Pressure transducer based fluid velocity sensor

A process for determining the velocity or density of a fluid comprising:

• producing a primary electrical signal with a varying frequency, said signal being a continuously varying signal or a discrete time varying signal,
• splitting said primary signal to provide first and second electrical signals, whereby first electrical signal is then used to create a first pressure wave signal, said first pressure wave signal to be transmitted through said fluid and said second signal comprising an internal reference signal,
• transmitting said first pressure wave signal through said fluid,
• receiving at a receiver a third signal which comprises potential multi-path interference signals and said first pressure wave signal which has passed through said fluid,
• mixing said third signal together with said second signal, generating a mixed signal,
• filtering said mixed signal to remove substantially all of said multi-path interference signals, generating a filtered-mixed signal
• measuring the frequency of said filtered-mixed signal to determine the propagation delay of said first pressure signal after it has passed through said fluid, and
• calculating the velocity or density of said fluid from said propagation delay of said first pressure wave signal after it has passed through said fluid,
• wherein the frequency of said primary electrical signal varies sufficiently rapidly that the frequency of said third signal and said second signal will be different when they are received at said receiver.