Device for measuring displacement

A device for measuring a displacement of a movable member relative to a fixed member, comprising:

• an AC signal source;
• a first coil mounted to said fixed member and including first and second coil sections which are electrically connected and coaxially aligned along a common axis so that the first coil has a first extreme end constituting an outside end of said first coil section, a middle portion defined between respective inside ends of said first and second coil sections and a second extreme end constituting an outside end of said second coil section, said first coil being connected to said AC signal source to receive said AC signal;
• a second coil coaxially disposed about said first coil and mounted to said fixed member so as to establish a magnetic coupling with said first coil;
• a short circuit ring fixed for movement with said movable member, said short circuit ring being axially disposed about said second coil so as to establish a magnetic coupling with said first and second coils and constructed to consume magnetic energy;
• a float connected to said short circuit ring to cause said short circuit ring to remain on top of a fluid;
• and
• means connected to said second coil for detecting a change in electromagnetic induction between said first coil and said second coil caused by said short circuit ring and for providing an information signal which is representative of said change;
• wherein the winding density of each of said first and second coil sections of said first coil is gradually decreased from the outside end to the inside end thereof, and the winding density of said second coil is substantially even throughout its length.