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Experimental physics i am very frustrated -- convert galvanometer into an ammeter

  1. Jan 7, 2015 #1
    I am trying to convert galvanometer in to an ammeter. But after finding Galvanometer resistance and shunt values, and cut a wire according to that thickness and connected. But still, the galavanometer reading is not similar to that of the standard ammeter reading connected in the circuit. Any one can help me please? In detail.
     
  2. jcsd
  3. Jan 7, 2015 #2

    Bystander

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    And, what is that resistance?
    What wire? What resistance?
    What current are you trying to measure?
     
  4. Jan 7, 2015 #3
    I've found that placing a variable resistance on the order of 1/4 - 1/2 the coil resistance is useful as you can never quite get the shunt wire correct and the resistor will allow you an added adjustment.
    Don't obsess over exact calculations as neither the meter resistance nor shunt will be exact.
    Also, don't attach the meter at the far ends of the shunt because the resistance of the connections will contribute error. Rather, attach the meter to the shunt a little ways in from one connection. Then, move the other meter lead along the length to get the correct reading while a test current flows.
    - Reference Kelvin Connection.

    Hope this helps a bit.

    - Mike
     
  5. Jan 8, 2015 #4
    Mike bro thanks a lot. Its great. Got some new tips. I will try. Thanks again.
     
  6. Jan 10, 2015 #5

    jim hardy

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    Mike pointed out the most common beginner's mistake.
    Think about it - you're using the galvanometer as a voltmeter to read the milivolts across your shunt, which is probably only milli-ohms.
    Here's a picture from a Kelvin link as Mike suggested
    00480.png
    http://www.allaboutcircuits.com/vol_1/chpt_8/9.html
    You need the millivolts across the shunt itself,
    NOT the millivolts across the shunt PLUS millivolts across the connectors.
    I used to cut my shunt wire a little long so there's room for the current connections outside my meter connections.

    old jim
     
  7. Jan 13, 2015 #6
    Thanks a lot
     
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