RMS Peak bench equipment , RMS for waveforms

Discussion in 'General Electronics Chat' started by davidowens, Oct 3, 2014.

Thread Status:
Not open for further replies.
  1. davidowens

    Thread Starter New Member

    Oct 3, 2014
    12
    0
    There is a RMS Peak voltage and load resistance for different bench equipment

    50 ohms = 5 volts Peak
    75 ohms = 10 volts Peak
    1K ohms = 15 volts peak
    1 Meg ohms = 20 volts peak

    Is there a relationship between the input load resistance and Voltage Peak input on bench equipment like frequency counter inputs?

    Why is it 50 ohms at 5 volts peak? and 1 meg ohms 20 volts peak
    What is the relationship between the input resistance and input load , i don't get it?
     
  2. davidowens

    Thread Starter New Member

    Oct 3, 2014
    12
    0
    Is the RMS always 0.707 for all types of waveforms listed? I measure the Peak volts and use 0.707 for any of these waveforms?

    Sine wave
    Square wave
    Triangle wave
    Pulse
    Sawtooth
    Rectangular Pulse
    Trapezoid Pulse
    Ramp Up and Ramp Down
    Rectified full wave
    Rectified Half wave
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,100
    3,036
    Nope. They all integrate to different values. If you search, you can find a table that will give you the results for each waveform.
     
  4. davidowens

    Thread Starter New Member

    Oct 3, 2014
    12
    0
    What is this table called please?

    Why do these integrate to different values?

    I thought you measure the peak voltage of any waveform and use 0.707 right?
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,100
    3,036
    All shall be revealed. Here.
     
    BR-549 likes this.
  6. MrChips

    Moderator

    Oct 2, 2009
    12,437
    3,360
  7. davidowens

    Thread Starter New Member

    Oct 3, 2014
    12
    0
    Mr chips I looks at the wiki and I'm still confused

    Sine wave 0.707?
    Square wave 0.707?
    Triangle wave 1.414?
    Pulse
    Sawtooth
    Rectangular Pulse
    Trapezoid Pulse
    Ramp Up and Ramp Down
    Rectified full wave
    Rectified Half wave
     
  8. davidowens

    Thread Starter New Member

    Oct 3, 2014
    12
    0
    on wiki its complex formulas just to get the RMS voltage of other waveforms besides a sine wave it seems

    I guess the easy way is just to use a digital Oscope and DVM to get the RMS voltage of all these waveforms?
     
  9. crutschow

    Expert

    Mar 14, 2008
    13,001
    3,229
    That makes two of us.

    The sin wave RMS value is correct at 0.707 of the peak voltage.

    The square wave RMS value for equal excursions around 0V (no DC offset) equals the peak voltage.

    The triangle wave or sawtooth RMS value is (1 / √3) = .577 times the peak voltage.

    Don't know where you got your values. :confused:
     
  10. wayneh

    Expert

    Sep 9, 2010
    12,100
    3,036
    The easy way is to look up one of the many tables shown by following the link I provided above. As crutschow notes, I don't know where you got your values.

    Note that some of the waveforms on your list are undefined:
    Pulse
    Trapezoid
    Ramp up
    Ramp down.

    You'll need to define those with specific values.
     
  11. davidowens

    Thread Starter New Member

    Oct 3, 2014
    12
    0
    Sine waveform AC RMS is V peak divided by 0.707?
    Square waveform AC RMS is V peak divided by 1?
    Triangle waveform AC RMS is V peak divided by 0.577?
    Half wave rectified sine AC RMS is V peak divided by 0.500?
    Full wave recfified sine AC RMS is V peak divided by 0.707?

    Take a look at the waveform chart and I'm trying to know how to get the RMS value for each waveform
     
  12. crutschow

    Expert

    Mar 14, 2008
    13,001
    3,229
    The full wave rectified is 0.707 then logically the half-wave rectified would be 1/2 of that or .343.
    How did you get 0.5?

    Are you AKA Billy Mayo, etc.?
     
    Last edited: Oct 4, 2014
  13. davidowens

    Thread Starter New Member

    Oct 3, 2014
    12
    0
    I get it off the internet RMS chart

    But anyways , my main point is why does each waveform has a different RMS formula? i would think they should all use 0.707 , and why don't they?

    A square waveform doesn't have an RMS value, its the same as the peak voltage, so the RMS voltage and the Peak voltage is the same for square waveforms , why is that?
     
  14. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,010
    3,785
    Ok, integration is the key. Look at time slices of a square wave and a sine wave (area between the curve and the zero-cross line). Each waveform will have a characteristic 'correction' factor.
     
Loading...
Thread Status:
Not open for further replies.