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Fire Detecting Thermometer?

  1. Dec 27, 2009 #1
    Is there a way that I could create a fire detecting thermometer that would detect a fire if the temperature went above a certain point? For example, if a thermometer went above 200 degrees C this would signal a fire? How would I create this?
     
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  3. Dec 27, 2009 #2

    cronxeh

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    Hmm..
    1) How long would it take for ambient temperature to affect the thermometer
    2) What area of the room would be under fire after the temperature reached the threshold.
    3) Would smoke reach the detector faster than the ambient heat?

    Given these 3 questions I think the current smoke detector system is a lot better at detecting fires
     
  4. Dec 27, 2009 #3

    Moonbear

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    If I'm not mistaken, sprinkler systems work by detecting heat. When the temperature reaches some threshold when you should assume there's a real fire burning, something in it melts to turn on the water...I think. You wouldn't want to still be in a building when the room temperature is already turning into an oven, so a temperature sensor for an alarm system isn't such a good idea. Just once the fire is enough out of control to be raising the room temperature to a certain level, it's time to dump water on everything.
     
  5. Dec 27, 2009 #4

    S_Happens

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    To see where this goes I'll ignore the two popular styles of smoke detectors.

    Temperature can be measured in multiple ways, so there are quite a few ways to accomplish this. Right now I'm sitting within a few feet of thousands of various temperature alarms. Can you be more specific in what you want to do or what your limitations are as far as materials?
     
  6. Dec 27, 2009 #5
    Let me explain more, I'm trying to detect a fire on a stove. I think maybe if I use an infrared thermometer it would be better.
     
  7. Dec 27, 2009 #6

    cronxeh

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    Depending on air flow and room volume, the ambient temperature in fire will be drastically different, so using a thermometer may not be the best idea. IR camera could be useful if you create exclusion zones (for stove outlets) to be ignored, and program an alarm for all other areas which will trigger fire suppression system

    This looks promising (but probably expensive)


    The cheapest option I can think of which will involve great deal of ingenuity is using near infrared pass filters (650nm-1050nm) on cheap CMOS pinhole cameras (1.3 megapixels and up). Could cost about $200 dollars if you get DAQ + CMOS + NIR pass filter on ebay
     
    Last edited: Aug 21, 2010
  8. Dec 27, 2009 #7

    cronxeh

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    Just hook up DAQ to Matlab, play with image acquisition and histograms, set up the detection zones you interested in and program outputs for same DAQ to activate.. a fire extinguisher? Play around with it.

    In case you wondering what those NIR pictures may look like..
     
    Last edited: Aug 21, 2010
  9. Dec 27, 2009 #8
    cronxeh, I believe that the temperature of a fire (not even a very hot one) is still dramatically hotter than room temperature. As long as we know the minimum temperature that a fire might start at, we can use an thermometer. Lets just say that the minimum temperature of a fire is 100 C (throwing numbers around). This is obviously, hotter than room temperature so anything hotter than 100 C will trigger an alarm.
     
  10. Dec 27, 2009 #9

    cronxeh

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    By the time the ambient room temperature (which is affected by air flow, distance from thermometer to fire - which you really can't predict where the fire will start at so your placement is randomly placed from fire source) - the fire will be in full blaze, it could take 5 minutes for the fire to raise the thermometer temperature to 100 deg C.

    Look up pictures of toys in fire room, some plastic toys are not even melted (and plastic melts at 350 deg C)
     
  11. Dec 27, 2009 #10

    FredGarvin

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  12. Dec 27, 2009 #11
    Most University halls have fire detectors using heat rather than smoke in the kitchens.

    Stops the problems of the firebrigade coming to put out some burnt toast that a drunk student has tried to cook after a night out.

    IIRC it worked on a thermostat (really not sure what type), that was triggered in the high 60 degrees c ambient.
     
  13. Dec 27, 2009 #12

    ideasrule

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    It should be feasible to make an IR camera watch a stove, calculate the number of pixels hotter than a certain temperature, and trigger an alarm if that number is greater than a certain limit. The stove element is guaranteed to be colder than any fire that might be of concern.
     
  14. Dec 27, 2009 #13
    You've piqued my curiosity. In some sprinkler heads there's is a low melting point solder joint between two mechanical elements. When it melts, it lets a cap pop off the end of the sprayer. http://books.google.com/books?id=64...esnum=1&ved=0CBEQ6AEwAA#v=onepage&q=&f=false" (Some Indium-Gallium-Tin Alloys are even liquid at around room temerature.)
     
    Last edited by a moderator: Apr 24, 2017
  15. Dec 27, 2009 #14

    mgb_phys

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    I worked on a system once that detected fire from existing CCTV cameras by looking at the changing light levels. Flames have a very characteristic flicker frequency,
    The idea was to detect fires in large warehouse/factories before the smoke/heat built up enough to trigger a smoke detector or sprinkler.

    ps. Sprinklers detect heat directly, they have a low melting point plug. By the time they trigger it's pretty much too late - they are just there to try and save the structure, and give time to people in other parts of the building.
     
  16. Dec 27, 2009 #15
    If it helps, i want to measure the heat in one certain place. If that place gets to hot how can I sound an alarm? This assuming were using an infrared thermometer.
     
  17. Dec 27, 2009 #16
    If you just want to measure heat in one small area any thermostat will work in a low temperature range, say up to 95 degrees f.

    There are a number of off the shelf thermostats available in the heating and cooling industry.

    Most forced air furnaces have a thermostatic switch built in to start the fan motor at about 120 degrees f. Many of them are even adjustable. On the other hand they are not highly accurate beyond + or - five degrees or so.

    As far as sounding an alarm use a door bell or furnace transformer and a bell wired through the thermostat.
     
    Last edited: Dec 27, 2009
  18. Dec 28, 2009 #17

    cronxeh

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    I think another way would be to use symbolic logic and a few temperature sensors. If you spread the sensors apart at a certain distance and surround the stove area, you can create a simple algorithm for when the alarm should be triggered, given that probability that over 50% of the sensors would never show a temperature increase of +2 standard deviations (you can trigger the parameters to whatever may suit your experimental setup) unless it was a fire
     
  19. Dec 28, 2009 #18
    That's a lot easier. A sensor diode can be placed remotely. Photodiode sensors detect photon radiation, as you known, right?
     
  20. Dec 28, 2009 #19
    No! That's what I thought. We must have heard the same wife's tale. (Did you catch it from me? :frown: ) See post 13.
     
  21. Dec 28, 2009 #20

    f95toli

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    Indeed. And there are fire detection systems (the kind that that trigger alarms) that work by detecting heat. Where I work they are used in most of the labs where we handle cryogenic liquid since we tend to generate a lot of "smoke" (vapour from the dewars) when transferring liquid helium. We know from experience that the vapour will trigger conventional smoke detection based fire alarms so heat-detection based systems are really the only sensible option.
    However, Heat detection systems are -as far as I understand less reliable- and react much more slowy than smoke detection systems which probably explains why they are not very common in normal rooms.
     
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