How do IR thermometer guns work?

April 1, 2011 10:22 PM

My goal is the detection of small temperature variations over a larger area than a single one would allow, monitored by a computer. What sensor do they use? I saw IR thermocouples on the web (starting at $150) and the fact these consumer devices are often under $30 leads to believe they are not using this, but something a lot cheaper.

I want to set up an array of these and avoid the expense of a Peltier cooled IR camera, etc. (I want a fairly large array of these, painstaking calibration is a given)

I don't care about the laser part, the plastic part that you hold, the digital part or the analog to digital conversion! What is the analog sensor that these things use?

Lastly what alternatives should I look into?

posted by santogold to science & nature (11 answers total)

I don't know anything about the technical aspect of this subject.

BUT your question did bring up the ghost shows on the sci-fy channel. The equipment they use to monitor "ghost presence" seems like the temperature variation detectors you seem to be looking for. I'll try to find some more info.
posted by hal_c_on at 10:33 PM on April 1, 2011

I actually saw some references to shows on "pay t.v." and laughed out loud while I goggled the topic.

If you do watch those shows, spend some time with google to read the sites that debunk them.

I guarantee you the shopping channel is 100 times more informative than these shows.
posted by santogold at 10:44 PM on April 1, 2011

Google "pyroelectric sensor"
posted by Pinback at 10:46 PM on April 1, 2011

santogold...no no...I don't watch the shows to "learn". its entertainment. you know those hungover weekend mornings when you're trying to decide between a tom green movie on comedy central or ghosthunter marathon...yeah. thats when i watch.

I recently turned to a tv show called "interview with a serial killer", only to find they do ghosthunter type stuff.

The funny thing is, you may end up buying from there.

Check out "ghost-mart.com". It seems they have a kinda large selection of what you want!
posted by hal_c_on at 10:58 PM on April 1, 2011

Specifically, you want a single element sensor, not a 2 (or more) element PIR motion detector sensor - although some of the 2-element ones can be used if they're side-by-side elements (not interleaved) by masking off one side.

Be aware, however, they're fairly insensitive in general and require high-gain amplification to produce useful output, which makes the whole thing susceptible to instability and noise unless your electrical design is spot-on & well-shielded. A NIR camera + video processing may be simpler for large areas, or even an array of contact temp sensors (e.g. LM335 or similar).
posted by Pinback at 11:03 PM on April 1, 2011

Have you considered a thermal imaging camera? They are expensive, but they do what you are looking to do out of the box. And they are pre-calibrated. And you can rent one from many equipment rental houses. I've seen them perform. (Fire departments usually have one, and they can show you the studs behind a sheet rock wall at room temperature, based on the temp variations present on a wall. Also, they can show hot spots on a circuit board or energy leaks out of your dwelling. Very cool.)

By the time you design, build, calibrate and debug a large number of IR sensors, you'd be in the same cost ball park. Doesn't sound to me like you have quite the experience to pull it off at this stage, considering the type of questions you pose. Your goal may be easier to realize if you stick to finding the money rather than painstakingly acquiring the expertise for a DIY of this magnitude.

I'm not trying to discourage or insult you, but a lot of technical problems boil down to economics, not engineering.
posted by FauxScot at 11:26 PM on April 1, 2011

Here's one.
posted by FauxScot at 11:28 PM on April 1, 2011

Sounds like you are looking for this?

MLX90614 IR thermometer
posted by wongcorgi at 11:34 PM on April 1, 2011

I think the search terms you want are pyroelectric sensors or microbolometer arrays.

If you don't need high speed

or slightly farther on the cost-performance curve
posted by hattifattener at 11:43 PM on April 1, 2011

Will this do? Cheap Thermoscanner Based on Arduino.
posted by scruss at 6:10 AM on April 2, 2011

Are thermocouples out of the picture? What about temperature loggers?
posted by Dmenet at 2:26 PM on April 2, 2011