What is the method for doing so?

 

RMS value = Peek value / SquareRoot(2)

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kypo, the kypo.

 

Or more simply, RMS = Peak Value x 0.707

 

that is only true for sinus waveforms about zero

 

multiply rms by 2.828 = peak-to-peak

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The great thing about electronics is unlimited ways to do the job. The only limit is one\'s imagination. I generally think my way is best.
Show me a different way. I have an open mind.

 

But as Styx said, only for sine waves that have no DC component.

 

True, but is is easy to subract the DC component. But, to find the RMS of a non sinusoidal waveform, you need to do some Calculus.

Len

 

After 20+ years of teaching electronics and the advent of inexpensive scientific calculators, I don't much like the idea of folks using truncated approximations for constants. It galls me to watch a student enter 3.14 on a calculator (4 keystrokes) rather than hitting the "pi" key (1 keystroke) for 10 digits of precision; or 1.414 (5 keystrokes) rather than 2 & the sqr-rt key (2 keystrokes) for 10 digits of precision. Granted, you don't need 10 digits of precision for any of these calculations but the time saved alone is worth using the simpler calculator entries.

Besides that, there's less to remember. 3.14159.... is harder to remember than the symbol on the "pi" key; if you need 0.707...., just do [2][sqr rt][1/x] for the full 10 digits of precision -- that's still 2 keystrokes shorter than entering 0.707!

In addition, you'll make fewer errors. I don't know how many times that I've seen a number entered where the decimal point didn't "catch", throwing the calculation off by several decades.

It took me too long to quit making students mule-haul all of their math just for the sake of the math section of the electronic course with the reason that "you'll know more easily if you've made a calculator error". I discovered that I can drive that point home without forcing students to add 1.47 x 10^-6 and 0.00349 x 10^2 by hand.

My time has been better spent teaching the students that dividing 1.81 by 3.0 does not give you an answer with 10 digits of precision even if the calculator does provide 10.

Dean

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Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

 

But.. since you are normally told only the RMS value how do you know the DC offset that is part of the rms value?

and very true ONLY revert to a number at the lastest stage of a caluculation 1.414 might be a decent approx to sqrt(2) but for statest 1.414 isnt (as stated) and it is easier (and less easy to get lost) by writing √2

 

Yes, it depends on what you know. eg. if told that the valtage is say 10 Volt RMS, you would not know what waveform it referred to.

I don't understand your second para.

Len

 

I think most people would assume that a stated RMS value refered to a sinusoidal waveform with no DC component, unless some information was given to imply otherwise. Or am I wrong?

 

ops: Sorry. This got double-posted

 

ya i think u r right pebe, otherwise the info wont not be complete

 

Each and every math teacher i have had during school didn't know how to make a pi on the scientific caclulator (shift + EXP) so they just told us to use 3.14.
I think that the problem starts from the old skool (usually aged 70+ :twisted: ) teachers that can't operate calculator...

 

Some of the younger people I know even need a calculator to multiply by 10!

Len