Temperature compensated magnetostrictive piston position detector

A cylinder apparatus made of a composite material comprising a cylinder tube having an inner cylinder made of a non-magnetic material and an outer cylinder formed on the outer periphery of said inner cylinder and made of a fiber-reinforced resin material, a piston slidably disposed in said cylinder tube, a rod having one end fixed to said piston and the other end outwardly projecting from said cylinder tube, a stroke sensor for detecting the stroke of said piston, said stroke sensor comprising a position indicating magnet provided on said piston and elongated sensor means provided on said cylinder tube, said elongated sensor means having a thin elongated tube extending along said cylinder tube between both ends thereof and containing at least one magnetostriction string having a large coefficient of magnetostriction, a drive coil wound on at least one of both ends of said thin elongated tube for producing magnetostriction phenomenon in said magnetostriction string for generating an ultrasonic wave when a pulsatile input current is applied thereto, a detection coil wound over a predetermined length of said thin elongated tube separately from said drive coil for detecting as a detection signal the induced electromotive force generated by the inverse magnetostriction phenomenon when said ultrasonic wave is passed through the position of said magnetostriction string corresponding to said position indicating magnet, and

• at least one pin-like magnet for correcting a measurement error due to a change in temperature of said stroke sensor, said at least one pin-like magnet being provided at each of positions axially inward of both ends of said detection coil and adjacent both ends of said cylinder tube.