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Author Topic: heat detection of a 1 mm^2 area  (Read 649 times)
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Hi,

I would like to know if anyone has some experience modyfying a general purpose bolometer to measure a very small area.

In my project I would like to measure the temperature of an object which is about 1 mm^2.
I have some 90 deg FOV MLX90614, which right in front of the bolometer window have already a very large sensing area.

I tried using a 1 mm square copper aperture which would limit the area seen by the bolometer. However, the energy going into the bolometer is greatly reduced. I tried to correct this by modifying the emissivity, but that seems not to be the best way.

Do you have any suggestions on how i can reduce the sensing area, but still have a similar accuracy?

BR
pnu  
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Not exactly my area of expertise but it sounds like you need a lens?

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maybe add sweeping with the sensor ? - you will get different readings on which you an apply some math - find max, average etc  -

just thinking out loud..
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Not exactly my area of expertise but it sounds like you need a lens?

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Not my area either, but yeah - I think a lens -is- what is needed, specifically a lens that can pass long-wave IR (heat)...

Note: Such a lens will -not- be cheap. But I think if you are working with a bolometer (which seems to be a fairly straightforward, if unique, form of temperature sensor that most here haven't heard of - indeed, I hadn't either, so I googled it) - you likely (possibly) are in a position (lab?) with some kind of funds to purchase the special lens needed (I'm thinking it will be some form of plano-convex lens, to spread the IR emitted across the larger area of the sensor - but I could be wrong)...

Good luck!

smiley
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I think the lens can be cheap - polythene in fact?  Anyway these people make plastic IR fresnel lenses which might be useful http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productid=2042
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Great to see so many replies.

I indeed thought about using a lens and did some research on it.
Germanium and polyethylene seemed very good materials, block visible and have a high transmission in the infrared, but Ge is very expensive.

For focusing the heat radiation into the bolometer I need 2 plano convex lenses, which would make it rather expensive.
And either way, the amount of radiation I would get from a 1 mm^2 spot would be very small and as far as I see it, it would be the same as placing an 1 mm^2 aperture in front of the bolometer, and putting it very close to the area of interest. Isn´t this true? Also, using lenses I expect that the bolometer would have to be further away from the sensing area, which would make it more prone to temperature fluctuations...

You can check more info about the sensor I have here: http://www.melexis.com/Infrared-Thermometer-Sensors/Infrared-Thermometer-Sensors/MLX90614-615.aspx


br
pnu
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How about lots of small front surfaced mirrors pressed into modelling clay?
Use a visible laser to set the alignment.

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I think my approach would be to attach a thermocouple junction to the 1mm^2 spot.  Is there a reason you can't simply contact it?

If you go buy a cheap IR thermometer, you can likely scavenge the lens and sensor out of that.  An IR in-ear fever thermometer might be a good choice.  Maybe something like this: http://www.walmart.com/ip/Non-Contact-Forehead-Digital-Infrared-Thermometer/14972332

PIR sensors have fresnel PE lenses in them that could be scavenged.
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