Measurements and Variance

Thanks for the clarification. That's the pieces of knowledge I was missing. I needed to know how the Multimeter and Face panel meter averaged the sample rate for their value, relative to the Oscilloscope values which like you said are real time. I suspected this would be the case, but just was not sure. I also found (right after I posted the question) that the part of the waveform that I was interested in for my data was not in the proper scale when I added the conversion value on the spreadsheet.

Thanks again for the information.

So even in a DC measurement the Multimeter calculates the RMS?

the multimeter reads DC. the RMS converter in the multimeter converts the AC to the equivalent DC voltage. a "True RMS" meter converts the AC to a DC value equivalent to the RMS value of the waveform, no matter what the waveform shape is. the value of 0.707x Vpk that was quoted earlier is only valid for sine waves. most multimeters take the peak value and multiply by 0.707 and that's the voltage displayed by the meter, even if the input is a square wave. only True RMS meters are accurate with waveforms other than sine waves. DMMs are also somewhat limited to being accurate below a certain frequency, which is another thing that needs to be verified if the AC is 20khz or above (some cheaper meters are only accurate below 1 or 2 khz).

Sounds like you would have to use some complex mathematical analysis techniques to get a very close approximation of the true signal amplitude. It also sounds like True RMS meters come close to doing just that.

Very informative. Wiki had different formulas for different kinds of wave forms. You would have to use more than one in some case on different sections of a signal.

Regards.

Reply #1 is a good guidance for you to learn your Test Equipment thoroughly; limitations & terms used by the manufacturers.

It is evident rom your later questions that you do not have the very basic concepts.

CRO [Oscilloscope] is really a good tool for Techies but needs everything clear in mind.

Panel Meters are normally for monitoring not for accurate measurements.

Hope you will consider my reply in good sense & progress your knowledge to step ahead in your job & life.

My Instructors advice to the students always was:

"Never feel ashamed by asking Question; and never be miser in sharing your knowledge & experiance.

It is a great deal with your society "

Have a fine Day !!!!!

It's true, but I learn fast. I'm a teachers worse nightmare because I tend to find the limit of the knowledge base quickly. I don't accept hand waving over things that are not known or poorly understood.

In other words I will learn to the point that I will find the limits of the knowledge base and if necessary do original research to fill the gap. That's what I'm currently doing.

I only learn what I need to know when I need to know it, but I can spot B.S. a mile away. I pride myself in being able to see the Trees from the Forrest and vise versa.

Always open to learning something new and being educated by those who know.

Thanks for the help.

More questions to come soon. In fact. What is a good no nonsense book or reference on electronic measuring equipment? I mean a book that tells you how these meters do what they do. There is very little information on how exactly a meter does what it does on the internet so that is why I ask. The references given before have been a great help, but I want to know more. Would it be better to just use software to analyze the signal? I'm open to suggestions here.

Regads &congratulatios for the goals you have set in your concience .

Hope & pray best of the future for you !

I remember something similar happening to me in a lab...different equipment. The problem turned out to be static electricity from my sweater...every time I moved, it caused a deflection on the instrument.

when handheld DMMs were young (about 1980 or so) i saw an expensive Beckmann True RMS handheld DMM destroyed by the static charge on a CRT screen. since then DMMs have been made more robust, but i still am very careful to note what the maximum voltage across the test leads, and the maximum meter body isolation voltages (shown on the meter, usually in red print next to the banana jacks) are before poking around in high voltage circuits.

Almost all scopes have measurement capability for the captured waveform. You can have it display P-to-P, average, RMS, mean, etc. Some scopes will even give you statistics such as mean and standard deviation. Try using those to get a better idea of how the signal is actually behaving.