Using inductive proximity sensors to measure displacement.

Basically yes. Thanks alot I'll have a look at these. These seem quite useful

Thanks everyone, I'll have a look at these alternatives and decide what can be done

Let me echo Doug W.'s concern about stray fields with the capacitance scheme.  To avoid this you may be able to build a Faraday shield.  This can be perforated, as long as the diameter of the holes is smaller than 1/4 wave at your highest frequency of interest.

If you google for it, you can find a capacitance multiplier circuit that can be constructed from an op-amp.  This works for a capacitor that is returned to the supply.   Also google for an 'op-amp relaxation oscillator.'  The output of which you can count.  Using the multiplier increases sensitivity, while using the CCO gives you a squared-up signal that is easy to transmit.  You can get all of this functionality integrated from vendors such as TI.  I think their trade name is CapSense.

You might want to use a machine scale on your 'slot' to know the point you are measuring.  You might use a ballscrew car to move your sensor.  If you get a dual-shaft motor, you can operate manually or by controller.

hi

I have a similar issue. I want to measure distance in micro meter range and then calibrate the movement to identify force applied to the system.

which sensor i should use ?

You need to specify or describe your system in  much more detail for anyone to make  a decent sensor recommendation:

The first question is " why not measure the force directly" - unless you describe the system we don't know.

Then you need to give other information like bandwidth (frequency range) resolution, accuracy, environment, size constraints, acceptable cost range etc etc.

MK

Well this is what the system looks like. As a replacement for now I am planning to use Linear Ratiometric Hall Effect Sensors to measure the displacement when the shaft vibrates. These are cheaper and for that I'll have to attach magnetic collars at different positions along the shaft.

please check details in this post

http://www.element14.com/community/message/142871/l/how-to-find-resolution-of-capacitative-sensors#142871

i Think you will be really good person to discuss this matter as you have way more experience in it.

If the frequency is high enough, you could try using guitar pickup sensors - or make your own.

For best performance, check out how to design a humbucker pickup and the various variants.

Doug

Hello I wanted to ask If I can measure the distance of a metallic indictor plate by the inductive sensor? Can the sensor be used where asphalt is used? I have checked few inductive sesnors which operate at more than 160 degrees centigrade. But what would be the affect of temperature fluctuation in the measurement?

Buried inductive sensors are used at road intersections to detect vehicles in the turning lane. They would need to be built with wire that has high temperature insulation for your application. The signal level would be proportional to the size of the plate, its material, its shape and its distance. Think of a metal detector circuit...