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This month's (December 2018) giveaway is a piece of junk. Or rather, a battered and beaten "historical artifact." It's a Philco oscilloscope from 1946. The manual, including schematic, is here. I picked it up on eBay a few years ago, and while it's kind of cool, have no real use for the thing. It powers up and displays a distorted waveform, usually, but is pretty much good for nothing other than as a desk ornament. I wrote about this here. (The thing is so old I'd be afraid to leave it plugged in while unattended). Enter the contest here.

Review of the DMMCheck (Reviewed December, 2013), by Jack Ganssle

August, 2017 update: The DMMCheck is no longer available. The company does make other calibration devices, though.

How accurate is your DMM? If you work for a decent-sized company they probably calibrate at least some of the test equipment every year. But many others never check calibration. Buy a meter off eBay and you have no idea if reads accurately.

I recently came across the Voltagestandard web site which offers a number of low-cost references and ordered one of their DMMCheck devices. The specs are amazing considering the price:

  • 5.000 volt output reference, accurate to 0.01% +/- 500 µV
  • 1.000 mA reference, accurate to 0.1% +/- 1 µA
  • Three 0.1% resistors: 1K, 10K and 100k

The unit runs off an included 9 V battery.

It comes with a calibration certificate, and its accuracy is guaranteed for six months. For the first two years recals are free (user pays shipping) and after that it's $5. The vendor checks each unit against an 8.5 digit DMM that is recalibrated every year.

Calibration certificate for the DMMCheck

DMMCheck calibration certificate

Output of the DMMCheck

The DMMCheck's 5 volt output

Obviously, this unit provides only a few fixed values and doesn't substitute sending your DMM to a cal lab, but at $35 (for 25 PPM resistors; add $4 for 10 PPM) it's a bargain for those who don't get regular meter calibrations.