# RMS Peak bench equipment , RMS for waveforms

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#### davidowens

Joined Oct 3, 2014
12
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?

#### davidowens

Joined Oct 3, 2014
12
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

#### wayneh

Joined Sep 9, 2010
17,153
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?
Nope. They all integrate to different values. If you search, you can find a table that will give you the results for each waveform.

#### davidowens

Joined Oct 3, 2014
12
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?

#### wayneh

Joined Sep 9, 2010
17,153
All shall be revealed. Here.

#### davidowens

Joined Oct 3, 2014
12
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

#### davidowens

Joined Oct 3, 2014
12
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?

#### crutschow

Joined Mar 14, 2008
27,739
................ I looks at the wiki and I'm still confused

Sine wave 0.707?
Square wave 0.707?
Triangle wave 1.414?
..................
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.

#### wayneh

Joined Sep 9, 2010
17,153
..the easy way is just to use a digital Oscope and DVM to get the RMS voltage of all these waveforms?
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.

#### davidowens

Joined Oct 3, 2014
12
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

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#### crutschow

Joined Mar 14, 2008
27,739
...............................
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?
............................
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.?

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#### davidowens

Joined Oct 3, 2014
12
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?
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?

#### GopherT

Joined Nov 23, 2012
8,012
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.

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