Ultrasonic gas densitometer

The need for a compact device to monitor density of gases gave rise to an R&D project to look into the possibilities of using ultrasonic probes to measure density of gases. Through measurements of ultrasonic transducer impedance around the resonant frequency, it is shown experimentally and through simple theoretical considerations that the density of gases can be monitored using equivalent impedance of ultrasonic transducers placed in the medium to be monitored. The simple theory behind the principle and experimental results are presented in this paper. The promising results indicate that the technique can be combined with ultrasonic volumetric flowmeters to give mass flow without resorting to a separate density meter, as is the practice nowadays. The preliminary results obtained using nitrogen are presented here.