Importance

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Abstract

There is provided a meter for measuring the mass flow rate of a gas, the meter comprising a conduit through which the gas flows in use, the conduit having a flow restriction orifice through which choked flow occurs in use, the flow restriction orifice dividing the conduit into an upstream portion upstream of said orifice and a downstream portion downstream of said orifice, the meter further comprising a sensor assembly including a first piezoelectric crystal oscillator in said upstream portion such that said first piezoelectric oscillator is in contact with said gas when the meter in use, a second piezoelectric crystal oscillator in said downstream portion such that said second piezoelectric oscillator is in contact with said gas when the meter in use, said sensor assembly being arranged: to drive the first and second piezoelectric crystal oscillators such that each of the first and second piezoelectric crystal oscillators resonate at respective resonant frequencies; to measure the resonant frequency of the first piezoelectric oscillator and the resonant frequency of resonant frequency of the first piezoelectric oscillator and the the second piezoelectric oscillator; and to determine, from the resonant frequency of the second piezoelectric oscillator, the mass flow rate of gas through said orifice.

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First Claim