Optical reflection sensor, standard part?

If it reflects enough light to trigger a sensor then the light going straight through must reduced by at least as much, probably a great deal more as light will be reflected in all directions, not to mention light will also be refracted. with a fine beam and small sensor I would think a gate type would give a stronger change in signal. Only a very flat optically coated surface aligned with the beam would cuase no signal change at all, a test tube is non of these.

Ive used an IR reflective type, both emitter and sensor in one tiny SMD package, I found it registers true on white plastic thats quite close, and false on black insulation tape thats not too close, crepe tape was better, made a simple 4 quadrant rotatary encoder, no idea what glass would do.

Colin =^.^=

Yes, but I forgot to mention that I only have space for the sensor above the ramp, not below it or on either side - so I would have to put a reflector on the bottom side. That's the other reason why I don't want a transmissive method with emitter on one side and detector on the other.

Part number or manufacturer?

Thanks.

Ah that would change things, I was wondering if it migh tbe a bit difficult anyway to usea gate with such a small thing on a conveyor anyway.

SHARP GP2S27CJ000F

Was about the smallest cheapest part from farnell.

Its discrete so you have to build an amplifier/comparator etc but at least you can set the gain to whatever it needs.

Colin =^.^=

Try this part: SG-2BC from Kodenshi. Farnell stock it - it works up to

Controlled and within 1cm, or controlled to within 1cm? If the former, someting like Hamamatsu p5587 photoreflectors might work. They are a one-part solution (emitter, detector, amp and schmitt trigger built-in), but like most all-in-one sensors of this type, the emitter and detector are close together. That means light hitting the test tube at close to a right angle, so much of it will be transmitted rather than reflected. I don't know if enough would get back for a reliable signal. A separate emitter and detector would allow you to set an angle closer to or even less than the critical angle, which would provide a stronger signal.

Tim

Without knowing all the details, an alternative approach may work better. I did see a vaguely similar application some years ago, rather than relying on variable optical reflections, this used a very light plastic arm that got "bumped" upwards each time an object went past. The arm had a tiny rear-earth magnet (about 1x1x2 mm) attached to it, and it triggered a Hall-effect sensor. Dead reliable and simple.

Barry Lennox

Hello Lewin,

If optical doesn't pan out for some reason ultrasound might be an alternative.

With a reflector at the bottom and a reflective sensor, you effectively have a transmissive gate with the object in the path twice.

for

What about mechanical? A "finger" that is lifted when the object passes??

sensors

be

Have you talked to an application engineer from Omron?

Controlled and within 1cm, +/- 2mm

Thanks for this part suggestion. My next step is to buy samples of all of the parts suggested here and look at what they do. I need to test them against a variety of possible different printing styles on the tubes.

I do very much like the thin-wire-and-magnet idea. I just have to find out if the company that will be making this can assemble such a delicate piece of apparatus.

Very nice, I like this idea a lot. I will try to build a prototype with a magnet on a piece of springy wire; if it works, I'll get the mechanical guys to make something real.

Thanks!

ISTR a sensor which was a microphone on an angled plate which the objects dropped onto.

Any of the major industrial photoelectric sensor manufacturers have 'transparent object' detectors of various kinds: Banner Engineering Sick Optik Cutler-Hammer Keyence etc Just contact an Applications Engineer and tell them what you're trying to do. Paul Mathews