Voltmeter Question

[jswingchun]

I think I finally understand how to set a limiter after reading thru posts here, especially the post in the Educational Links section of the forum.

I want to pick up a True RMS voltmeter and thought I would ask here if anyone has any suggestions for a good, inexpensive one for someone who won't be using it all that often. I saw Sear's had this one, which isn't too expensive:

http://www.sears.com/shc/s/p_10153_1260 ... 921x00003a

If anyone has any better suggestions let me know.

[David Carter]

That's the one I've got. Works great for me. Of course, I'm a novice at all this...

[djohnson573]

I have this one and have no complaints:

http://cgi.ebay.com/Greenlee-CM-450-Tru ... 7C294%3A50

Plus it will save you a few $$$$$

[thijs666]

Guys, guys Why so expensive ?

If you use a sine wave to adjust your limiter, you can just as easy use a $5 multimeter in AC mode. That'll get you in the ballpark. Yeah, I know, the cheap ones measure effective voltage, not RMS, but the wattage stated by the manufacturer is also not very precise.

U = sqrt(watts * impedance)

For example U = sqrt (100W * 8 Ohms) = 28.28 V

Or am I missing something

[Sydney]

Or am I missing something

I have compared inexpensive meters against my friend's Fluke and found them to give the same level of accuracy for most practical purposes. Since I subject meters to field use ( literally ), I tend to use cheapos for this purpose.
BTW: I have acquired many meters over time ( including antique Simpson and Heathkit ).
The cheapos also seem to have less chance of pilferage.

[SoundInMotionDJ]

If you use a sine wave to adjust your limiter, you can just as easy use a $5 multimeter in AC mode.

I use an older RMS volt meter (not a True RMS meter) for almost everything - including setting limits for my speakers.

The "True" parts accounts for DC offsets, can account for a wave that is not symmetric about 0v, and also can account for temperature differences in the resistance load that is being measured. None of that is present when setting a voltage limit from an amp using a pure tone (e.g. 1kHz, 100Hz, etc).

That said, I do generally advise noobs to get a True RMS meter. If they are not experienced with things electrical, that will be a better meter for them to have - if for no other reason that no one will even claim that is it not and cause confusion. If they are experienced with things electrical, they will already have a meter, and will understand that RMS is good enough.

--Stan Graves

[bgavin]

My Fluke came from my days at IBM... this thing must be at least 20 years old, and runs like a champ.
It has worked consistently through the mud, blood, and toner.

For casual use, the inexpensive DVOM will do the job.
If used with adult supervision, they will probably last quite awhile.
However, if you drop it... kiss it good-bye. Same as a laptop...

[jswingchun]

Thanks all for the replies. I will read up a bit more and make a decision...

[thijs666]

I have compared inexpensive meters against my friend's Fluke and found them to give the same level of accuracy for most practical purposes.

That's what I meant .

[Sydney]

I know

[Gregory East]

So I'm looking at multimeters for sale and there are 4 kinds: Uber expensive, too expensive, "I can afford that" and "that's so cheap it must be crap".

The only ones saying "true rms" fall into the first two sets. The rest seem much of a muchness aside from price.

So please tell me more of the "average AC" measuring cheap voltmeter method of not blowing stuff up.

[cjd]

wikipedia has a good explanation: http://en.wikipedia.org/wiki/True_RMS_converter. in a nutshell: as long as the signal you are measuring is a sine wave with no dc offset (which is pretty common) you'll get the right answer.

[more4me]

My first cheap one, could not really handle AC Ampere. It was only DC or (pulsing DC?). So I had to find a new one. Be sure to check that it really can handle AC and up to what freqency.

[Gregory East]

wikipedia has a good explanation: http://en.wikipedia.org/wiki/True_RMS_converter. in a nutshell: as long as the signal you are measuring is a sine wave with no dc offset (which is pretty common) you'll get the right answer.

Ha! Thanks for that.
So if I'm understanding it properly a true rms meter is total overkill. They're ALL rms but assume the signal is approximately sinusoidal so feeding a true sinewave gives the exact same result as a flash one with the fancy computer. DOH.

[Harley]

So if I'm understanding it properly ....

Umm... Wikipaedia is not the smartest authority in the world!