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Thread: High-quality black-and-white photographs of large old machines and tools

  1. #221
    Supporting Member mklotz's Avatar
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    Quote Originally Posted by Toolmaker51 View Post
    What great site! I have a decent [?] meter but I suspect not in keeping with Marv's description.

    The problem with measuring very small resistances is that the resistance of connections becomes so important relative to the resistance one is attempting to measure.

    Put your ohmmeter on its lowest scale and, with fingers off the exposed metal on the probes, press the metal tips together. Now, by adjusting the pressure with which you press the tips together, you should be able to change the indicated resistance by a large relative amount.

    Keep this in mind when you make your resistance measurements.
    ---
    Regards, Marv


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  3. #222
    Supporting Member Toolmaker51's Avatar
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    I did that with my fingers.
    Are resulting figures weight, blood pressure or a grip test?
    Sure doesn't appear to be IQ!
    Sincerely,
    Toolmaker51
    ...we'll learn more by wandering than searching...

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    Supporting Member hemmjo's Avatar
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    when doing tests like this, where the connection is so important, it is good to use alligator clips. to assure a good connection. I have a short pair of red and black cords with a clip on each end. The teeth cut through any surface corrosion on the wire so you get good consistent readings.

  5. #224
    Supporting Member mklotz's Avatar
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    Don't forget that there is another set of connections where the meter test leads connect to the meter itself. These are generally banana plugs so wiping occurs with every insertion.

    I'm trying to remember the Wheatstone bridge we used in physics lab at college. I seem to remember screw-down connectors for attaching the unknown but it's been a long time.
    ---
    Regards, Marv


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    Supporting Member mklotz's Avatar
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    Rather than the error-filled minefield of resistance measurements, why not do it with weight? Weigh a small piece, weigh the coil and the math is the same as I indicated above.

    Accurate scales are available and, if all fails, you can use a balance scale with measured quantities of water as the balance weights.
    ---
    Regards, Marv


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  8. #226
    Supporting Member jimfols's Avatar
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    Quote Originally Posted by mklotz View Post
    Rather than the error-filled minefield of resistance measurements, why not do it with weight? Weigh a small piece, weigh the coil and the math is the same as I indicated above.

    Accurate scales are available and, if all fails, you can use a balance scale with measured quantities of water as the balance weights.
    The measured quantities of water is what made me fall in love with the metric system.
    Jim

  9. #227
    Supporting Member mklotz's Avatar
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    Quote Originally Posted by jimfols View Post
    The measured quantities of water is what made me fall in love with the metric system.
    Indeed, only an idiocy like the inferial system would have a unit called fluid-OUNCE (caps mine) that is a measure of volume, not weight.
    ---
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  11. #228
    Supporting Member Ralphxyz's Avatar
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    I have lost track of what is trying to be accomplished here?

    Ralph

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    Supporting Member Big Sexy's Avatar
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    Which I prefer my first suggested method of counting loops and multiply by the diameter of the loops. Then you can do a ohm test to confirm a length is good to go without breaks.

  13. #230
    Supporting Member mklotz's Avatar
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    Quote Originally Posted by Big Sexy View Post
    Which I prefer my first suggested method of counting loops and multiply by the diameter of the loops. Then you can do a ohm test to confirm a length is good to go without breaks.
    And then multiply the result by pi because the length of a loop is the circumference, not the diameter.
    ---
    Regards, Marv


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