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pot issues!!

Discussion in 'Electronic Basics' started by Kristen, Jun 15, 2005.

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  1. Kristen

    Kristen Guest

    -------------------------------------

    I have just replaced a pot that was replaced by one of my operators
    because I thought that he had connected it up badly but it seems we have
    greater issues.

    The pot controls the speed at which a cnc mahine runs. It originaly was 0%
    - left, 50 - %center and 100% full right. Now at about one twentieth of
    the way round it is already at 100%.

    Could it be that the cnc tech told me to get a pot with wrong amount of
    resistance?

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  2. Could be, but more likely, you replaced a linear pot with an audio
    (log taper) version. They have most of the resistance change
    concentrated at one end.
    http://sound.westhost.com/pots.htm#taper
     
  3. John Smith

    John Smith Guest

    .... maybe you need a "medicinal pot!" <grin>

    John
     
  4. Chris

    Chris Guest

    Good morning, Kristen. You're right -- it might be possible the tech
    told you the wrong part number. As another post mentioned, it could
    also be that you've got a log taper. And pots have been known to be
    mislabelled - checking with an ohmmeter is a good idea.

    A couple of other things:

    * If there are three wires going to the pot, it's possible the wiper
    wire and one of the leg wires were accidentally exchanged.

    * A defect in manufacturing may result in intermittent contact between
    the wiper and the resistive element in the pot. It's a good idea just
    to take out the pot and check for this. You can also look at the log
    taper issue, as well as that it has the right value, and is not
    mislabelled.

    * Be sure to recheck the relevant connections and solder joints --
    you're in an environment with some significant vibration, and something
    may have worked its way loose.

    Good luck
    Chris
     
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