Patent ID: 7832706

Claim:
A ram-type blowout preventer, comprising: a body; a vertical bore through the body; a horizontal bore through the body intersecting the vertical bore; a pair of ram assemblies disposed in the horizontal bore on opposite sides of the body, wherein the ram assemblies are adapted for controlled lateral movement to and from the vertical bore, wherein each ram assembly comprises a hydraulic piston connected at a first end to a ram block and at a second end to a piston tail; a pair of cylinder heads configured to be attached to the body and to receive corresponding piston tails; a magnetostrictive waveguide tube attached with a first end to one of the pair of cylinder heads, a second end of the magnetostrictive waveguide tube being free standing and extending into a bore formed within at least one piston tail; a permanent magnet disposed upon the at least one piston tail; and the magnetostrictive waveguide tube comprising a conducting wire to receive an interrogation pulse from a transducer, wherein the interrogation pulse generates a helical return signal in response to a relative position of the permanent magnet with respect to the waveguide tube, wherein the transducer is configured to receive the helical return signal and output a position of the ram block corresponding to the at least one piston tail.