On 2016-01-12, John Heath wrote:
On Monday, January 11, 2016 at 12:34:11 PM UTC-5, Kaz Kylheku wrote:
On 2016-01-11, Ivan Vegvary wrote:
"Peak-to-Peak" meter.
For what are (were) they used? Got it for free.
Is it simply so I don't have to multiply by 1.414?
Be gentle. I'm new at all this and trying to learn.
Ivan Vegvary

To be useful, the p-2-p meter should sample and hold the top and bottom
values, and not simply measure RMS and multiply. If we measure p-2-p
with a scope we get a stable trace, and then actually find the highest
and lowest voltages.

Note that the 1.414 factor between RMS and peak voltage only applies to
a sinusoidal signal!

It is incorrect for other signal shapes.

For instance, a square wave's RMS is the same as peak.

(Peak-to-peak is twice peak, so the factors double: p-2-p/RMS is 2.828 for
sinusoidal, 2 for square.)

I have a current probe , hall effect , that claims to be true RMS.
When looking at the fine print it says it is true RMS providing it is
a sine wave??

If it is a sine wave then who needs a RMS mater.

Someone who only has a DC meter, and wants to measure AC.

In many situations we know we have a sine waves; we just want to know
how big, as an RMS figure.

For instance, I can stick my here handy multimeter into the wall,
configured for AC, and it tells me that the line voltage is 118.7.
That's an RMS (predicated on it being sinusoidal), and it is useful.
If it is true RMS, and accurate, then I know that the peak voltage
is 1.414 times that, or 167.9, and peak-to-peak is twice that.

This is
somewhat like a USB powered speakers for a computer claiming 100 watts
of power. That would be 20 amps at 5 volts , extremely unlikely. In

But there isn't any condition under which the speakers can continuously
deliver that much power without a source other than the USB port; no USB
host chip provides that much current. Thus it is unconditionally a lie.

the old days they would not lie like this just to make a sale.

Oh, if we pull out some old Popular Mechanics issues from, say, the
1940's, we will see all sort sof snake oil.