Apparatus and method for measuring relative speed between a fluid and a reference

A method of measuring the relative speed of movement between a reference and a fluid, said method comprising the steps of:

• providing a reference in contact with and movable within said fluid;
• providing first and second spaced apart transducers supported by said reference in communication with said fluid;
• providing an amplifier coupled between said first and second transducers having a signal gain;
• coupling a bandpass filter to said amplifier causing said amplifier to exhibit greater gain for signals having frequency components within said bandpass filter;
• said first and second transducers, said amplifier, said bandpass filter and said fluid forming a closed loop circuit which defines a loop passband and which is regenerative solely to signal frequencies within said loop passband, said regenerative frequency being determined by the relative speed of said fluid;
• and
• detecting the frequency of said regeneration for use as an indication of relative speed of movement between said fluid and said reference.

Speed measurement apparatus for measuring the relative speed of movement between a reference and a fluid, said apparatus comprising:

• a pair of spaced-apart transducers supported by said reference and coupled to said fluid each having means for transferring energy between said transducers through said fluid subject to a time delay;
• a regenerative circuit coupled between said transducer, said circuit including frequency filtering means and amplifying means, said circuit having signal gain but no signal producing source;
• and
• frequency detecting means coupled to said regenerative circuit producing a frequency-dependent speed-indicative output,
• said pair of transducers, said regenerative circuit and said fluid forming a regenerative loop through which a regenerated signal travels at a frequency determined in part by said time delay.

A method of measuring the relative speed of movement between a reference and a fluid;

• said method comprising the steps of:
• forming a closed loop system having a loop gain and a loop bandpass and a loop component formed by an electro-acoustic transducer, an acousto-electric transducer and said fluid therebetween;
• allowing said closed loop system to regenerate and produce a regeneration signal;
• propagating said regeneration signal as acoustic energy in said fluid between said electro-acoustic transducer and said acousto-electric transducer;
• said fluid imposing a time delay upon said acoustic energy;
• amplifying and filtering said regeneration signal in a regenerative frequency selective manner to produce a regenerative signal having a frequency dependent upon said time delay;
• and
• detecting said regenerative frequency to measure said speed.