Fast-response algorithm for calculating polyatomic gas concentration using ultrasound

Abstract

A careful and safe method is crucial for measuring the concentration of gasses, such as a refrigerant gas that causes global warming or a combustible gas that has a risk of explosion. In this regard, we propose an ultrasonic measuring method for a gas concentration without making direct contact with the hydrofluorocarbon, a refrigerant gas. Because refrigerant gasses are polyatomic gas with specific heat ratios different from those of diatomic gasses such as hydrogen, oxygen, and nitrogen, calculating the concentration of these mixed gasses requires a calculation algorithm. In addition, mixing gasses with different specific heat ratios increases the complexity of the calculation algorithm, thereby increasing the calculation time. Brent's method is an algorithm in numerical analysis that is used to solve these types of problems. A design-based method suitable for implementing high-speed calculation algorithms was introduced in this study by using a field-programmable gate array (FPGA) in conjunction with a model-based design. The gas concentration was calculated using parameter values from the reference data and difference in sound traveling time obtained from measurements. The reliability results show that when the difference in sound traveling time is used for the calculation of the gas concentration, it can be predicted that there is no need for calibration of the measuring equipment.