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Markings on analog moving coil meters...

Discussion in 'General Electronics Discussion' started by Externet, Jan 17, 2019.

  1. Externet

    Externet

    711
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    Aug 24, 2009
    Hi.
    V. A, VU meters usually have markings on the bottom of the scale. I suppose tell full scale current, internal resistance... Were to look for the meaning ? Is there a standard for markings ?
    Several types:
    [​IMG]
    [​IMG]
    [​IMG]

    [​IMG]
     
  2. Bluejets

    Bluejets

    3,452
    698
    Oct 5, 2014
    Ohms per volt is the meter impedance as seen by the test circuitry.
    Other markings usually scale size and probably model numbers or manufacturer details.
     
  3. Harald Kapp

    Harald Kapp Moderator Moderator

    9,210
    1,856
    Nov 17, 2011
    Also:
    instrument class, e.g. KL. 2.5 meaning accuracy is 2.5 % of scale
    Orientation of use, type of measurement etc. I found this page in German. Here's a table from the page with my translation:
    upload_2019-1-20_13-3-6.png
     
    davenn, (*steve*) and Externet like this.
  4. Externet

    Externet

    711
    145
    Aug 24, 2009
    That's it ! Thanks.
     
  5. Colin Mitchell

    Colin Mitchell

    1,419
    314
    Aug 31, 2014
    A meter that consists of a coil and pointer is called a MOVEMENT. And it has a certain sensitivity. Generally the sensitivity is 30uA or 10uA.
    For a movement with a sensitivity of 30uA, it will take 30 microamps to defect the pointer full scale.
    At this stage you cannot use the term OHMS PER VOLT. It is simply a MOVEMENT.
    If you add a resistor in series with the coil, the movement will be turned into a VOLTMETER.
    If a resistor is placed across the coil, it will be turned into an AMMETER.
    When you create a VOLTMETER with a 30uA movement, and say you want a full scale reading of 10 volts, you want the 10 volts to create a current through the coil and series resistor of 30 microamps. At the moment we will neglect the resistance of the coil.
    To get a current-flow of 30 microamps, we need a resistor of:
    Now, without any calculator, we look at it this way: If the resistor is 10 ohms, the current will be 1 amp. If the resistor is 10k, the current will be 1mA. But we want one-third of a milliamp and so the resistor needs to be 30k.
    A VU meter is generally connected to an amplifier circuit and the designer of the circuit will choose a movement or even a voltmeter or milliamp meter and connect it to the circuit and add resistors in either series or parallel until he gets the desired reading.
    That's why a VU meter does not have a standard value. It's a movement that's adapted to the circuitry.
     
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