Multimeter Question -solved-

Multimeter Question -solved-
Posted by Luciano2572 on 06 Feb, 2014 15:39
Hey guys,
Been watching Dave vids for some time, and finally decided to order a better multimeter , a ET-997 (ordered on dx.com - this one: http://dx.com/p/3-0-lcd-handheld-digital-multimeter-voltage-current-resistance-temperature-1-6f22-42269 ) to replace my old crappy 15$ one.
But when checking just the basic DC, it gave me way different voltages than my old meter, see pics
http://i58.tinypic.com/25q7rip.jpg
http://i60.tinypic.com/2ep5a52.jpg
http://i60.tinypic.com/14vqtle.jpg -> from a lm7805 (also from china), with a ~9.5V input, no load

I saw a pic from a user in the forums here, here: https://www.eevblog.com/forum/testgear/minipa-et-997-$50-multimeter-review/15/
where he compared the results with a fluke 89 and they were pretty similar (Didn't post there to avoid reviving the thread - almost 2 yrs)

The ET-997 has a 0.5% on DC, while the old ET-1002 has 0.8%, which should only be 0.025 vs 0.04 off

I don't have a precision voltage source (Wish I had one in times like this...)

Which one should I trust? =/

Thanks in advance!

#1 Reply
Posted by Excavatoree on 06 Feb, 2014 15:42
I don't know if anyone will concur with me, but I'd say until you get some type of known reference to use, you can't be sure which one is more correct.

If you know someone with a calibrated meter that you can borrow, you could use that to compare, but comparing one unknown instrument to another won't tell you anything.

#2 Reply
Posted by Luciano2572 on 06 Feb, 2014 15:50
Was thinking about that, too - and hoping the lm7805 would be of any help to the case
Seems like I'll have to spend some more and buy a voltage reference, since everyone I know has either a 10$ dmm or none

#3 Reply
Posted by Excavatoree on 06 Feb, 2014 15:57
Perhaps someone with more experience about 78xx regulators can explain further, but the first data sheet I looked at specified that the Vout could be anywhere from 4.75 min to 5.25 max.

#4 Reply
Posted by Wytnucls on 06 Feb, 2014 16:08
Like Excavatoree said.
If you have a fresh Duracell AA size battery, it should measure close to 1.6V. The meter which is not in the ballpark is probably the one out of specs.

#5 Reply
Posted by Luciano2572 on 06 Feb, 2014 16:28
Thanks for the replies!

Tested on a new duracell battery,
1.663 on the et-997 (new)
1.60 on the et-1002 (old)

#6 Reply
Posted by Wytnucls on 06 Feb, 2014 16:34
1.663V sounds a bit excessive. So the new meter could be slightly out. Try to compare it to your friends cheap meters. They should be accurate enough for such a discrepancy.

#9 Reply
Posted by Luciano2572 on 06 Feb, 2014 17:12
Quote from: Wytnucls on 06 Feb, 2014 17:04
Good luck with Minipa. Have they still got an office or factory in Brasil?
Yea, they have an office here & I believe a factory too, since they offer lots of products for a good price and they are pretty popular here

#10 Reply
Posted by rsjsouza on 06 Feb, 2014 17:14
Quote from: Wytnucls on 06 Feb, 2014 17:04
Good luck with Minipa. Have they still got an office or factory in Brasil?
They do have an office in Brazil. They moved manufacturing to China about twenty years ago, though.

#11 Reply
Posted by retiredcaps on 06 Feb, 2014 17:15
Try a new fresh battery in the Minipa. Some meters I find give high incorrect readings when the battery is weak even though the low battery indicator is not on.

#12 Reply
Posted by Luciano2572 on 06 Feb, 2014 19:42
Quote from: retiredcaps on 06 Feb, 2014 17:15
Try a new fresh battery in the Minipa. Some meters I find give high incorrect readings when the battery is weak even though the low battery indicator is not on.
It was already on a new one, forgot to mention that

#13 Reply
Posted by IanB on 06 Feb, 2014 20:20
Another helpful reference for ball park voltage measurements is a brand new super heavy duty (zinc chloride) 9 V battery. This should read very close to 10 V. (An alkaline battery will read closer to 9.6 V)