Modulated sine wave flowmeter

Claim 1

A modulated sine wave flowmeter for measuring, as induced E.M.F., the rate of flow of blood in a blood vessel, and eliminating unwanted quadrature signals, comprising: an electromagnet adapted for partially encircling the blood vessel, said electromagnet generating a magnetic field on the blood vessel transversely to the direction of flow; a pair of signal sensing means positioned adjacent said electromagnet and adapted for location diametrically opposite one another on either side of the blood vessel for detecting a first signal, said first signal corresponding to the induced E.M.F. caused by the flow of blood through said magnetic field, and for detecting a second signal, said second signal being in quadrature with said first signal; an electric coil wound about said electromagnet for driving said electromagnet; coil energizing means electrically connected to said coiL for producing a drive voltage for energizing said coil; a modulator electrically connected to said coil energizing means; a first oscillation means electrically connected to said modulator for supplying a sine wave to said modulator at a first frequency for the energization thereof; a second oscillation means to modulate the amplitude of the voltage of said coil energizing means and thereby modulating said second signal, said second ocillation means operating at a second frequency which is a fraction of said first frequency, said second oscillation means including means for electrically connecting and disconnecting said second oscillation means to said modulator; demodulation means electrically connected to said sensing means for separating said first and second signals, said demodulation means including adjustable electronic gates; gate pulse generating means for adjustably modifying the position of said electronic gates during zero blood flood to null said second signal; and readout means connected to the output of said demodulation means.