The volatile organic compound (VOC) is contained in indoor materials in buildings, such as paints and adhesives. The formaldehyde is a representative example of the chemical substances which affect people’s health. For detection of formaldehyde, we made SnO
2 thin-film type sensors by the DC magnetron sputtering method. The sensor has Pt electrodes on one side of a glass substrate as the heater. The thickness of the heater is 500 nm. The SnO
2 thin film is sputtered on the opposite side of the heater. The thickness of SnO
2 thin film is 200 nm. Ag(1.6 wt.%) is added as a catalyst metal. As formaldehyde is low concentration of less than 1 ppm, the output signal from sensor is buried in noise, which is generated from the heater. The noise is considered as white noise. In this paper, noise cancellation method by using Adaptive Line Enhancer(ALE) is proposed to extract the sensor outputs. The least-square method (LMS) is adopted for the adaptive algorithm in the ALE. As a result of noise cancellation by using the ALE, the formaldehyde of 0.1 ppm concentration can be detected.
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