Flow sensor for an infusion pump

A flow sensor for monitoring and verifying actual flow of a medication from a medication dispensing pump through a pump discharge conduit for delivery to a patient, said flow sensor comprising:

• an inductor coil mounted about the pump discharge conduit;
• a core pin of a magnetically attractable material mounted along the pump discharge conduit;
• means forming first and second generally opposed end stops along the pump discharge conduit for limiting movement of said core pin along the conduit between a first position generally retracted from said inductor coil and a second position generally coaxially within said inductor coil;
• and
• retraction means for normally drawing and retaining said core pin at said first position, said core pin responding to medication flow through the pump discharge conduit for movement to said second position for the duration of said flow, said core pin cooperating with the pump discharge conduit to permit medication flow through the conduit and past the core pin;
• said retraction means comprising a magnet mounted along the pump discharge conduit at a position generally axially adjacent to said inductor coil.

An inductance flow sensor for monitoring and verifying fluid flow through a flow passage, said flow sensor comprising:

• a generally tubular member adapted for in-line connection with the flow passage for flow of the fluid therethrough;
• a core pin of a magnetically attractable material mounted within said tubular member for movement therein between a first position seated against a first end stop defined by said tubular member, and a second position spaced from said first end stop;
• an inductor coil mounted externally about said tubular member at a position with said core pin generally retracted axially therefrom when said core pin is in said first position, and with said core pin disposed generally coaxially therein when said core pin is in said second position;
• and
• retraction means for magnetically drawing and retaining said core pin in said first position during nonflow of the fluid through said tubular member, said core pin being displaced upon flow of the fluid through said tubular member to said second position, said core pin cooperating with said tubular member to permit fluid flow therethrough past said core pin when said core pin is spaced from said first end stop.