Magnetostrictive position indicator

Apparatus for indicating the position of a movable member without establishing contact with such member comprising:

• a magnetic field generator mounted on the movable member for movement therewith;
• an elongated ferromagnetic member;
• means mounting said ferromagnetic member adjacent to and spaced from the movable member, said ferromagnetic member extending parallel to the direction of movement of the movable member whereby the spacing between said field generator and said ferromagnetic member will remain substantially constant during movements of the movable member and the field emanating from said magnetic field generator will induce a localized region of discontinuity in the Young's modulus of elasticity of said ferromagnetic member;
• means for inducing a sonic strain pulse in said ferromagnetic member, said sonic strain pulse inducing means being fixed in position with respect to both of said ferromagnetic and movable members, sonic strain pulses from said inducing means traveling along said ferromagnetic member and being at least partly reflected from said region of Young's modulus discontinuity;
• first sonic strain pulse detector means fixedly mounted along said ferromagnetic member in proximity to said inducing means, said first detector means providing an output signal commensurate with the arrival at said first detector means of a sonic strain pulse reflected from the region of Young's modulus discontinuity in said ferromagnetic member;
• and
• means connected to said first detector means and responsive to signals provided thereby for providing an output signal commensurate with the time required for a sonic strain pulse to travel along said ferromagnetic member from said sonic pulse inducing means to said region of Young's modulus discontinuity and for a reflected pulse to travel to said first detector means, said time being an indication of the position along said ferromagnetic member of said magnetic field generator.