Fluctuation Enhanced Gas Sensing at Modulated Temperature of Gas Sensor

Fluctuation Enhanced Gas Sensing at Modulated Temperature of Gas Sensor

Mateusz Kotarski, Janusz Smulko
DOI: 10.4018/ijmtie.2012040104
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Taguchi gas sensors are commonly used to measure gas concentration. The standard detection method utilizes only changes of sensor DC resistance to determine various gases concentration. Unfortunately, such technique leads to false results due to cross-sensitivity of gas sensors at presence of other gases. Such adverse effects can be reduced by applying fluctuation enhanced sensing and temperature modulation of the sensor what allows to gather more information about ambient atmosphere than the sensor DC resistance only. The measurement setup of voltage fluctuations across the gas sensor as well as the selected measurements results of DC resistance under temperature modulation are presented. New indicators of gas detection have been proposed which utilize voltage fluctuations and DC resistance measurements at two selected different temperatures of the gas sensor.
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Measurement Setup

Low frequency voltage fluctuations across the polarized gas sensors are usually characterized by their power spectral density S(f) that means application of FFT algorithm and averaging over spectra to limit estimation accuracy (Beeson, 1985, Clark, 1973). Thus, the data acquisition system should not measure DC resistance only but has to amplify and record voltage fluctuations.

For laboratory measurements the designed gas distribution system has been used, to obtain the desired gas concentration. The system allows mixing two various gases of a concentration accuracy about 1 ppm for the applied calibration gases. In this exploratory study we present measurement results obtained for a gas sensor placed into a gas chamber and measurements made by a low noise electronic circuit. The gas sensor was located in ambient atmosphere of a mixture of synthetic air and two other calibrating gases, which flow was controlled by separate flow-meters.

The electronic circuit used to polarize the gas sensor presents Figure 1. The sensor current is determined by the resistance R1 which was equal to 100 kΩ. The reference voltage Uref was set to 1.25 V and the gain K of voltage fluctuations was set to 500 V/V by selection of resistors R2 and R3. The DC voltage component U1 across the sensor and the amplified AC voltage component U2 were connected to the input of the 24-bits A/D converters to record the data. The frequency range where the 1/f noise component dominated up to tens of kHz for the investigated sensors.

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