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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 pulses of three times 5 ppm and two times 10 ppm NO for 100 s each.
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f5-sensors-12-02831: Sensor response on pulses of three times 5 ppm and two times 10 ppm NO for 100 s each.

Mentions: Another interesting point is to investigate whether the sensor also works as an integrator if the NO concentration varies. The sensor response to alternating 0, 5, and 10 ppm NO for 100 s each is plotted in Figure 5. Again, the sensor response increases during NO exposure but remains constant in the absence of the analyte (Figure 5(a)). In the case of 10 ppm NO, /ΔR//R0 increases faster than in the presence of 5 ppm—the slope seems to be doubled. By calculating ANO from Equation (1), the doubled concentration is taken into account. Looking at the characteristic line in Figure 5(b), it becomes obvious that the measurement points form a straight line if plotted versus ANO. This means that the characteristic line in Figure 5(b) is independent on the actual concentration and that the sensor works as an NO-accumulating device, detecting the total amount of NO in the low ppm range. The sensitivity of this sensor device (100 μm Pt-IDE) is 0.010%/ppm·s NO. The sensitivity obtained in this measurement is much smaller compared to the sensitivity reported in the previous section (0.078%/ppm·s NO) in Figure 4. The measurement results presented were obtained with different sensor samples that were coated by screen-printing or dipping in an aqueous solution of the LNT-material resulting in sensitive layers with varies thicknesses and morphologies. In further tests, it was found that the sensitivity to NOx varies with the thickness of the sensitive layer, which can be explained by the dependency of the number of accessible storage sites on the volume and the morphology of the sensitive layer influencing the diffusion of NOx into the storage material and therefore the rate of storage. In Figure 5(c), /dR/dt/ is plotted in parallel to cNO and follows it. In the presence of 5 ppm NO, the resistance changes by about 1.25 kΩ/s, in 10 ppm it is about 2.5 kΩ/s, which demonstrates once more the linearity. Again, the sensor signal responds and recovers very fast (5 to 6 s) with only a slight dependency on the actual NO concentration.


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 pulses of three times 5 ppm and two times 10 ppm NO for 100 s each.
© Copyright Policy
Related In: Results  -  Collection

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

f5-sensors-12-02831: Sensor response on pulses of three times 5 ppm and two times 10 ppm NO for 100 s each.
Mentions: Another interesting point is to investigate whether the sensor also works as an integrator if the NO concentration varies. The sensor response to alternating 0, 5, and 10 ppm NO for 100 s each is plotted in Figure 5. Again, the sensor response increases during NO exposure but remains constant in the absence of the analyte (Figure 5(a)). In the case of 10 ppm NO, /ΔR//R0 increases faster than in the presence of 5 ppm—the slope seems to be doubled. By calculating ANO from Equation (1), the doubled concentration is taken into account. Looking at the characteristic line in Figure 5(b), it becomes obvious that the measurement points form a straight line if plotted versus ANO. This means that the characteristic line in Figure 5(b) is independent on the actual concentration and that the sensor works as an NO-accumulating device, detecting the total amount of NO in the low ppm range. The sensitivity of this sensor device (100 μm Pt-IDE) is 0.010%/ppm·s NO. The sensitivity obtained in this measurement is much smaller compared to the sensitivity reported in the previous section (0.078%/ppm·s NO) in Figure 4. The measurement results presented were obtained with different sensor samples that were coated by screen-printing or dipping in an aqueous solution of the LNT-material resulting in sensitive layers with varies thicknesses and morphologies. In further tests, it was found that the sensitivity to NOx varies with the thickness of the sensitive layer, which can be explained by the dependency of the number of accessible storage sites on the volume and the morphology of the sensitive layer influencing the diffusion of NOx into the storage material and therefore the rate of storage. In Figure 5(c), /dR/dt/ is plotted in parallel to cNO and follows it. In the presence of 5 ppm NO, the resistance changes by about 1.25 kΩ/s, in 10 ppm it is about 2.5 kΩ/s, which demonstrates once more the linearity. Again, the sensor signal responds and recovers very fast (5 to 6 s) with only a slight dependency on the actual NO concentration.

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