Linear Measurement Using Sin Cosine Principal

Have you researched "linear variable differential transformer (LVDT)"?

This sounds like what your describing.

Yes, it does sound like LVDT is the ticket.

How long of a stroke do you need to measure?

Schaevitz makes some good economical LVDTs.

Measurement Specialties sells an economical LVDT conditioner board for under $200 USD. We bought ours at DigiKey.

We really need to know what specifications you need (length of stroke, etc.) to help you.

750mm stroke required for this rod diameter will be 22 to 30mm

For that length of stroke you will need something like this LVDT.

3) almost output sine ware move up to 37.5 % but not 100%
of what ? how do you define 100 %? Make a sketch of windings in order to give a better understanding of your problem.

This is basic design found on web i am trying to test but not able to execute as only +/- 37.5% approx distance i am measuring.
simply as per this complete sine wave should move left /right depending upon which direction rod move. but same principle which is used in rotary measurement it work fine. probably may be problem with winging center and rod magnetic / not magnetic point.

Basically there are 2 main types of magnetic sensors for such linear systems:

- the rod is of magnetic material (steel) with a thread cut on and covered by a magnetically transparent material in order to obtain a smooth cylindrical surface. 2 heads are placed at 90° in same plane each one having a coil which is supplied by a AC. The distance to the thread profile modifies the inductance and generates a signal almost sinus the second generates same signal but with 90° phase shift thus a cos.

the other most used system is to have a series of permanent magnetized zones alternating N and S poles. The sensing head is a Hall sensor which gives a signal proportional to the field intensity. The 2 heads are at such a distance that the 2 signals are shifted with same 90°

If you can only measure over a smaller length than the expected it is most probable that you have a system of the second type and the PM are demagnetized.

Yes you are right i want to use first principle and my ac source will be 5 KHz. probably i found mistake in rod may be layer on non magnetic material as it very sensitive for flux and try with different voltages it ok but result not yet recv

You can also a magnetostrictive measuring device, it's absolute and very reliable though unlike LVDTs there are electronics at the end of the rod. They're often used instead of conventional linear measuring potentiometers which are a PITA.