flame detection at distance.

Ben325e

Hi folks,

I'm in a class at school where we want to find a candle in an area about 9 x 9 feet square, with 2x4's as the boundaries (so 1.75 inches high "walls"). The only thing I've found online that can detect flame at more length distance costs about 70 or so dollars. We're doing this a very large room with fluorescent lights and 2 story glass walls on opposite sides (an atrium).

I know how to detect at close distances, but is there any other viable way that I could explore where I could make a candle detector at longer distances?

(btw - our fan to blow out this candle is an 8'' oscillating RV fan - runs of of 12 volts 1.2amp/hour battery, and can put out a candle at over 4 feet away.. this is why we want to detect at further distances - to use the capability of our fan.)


Thanks,

Ben R.

erco

I had amazing results with plain old phototransistors when I won the Trinity Firefighting Robot contest in 1994. But I do mean OLD phototransistors. I went through a large accumulation of accumulated phototransistors in my junk box and tested them individually while pointing them at a candle flame. When the needle really jumped, I knew it was very sensitive to the infrared energy emitted by the flame. I used an analog multimeter set to measure megohms. Unfortunately, I haven't seen any modern transistors that come close, they're mainly optimized for 940 nm IR communication now. But if you have access to someone's collection of older parts, give it a whirl. The best ones I found weren't marked with a number, but had three leads and came in a metal can except for the glass lens on top. (Naturally, I used the Basic Stamp 1 in my robot.)

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·"If you build it, they will come."

Tracy Allen

That is interesting about the phototransistors. It may have had more to do with the type of glass used in the lens than the transistor itself.

The Hammamatsu R2868 UVtron flame detector uses a special UV glass. That is probably the one that retails for over $50.

I wonder if a pyroelectric detector such as those used in motion detectors could work. It would need to be at the focal point of an infrared lens. But it might give a sharp bi-phase pulse as it rotates past a heat source like a candle.

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Tracy Allen
www.emesystems.com

LilDi

Very interesting indeed! Why would the manufacturer of a simple inexpensive photo transistor use a very expensive polycrystalline iridium lens. My guess is the photo transistor was not inexpensive at all.
You can buy an inexpensive motion detector from wal mart for about ten dollars that will work or Parallax's PIR sensor for the same price. Some people on this forum have said that a PIRs don't work as flame detectors, but they have worked for me.

erco

Based on the interest you fine folks expressed, I had a second·look at my robot and one of my precious winning phototransistors DID have markings. Pic attached.

Drum roll, please:··· FPT540A,··· probably Fairchild,· I Googled it and saw a data sheet online. Again, I found these in my junk drawer in 1994, they·must have·come from a Radio Shack bulk pack, so they weren't expensive as I got them. I used them in a voltage divider arrangement with a series 1M resistor and found they were·the most sensitive ones I had to detect the candle flame. Not sure if they're easily available, but now you have something to hunt.

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·"If you build it, they will come."

Post Edited (erco) : 3/27/2008 9:59:39 PM GMT

Ben325e

Thanks for the responses, guys. Now to lookup voltage divider arrays.... [noparse]:)[/noparse]

This has been a great learning experience for me. Just from doing this first robot, I feel like my knowledge on the subject is at 15000 percent of what it was!

have a good one,

Ben

erco

FPT 540a

Looked around for these obsolete phototransistors, but I only found one (overpriced) source. Rose at American Micro (973.377.9566) can supply them for $25.14 each.

At that price, I'd wait for a bulk buy on eBay!

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·"If you build it, they will come."

Ben325e

thanks again for your help and research. The ir sensors aren't doing to well for us, so we've switched to a pair of photo sensors, which seem promising for us.
We've got a week and a half to get things together, and I'll try to remember to post how it went for us!

Thanks again,

Ben

erco

Good luck! Buy samples of all the cheap local phototransistors you can, at Radio Shack (they sell one by itself and one with an IR LED) and elsewhere. Test their sensitivity to a candle flame; use them just like a variable resistor with the Stamp (use with a capacitor and the RCTIME command) see http://www.emesys.com/BS2rct.htm ·. Remember, phototransistors have polarity, long lead toward B+. Radio Shack phototransistors have widely variable reponse sensitivity in this mode. Test 10 different ones, rank their sensitivity, use the best ones. Remember to shield them from outside light. Recess them in a dark tube or hole so they only see out a small opening, and aim them carefully. And don't let any light sneak in the back side either (near the leads). Use lots of ULTRA FLAT BLACK paint and/or multiple layers of black electrical tape.

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·"If you build it, they will come."

erco

Also see page 4 here: http://www.seas.upenn.edu/~robo2005/Electronics%20Lab%202%20v6.doc

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·"If you build it, they will come."