Computing stuff tied to the physical world

TK – Multimeter accuracy

In Hardware on May 31, 2012 at 00:01

Welcome to the Thursday Toolkit series, about tools for building Physical Computing projects.

Once you get into calibration stuff, it’s hard to stop. I recently bought this DMMCheck from

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The nice thing about this unit is that it’s fully self-contained (with a 9V battery on the back) and that it has all the bits and pieces on board to check a multimeter’s (DC) voltage, (DC) current, and resistance measurements.

It comes with a calibration report – the voltage has been trimmed to exactly 5V, but the rest will have slightly different values due to component and temperature tolerances. Also, it was calibrated at 70°F (21.1°C):

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Here are my HP 34401A measurements, with only 15 minutes warm-up (it’s now about 23.5°C here at JeeLabs):

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Very close – more than close enough to start checking the VC170 multimeter I described recently, for example:

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Easily within spec. Note that a VC170 only has 400 µA + 400 mA ranges, and 1 mA only shows 2 decimal points.

Here’s a higher-spec VC940, which I find unconvincing – I use it rarely anyway, due to its slow refresh rate:

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Here’s a very low end Extech MN15 – it performs worse than the VC170 and can only display values up to 1999:

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And finally, as flash from the past, a cheap analog multimeter – this one is probably over 30 years old:

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We’ve sure come a long way, from trying to guess the value while not mixing up all those scales!

This reaffirms my choice of using the VC170 for day-to-day use, with the high-end HP 34401A used for top accuracy and for long-running experiments (handheld multimeters always auto-shutdown much too quickly).

As you can see, the DMMCheck is an superb little tool to quickly do a sanity check of your multimeter(s). There’s now also a DMMCheck Plus with extra signals to check AC voltage + current, and even frequency + duty cycle.

If you take lots of measurements over the years, it’s well worth getting something like this to verify your DMM.

This all relates to a discipline called metrology (no, not “meteo”, but “metrics”) – i.e. the science of measurement.

  1. [rant]Took me a while to decipher “DMM.” Digital Multimeter.

    I’m not sure why, but I hate acronyms that are not immediately apparent. Worse are those that people make up.

    Ever since moving to the US (from Germany) ten years ago, I’ve noticed how much Americans use the “made up” kind. Over the years I’ve come to believe that they probably do this, because they don’t know how to spell the word that they are abbreviating this way.

    Why is it so hard for people to spend an extra second and write out a word instead of mutilating it? How many people are stopped in their tracks, because they are trying to figure out for more than one second what that acronym means? One second spent by the author can save dozens of seconds for the readers.

    Btw, ever since I ran into your blog a few days ago and spent too many long nights soaking up its fascinating content, I’ve wondered what “i.s.o.” meant. If I’m right and it means “instead of”, then this is even worse than those “made up” acronyms, because it’s not even an acronym. And I don’t even want to bring up “IOW.” The only acronyms that should be used for the general public are BTW and LOL. But yeah, your audience is hardly the general public. Ok, finished with this [/rant] now.

    Keep up the excellent work you do. You are insane for the amount of time you spend on this; unless this is your day job.

    • Heh, and yes you do have a point. FWIW (whoops…), I did not invent any of the acronyms, but some of them depend quite a bit on the crowd one mingles with. Google is your friend (or should I say GIYF?). I admit that DMM was a bit harder to find, but googling for “DMM electronics” does the trick.

      BTW is the Dutch word for VAT (DE: MwSt, FR: TVA). LOL will not be understood by most people over 50. So, as you see, YMMV.

      But you’re right. I should never have allowed “i.s.o.” to creep in.

      And no, JeeLabs is not my day job. It’s my day and night job :)

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