Patent ID: 7874801

Claim:
A device for measuring the displacement travel of a hydraulic displacement mechanism for blades of an impeller of an axial-flow fan, comprising: a displacement mechanism that includes as components a displacement cylinder and a piston rod having a piston, wherein one of said components is axially displaceable and the other component is not axially displaceable; a displacement disk to which are secured, via rotatable displacement levers, respective spindles of said blades, wherein said axially displaceable one of said components of said displacement mechanism is connected to said displacement disk, wherein said displacement disk is rotatable; an oil transfer element that is adapted to supply oil to said displacement cylinder, wherein said oil transfer element surrounds an extension of said piston rod that extends out of said displacement cylinder, wherein said oil transfer element is non-rotatable; and a magnetostricitive displacement-measuring device that includes a sensor housing having a wave guide, a sensor head, and an annular magnet, wherein said displacement mechanism is coupled to said magnetostrictive displacement-measuring device, wherein said sensor housing and said sensor head of said magnetostrictive displacement-measuring device are connected with said oil transfer element, wherein either said oil transfer element or one of said components of said displacement mechanism is axially displaceable relative to the other component of said displacement mechanism, and wherein said annular magnet is connected to that component of said displacement mechanism for which said axial displacement relative to said oil transfer element exists.