Skip to content
  • Register
    • Advertisement
    If you have a new account but are having problems posting or verifying your account, please email us on hello@boards.ie for help. Thanks :)
    Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact hello@boards.ie

    Total Harmonic Distortion

    • 17-04-2015 07:24AM
      #1
      2011
      Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,659
      Mod ✭✭✭✭


      I have a fundamental sine wave with high harmonic content. I have all of the information that I require to graph the fundamental and the 3 other sine waves. In fact I have graphed all 4 individually and the final combined wave in Excel.

      It has been a few years since college :)
      My question is, how do I calculate the THD and express it as a percentage?

      Many thanks,

      2011


    Welcome!

    It looks like you're new here. Sign in or register to get started.
    Sign In
    Register

    Comments

    • #2
      rob w
      Registered Users, Registered Users 2 Posts: 1,205 rob w
      ✭✭✭


      2011 wrote: »
      I have a fundamental sine wave with high harmonic content. I have all of the information that I require to graph the fundamental and the 3 other sine waves. In fact I have graphed all 4 individually and the final combined wave in Excel.

      It has been a few years since college :)
      My question is, how do I calculate the THD and express it as a percentage?

      Many thanks,

      2011

      Sum the squares of all the harmonics amplitudes.....take the square root of that.....then divide by the fundamental....and multiply by 100 for your percentage! Make sure all values are in RMS though first!

      e.g.

      THD% = (sqrt(V2^2 + V3^2 + V4^2....)/V1)

      Where V1 is your fundamental and V2, V3 and V4 are your harmonics (In RMS)


    • #3
      2011
      Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,659 2011
      Mod ✭✭✭✭


      rob w wrote: »
      Sum the squares of all the harmonics amplitudes.....take the square root of that.....then divide by the fundamental....and multiply by 100 for your percentage! Make sure all values are in RMS though first!

      e.g.

      THD% = (sqrt(V2^2 + V3^2 + V4^2....)/V1)

      Where V1 is your fundamental and V2, V3 and V4 are your harmonics (In RMS)

      Thank you!


    • #4
      2011
      Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,659 2011
      Mod ✭✭✭✭


      rob w wrote: »
      Where V1 is your fundamental and V2, V3 and V4 are your harmonics (In RMS)



      Converting each to r.m.s. values doesn't change anything as its a common factor?


    • #5
      Michael Collins
      Moderators, Science, Health & Environment Moderators Posts: 1,852 Michael Collins
      Mod ✭✭✭✭


      2011 wrote: »
      Converting each to r.m.s. values doesn't change anything as its a common factor?

      Yes, it doesn't matter if it's RMS or not, since the harmonics are sine waves by definition.

      Sometimes the RMS value might be more readily available, so you might as well just use that, but peak amplitudes are also fine, once you're consistent.


    • #6
      2011
      Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,659 2011
      Mod ✭✭✭✭


      Michael Collins wrote: »
      Yes, it doesn't matter if it's RMS or not, since the harmonics are sine waves by definition.

      Sometimes the RMS value might be more readily available, so you might as well just use that, but peak amplitudes are also fine, once you're consistent.

      That makes sense, thanks.


    • Advertisement

    Welcome!

    It looks like you're new here. Sign in or register to get started.
    Sign In
    Register
    Advertisement