Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Current sensor

  1. Apr 28, 2016 #1
    I am desgning a circuit(network), where i need to show the path traversed by the greater part of the current at each node, consecutively. using an ammeter (or voltmeter) in every branch (around 20) makes it too tedious. Will LEDs do the required work? But they would light up at all locations, though their intensity might be different, will it be detectable to the eye? what should be the typical values of current (differences) for it to get detectable?
    is the any better (cheap) method?

  2. jcsd
  3. Apr 28, 2016 #2


    Staff: Mentor

    I need a picture to understand what you want to do.

    You can use the upload button.
  4. Apr 28, 2016 #3
    So you don't need to measure the current? You just have to detect it's presence? How about a small sense resistor at each node with an op amp? As in a simple comparator configuration. It will detect the direction of current flow as well.
  5. Apr 28, 2016 #4
    The output of the op amp will be positive for a current in one direction and negative for current in the opposite direction. The op amp will latch for very small currents, however.
  6. Apr 28, 2016 #5
    Thank you for the suggestion,
    But i need to "show" the path. some sort of a detectable illumination (or even numerical values would do, provided the path is shown instantaneously, not manually moving with meters) like, any person seeing the circuit should know where all the larger portion of the current from the required node flows.
    Actually, the deeper requirement is to follow from the first node, the branch with more current, then the same follow-scheme at the node this branch comes across and so on : This is what i mean by "path".
    Sorry couldnt phrase it properly the first time.
  7. Apr 28, 2016 #6
    The deeper requirement is to follow from the first node, the branch with more current, then the same follow-scheme at the node this branch comes across and so on : This is what i mean by "path".
    Sorry couldnt phrase it properly the first time.
    Thus any person seeing should be able to tell the "path".
    this is in an effect to test "shortest path problem", using current follows least resistive path.

    Attached Files:

    • path.png
      File size:
      105.5 KB
  8. Apr 28, 2016 #7
    Could you just buy multiple op amps? They're cheap. Problem with leds is there is significant voltage drop across them provided they are forward biased. An op amp current sensor with small sense resistor will not affect your circuit. Very small voltage drop.
  9. Apr 28, 2016 #8
    But what shall be the output of this opamp current sensor? In electrical form? Could you tell me how to make the path be "seen" then?
  10. Apr 28, 2016 #9
    Yeah. It will be a voltage. You could even connect two leds to the output of the op amp with opposite polarity to tell if the current is positive or negative. One led will light up for a positive current in a branch and the other will light up for a negative current in the same branch.
  11. Apr 28, 2016 #10
    The output of the opamps will drive the leds BTW. Just make sure you put a properly sized resistor in series with each led
  12. Apr 28, 2016 #11
    Agreed. But will this arrangement help in enhancing the difference in brightness of LED glow (due to different current sensed)? Making it detectable to the eye?
  13. Apr 28, 2016 #12
    Placing Hall-effect sensors on each current leg, and monitoring their outputs on a multi-trace oscilloscope might be helpful.
  14. Apr 28, 2016 #13
  15. Apr 28, 2016 #14
    You'll need permanent magnets though to generate a magnetic field. Hall sensors will not show a transverse voltage across the sensor unless there is a magnetic field present. This could work however.
  16. Apr 28, 2016 #15
    Sure is a good option,
    thank you for your time.
  17. Apr 28, 2016 #16
    I would use one of the amplifier based current sensors in the lin kthough instead of a comparator. The comparator will latch for very small currents.
  18. Apr 28, 2016 #17
    Good luck!
  19. Apr 28, 2016 #18

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    leright is on the right track, i think....

    How far do you want to go ?
    There exist integrated circuits designed to measure current in a wire
    search on "High Side Current Sense"
    they include the differencing amplifier and deliver an output in proportion to current measured.
    Some will even use a length of printed circuit trace or small wire as current sensor

    http://www.mouser.com/new/semiconductors/amplifier-ics/current-sense-amplifiers/n-6o48g [Broken]

    I suppose this is a hardware demonstrator of some sort ?

    I'm old fashioned and would use galvanometers.
    But recognizing that the eye detects motion quicker than it does intensity
    and that these days computers do everything
    it'd be a good Arduino or RaspberryPi project.....
    behind the board , read the analog current signals into a program
    and have it flash individual two-color LED's at rate and color determined by their respective current's magnitude and direction ?
    Measurement points in series with one another , like 5-8 or 10-14, should flash in unison to drive home Kirchoff's Current Law.
    Last edited by a moderator: May 7, 2017
  20. Apr 29, 2016 #19


    User Avatar
    Homework Helper
    Gold Member

    I recently did a small project based on arduino which involved measurement of power system parameters like voltage, current, pf and power. I used a hall effect current sensor IC and it did a very good job. You get an output voltage proportional to the current and that voltage can be read by arduino and displayed on the screen.
  21. Apr 29, 2016 #20
    As old tele man and cnh1995 mentioned, another possibility is a hall sensor. I believe you would need a magnet also in this type of sensor, but I think magnets are integrated into hall effect current sensors.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted