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Wind chill

Discussion in 'Electronic Design' started by Howard Eisenhauer, Jan 29, 2005.

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  1. Anybody know of a circuit to measure wind chill? I'm guessing the
    best/simplest/cheapest way would be to measure how much current it
    takes to keep a resister at certain temperature while exposed to Ma
    Nature's little tantrums but I really don't feel like getting into a
    theoritical design/prototype/troubleshoot/revise/build/yadda yadda
    yadda project on this. Something I could get built & calibrated
    before next summer would be nice- by next week would be fantastic :).

    Thanks,

    Howard.
     
  2. Leon Heller

    Leon Heller Guest

    A temperature sensor and anemometer connected to a suitable MCU should do
    what you want. You could use a lookup table based on this:

    http://www.nws.noaa.gov/om/windchill/index.shtml

    Leon
     
  3. IMO, machines don not feel windchill. It appears to be
    connected to evaporating moisture from a surface.
    As close a machine could come would be measuring
    temperature, wind and moisture content of the air.

    Rene
     
  4. Fred Bloggs

    Fred Bloggs Guest


    Wind chill cannot be measured directly, the assumptions of core body
    temperature and heat diffusion through facial tissue are statistical and
    it would make no sense to simulate this with analog electronics when it
    can be computed, also, it appears that the extrapolation of wind speed
    measurement at a standard height of 10m to a 1.5m average by
    multiplication by ~2/3 assumes an orographical surface roughness factor
    of ~0.1m, which again is another statistical artifice. The purpose of
    wind chill estimation is to obtain a probabilistic risk assessment of
    frostbite and is therefore not really a physical measurement in the
    ordinary sense. Why don't you just buy a weather station and use a chart
    or something.
     
  5. Gareth

    Gareth Guest

    Yes, but a heated resistor will loose heat faster in moving air compared
    to still air. In fact it is quite common to measure wind speed by
    measuring the rate of heat loss from a heated coil or thermistor
    (hotwire anemometer).

    It seems reasonable, to me, that measuring the heat loss from a heated
    resistor could enable you to calculate windchill in the way the OP
    suggested.
    Temperature and wind speed yes, but surprisingly, humidity has very
    little effect on windchill. See:

    http://www.nws.noaa.gov/om/windchill/windchillglossary.shtml#13

    Gareth.

    --
     
  6. Mac

    Mac Guest

    Wind chill is very close to being a bogus idea. To the extent that it is
    meaningful, it is meant to assess how much faster a person will cool down
    in a moving stream of air than in a still stream of air of the same
    temperature. So it is mostly about heat transfer under convection
    conditions.

    I think you are right that what the OP should do is focus on measuring
    air speed and temperature, and possibly humidity. The wind chill could
    then be looked up or calculated or whatever. I don't know exactly how they
    calculate it.

    --Mac
     
  7. Fred Bloggs

    Fred Bloggs Guest

    If you don't know anything about it, then why are you posting an opinion
    about what the OP should do?
     
  8. Guest

    Because this is Usenet.
     
  9. Fred Bloggs

    Fred Bloggs Guest

    HAAHAH
     
  10. Mike Diack

    Mike Diack Guest

    Twc=33 + (T-33)(.474+.454sqrt(S)-0.0445 S) {siple (1945) }
    T=ambient temp Celsius
    S=Windspeed m/s
    Holler if you need a version of this rendered down to 8051 assembler (needs
    a 16 bit math package)
    M
     
  11. Mac

    Mac Guest

    There is a difference between "not knowing anything about" wind chill
    (your words) and not knowing "exactly how to calculate it," my words.

    You sure are a surly one. ;-)

    --Mac
     
  12. Guy Macon

    Guy Macon Guest

    And it has to be a naked person. It was developed by the military
    to act as a baseline for cold-weather gear. Anyone wearing clothes
    will find that a 10 degree wind chill is much warmer than a real
    10 degrees.

    So why is it so popular? It makes the weather report on your local
    TV station more exciting. A REAL correction factor that tells you
    how cold it will seem while you are wearing a good coat would be
    far more useful, but instead they give the bogus numbers.

    Trivia: Inb the military tests, females complained about the cold
    sooner but could tolerate a colder environment without having it
    disable them.

    (This spot reserved for Rich Grise so he can insert a joke about
    frigid naked females...) :eek:
     
  13. Jim Thompson

    Jim Thompson Guest

    You misspelled "Shirley" ;-)

    ...Jim Thompson
     
  14. James Meyer

    James Meyer Guest

    That's been my take on wind chill from the beginning.

    Jim
     
  15. Fred Bloggs

    Fred Bloggs Guest

    In your case a much more literal measurement of WCT is required: paste a
    temperature indicating strip to your forehead and stand outside for an hour.
     
  16. Jim Thompson

    Jim Thompson Guest

    Eh? Never been in Detroit this time of year have you ?:)

    ...Jim Thompson
     
  17. The US and Canada switched to a new formula for calculating wind chill
    in the fall of 2001. The difference between dry bulb temperature and
    wind chill temperature is not as great with the new formula.



    Best regards,
    Spehro Pefhany
     
  18. I took the dog for a walk at night a week or two ago- the wind was
    ~20-30mph and temperature -22°C (-8°F). Taking a glove off to use my
    Maglite and bag the leavings, I wasn't across an open field diagonally
    before all the feeling was out of my little finger in that hand. Wind
    chill is real enough!

    A few miles in that sort of environment without proper clothing and
    you could be dead. It's not nearly as bad without the wind.

    A comfortable -1°C (30°F) and sunny today.


    Best regards,
    Spehro Pefhany
     
  19. Jim Thompson

    Jim Thompson Guest

    I always seem to have business back east at the worst-weather times of
    the year... Pittsburgh on Wednesday :-(

    It's cold here today... a cold front with rain came thru yesterday
    afternoon... it's only +60°F, +15.5°C, here ;-)

    ...Jim Thompson
     
  20. I read in sci.electronics.design that Spehro Pefhany <[email protected]
    Just hold the bag. Your canine friend provides you with a lovely squishy
    hand-warmer. (;-)
     
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