Voltage, AC Voltage, and Phase

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charlie b

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Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
winnie said:
Charlie. . . On the use of 'average', do you consider "The American Heritage Dictionary" sufficiently authoritative?

I will accept that source as authoritative. Did you notice that,
winnie said:
"A number that typifies a set of numbers of which it is a function."

Is not the same thing as
winnie said:
. . . a function that is used to typify the magnitude of a constantly changing function.

In attempt to force-fit “RMS” into the definition of “average,” you altered the definition. Not allowed.


winnie said:
Notice that meaning _b_ is "arithmetic mean", whereas meaning _a_ is the rather general.

Yes, “meaning a” is rather general. But the RMS value is not typical of the set of values of which it is a member. Most of the values in a sine wave are lower than the RMS value. The actual average, as you pointed out earlier, is zero. You will note that there are as many values higher than zero as there are lower than zero. On this basis, one can say that “zero” is a typical value. The concept of RMS does not fit the definition of “average.”


I have no interest in pursuing this further either. My one and only point here is that if you intend to teach, you have to be clear as to when you are being precise for the benefit of those students who come into the course with a basic understanding of the fundamental science, and when you are simplifying the concept for the sake of the students who do not.
 

Mike03a3

Senior Member
Location
Virginia
rattus said:
Agreed, a good engineer knows how to approximate. He also knows that three significant figures are usually close enough.

At least they were all those years when this was my pocket calculator:
KEsliderule.jpg
 

charlie b

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Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
You've got a really good model there Mike. It looks a lot like mine. Every once in a while, if I have a simple calculation to do, I'll bring it out, just to show the youngsters what life was like in the good old days. :)
 

rattus

Senior Member
I have to agree with Charlie here:

RMS means the square ROOT of the MEAN value of the voltages or currents SQUARED. Give them the formula even if they don't understand integral calculus.
 

hillbilly

Senior Member
Mike03a3 said:
At least they were all those years when this was my pocket calculator:
KEsliderule.jpg

Ah yes...the good old days. Slide rule, Smoley's and T-square....Wake up Maggie, I think I've got something to say to you......(Rod Stewart).
steve
 
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