testing student understanding of DMM

Discussion in 'The Projects Forum' started by savini, May 20, 2015.

  1. savini

    Thread Starter New Member

    May 20, 2015
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    I am working on a project in the southwest USA that is teaching students in upper elementary school
    to generate hydrogen fuel. One part of the instruction is making measurements of current, voltage, and resistance using a digital multimeter (DMM). I am looking for tests of knowledge of and skill in
    such measurement.
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
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    one real test is to check the fuse in the dmm, if it is blown, they dont know how to measure voltage or current. voltage across the line, current in series. fuse blown most by trying to measure current across the line.
     
  3. savini

    Thread Starter New Member

    May 20, 2015
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    0
    Very good. Had not thought of that.
    However my main interest at this stage of their learning is their interpretation of readings.
    Thanks much
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
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    fortunatly, dmm readings are much easier than the old vom and vtvm's. trying to see where the needle is pointing on a bunch of scales was a problem. the rest is what dmm you have, auto ranging or manual.
     
    savini likes this.
  5. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    One of the critical things in using a DMM is knowing how to properly connect the DMM to measure voltage, resistance and current. Connecting it up incorrectly can result in damage to the DMM and/or the circuit being measured.

    Voltage is measured in parallel with the circuit under test.

    Current is measured in series (never, ever in parallel) with the circuit. This is probably the most common mistake for newbies.

    Resistance must always be measured with the circuit unpowered.

    It all cases you must make sure that the correct meter terminals are used for the specific measurement. Having the meter connected for current when you are attempting to measure voltage will often result in letting out the magic smoke.
     
    savini likes this.
  6. dl324

    Distinguished Member

    Mar 30, 2015
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    One mistake most novices make is not considering the affect the meter has on the circuit. With digital meters, current measurements are the primary consideration. Old timers had to consider this for all measurements because analog meters were far from ideal; but they also had advantages over their digital counterparts.
     
    savini likes this.
  7. WBahn

    Moderator

    Mar 31, 2012
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    In addition to only making resistance measurements with the circuit unpowered, you generally can't make meaningful resistance measurements on a part while that part is still in the circuit. It CAN be done, but only if you take into account the entire circuit that exists between the two points where you are placing the probe tips. Many, many people seem to think that they can put the probes across a resistor that is in a circuit and expect the reading to be the resistance of that resistor.

    But getting back to your basic problem -- do these kids (I'm guessing 4th and 5th grade?) understand enough about voltage and current and resistance to even begin to understand what they are measuring, let alone what a specific measurement result means?

    How are you generating and capturing this hydrogen fuel? What are you then doing with it?
     
    ebeowulf17 likes this.
  8. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    ebeowulf17 and Sinus23 like this.
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