METHOD OF, AND APPARATUS FOR, MEASURING THE MASS FLOW RATE OF A GAS

摘要

There is provided a meter (200; 350) for measuring the mass flow rate of a gas. The meter comprises a conduit (206) through which the gas flows in use. The conduit has a flow restriction orifice (212) through which choked flow occurs in use. The flow restriction orifice divides the conduit into an upstream portion (214) upstream of said orifice and a downstream portion (216) downstream of said orifice. The meter further comprises a sensor assembly (204), the sensor assembly including a piezoelectric crystal oscillator (218) in said upstream portion such that said piezoelectric oscillator is in contact with said gas when the meter in use. The sensor assembly is arranged: to drive the piezoelectric crystal oscillator such that the piezoelectric crystal oscillator resonates at a resonant frequency; to measure said resonant frequency of said piezoelectric crystal oscillator; and to determine, from the resonant frequency, the mass flow rate through the orifice.