Wide range, high accuracy flow meter

A turbine type flow meter comprising:

• a housing with an inlet port and an outlet port at opposite ends of a longitudinal cylindrical opening;
• a shaft centrally supported within said cylindrical opening along the axis thereof;
• first and second rotors mounted on said shaft;
• a pickoff coil mounted on said housing and excited by an a-c signal at a given carrier frequency;
• said inlet port and said outlet port being fashioned to facilitate connections to fluid flow passageways through which the rate of fluid flow is to be measured;
• said second rotor being positioned by a rotor spacer a short distance downstream from said first rotor and adjacent said pickoff coil;
• said first and second rotors having oppositely canted vanes which cause said first and second rotors to rotate in opposite directions when a fluid entering said inlet port passes through said first and second rotors and exits said outlet port;
• said second rotor having said vanes that are made from a magnetic material;
• whereby a fluid flowing through said first and second rotors causes said first and second rotors to turn at velocities proportional to the rate of fluid flow through said flow meter, said vanes of said second rotor passing through the magnetic field of said pickoff coil causing pulses to be superimposed upon said carrier frequency of said a-c signal of said pickoff coil, the repetition rate of said pulses being proportional to the flow rate of said fluid flowing through said flow meter and said repetition rate being convertible to rate of flow values by an external flow rate computer;
• said first rotor serving to precondition and alter the flow pattern at the entrance of said second rotor in such a way as to extend the effective metering range to lower flow rates and providing improved accuracy and linearity at such lower flow rates of fluid flow.