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Impedance Measurement

Discussion in 'Electronic Basics' started by Pete M, Mar 30, 2007.

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  1. Pete M

    Pete M Guest

    I would like to measure the resistance (impedance) of a soldering iron tip
    to ground with power on - When I use a standard ohm meter I am getting
    fictitous readings.

    With no power I get a 1 ohm (typcical)dc resistance. When I power I get
    readings all over the place. Any suggestions on a circuit?

    Thanks
     
  2. Phil Allison

    Phil Allison Guest

    "Pete M"

    ** Just use an analogue multimeter on ohms X1 range - you know the funny
    old ones with skinny needles on them.




    ........ Phil
     

  3. The tip and sleeve need cleaned. They expand from the heat and don't
    make good contact. A soft brass brush and a tiny spot of "Anti seize"
    compound will correct the problem, but if you need a grounded tip for
    ESD sensitive work, the iron needs to be cleaned daily. (Or every few
    hours of use). Our limit was 3 ohms from the tip to the metal box the
    iron was plugged into, whenever any soldering iron was hot.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  4. Chris

    Chris Guest

    Hi, Pete. You might be seeing the effects of leakage current on your
    ohmmeter when the power is on. You should try measuring with power
    off.

    Using a cheapie DMM to measure low ohms can be kind of chancy. If the
    measurement is critical, and you don't have a Kelvin (4-terminal)
    ohmmeter, use a 10V supply with a series 10 ohm, 10 watt resistor as a
    voltage/current source, and then measure the actual voltage you get
    from tip to GND when you apply current. You can then infer resistance
    using Ohms law. That will be accurate to within the tolerance of the
    resistor.

    Good luck
    Chris
     

  5. If there is enough leakage current to affect the reading, the iron is
    defective.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  6. jasen

    jasen Guest

    try it with an moving-coil meter.

    Bye.
    Jasen
     

  7. Why would that make any valid difference? In fact, it would make it
    harder to get a valid reading.

    I used a Data Precision digital meter on my bench for four years. If
    any of the hot soldering irons hadn't been used in 15 minutes or more,
    the hot tip was touched to a scrap of copper clad PC board, with a drop
    of solder. If they read under three ohms, I used it. if not, I cleaned
    it and retested. I also tested and calibrated every soldering iron in
    the company a couple times, after one of the MEs died of a Brain
    Aneurysm.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
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