A device for measuring the flow rate of a fluid flowing in a pipe having an upstream portion with an upstream pressure and a downstream portion with a downstream pressure, said device comprising:
- a body member connected to said pipe;
- means for creating a differential pressure between said upstream pipe portion and said downstream pipe portion disposed within said body member and integral with said body member wherein said body further comprises a flow channel formed within said body member for fluidly communicating said upstream pipe portion with said downstream pipe portion;
- first pressure intake means fluidly communicating with said communication channel upstream from said differential pressure means;
- second pressure intake means fluidly communicating with said communication channel downstream from said pressure differential means;
- a pressure sensor connected to said body member, wherein said pressure sensor further comprises;
- a piezoelectric plate in contact with an outer surface portion of said body member and rigidly fixed thereto;
- a first active elastic surface wave oscillator disposed on said piezoelectric plate;
- a second active elastic surface wave oscillator disposed on said piezoelectric plate proximate to said first elastic surface wave oscillator;
- a first amplifier operatively associated with said first oscillator;
- a second amplifier operatively associated with said second oscillator;
- a first delay line for propagating elastic surface waves operatively associated with said first oscillator;
- a second delay line for propagating elastic surface waves operatively associated with said second oscillator;
- a first pair of electromechanical split-finger transducers operatively associated with said first oscillator and disposed on a first portion of the outer surface of said piezoelectric plate upstream from said differential pressure means;
- a second pair of electromechanical split-finger transducers operatively associated with said second oscillator and disposed upon a second portion of the outer surface of said piezoelectric plate downstream from said differential pressure means;
- means for exposing a first inner surface portion of said piezoelectric plate to said first pressure intake means located radially within said first portion of said outer surface of said piezoelectric plate;
- means for exposing a second inner surface portion of said piezoelectric plate to said second pressure intake means, said means for exposing said second inner surface portion being disposed radially within said second surface portion of said outer surface of said piezoelectric plate such that changes between said upstream pressure and said downstream pressure modify the propagation time of said elastic surface waves over said first delay line and said second delay line, respectively, and wherein said first and said second elastic surface wave oscillators generate respective first and second signals dependent upon said upstream pressure and said downstream pressure, respectively;
- and
- a mixer for receiving said first and second signals and for generating an output beat frequency equal to the difference between said first and second signals.