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Traveling microscope vs vernier calliper

  1. May 10, 2016 #1
    Hi, there is a question I am not sure about. We are trying to measure the width(thickness) of water as it is streaming from the tap and draining into the sink, my question is why use of vernier calliper is inappropriate and travelling microscope is suitable for this measurement? Thanks
     
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  3. May 10, 2016 #2

    Nidum

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    It is difficult to get an accurate measurement of something as erratic as a water stream using a hand held measuring device . Judging the actual points of contact between gauge faces and water stream is very subjective and the measuring device would have to be continually moved to new positions as the water stream wandered around .

    A travelling microscope can be set up in a fixed position which is much better . Long observations can now be used to establish the mean position of the left side of the water stream and similarly the right side and thus get a reasonably accurate average stream width . Other averaging methods are also possible .

    In practical terms neither vernier nor microscope perform very well in water unless they have special protection built in . Use an IP64 or better Vernier and arrange some splash guarding for the microscope - plastic bags will do .
     
  4. May 10, 2016 #3

    BvU

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    Ideally, a measurement does not influence the 'thing' to be measured. But: experiment !
     
  5. May 10, 2016 #4

    berkeman

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    Maybe parallax is too much of a problem with the calipers, since you have to move your head back and forth to try to take the reading. You don't have a way to be sure that your eye is looking at a right angle to the stream, but with the traveling microscope, you are assured of no parallax issues.

    http://suryaengineering.com/image/travelling%20microscope.jpg [Broken]
    http://suryaengineering.com/image/travelling%20microscope.jpg [Broken]

    EDIT -- Too slow again!
     
    Last edited by a moderator: May 7, 2017
  6. May 10, 2016 #5

    berkeman

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    I'm guessing that the scale goes behind the stream, and the microscope goes in front of it. As long as the arm supporting the microscope is offset enough, nothing seems like it should get wet...
     
  7. May 10, 2016 #6
    Why wouldn't you simply measure the diameter of the tap, the diameter of the drain, and the distance from drain edge to water stream (assuming the tap pours directly into the drain)? Is there some sort of dispering screen or object causing a change in the stream?

    Another idea is to get a laser level with a rotating beam, place it on one side of the stream of water with a scale on the other side, and use a camera to record the distortion of the beam as shown on the scale. "Rinse and repeat" at multiple heights above the drain.
     
  8. May 11, 2016 #7

    Andy Resnick

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    People measure the properties of fluid jets all the time: take a photo and use whatever you like to measure the width at various locations. Why make the measurement as complicated as possible?
     
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