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

Rms voltage

  1. Aug 14, 2012 #1
    Suppose at a test point in my circuit ,I need to measure rms voltage, how I should measure it with DMM?
  2. jcsd
  3. Aug 14, 2012 #2
    DMM provide rms voltage when set to measure AC voltage. If Set to measure DC Voltage they measure Average.
  4. Aug 14, 2012 #3


    User Avatar
    Gold Member

    Peak to peak voltage (non-RMS) typcially only shows up on an oscilloscope.
  5. Aug 15, 2012 #4
    Some DMM measure RMS voltage and some DMM measure average voltage.

    Check the manual for your DMM and if it reads average voltage, get a DMM that reads RMS voltage.
  6. Aug 15, 2012 #5


    User Avatar
    Science Advisor

    Voltmeters that don't describe themselves as being "true RMS" generally measure scaled average voltage. That is, they display the average voltage times [itex]\pi / \sqrt{8}[/itex], (approx 1.11). This scaling factor makes the average voltage equal the RMS voltage, but only for a sinusoidal waveform.
  7. Aug 19, 2012 #6
    In one of replies to my post, I got an answer that AC voltmeters measure rms voltages, further I want to know that at AC volt position 1V RMS will be shown as what, 1v or less or more?
  8. Aug 19, 2012 #7


    User Avatar

    Staff: Mentor

    Providing you are measuring a sinewave, and there is no DC component, then on the AC scale your meter will read 1.00v for a sinewave having an RMS value of 1.00v

    DMM probably work reliably only for sinewaves up to a few kHz.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook