Detect presence of a thin wire

[alan.alanzhang@gmail.com]

I have a small gap (5mm-10mm) where a thin Nitinol wire passes through. I'd like to detect the presence/passing through of the Nitinol wire with a sensor. It can be contactless or a contact based sensor. The wire could make direct contact with the sensor but only at the sensor so it doesn't form a complete circuit (the wire dangles from a quad copter drone in mid air while the write enters the gap).

Ideally the sensor detects in under 100ms.

Thank you in advance.

[Dan123456]

Would a photo interrupter work?

They are basically an IR LED and IR receive in one and will give 6ou a signal is something blocks the gap.

[dobsonr741]

A sketch would be helpful to understand the wire’s position and also to tell why the wire would not be there, or move out of position. Just to avoid becoming a XY problem https://xyproblem.info/

[Marco]

IR reflection sensor would be my first pick if it had to be done with minimum engineering.

Capacitive sensing would have the advantage of not responding to non conductive debris.

[Infraviolet]

As the wire is thin any IR transmission gap sensor would liekly need to be sensitive with an analogue output, to detect a drop in intensity as the wire crosses rather than a total blocking. Whether reflective IR could work will depend on how shiny the wire's surface finish is.

You want to avoid any sensor that could cause a complete circuit, does that mean a current is running in that wire between the drone and somewhere else, or that the wire is held at a particular voltage? Either of those possibilities would open up more sensing possibilities, Hall sensor ifa current is flowing for example.

[MarkF]

This may be a little unorthodox...

Would you be able to fit a strain gauge to sense whatever you're going to hang from the end of the wire.

I have not worked with strain gauges; so I don't know the range of weights they can detect or what kind of output they have. 
I just saw that the new Prusa 3D printers detect zero Z-height with a strain gauge mounted on the corner of the bed instead of a micro-switch.  Which is where I got the idea from.

[themadhippy]

would something along the lines of a metal detector work

[jpanhalt]

How thin is "thin?"

If thick enough, I second the IR reflection method.  That is what used to detect the position of a 1/8" (3 mm) thin wire on a device I made several years ago  It's very simple, and I have never had a false detection even in bright sunlight.

[Circlotron]

Have a look at a toroid winding machine. Some have a sensor that counts how many times the wire passes through a gap.

[jonpaul]

Wire size: AWG #32?
40?
50?

See cat pages from MWS for wire tables /metric etc.

https://mwswire.com/

Jon