Capacitive linear position sensor

edmunds

Senior Member
Dear all,

Would it be possible to build a capacitive linear position sensor around picaxe Touch functionality? I'm thinking something like digital callipers, but a good 20 times smaller. To detect 10mm position with accuracy of 0.05-0.1mm. I realise that would require custom PCBs, but that is no problem.


Thank you for your input,

Edmunds
 

AllyCat

Senior Member
Hi,

If you want to measure the spacing of the two plates of a "parallel plate capacitor" (separated by up to 10mm) using their change in capacitance, then certainly not to the resolution you've suggested. I have used the PICaxe touch command to detect if a (water) valve was being opened or closed, using such a method, but not for any "absolute" measurement of its position (or status).

A quick google revealed this link where Jack gives a reasonably useful "technical" answer for how digital calipers work. But a problem with the PIC{axe} touch sensor method is that it counts the number of oscillations over a significantly long period of time, so the capacitance measurement is inherently "slow". The capacitance measurement will also "drift" with physical parameters such as temperature or the humidity of the (air) dielectric, etc..

Cheers, Alan.
 

edmunds

Senior Member
Ok, seems like I was wandering down the wrong path. I'll keep playing with inductive/hall options then.


Thank you all for your inputs,

Edmunds
 
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Buzby

Senior Member
Hi Edmunds,

What exactly is it you are trying to measure, or are you just trying to build some callipers ?.

The reason I ask is that depending on the exact requirement there may be a few different ways to skin this cat.

For example, is this measuring device an active part of a bigger machine, or is it a general purpose tool ?

Does the measurement need to be continuous, or can it be 'measure, reset, repeat' ?

Are you measuring a gap where you can 'view' it from the side ?

I've come across lots of measuring techniques, but never one that could be used in every application.

Horses for courses.

Cheers,

Buzby
 

oracacle

Senior Member
You can get digital depth gauges that aren't really any bigger than the display. But if you need a non contacting measurement then look into capacitive sensors for 3d printer need leveling. There are also inductive sensors too. Neither of which will user touch, but more likely the ADC.
 
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