Which sensor to use

Hello guys,

This is the problem:

I have 1m diameter glass tube, circle shape, like a donat. Inside is water. Metal ball 1cm diameter is spining around. Ball is overlayed with sealing-wax, to keep from sinking. Glass is 0.5cm wide.

I need to detect metal ball in two location in a donat.

What kind of sensor should I use?

Thank you.
Best Regards

How about an inductive sensor?

Edit: Or two, one for each location to be sensored.

Is the waterlevel fixed?

Can inductive sensor work through 0.5cm glass, max 0.5 water and wax? If can please recommend.

I looked a little bit on Omron sensors but cannot find such.

Edit: if I use 4 or 8 there is stil 0.5m of water. Water level is fixed. Tube is 100% full.

A simple LED through-beam sensor should work fine. Water will cause a little difraction, but this can be compensated for. I assume you will always have the water there.
With the sensors close to the tube, I doubt diffraction would even be a factor.

A proximity sensor may also work.

I agree. You can use a D18 Inductive sensor or a D30 Capacitive sensor.

Is D = diameter or width of active sensing face?
D18 means 18mm.
D30 means 30mm.

Yes. Most manufacturers have the diameter in the part number. A 8mm prox would have about 2-4mm sensing distance. A 30mm capacitive has much more. Using a capacitive to sense metal gives you the longest range possible, so thickness of the glass and round surface of the metal object won't have an impact. A capacitive might be too sensitive, but I believe it's adjustable. Make sure it doesn't give false trips with water, dirty water, etc.
Proximity sensing is based on a flat piece of metal. Your 10mm ball probably has about 4 to 5 mm surface that we would consider the sensing surface. Add the thickness of the glass tube, and you can see why a sensing distance of 2-4 mm might be troublesome.
The larger the diameter, the longer the range.
That's why 18mm prox or 30mm capacitive are suggested as good starting points. The 30mm capacitive ought to be a guarantee if you have the room for it. The other problem is repeatability.
Is the position of the ball critical? If so, you will have better repeatability as you go down in diameter (using prox instead of capacitive).

In any case, you haven't presented anything really strange. Sensing metal is easy. You have many choices that should all work equally well. Consider 'break-the-beam' photo type first if you need position accuracy.

Hello keithkyll,

Thank you for replays, you were wery helpful but I cannot find Inductive proximity switch or Capacitive proximity switch for my system.

If you look at pepperl-fuchs sensors at this address: http://www.pepperl-fuchs.com/selector/gui/show_product_selector.kly
or Omron sensors at this address: http://www.ia.omron.com/product/64.html

I cannot find proximity sensor that can detect more than 100mm.

Thank you.

Lesa said:

Hello keithkyll,

Thank you for replays, you were wery helpful but I cannot find Inductive proximity switch or Capacitive proximity switch for my system.

If you look at pepperl-fuchs sensors at this address: http://www.pepperl-fuchs.com/selector/gui/show_product_selector.kly
or Omron sensors at this address: http://www.ia.omron.com/product/64.html

I cannot find proximity sensor that can detect more than 100mm.

Thank you.

Click to expand...

You wont find a proximity sensor of more than 100mm range, thats why they are called proximity switches, it implies something is going to be close to the switch, 100mm is not close.

You need to look at optical sensors with teach capabilities so you can set it up and tune to your application, most manufacturers will have sensors that are capable of looking through glass.

Talk to you nearest distributors of sensors they should be able to give you some application support and suggest a sensor to use.

Water in tube is very fizzle and that ball to too little, so i belive, optical sensor could not detect it.

A vision cam from above should do the trick, but it may be to expensive?

I belive so, but money matters in this case.

And you cannot place inductive sensors at the 2 positions inside the glass tube?

Can you post a picture of your application, i am struggling to visualise it.

I reread the first post. I missed that the tube is 1 Meter (39 inches, a little over a yard). The ball is 10 millimeters (.39 inches). I'm lost trying to see the donut shape. Is the donut 1 meter diameter, or the glass? Lesa is looking for 100mm sensing distance. That's only 4 inches.
No matter what, prox and capacitive are ruled out. Optical (thru-beam or reflective), Laser, camera, or ultrasonic are the choices now. Water is a factor, but we can compensate for beam-shift if the water is a constant (no waves).
Lesa, give us a photo or drawing.
Keyence and Banner are the vendors you need to check now for ideas.