1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

    User Avatar
    Science Advisor
    Homework Helper

    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

    current-shuntb_r260_c20.jpg
     
  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

    User Avatar
    Science Advisor
    Homework Helper

    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.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook