1. Home
  2. Hobby Electronics Basics
  3. Sanity check for a cheap DVM

Sanity check for a cheap DVM

I'd like to check an old Radio Shack DVM for accuracy around 5 volts DC. On a brand-new cr2032 coin cell it measures 3.25 volts open circuit, about 3.15 volts with a 3 kohm load. That's rather high compared to

formatting link
which shows ~2.95 V with a

15 kohm load.

I've noticed that brand-new alkaline D cells seem to measure around

1.65 volts and credited it to improved battery chemistry. Now I'm not so sure and a reading that is 200 mV high might explain some trouble I'm seeing.

Thanks for reading, and any thoughts.

bob prohaska

Reply to
bob prohaska
Loading thread data ...

For a buck and a quarter at Digikey you can get a 5V reference with 0.2% accuracy in a convenient through-hole TO92 package:

If you're okay with surface mount stuff, 78 cents will get you a 4.096V

+- 0.1% reference,

For about $5 you can get 5V +- 0.01%:

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com
Reply to
Phil Hobbs

Make an electrochemical cell. Look up the resulting voltage using , say silver and copper, then check your dmm. We make our on humidity references using different salt pastes.

Reply to
sdeyoreo

For $28 you can get a reference in this class, fully assembled into a battery operated module, trimmed and calibrated.

See

formatting link

They also have other versions for voltages from 1 to 10 V as well as a DMM check module ("DMMCHECK Plus"), which also includes precision resistors and a current source to cover the other basic functions.

These modules seem to have some popularity among the members of the "volt-nuts" mailing list.

Regards Dimitrij

Reply to
Dimitrij Klingbeil

Cool, thanks.

I generally use an ensemble of 5-1/2 and 6-1/2 digit meters plus some HP

61xx precision power supplies. Last week I got a 6114A (0-20V @ 2A, 20-40V @ 1A) supply that tests out within 0.01% everywhere. $79 plus shipping--eBay rocks.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com
Reply to
Phil Hobbs

** 3.25V open cct is normal IME, that data sheet is miseading.

** Also normal, been like that for decades.
** Your cheap DVM is fine.

.... Phil

Reply to
Phil Allison

That's a relief, sort of. The trouble in question is then more complicated than a bum wallwart.

Thank you very much!

bob prohaska

Reply to
bob prohaska

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.