Using inductive proximity sensors to measure displacement.

Question

http://uk.farnell.com/multicomp/mcpip-t30l-001/sensor-m30-pnp-shielded-no/dp/2218049

I just bought these, later did I found out that inductive proximity sensors can detect metal in close proximity rather than the distance. I wanted to know if it's possible to by any simple modifications to this sensor that may result in measuring distance. I want to measure displacements of a steel shaft from 0~10mm and I am unable to find a cheap non-contact sensor for that purpose.

I had a read here: Position – Sensor Solutions | DigiKey TechZone

"Inductive sensors use a coil to generate a high frequency oscillating magnetic field to detect metallic objects. When a metal target enters the sensing field, eddy currents are induced in the target, which reduces the signal amplitude and triggers a change of state in the sensor output."

dougw · Answer

A simple way to convert distance to voltage in this geometry is to use a capacitance-to-voltage circuit. Form your variable capacitance by connecting one electrode to the metal bar and the other to a metal probe positioned 1 cm from the bar. Build a capacitance to voltage circuit that uses a fairly high frequency - well above the highest vibration frequency of the bar, and view the output voltage on an oscilloscope. As the bar vibrates the capacitance will oscillate and the scope will show both the frequency of vibration and the amplitude at the monitoring point. For best results ensure the probe wire is kept far from the bar except for the probe tip. You can look up capacitance to voltage circuits or capacitance meter circuits on the internet but be sure the one you choose has enough bandwidth to track the maximum vibration frequency.

Using inductive proximity sensors to measure displacement.

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