Capacitive proximity sensor

Hi guys,

I am doing a project for school using a NPN capacitive proximity sensor. My teacher said to me that it is possible to measure different values with this sensor?
But I can’t find it on the Internet! Is this possible or not and how?
Ward Bellers

It depends on the sensor have you got a link to it?

Different values of what ?

the sensor i have is a NPN LJC18A3-H-Z/BX

Can I suggest you simply type "LJC18A3-H-Z/BX" (missing out the quotation marks) into the likes of a Google search tool where you will get lots of hits.

It would be wrong of us to compromise your educational process by simply providing answers

okey, i understand you but i just want to know if its possible or not? can you give me an answer on that :wink:

The way sensors like this work is that their is a free running oscillator with an inductor and capacitor. Part of the capacitor is a plate allowing external materials to become part of the capacitor. This affects the capacitor value in the circuit and so shifts the frequency of the oscillator as it gets closer to the external material.

This oscillator is running at its resonance frequency in a high Q circuit. When it is close to something the oscillator's frequency shifts away from resonance, the oscillator stops and so draws a lot more current. It is this sudden current change that is detected to give a signal.

Their is a sharp threshold here with a bit of hysteresis. This is not suitable to measure any intermediate state. I worked with sensors like this, and their inductive counterparts, a lot when I left school and went to work for an industrial electronics company.

So in short, it is not possible to do what you want to do with this type of sensor. Their are other capacitive sensors you can get proportional reading from but not this one.

ow, but other sensors can be used fot it. are these sensors availeble on the internet?

ow, but other sensors can be used fot it. are these sensors availeble on the internet?

You could google capacitive proximity sensors.