Electronics > Electronics

FOLLOWING HIGH INFRA RED EMITTING BODIES???

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Soeren:
Hi,


--- Quote from: HAPPY BOY on October 31, 2012, 07:36:03 AM ---hi.. i want to detect Mid-wavelength infrared ranging from 3 micrometere to 8 micrometer that  include flame , exhaust etc

and ignoring the human bodies / tables / chairs /sunlight ..

--- End quote ---
No single IR sensor will detect flames while excluding other IR sources, but it's solved in pro-equipment by either UV/IR sensors that detects two bands and check the amount of each, to exclude other IR sources, or by eg. double- or triple-IR sensors that checks at 4.4Ám as well as 1 or two bands used as reference (again to exclude non-flame IR).

Hamamatsu makes en UV only sensor for flame detection btw, but you only asked for IR, so that may be of little interest.

Those detector types are all expensive compared to a simple photo transistor, of course, so unless you need absolute perfection, you might wanna go with a photo diode and use software to distinguish the type of source its looking at and experimenting to find usable signatures for wanted as well as unwanted sources.

The above is for flames, I have no idea of what IR band(s) an exhaust pipe delivers (but I guess it's very faint, compared to flames).
What are you making - a robotic dog chasing cars? ;D

HAPPY BOY:
hi,, wanted to ask how to plac the convex lens on an ir receiver??  waned to focus its rays to increase the range ?
thanks

Soeren:
Hi,


--- Quote from: HAPPY BOY on November 16, 2012, 10:54:40 AM ---hi,, wanted to ask how to plac the convex lens on an ir receiver??  waned to focus its rays to increase the range ?

--- End quote ---
That depends entirely on the focal length of the lens and whether you want it to be close to a parallel beam (place it in the focal point), or you want it to cover a wider area (place it closer to the lens than the focal point).

If you haven't got access to a LASER bench or similar, the easiest way to find the focal length of a lens is to use the sun and focus it on a dark grey or black target (to enable you to see the dot when in focus, a light surface will make it too bright to see) - this will be the focal length, as the sun is far away and can be considered a (near) single point, while a table lamp will give a false focal length.

Use the largest diameter lens you can, to get the most light at the receiver.

Even better... Mount the receiver backwards in a parabolic mirror (like one salvaged from a round car head lamp). This will get you more optical amplification, without the glass/plastic of a lens to dampen some wavelengths.
(Don't touch the mirror surface of such a reflector, trying to polish it with even the softest cloth will scratch the mirror).

HAPPY BOY:
thanks alot..it was really helpful
one more query regarding your advice
 
--- Quote --- "Even better... Mount the receiver backwards in a parabolic mirror..."                                                   
--- End quote ---


is it similar to the one as shown in the image below in the link? means in my case the ir receivers will be placed instead of lamps/bulbs....

[/img]

http://images01.olx.com.pk/ui/5/54/03/1269444033_82695103_1-Pictures-of--24V-LED-HeadLights-Aux-Lights-for-sale.jpg


and if i want to use multiple ir receivers ,each looking in different angle , shall i use a single lens/ mirror for all of them( as the lamps placed in the above image )  or differernt mirror/lens for each sensor?

thanks

Soeren:
Hi,


--- Quote from: HAPPY BOY on November 16, 2012, 11:35:06 PM ---is it similar to the one as shown in the image below in the link? means in my case the ir receivers will be placed instead of lamps/bulbs....

--- End quote ---

No, read this page:
http://www.edunewz.com/2007/07/testing-parabolic-reflector-with-light.html
It should help you get the idea.



--- Quote from: HAPPY BOY on November 16, 2012, 11:35:06 PM ---and if i want to use multiple ir receivers ,each looking in different angle , shall i use a single lens/ mirror for all of them( as the lamps placed in the above image )  or differernt mirror/lens for each sensor?

--- End quote ---

If you want optimum focus, you need one for each, but read the article, it will be very informative :)

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