Low-cost quartz tuning fork based methane sensor for coal mine safety applications

This paper reports a simple but effective methane sensor based on off-the-shelf quartz tuning forks (QTFs). The operation of the sensor is based on the fact that the presence of methane will increase QTF's resonant frequency since methane is lighter and less viscous than air. Unlike other resonant gas sensors based on the gravimetric principle, this new QTF sensor is not coated with any sensitive layer to absorb methane molecules, thus minimizing the hysteresis, reducing response and recovery time, and potentially improving long-term stability. It has been experimentally demonstrated that the presence of methane increases the resonant frequency of QTF with a sensitivity of 0.0063 Hz/1% or 0.19 ppm/1% and a detection limit of 0.025% at 0.5 Hz sampling rate. An excellent selectivity to carbon dioxide, which causes a decrease of the resonant frequency, has been illustrated. Temperature, pressure and humidity responses have been characterized. This new methane sensor is expected to meet the requirements of cost, power, size, reliability and explosion permissibility for coal mine safety applications.