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How can i use ADC to measure Current?

  1. Dec 3, 2008 #1
    I need please ideas how to use DAC to measure current.Currently I have built DAC to measure voltage, the type i built is the STAIRSTEP RAMP the 8 bit one.
     
  2. jcsd
  3. Dec 3, 2008 #2

    mgb_phys

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    An ADC measures an analogue voltage a DAC generates one.
    Since it measures voltage you have to convert the current into a voltage.
    The normal way to do this, eg in a digital multimeter - is to connect a small resistor in series and measure the voltage across the resistor, then use ohm's law to calculate the current. With AC it's a little more complicated - you will have to measure the voltage at many points in the AC cycle and calculate the RMS.


    What sort of current / voltage are you looking at?
    If you are doing this with very high currents (eg car battery) or high voltages (eg household wiring) you probably want to learn a little more before you try.
     
  4. Dec 3, 2008 #3
    These are known as current shunts and are used everywhere in industry. You can buy them for less than $50 from a lot of industrial suppliers and they usually come pre-calibrated. Most shunts available are 50/50 shunts which basically means 50 amps = 50 millivolts so all you have to do is just shift your decimal point.

    http://www.rc-electronics-usa.com/current-shunt.html

    [​IMG]
     
  5. Dec 3, 2008 #4
    DC current i need to measure.I have a problem because it reads a resolution of 5V/256 0.02Volts the voltage is too large i think.Beause the voltage generated by the shunt is too small i think.
     
  6. Dec 3, 2008 #5

    mgb_phys

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    For a real world application you will need an amplifier before the ADC.
    In order to get a larger voltage, you would need a larger shunt resistance which will waste energy and reduce the voltage in the circuit.

    For somethign like a simple science fair experiment or just to roughly monitor a voltage in a low current application you could use a large eg 1 Ohm resistor.
     
  7. Dec 3, 2008 #6
    Thanks an amplifier like a non inverting one fits well in my circuit.
     
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