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Dual mode NOx sensor: measuring both the accumulated amount and instantaneous level at low concentrations.

Groß A, Beulertz G, Marr I, Kubinski DJ, Visser JH, Moos R - Sensors (Basel) (2012)

Bottom Line: Experimental results are presented demonstrating the sensor's integrating properties for the total amount detection and its sensitivity to both NO and to NO(2).The long-term detection of NO(x) 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Functional Materials, Bayreuth Engine Research Center (BERC), University of Bayreuth, 95440 Bayreuth, Germany.

ABSTRACT
The accumulating-type (or integrating-type) NO(x) sensor principle offers two operation modes to measure low levels of NO(x): 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 NO(x). Experimental results are presented demonstrating the sensor's integrating properties for the total amount detection and its sensitivity to both NO and to NO(2). We also show the correlation between the derivative of the sensor signal and the known gas concentration. The long-term detection of NO(x) 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.

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Sensor response on alternating pulses of 5 ppm NO (orange) and 5 ppm NO2 (red) for 50 s.
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f6-sensors-12-02831: Sensor response on alternating pulses of 5 ppm NO (orange) and 5 ppm NO2 (red) for 50 s.

Mentions: NO and NO2 were added alternately to the lean base gas (Figure 6). Each step consisted of 5 ppm NO or 5 ppm NO2 lasting 50 s which were separated by 100 s intervals of 0 ppm NOx. Figure 6(a) shows the sensor response as a function of time together with the dosed analyte gas concentrations. NOx dosing started with NO (orange line) which was later followed by a NO2 pulse (dark red line), with this cycle repeated five times. The sensor responds to NO in an integrating manner as already discussed in Figures 4 and 5. In the presence of NO2, /ΔR//R0 increases with a constant slope and after switching off the NO2 flow, /ΔR//R0 remains constant. Comparing the course of /ΔR//R0 during NO and NO2 exposure, the sensor works accumulative for NOx: both linearity and holding abilities seem not to be affected whether NO or NO2 is added to the gas. This observation is verified by plotting the measurement data as a characteristic line similar to that shown in the previous two figures. The correlation between /ΔR//R0 and ANOx, with ANOx being the sum of ANO and ANO2, gives a linear line up to a sensor response of about 40% with a sensitivity of 0.021%/ppm·s (50 μm Au-IDE). This demonstrates graphically the relative independency of the sensor response on the NO/NO2-ratio. Like the sensitivity, the difference in the range of linearity varies between the used samples. Having a closer look on the timely derivative in Figure 6(c), the correlation between /dR/dt/ and the NOx composition can be seen in much more detail. In the presence of 5 ppm NO, the resistance decreases about 0.30 kΩ/s compared to about 0.25 kΩ/s at 5 ppm NO2. Again, we also see in Figure 6(c) the trend of a smaller sensor response with increasing NOx loading, when the saturation becomes noticeable. As in the previous measurements, the sensor response time is in the range of the gas exchange time of the system (6 s) and is not influenced by the composition of the dosed NOx. Unlike before, the curve of /dR/dt/ recovers after a NO2 step in 12 s whereas it takes 17 s after NO exposure.


Dual mode NOx sensor: measuring both the accumulated amount and instantaneous level at low concentrations.

Groß A, Beulertz G, Marr I, Kubinski DJ, Visser JH, Moos R - Sensors (Basel) (2012)

Sensor response on alternating pulses of 5 ppm NO (orange) and 5 ppm NO2 (red) for 50 s.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3376581&req=5

f6-sensors-12-02831: Sensor response on alternating pulses of 5 ppm NO (orange) and 5 ppm NO2 (red) for 50 s.
Mentions: NO and NO2 were added alternately to the lean base gas (Figure 6). Each step consisted of 5 ppm NO or 5 ppm NO2 lasting 50 s which were separated by 100 s intervals of 0 ppm NOx. Figure 6(a) shows the sensor response as a function of time together with the dosed analyte gas concentrations. NOx dosing started with NO (orange line) which was later followed by a NO2 pulse (dark red line), with this cycle repeated five times. The sensor responds to NO in an integrating manner as already discussed in Figures 4 and 5. In the presence of NO2, /ΔR//R0 increases with a constant slope and after switching off the NO2 flow, /ΔR//R0 remains constant. Comparing the course of /ΔR//R0 during NO and NO2 exposure, the sensor works accumulative for NOx: both linearity and holding abilities seem not to be affected whether NO or NO2 is added to the gas. This observation is verified by plotting the measurement data as a characteristic line similar to that shown in the previous two figures. The correlation between /ΔR//R0 and ANOx, with ANOx being the sum of ANO and ANO2, gives a linear line up to a sensor response of about 40% with a sensitivity of 0.021%/ppm·s (50 μm Au-IDE). This demonstrates graphically the relative independency of the sensor response on the NO/NO2-ratio. Like the sensitivity, the difference in the range of linearity varies between the used samples. Having a closer look on the timely derivative in Figure 6(c), the correlation between /dR/dt/ and the NOx composition can be seen in much more detail. In the presence of 5 ppm NO, the resistance decreases about 0.30 kΩ/s compared to about 0.25 kΩ/s at 5 ppm NO2. Again, we also see in Figure 6(c) the trend of a smaller sensor response with increasing NOx loading, when the saturation becomes noticeable. As in the previous measurements, the sensor response time is in the range of the gas exchange time of the system (6 s) and is not influenced by the composition of the dosed NOx. Unlike before, the curve of /dR/dt/ recovers after a NO2 step in 12 s whereas it takes 17 s after NO exposure.

Bottom Line: Experimental results are presented demonstrating the sensor's integrating properties for the total amount detection and its sensitivity to both NO and to NO(2).The long-term detection of NO(x) 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Functional Materials, Bayreuth Engine Research Center (BERC), University of Bayreuth, 95440 Bayreuth, Germany.

ABSTRACT
The accumulating-type (or integrating-type) NO(x) sensor principle offers two operation modes to measure low levels of NO(x): 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 NO(x). Experimental results are presented demonstrating the sensor's integrating properties for the total amount detection and its sensitivity to both NO and to NO(2). We also show the correlation between the derivative of the sensor signal and the known gas concentration. The long-term detection of NO(x) 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.

Show MeSH