Variable power circuit

Discussion in 'The Projects Forum' started by bart_dood, Aug 8, 2010.

  1. bart_dood

    Thread Starter New Member

    Jul 14, 2010
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    Hi folks, I had another post on a circuit with constant current but it turns out I was wrong and what I actually need is to do is to put power through an RTD which causes it to heat up (and thus increase its resistance, nominally 100ohms at zero centigrade which rises to about 125 ohms at 70 centigrade).
    When air blows over the RTD it causes cooling of the RTD and so its temperature (and resistance) lowers, the circuit then increases the current going through it to bring its temp and resistance back up.
    The measurement of how much extra power (current) it takes to keep the temp of the RTD is a measure of the air flow.
    I have done some measurements and it takes about 80-150mW of power to heat the RTD up to 60-70 degrees which seems like a good temp to run it at.
    I have got a circuit here that I think should work but I can't get it to...I really suck at this so any help anyone can give me would be great.
     
  2. beenthere

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  3. bertus

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  4. bart_dood

    Thread Starter New Member

    Jul 14, 2010
    22
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    Yes, I plan on adding offset adjustment based on background temperature. I was just trying to get the basic feedback circuit running correctly first. Thanks for the link.
     
  5. bart_dood

    Thread Starter New Member

    Jul 14, 2010
    22
    0
    Thanks a lot thats very helpful!
     
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