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4hv.org :: Forums :: General Chatting
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quality of Lafayette DMB-USB2

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TheMerovingian
Sat Feb 12 2011, 04:20PM Print
TheMerovingian Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
I came accross this multimeter for 99Euros at ebay. It says true-rms but i don't trust it. It is worth buying? Anyone has it?

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Adam Munich
Sat Feb 12 2011, 04:43PM
Adam Munich Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
I can't find any info on that meter, but may I suggest this one? It was an amazing meter until I killed it... Link2
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TheMerovingian
Sat Feb 12 2011, 07:26PM
TheMerovingian Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
How did you kill it?
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Adam Munich
Sat Feb 12 2011, 08:55PM
Adam Munich Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Lots o' volts.
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Martin King
Sat Feb 12 2011, 10:46PM
Martin King Registered Member #3040 Joined: Tue Jul 27 2010, 03:15PM
Location: South of London. UK
Posts: 237
What reason do you have for not trusting it ?
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TheMerovingian
Sun Feb 13 2011, 02:12PM
TheMerovingian Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
Because it says it is true-rms and then says that the waveform must be sinusoidal.... maybe they mean it must be alternating, who knows... i have to use my oscope math to get the rms reading
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Martin King
Sun Feb 13 2011, 03:23PM
Martin King Registered Member #3040 Joined: Tue Jul 27 2010, 03:15PM
Location: South of London. UK
Posts: 237
Ah! Email them and ask for clarification? BTW if True RMS is important to you then this is worth a read Link2

Martin.
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Steve Conner
Sun Feb 13 2011, 04:27PM
Steve Conner Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
We've discussed that before. All "true RMS" meters are like that by design, even though it's not technically true RMS. I've never seen one that took the DC component into account, if it did then it wouldn't even make sense to have separate AC and DC ranges on the thing. They would have to be called "RMS" and "Average" instead.

For 99 euros I'd rather buy a second hand Fluke.
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TheMerovingian
Wed Mar 02 2011, 04:15PM
TheMerovingian Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
Good point. I received the multimeter and it works correctly but , as pointed out, with simmetric waveforms. Fortunately the (FalseRMS^2 + DcAverage^2)^0.5 is a good workaround. For the rest , my Digital Scope will easily calculate true RMS (if i use DC and not AC coupling :D)
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Nicko
Wed Mar 02 2011, 04:35PM
Nicko Registered Member #1334 Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615
Steve McConner wrote ...

We've discussed that before. All "true RMS" meters are like that by design, even though it's not technically true RMS. I've never seen one that took the DC component into account, if it did then it wouldn't even make sense to have separate AC and DC ranges on the thing. They would have to be called "RMS" and "Average" instead.

For 99 euros I'd rather buy a second hand Fluke.
Tek DMM916 - Link2 - See page 1-24

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