RMS varia

        RMS varia
        Wed, 9 Apr 97 14:53:33 EDT

[these are out of order...]
[And the attributios are gone, 'coz i am discussing the ideas, not the

>Whoa there LT! Most meters measure RMS.
        'most meters' is hard to define.  most AC meters (in my
        esp. voltmeters) are 'rectifier type.  They measure AVERAGE,
        and are MARKED ont he face to INDICATE RMS.  This works ASSUMING
        the waveshape is a sine wave.

>You'd better know p-p to rate your caps. 
        Yep.  Or a little over.  Maybe a LOT ove.

        Yep.  Assuming 'P' equals peak....

>VA Ratings (or Volt-Ampere ratings) refer to power capabilities.
        Sort Of.
        But VA is not equal to watts is not equal to power in AC work.
        SOMEtimes VA == power.  Sometimes not.  (in AC work).
        Specicially, for a reactive load (inductive, capacitive, VA is
        than Watts.  Measuring, unless a scope is to hand is nontrivial.


>RMS stands for "Root Mean Square"  to find it, take your peak to peak
>voltage and multiply by .707.
        This assumes a sine wave.  And
        RMS is .707 the Vpeak.

>or take RMS voltage and divide by .707 to get back to the VP-P
        This would get U to Vpeak.  Vp-p would be twice that.

>that most meters measure.
        See above.  Common Meters _measure_ average, _indicate_ (by
means of
        calibration). in RMS.  (Digital meters, well, read the manual. 
SOME are
        true RMS, some have little corrections built in.

>I need to know about RMS of my xformer when calculating the capacitor
>value needed.
        The questions not answerable, as posed.
        'RMS' is a modifer of volts (or amps (milliAmps...))

>What is the RMS and how do I find it?
        RMS voltage and RMS current are stated on the nameplate or spec
        In general a stated value in AC work is in RMS volts or amps,
        stated otherwise.

>Also volt amps is something I need to know about
        See Above, also RH explanation.


>Root Mean Square or RMS can refer to voltage, current, power, etc. 
        My first thought was 'RMS power'?  My second was Richard is
        as usual.

>Scince you stated you needed to know this for capacitor purposes I'll
>assume you are talking about RMS voltage.  This is actually the name
>plate voltage.  It is the voltage measured by most common AC voltmeters
>for a sine wave. 
        Fine finicky point.  MOST meters measure something else, usually
        _average_ and then play games with the calibration to _indicate_
        RMS ASSuming a sine wave.  When dealing in large blocks of
        current and voltage and 'unusual' loads, as in coiling, this can
        be a BAD assumption, as the waveforms get distorted.

        This is critical because the peak-rms conversion for 'some other
        waveform' will be different than the .707 for a sine wave.  Most
        tesla coil related waveforms are not sufficiently well behaved
        use a 'canned' conversion like '.707'.  A true RMS meter is the
        way to go, tho they can be costly.

>>I am starting to get into more serious coiling and I am going to go for Q and
>>preformance so I guess Ill have to do some stinking math.
        A very Knowledgable and practically skilled man of my
acquantance (
        his specialty was mesuring microvolts, one at a time..., in
        quantity instrumentation) once said, praising a coworker:

                He understands that the numbers are REAL and have real

        In some cases, as in coiling, much of what is done involves
        paramters which are too complicated to be conveniently reduced
        numbers, but much else can be.  And dealing with the smallest
set of
        unknowns, at any one time, is generally a good thing.