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Kryptonite
Joined: 07 Feb 2006
Posts: 333
Helped: 10
Location: AUH, UAE
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 25 Jun 2006 1:41 [Q] RMS vs. TRMS values ... |
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Just a quick question;
What's the difference between RMS value & True RMS value???
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IanP
Joined: 05 Oct 2004
Posts: 6490
Helped: 1542
Location: West Coast
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25 Jun 2006 2:33 Re: [Q] RMS vs. TRMS values ... |
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In short, the RMS value will be used with relation to sine waves which are AC-coupled to eliminate the effect of DC bias, whereas the True-RMS value will be use to measure the RMS of complex waveforms, such as sine waves chopped by a triac, triangle or square waves ..
More info:
"AC MEASUREMENT APPLICATION GUIDE"
http://www.newportus.com/manuals/ACGUIDE.htm
"Root mean square"
http://en.wikipedia.org/wiki/Root_mean_square
Regards,
IanP
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Miguel Gaspar
Joined: 06 Mar 2006
Posts: 391
Helped: 36
Location: Culiacán, Sinaloa, Mexico
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25 Jun 2006 2:54 [Q] RMS vs. TRMS values ... |
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First Voltmeters givesyou RMS value in thefollowing form: peakvalue *0.7071 wich is true for a perfect sinusoidal wave form, but not true for another wave form.
TRUE RMS gives a real RMS value for any kind of wave form.
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25 Jun 2006 2:54 Ads |
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matteo128
Joined: 19 Oct 2001
Posts: 25
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25 Jun 2006 3:11 Re: [Q] RMS vs. TRMS values ... |
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RMS vs. true RMS comes from the method used to measure RMS voltage.
Some (simpler or older) instruments have detectors that measure average value of the voltage but the display is calibrated to show RMS value with assumption that input signal is sine wave.
Of course, this instrumentst will give correct reading only for sine waveform since the scaling factor depends on the form of the input signal.
True rms instruments give correct rms value of the input voltage (within specified frequency range and crest factor) They are usually made either by analog circuit that calculates the rms value , or they use thermocouples.
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