[sdiy] Multimeter calibration (Extech MM560)

[Nicholas Gregorich]

Well, I figured out my problem this evening!

I DID read the manual before using the MM560 but I guess it didn't sink in all the way.  The meter was in the true RMS mode, causing it to read out "random" voltages (noise?).  After pushing the select button to enter DC only mode the multimeter sits at 0V when idle and it updates 5 times as fast, obviously not calculating RMS values like before.

I am much more impressed with the multimeter now that I know how to use it!  ;)  I will be sure give it a good comparison to the Fluke 179, especially since its available on eBay for $50.

Also be sure to check the battery when your multimeter gets whacky.  It wasn't the problem for me today, but it has been a good noodle scratcher in the past.  "How is this thing running at 0.35V?!".

Anyhow, thought I should report back that its good to know how to operate your toys before questioning them!

Nick.

On Sunday, May 14, 2006, at 07:44PM, Nicholas Gregorich <nicksdsu at mac.com> wrote:

>I picked up one of the Extech MM560 digital multimeters mentioned a month or two ago.  It was a surplus auction on eBay.
>
>The item I received was unopened in its box, and came with a certificate of calibration dated 10/17/00, due for another exactly a year after.
>
>With no probes attached, the multimeter reads 0.0464VDC when I turn it on into VDC mode.  The voltage decreases by about 10mV each second for 10 seconds until it hangs out at 0.0040V, fluctuating each second.  In mVDC mode, it hangs around 0.03mV but doesn't fluctuate as much.
>
>When I attach the probes and touch them together, the fluctuation in VDC mode is the same as before, but in mVDC it hangs out lower, near 0.01mV.  When I move the probes in the air, voltage is seen in mVDC mode, which I've never seen on another multimeter.  Maybe I never paid attention or used one with a mVDC setting.  There also is offset in VAC mode.
>
>The calibration sheet shows that the meter was calibrated in accordance with ISO10012-1 and ANSI/NCSL Z540-1-1994.  I was surprised to see that the meter was only tested at 400VDC, 400VAC, 400mADC, and 400mAAC.  All measurements on the meter passed, so no changes were made.
>
>What confuses me is that measuring 400VDC means the lower limit is at 399.78V and 400.22VDC.  Even with the DC offset I am seeing, the meter is still in spec.
>
>For what its worth I measured 120.xx VAC from my AC mains at 60Hz, and continuity works, so the meter seems fine.
>
>Is DC offset common in multimeters?  I would think not.  My el cheapo meter reads 0V while sitting on my desk, so I expect this one to as well.  Should I send it into Extech?  Can I adjust offset myself?  Should I forget about it?
>
>Its unfortunate, I use a Fluke 179 at work and I have some nice things to say about the MM560 but I would like to resolve this issue first.
>
>Thanks for any help.
>
>Nick.
>
>