor is not gas consuming. This allows us to fill the measurement chamber once, instead of establishing a gas flow for the measurement. This feature simplifies the device architecture. In this paper, we report on sensor characteristics, system architecture and measurement with artificial breath-gas as well as with human breath with the device.

NOx-detection by pulsed polarization of lambda probes

Conventional thimble type lambda sensors combined with a pulse discharge technique were used for NOx detection in a simulated combustion exhaust gas with varying oxygen and moisture levels. Open circuit discharge characteristics after defined polarization pulses with alternating polarity show strong dependencies on NOx (112 mV / decade) in the lowest ppm range (0.5 – 50 ppm). Increase in NOx concentration accelerates sensor discharge, whereby the discharge curves following negative pulses are more affected by the NOx content compared to positive pulses. The sensitivities to NO and NO2 are equal and measurement of total NOx is possible. The discharge curves are affected by the oxygen and the water content. An increase in O2 concentration results in a shift of the discharge curves to negative voltages. Additionally a decreased sensor response to NOx is obtained for both polarization polarities. The water concentration has the opposite effect. All discharge curves are shifted to positive voltages with increasing H2O content. As a result, the sensor response increases strongly. The voltage shifts due to O2 and H2O are expected from Nernstian behavior of a lambda probe, whereby moisture influence is stronger compared to O2. The feasibility of the method as an exhaust gas total NOx measurement system is confirmed.

NOx - Detektion an YSZ-Sensoren mittels Spannungspulsen

Zusammenfassung Diese dynamische Messmethode mit wechselseitiger Polarisation der Elektroden und Auswertung der Entladekurven bietet den grosen Vorteil, dass an einfachen Sensorelementen Stickoxide in kleinem Konzentrationsbereich detektiert werden konnen. Bei dieser Spannungs-Puls-Methode ist die Form und Lage der Selbstentladekurve charakteristisch fur die Gaskonzentration. Da bei allen Anwendungen der Wassergehalt eine grose Rolle spielt, wurde in dieser Studie dieser Einfluss genauer betrachtet.