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Multimeter (VOM) Design in Electronics Engineering

  1. Mar 8, 2013 #1
    1. The problem statement, all variables and given/known data
    The statement is this one... (from the horowitz "The Art of Elctronics")
    http://www.electroyou.it/forum/download/file.php?id=13691


    2. Relevant equations
    How should I proceed, i really didn't understand how this VOM works, i mean, i understood, that there a max scale value of a VOM which in this case is 1V, so when i attach a resistor, a voltage divider is created, and i'm going to read the value of voltage on the internal resistance of my voltmeter, is this right ? And how is the second point of the exercise solved?
    Can you explain me how this works? and what does it mean a VOM 50μA 20kΩ/1V ??


    3. The attempt at a solution
    I think it's right for the first point to proceed like this :

    Vout=Vin*(Rint/Rint+Rload)

    but for the second point i have no idea...
     
  2. jcsd
  3. Mar 8, 2013 #2

    berkeman

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    Staff: Mentor

    Your link is not working for me, and the website has some pretty dubious advertisements. Can you upload an image of the problem? Or sketch it yourself and upload it?

     
  4. Mar 8, 2013 #3
  5. Mar 8, 2013 #4

    berkeman

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    Staff: Mentor

    Your second link is worse than the first. Can you just upload the image as an attachment please? The advertisements in those pages are quite risque.
     
  6. Mar 8, 2013 #5
    here you are !
     

    Attached Files:

  7. Mar 8, 2013 #6

    berkeman

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    Staff: Mentor

    Thank you. It looks like they are defining the VOM configuration as a 50uA output test current that is monitored by an infinite input impedance voltmeter. So that's why an external 20kOhm resistance will produce a test voltage of 1V.

    So I would approach these questions as having a 50uA current source (from some higher voltage) driving the loads that they mention. So for the first question, draw the circuit as a 50uA current source driving down into a 10k resistor and a 1V power supply. What voltage would you then see at the junction of the current source output terminal and the input of the 10k resistor?

    And for the second question, the 50uA current source drives the mid-point of the voltage divider. What voltage would be measured between the low-side output of the current source and ground?

    (TBH, I'm not sure I'm understanding this question because of the terminology issue. I'll ask for help from other HH'ers to check this.)
     
  8. Mar 10, 2013 #7
    anyway i still didn't understand how a VOM works, can you put me a very simple and basic schematic telling me how does it works ?
     
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