Abstract
The accumulating-type (or integrating-type) NOx sensor principle offers two operation modes to measure low levels of NOx: The direct signal gives the total amount dosed over a time interval and its derivative the instantaneous concentration. With a linear sensor response, no baseline drift, and both response times and recovery times in the range of the gas exchange time of the test bench (5 to 7 s), the integrating sensor is well suited to reliably detect low levels of NOx. Experimental results are presented demonstrating the sensor’s integrating properties for the total amount detection and its sensitivity to both NO and to NO2. We also show the correlation between the derivative of the sensor signal and the known gas concentration. The long-term detection of NOx in the sub-ppm range (e.g., for air quality measurements) is discussed. Additionally, a self-adaption of the measurement range taking advantage of the temperature dependency of the sensitivity is addressed.
Highlights
Due to the tightening emission and safety regulations, the detection of harmful or toxic gases has become a large field of research in the past decades
A concentration-detecting NOx sensor based on two pumping cells is applied to control the proper function of the NOx reduction catalysts and for On-board diagnostics (OBD)
We focus on carbonate-based lean NOx trap (LNT) materials, known from automotive catalysts, that have been found to change their electrical properties during NOx exposure [18,31] and were tested as NOx-sensitive materials working accumulatively like a dosimeter [14,15]
Summary
Due to the tightening emission and safety regulations, the detection of harmful or toxic gases has become a large field of research in the past decades. It may be insufficient to determine the time averaged emission by an integration over time of the response of a concentration-detecting sensor To overcome this problem and to be able to detect reliably even small levels of an analyte gas over a longer period, the integrating ( called accumulating) sensing principle has been developed for NOx detection [15,16,17]. We find that the sensor response is linear even in the very low ppm region and responds quickly to rapidly changing NOx concentrations Both response and recovery times are about 5 to 7 s which is in the range of the gas exchange time of the test bench upstream of the sensitive device of 6 s.
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