On Tuesday, January 12, 2016 at 12:11:53 AM UTC-5, Kaz Kylheku wrote:
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.

Yes but in my case I needed to evaluate the power consumption of a 2000 watt LED display board. The current for this puppy is spikes of current off the top of the hydro sine wave from all the DC switching power supplies for the sign. This means a peak detector of the current is the wrong answer. For this reason I bought a true RMS current meter to average out the net current to know what the breaker should be for the sign. You can imagine my disappointment when I read the small print that said true RMS provided it is sine wave current. Root Mean Square has a precise meaning and a cheap peak detector divide by .7 is not it. I am just ventilating but it really ticked me off when I found this out the hard way. Worse the biggest letters on this current meter was TRUE RMS. To give this balance it could have been marketing without the support of the engineering. Just the same when those engineers saw the final product with TRUE RMS bigger than life they knew it was a lie. To give this balance again I still use this little current meter and it has a added benefit of measuring DC current as well being a hall effect type meter. And it only cost 50 bucks so you really can not complain other than the lie about True RMS.



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.

I see your point. Basic human nature will not change over time.