Matching voltages from signal to multimeter. - Home Theater Forum and Systems - HomeTheaterShack.com

Old 03-22-13, 10:49 PM Thread Starter
Shackster
Bruce

Join Date: Mar 2013
Location: Swift Current, SK
Posts: 10
Matching voltages from signal to multimeter.

So that I can match or calibrate an oscilloscope level with an output signal level in a/c voltage taken by a Fluke 88 multimeter, is there a good reference document to show me how? I am simply trying to essentially calibrate the scope to the multimeter. I think the multimeter is measuring RMS but still looking into it.

Take care;

John
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Old 03-23-13, 01:08 AM
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Wayne Myers

Join Date: Jun 2012
Location: Lincoln, NE
Posts: 4,838
Re: Matching voltages from signal to multimeter.

Quote:
BRUCEMX wrote: View Post
So that I can match or calibrate an oscilloscope level with an output signal level in a/c voltage taken by a Fluke 88 multimeter, is there a good reference document to show me how? I am simply trying to essentially calibrate the scope to the multimeter. I think the multimeter is measuring RMS but still looking into it.
The Fluke 88 specs do not mention RMS, so you have to assume it is average sensing and calibrated to give RMS readings with sine waves. The relationship between RMS and peak is the square root of 2, or x1.414 going from RMS to peak. Using a sine wave source which gives a 0.707Vac reading on the Fluke, you should see a reading of 1V peak or 2V peak-to-peak on the oscilloscope. The Fluke 88 is accurate up to 5Khz, so readings above that frequency would be suspect.

A sanity check would be with square waves, where the RMS and peak (and average) reading should be the same, but it would have to be a lower frequency square wave, say 100 Hz or so to be accurate.

I like this reference page showing the relationships between different types of waveforms.
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Old 03-23-13, 10:33 AM
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Bob

Join Date: Jan 2010
Location: Idaho
Posts: 452
Re: Matching voltages from signal to multimeter.

The Fluke 88 is one of Fluke's multimeters designed with automotive applications in mind. Although it might be considered a "Deluxe Automotive" meter, that doesn't necessarily mean it's good at making audio measurements. Fortunately, it lists its bandwidth as 5kHz which is a prime consideration if you want to use a multimeter for audio measurements. Some meters are designed with 60Hz in mind and by the time you get to a kilohertz, the AC measurements won't correspond to those of an oscilloscope at all. This meter appears to have sufficient bandwidth but it wouldn't hurt to compare its readings against an oscilloscope at the higher frequencies to be sure. In any case, readings beyond 5 kHz probably won't be accurate.

If you have an oscilloscope and signal generator, you can set up the following test. Feed a sinewave into the oscilloscope while simultaneously measuring it with the meter. Set the signal generator level as shown (as noted by AudiocRaver, 2V peak-to-peak) and use a relatively low frequency (say 100 Hz). You should get one of the readings noted. Increase the frequency of the generator, keeping the same amplitude on the oscilloscope, and at some point (probably a little beyond 5 kHz) you'll note the meter reading start to fall. That's the limit of the meter in terms of frequency and it wouldn't be considered accurate there.
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Last edited by RBTO; 03-23-13 at 11:04 AM.
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Old 03-24-13, 01:49 AM Thread Starter
Shackster
Bruce

Join Date: Mar 2013
Location: Swift Current, SK
Posts: 10
Re: Matching voltages from signal to multimeter.

Hi Guys and Gals;
Wow, I really appreciate your answers and i am learning a lot right now. I am glad that you are responding to new members and sharing your hard earned experience freely. I am going to work on this and learn all I can. I love this stuff.

Thanks again.

Take care;

John
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