Multimeter accuracy

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Eric G   1 kW

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Multimeter accuracy

Post by Eric G » Oct 16 2007 9:13am

Hello All...
I've got 4 multimeters and all 4 show different voltages when measuring the same 12 volt battery the difference can be of up to ~2/10's of a volt.

These are the meters...
1 - Cheap $10. Walmart "Superex" multimeter stated accuracy .08%
2 - A $30. "Equus"multimeter stated accuracy .05%
3 - A Canadian Tire $40. "Mastercraft" multimeter stated accuracy 1%
4 - A Watt's Up meter $ 50. (don't remember the accuracy).

The cheap Walmart meter reads closest to the Watt's Up meter by 1/100th of a volt.The Mastercraft reads the lowest to the Watts Up by being under 2.5/10's volt.The Equus reads under by 2/10's to the Watt's Up.

I'm comparing all the meters to the Watt's Up because it's used on the road to measure the battery usage and it's used to measure the power going back in while charging the battery.

Which one do I believe???

Thanks
Eric
600 watt Brushed Clyte/20in.wheel/36v7.2ah sla /25amp controller/34kmh. on level ground
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TylerDurden   100 GW

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Post by TylerDurden » Oct 16 2007 9:46am

I noticed one of my older DMMs taking some time to settle... I think it has a funky capacitor. Bummer, since it's the one with the PC link.

Did you leave the meters on for a while?
Have a Nice Day,

TD

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Doctorbass   100 GW

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Post by Doctorbass » Oct 16 2007 10:29am

Buy a fluke and let you stop bordering you with innacurate cheap DMM :wink:

I know alot about multimeter and i have 9 different in my home lab.

some of those will have different reading because:

some have an internal load (like mastercraft that have a load to test 1.5, 6, 9 and 12V battery) they dont test in floating mode).. they will read lower value and it's the load that make the voltage droping a bit...

-some have cheap DAC and op amp ic and resistors that have tolerence that drift with temperature...

-some are affected by the soc of the battery that power the multimeter!.. a lower 9V battery give often higher reading!!!

-buy a fluke...

buy a fluke...

but a fluke...

... ....

... ...

Zzzzz zzzz zzzz...


Doc :wink:
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Ypedal   100 GW

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Post by Ypedal » Oct 16 2007 11:00am

I agree about the Fluke meter, but unless you do alot of this stuff it's not critical to be exact in the readings.. as long as you can get a general V reading it's usually good enough to spot problems and troubleshoot for the average joe.
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Drunkskunk   100 GW

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Post by Drunkskunk » Oct 16 2007 1:59pm

Fluke Meter's are about the best you can buy.

But if you want to test the accuracy, measure the voltage on your PC. the power supply has to keep 12 volts as stable and as exact as possible, so its a good 12V referance when you have nothing else

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Jozzer   100 kW

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Post by Jozzer » Oct 16 2007 2:36pm

Watts up on the other hand is NOT accurate, mine reads more than 50% too high below about 10v, and more than a volt LOW at high volts!
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Countless ebikes and trikes..
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Toorbough ULL-Zeveigh   100 MW

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Post by Toorbough ULL-Zeveigh » Oct 16 2007 2:42pm

If you think about it, one or two tenths of a volt difference is about as accurate as an analog voltmeter, I still use my Triplett 310.
If it really bothers you, do all your readings at the next higher voltage range where the difference won't show & you have comparable analog resolution.
Y is right, I can't image anything ebike related where hundredth volt accuracy would be critical.
Yes a Fluke is about 10 times more accurate, but no, you don't absolutely require one if this is all you use a DMM for.

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TylerDurden   100 GW

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Post by TylerDurden » Oct 16 2007 5:43pm

Toorbough ULL-Zeveigh wrote:If it really bothers you, do all your readings at the next higher voltage range where the difference won't show & you have comparable analog resolution.
If your engine knock bothers you, turn-up the radio.

If your reflection bothers you, turn-on a hot shower.

If your spouse bothers you, turn-on your hot neighbor.
Have a Nice Day,

TD

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Doctorbass   100 GW

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Post by Doctorbass » Oct 16 2007 5:45pm

TylerDurden wrote:
Toorbough ULL-Zeveigh wrote:If it really bothers you, do all your readings at the next higher voltage range where the difference won't show & you have comparable analog resolution.
If your engine knock bothers you, turn-up the radio.

If your reflection bothers you, turn-on a hot shower.

If your spouse bothers you, turn-on your hot neighbor.
:P
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Eric G   1 kW

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Post by Eric G » Oct 16 2007 6:18pm

TylerDurden wrote:
Toorbough ULL-Zeveigh wrote:If it really bothers you, do all your readings at the next higher voltage range where the difference won't show & you have comparable analog resolution.
If your engine knock bothers you, turn-up the radio.

If your reflection bothers you, turn-on a hot shower.

If your spouse bothers you, turn-on your hot neighbor.

:P :P


Merci Doc for the explanations you outlined as as to why readings are different.Very helpfulI don't use the CT battery load tester,I use two 12 volt 50watt RV lights in parallel ~8 amp draw.

No Tyler I just turn um on and use them I'll turn them on for a bit then try measuring.

DS,excellent thought on measuring the PC's power supply 12v line to figure out which one is best.

Jozzer, thanks for the enlightenment on the Watts Up...

Actually I scrounged all these meters up and gave them a whirl and was just curious as to the differences. I do like accuracy tho.

What's one of those Flukes cost ???

Oh and thanks also Ypedal and Toorbough

Eric
600 watt Brushed Clyte/20in.wheel/36v7.2ah sla /25amp controller/34kmh. on level ground
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TylerDurden   100 GW

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Post by TylerDurden » Oct 16 2007 6:30pm

Eric G wrote: What's one of those Flukes cost ???
Couple hundred bucks.
Have a Nice Day,

TD

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mvadventure   1 kW

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Post by mvadventure » Oct 16 2007 8:56pm

Never having had a Fluke meter I can't speak about but I have about six different ones, three digital and three analog and I have managed to blow fuses, innards and other important stuff. My favorite analog no longer reads ohms but does have a audible alarm ohm part that works and so far that's good enough.

Some will read a 1.5 volt battery, some no longer will. Biggest problem for me is to remember which one will do what. Really need to throw a couple of the analogs away and at least one of the digitals as they get tangled up in the drawer, the leads always fall out and it would be easier to remember the working parts if I had fewer.

Or, I could buy a Fluke. Maybe once the LiPO4's get here I'll do that. The electronic wizard from RayMarine that works on my boat has a Fluke and he's pretty darn smart. He also has a Harbor Freight electric screwdriver though.

Mike

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TylerDurden   100 GW

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Post by TylerDurden » Oct 16 2007 9:12pm

mvadventure wrote: The electronic wizard from RayMarine that works on my boat has a Fluke and he's pretty darn smart. He also has a Harbor Freight electric screwdriver though.
Smart he is.

HF multimeters work too... not Fluke, but you won't speak in tongues if you burn em up.
Have a Nice Day,

TD

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Eric G   1 kW

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Post by Eric G » Oct 17 2007 7:18am

TylerDurden wrote:
Eric G wrote: What's one of those Flukes cost ???
Couple hundred bucks.
I guess you get what you pay for,I paid that for my c-lyte brushed.

Edit:OOPS...in the above post with the aquus meter I should have said /100th's instead of /10th's...
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