# True RMS calculation Window size

Discussion in 'Embedded Systems and Microcontrollers' started by neonwarrior, Apr 28, 2014.

1. ### neonwarrior Thread Starter New Member

Apr 22, 2014
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Hello everyone, I want to calculate true rms from samples and wonder if the window size must be an integer of the period of the signal. (I'm very lazy to measure the frequency of signal )

If there is an error with using non integer window size, how can be calculated?
Ah, the formula I saw in internet is
w
Vrms= sqrt(sum(V[n]*V[n])/Window)
n=1

2. ### ErnieM AAC Fanatic!

Apr 24, 2011
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That would require knowing the frequency.

And welcome to the forums!

3. ### Alec_t AAC Fanatic!

Sep 17, 2013
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By 'non-integer' presumably you mean not an integral multiple of the signal period?

4. ### neonwarrior Thread Starter New Member

Apr 22, 2014
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Yes not integral multiple of signal period, for example if signal is 20 ms then I use a window of 205 ms (20 *10.25). Is it the same as using 200 ms ??

Thanks

5. ### Alec_t AAC Fanatic!

Sep 17, 2013
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No, it isn't.

6. ### neonwarrior Thread Starter New Member

Apr 22, 2014
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Do you know any literature that describes this in detail...
Thanks

Apr 24, 2011
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Yes.