Information about AC on Multimeter page is incorrect...

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Tcepsa
 
Posts: 26
Joined: Tue Jan 13, 2009 7:14 pm

Information about AC on Multimeter page is incorrect...

Post by Tcepsa »

Hi ladyada! While I am very excited about your site and all of the potential and great projects it contains, the information about AC power in your multimeter tutorial is off far enough that I think it warrants correction. (I'm referring to the section "Alternating current voltage is what comes out of the wall" here: http://www.ladyada.net/learn/multimeter/voltage.html)
The generator at the US power plant creates a voltage that oscillates, going from -60V to 0 to +60V to 0 again, 60 times a second. At the European power plant its -120V to +120V at 50 times a second.
While I can't speak on the European side of things, I'm reasonably certain that the power generated by US power plants is much higher than 120 volts peak-to-peak. More relevantly, the 120V that people talk about when they say that US AC power is "120 volts" is the root-mean-square of the actual value of the sinusoidal voltage waveform, which you get by taking the peak value of the waveform and multiplying by the square root of two (for sine waves, anyway). So 120 = V_peak * sqrt(2), from which you can calculate that the peak voltage is actually about 170 V. Furthermore, that is from ground-to-peak. In other words, regardless of what happens at the power plant, when the power gets to your wall socket it should be oscillating from about +170V to 0V to -170V and back.

While as far as I can tell it doesn't actually impact the multimeter tutorial's effectiveness, I can see how that could lead to confusion and possibly unfortunate failures for people trying to make things that involve AC power.

Cheers!
Tcepsa

(P.S. In the future would there be a better place to put this sort of troubleshooting and/or a better way to go about it?)

adafruit
 
Posts: 12151
Joined: Thu Apr 06, 2006 4:21 pm

Re: Information about AC on Multimeter page is incorrect...

Post by adafruit »

yea you are right. i messed up on that, because for some reason i thought that my meter was not RMS, but lately ive been hacking mains and obviously it is
so ill fix it!

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