++ help with some electricity questions! ++ - Page 1
Forum section: electronics / general

author: Mugiwara303
author_rank: Contributor
timestamp: October 28, 2016, 07:10:47 pm
content: #1 in AC the value of voltage that we measure with a voltmeter are effective or average?#2 in DC the value of voltage that we measure with a voltmeter are effective or average?#3 what energy pay the customers of electricity is it active Pa or reactive Q or apparent S?#4 see the image, sorry it's in french, the voltage is AC

author: helius
author_rank: Super Contributor
timestamp: October 28, 2016, 07:37:14 pm
content: These look like homework questions... please try to find the answers yourself.Try this if you need help:https://www.khanacademy.org/science/electrical-engineering/ee-circuit-analysis-topic/ee-ac-analysis/v/ee-ac-analysis-intro1

author: Mugiwara303
author_rank: Contributor
timestamp: October 28, 2016, 07:44:28 pm
content: it's not a homework, it's a workworkthank you for the link but i can't watch the videos there are a lot and i don't have time because i am dealing with other problems now i am really supper busy, i hope someone can answer me directly i really don't have time to learn now, i hope you guys understand me

author: Zero999
author_rank: Super Contributor
timestamp: October 28, 2016, 07:54:28 pm
content: There doesn't appear to be enough information. At least the current, frequency or impedances need to be known.And what do you mean by effective or average? It doesn't make any sense.

author: Mugiwara303
author_rank: Contributor
timestamp: October 28, 2016, 08:01:57 pm
content: i have translated them to english, i study in french, for example the oscilloscope can give you Vmax and there is Veff and Vm i don't know which one the voltmeter is giving, in the picture they are only giving U and asking for the total of Ur+Ui+Uc

author: Zero999
author_rank: Super Contributor
timestamp: October 28, 2016, 08:19:19 pm
content: In that case, you do have enough information. A proper meter measures RMS which I presume what you mean by Veff. Counting the number of squares on an oscilloscope will give the peak to peak voltage, which, assuming a symmetrical waveform, is twice the peak voltage.For a sine wave: Vpeak = root(2)*VRMSIn an AC circuit, the total voltage is equal to the phasor sum of the voltage across the resistor (the real part) and the inductors and capacitors (imaginary). The voltage across the capacitor will be out of phase with the voltage across the inductor so it will cancel it out.V = root(VR2+(VL- VC)2)

author: Mugiwara303
author_rank: Contributor
timestamp: October 28, 2016, 08:35:40 pm
content: thank you for the last equationso the voltmeter is giving the average voltage not the eff, i just want to know if it's valid for both AC and DC

author: IanB
author_rank: Super Contributor
timestamp: October 28, 2016, 08:52:32 pm
content: We don't know what the difference is between effective voltage and average voltage? Voltmeters will indicate some kind of average voltage, but how the averaging is done depends on the meter. If you want a good result you need to use a true RMS meter, and then you also need to consider the DC component and the AC component since in some cases both may be present.

author: Mugiwara303
author_rank: Contributor
timestamp: October 28, 2016, 09:04:01 pm
content: the average voltage we call it Vmoyenne i don't know if average is the best word

author: IanB
author_rank: Super Contributor
timestamp: October 28, 2016, 09:09:35 pm
content: Quote from: Mugiwara303 on October 28, 2016, 09:04:01 pmProbably the "effective" voltage is the RMS voltage, which is equivalent to a similar DC voltage. The "average" voltage could be a simple average, which is not very useful.However, what you will see on a meter depends on the meter and it depends whether you are measuring DC, AC, or AC + DC.

author: Mugiwara303
author_rank: Contributor
timestamp: October 28, 2016, 09:16:06 pm
content: ok thank you guys for your replies

author: Ratch
author_rank: Regular Contributor
timestamp: October 29, 2016, 04:15:42 pm
content: Quote from: Mugiwara303 on October 28, 2016, 07:10:47 pmA d'Arsonval meter is a average responding unit. It measures rectified AC, and its face scale is usually calibrated in sinusoidal RMS.QuoteEffective and average DC voltage are the same.QuoteIn the USA, customers pay for the resistive energy they use. The rates increase if the power factor is excessive. I image that it is the same in France.QuoteU=Sqrt(8^2+(20-12)^2)=8*Sqrt(2) = 11.3 volts

author: Mugiwara303
author_rank: Contributor
timestamp: October 30, 2016, 04:38:21 pm
content: thank you @Ratch