D3.4 - Pulsed-Potential Method for NOx-Detection Using Standard Zirconia-Based Lambda Sensors.

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
D3 - Gas Sensors I
S. Fischer - Universität Bayreuth, R. Pohle, M. Fleischer - Siemens AG, München, U. Guth - Kurt-Schwabe-Institute for Measuring and Sensor Technology Meinsberg, Ziegra-Knobelsdorf (Germany), B. Farber - BJR Sensors, Solon, Ohio (USA), R. Moos - University of Bayreuth
568 - 573


A measurement technique is presented to increase the differentiation between single exhaust gas components using a pulsed-potential method. After applying a pulsed charging voltage (2.5 V) for a defined duration (100 ms) to a standard thimble-type zirconia-based potentiometric lambda probe, the self-discharge voltage of the sensor is recorded for a defined time duration (10 s) and repeated using a voltage with opposite sign. This pulse sequence with electrode polarizations of opposite signs is used permanently and the discharge curves are measured continuously.
The effect of different gas components NO, NH3, H2, ethanol, and a mixture of hydrocarbons in a range of 5 ppm to 150 ppm (HC to 240 ppm) in N2 base gas is evaluated. The sensor is operated at approximately 590 °C.
Already in the lower ppm-range, the self-discharge characteristic after polarization shows a strong dependency on the NO concentration for both signs. Also an individual discharge characteristic for all investigated gases can be distinguished. This leads to the conclusion, that several gas species can be measured.
The differences U(cgas)–U(0 ppm) for each gas component and concentration are calculated to investigate the cross-sensitivities. The characteristic semi-logarithmic curves are analysed for a defined evaluation time after voltage pulses for positive and negative direction. After polarization with positive voltages, the response to NO is most prominent compared to other gases, whereas ethanol shows a larger slope after negative polarization. Nevertheless, a gas component can be specified by the characteristic appearance of the curves after positive and negative polarization.
In summary, this pulsed-potential method is capable to enable NO sensing in exhaust gas with improved selectivity using standard lambda probes.