Hot wire anemometer calibration

Discussion in 'General Electronics Chat' started by laura_c, Apr 11, 2013.

  1. laura_c

    Thread Starter New Member

    Apr 11, 2013
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    Hi guys, I am calibrating my hot wire anemometer in the wind tunnel, through the use of an amplifier. Now, as I am calibrating, the voltage is set to a maximum of 9V since if exceeds 10V, it damages the card data reader. My question is that: for hot wires, when the velocity increases, the voltage should too. but the reading I got were of a decreasing voltage as the speed of the wind tunnel was increased.

    does anyone has an explanation for that? thanks :)
     
  2. #12

    Expert

    Nov 30, 2010
    16,298
    6,809
    You connected something backwards. Post a schematic.
     
  3. joeyd999

    AAC Fanatic!

    Jun 6, 2011
    2,684
    2,747
    If the hot-wire operates at constant temperature, then the voltage across the wire will increase at higher air velocities. This is because more power is required to maintain the wire's temperature as heat is drawn away from it.

    If it is operated at constant current the voltage will decrease at higher airflows as the wire resistance decreases as the temperature drops.
     
  4. laura_c

    Thread Starter New Member

    Apr 11, 2013
    2
    0
    I do not possess a schematic of the connections... but basically, when I used negative voltages, (with the same connections), as the velocity increased, the voltage decreased negatively...and converting the -ve voltage to positive values on the voltage - velocity graph, the graph followed King's law...

    while this did not occur when I used a positive voltage...
     
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