Fluctuation Enhanced Gas Sensing at Modulated Temperature of Gas Sensor

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 U_ref 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.