Method and apparatus for monitoring the flow of liquid and the like

In an apparatus for monitoring the speed of flow of a liquid along a conduit provided with emitter and receiver means capable, in response to an applied driving signal, of emitting a continuous acoustic signal of predetermined frequency into the liquid and capable of receiving at least a portion of the reflected signal which due to the Doppler effect has a different frequency than the emitted signal;

• said apparatus being connectable to said emitter and receiver means, the improvement comprising, oscillatory signal generating means for producing the driving signal at said predetermined frequency, filter means for demodulating the emitted frequency from the received frequency to give a first electrical output signal at a frequency equal to the Doppler difference frequency, first variable frequency divider means for dividing the Doppler difference frequency by a first selectively variable predetermined divisor to give an electrical signal at a first quotient output frequency which is a predetermined function of the Doppler difference frequency per unit increment of liquid speed relative to the emitter and receiver means, second variable frequency divider means to further divide said first quotient frequency by a second selectively variable predetermined divisor to give an electrical signal at a second quotient output frequency correlated to the speed of the liquid, and means for utilizing said signal at the second quotient frequency to indicate variation of a parameter with respect to time which derives from movement of the liquid along the conduit.