Electromagnetic water current meter

Abstract

A body means of electrically non-conductive material supports at least one pair of electrically conductive detecting electrodes disposed at opposite portions of the body means. Means is supported within the body means between the electrodes for producing an alternating magnetic field. An electrical circuit is connected to the detecting electrodes and includes indicating means. In one form of the invention, electrically conductive guard means is disposed adjacent the electrodes and means is provided for establising a potential on the guard means which is directly proportional to the potential on the detecting electrodes. In another form of the invention, means is provided for driving the electromagnet to produce an alternating magnetic field at a predetermind frequency wherein the magnetic field is driven to a finite value for a predetermind time interval during each cycle, and the electrical circuit includes means for measuring the signal from the detecting electrodes during a time delayed portion of said time interval. In a further form of the invention, pairs of oppositely disposed detecting electrodes are provided at right angles to one another so as to indicate the direction of water current flow. In each form of the invention, shield means is preferably employed in the form of electrically conductive material disposed between the detecting electrodes and the means for producing the magnetic field.

What is claimed is: 
     
       1. An electromagnetic water current meter comprising body means formed of non-conductive material, a pair of electrically conductive detecting electrodes supported by said body means at opposite portions thereof, means within said body means and disposed between said electrodes for producing an alternating magnetic field and including an electromagnet, drive means for driving said electromagnet to produce an alternating magnetic field at a predetermined frequency wherein the magnetic field is driven to a finite value for a predetermined time interval during each half cycle thereof, and an electrical circuit connected with said detecting electrodes for measuring the electrical signal from said electrodes during a time delayed portion of each said time interval whereby undesired portions of the signal from said detecting electrodes due to transformer effect voltage are substantially eliminated, said electrical circuit including a single sample-and-hold circuit gated by said drive means and having an alternating current output, and means for processing said alternating current output to produce an analog output signal proportional to the peak-to-peak amplitude of said alternating current output including a band pass filter connected with the output of said sample-and-hold circuit. 
     
     
       2. Apparatus as defined in claim 1 wherein said means for producing an alternating magnetic field is surrounded by said body means, said body means being formed of waterproof material to prevent water from coming into contact with said means for producing the alternating magnetic field. 
     
     
       3. Apparatus as defined in claim 1 including a coating of electrically non-conductive anti-fouling material disposed on the outer surface of said body means. 
     
     
       4. Apparatus as defined in claim 1 wherein said detecting electrodes are disposed at the outer surface of said body means and are formed of an electrically conductive mixture of anti-foulant and carbon. 
     
     
       5. Apparatus as defined in claim 1 including a second pair of detecting electrodes supported by said body means at opposite portions of the body means. 
     
     
       6. Apparatus as defined in claim 5 wherein the electrodes of said two pairs of electrodes are disposed at 90° intervals from one another. 
     
     
       7. Apparatus as defined in claim 1 wherein said means for producing an alternating magnetic field includes an electromagnet having a coil and a core, said core being formed of substantially eddyless material to reduce eddy currents. 
     
     
       8. Apparatus as defined in claim 1 including shield means for electrically shielding said detecting electrodes from said means for producing the alternating magnetic field. 
     
     
       9. Apparatus as defined in claim 8 wherein said shield means comprises electrically conductive material disposed between said detecting electrodes and said means for producing the alternating magnetic field. 
     
     
       10. Apparatus as defined in claim 9 including lead means connected with said means for producing the alternating magnetic field, said shield means also including electrically conductive material around said lead means. 
     
     
       11. Apparatus as defined in claim 1 wherein said means for processing includes a phase-sensitive detector connected with the output of said band pass filter. 
     
     
       12. An electromagnetic water current meter comprising body means formed of non-conductive material, a pair of electrically conductive detecting electrodes supported by said body means at opposite portions thereof, means within said body means and disposed between said electrodes for producing an alternating magnetic field and including an electromagnet, drive means for driving said electromagnet to produce an alternating magnetic field at a predetermined frequency wherein the magnetic field is driven to a finite value for a predetermined time interval during each half cycle thereof, and an electrical circuit connected with said detecting electrodes for measuring the electrical signal from said electrodes during a time delayed portion of each said time interval whereby undesired portions of the signal from said detecting electrodes due to transformer effect voltage are substantially eliminated, said electrical circuit including a single sample-and-hold circuit gated by said drive means and having an alternating current output, and means for processing said alternating current output to produce an analog output signal proportional to the peak-to-peak amplitude of said alternating current output, the last recited means including a filter for eliminating dc components of said alternating current output. 
     
     
       13. Apparatus as defined in claim 12 including a second pair of detecting electrodes supported by said body means at opposite portions thereof. 
     
     
       14. Apparatus as defined in claim 13 wherein the electrodes of each of said pairs of electrodes are disposed at substantially 90° intervals to one another. 
     
     
       15. Apparatus as defined in claim 12 wherein said means for producing an alternating magnetic field includes a coil and a core, said core being of eddyless construction and being formed of ferrite material to reduce eddy currents. 
     
     
       16. Apparatus as defined in claim 12 including shield means for shielding said detecting electrodes from said means for producing the alternating magnetic field. 
     
     
       17. Apparatus as defined in claim 16 wherein said shield means comprises electrically conductive material disposed between said detecting electrodes and said means for producing the alternating magnetic field. 
     
     
       18. Apparatus as defined in claim 17 including lead means connected with said means for producing the alternating magnetic field, said shield means including electrically conductive material surrounding said lead means. .Iadd. 19. Apparatus as defined in claim 5 in which said body means is a cylinder of circular cross-section. .Iaddend..Iadd. 20. Apparatus as defined in claim 6 in which said body means is a cylinder of circular cross-section. .Iaddend..Iadd. 21. Apparatus as defined in claim 13 in which said body means is a cylinder of circular cross-section. .Iaddend..Iadd. 22. Apparatus as defined in claim 14 in which said body means is a cylinder of circular cross-section. .Iaddend.