Sanity check for a cheap DVM

Started by bob prohaska June 22, 2018
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
http://data.energizer.com/pdfs/cr2032.pdf, 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

On 06/22/18 20:12, bob prohaska wrote:
> 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 > http://data.energizer.com/pdfs/cr2032.pdf, 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 >
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: <https://www.digikey.com/product-detail/en/texas-instruments/LM4040BIZ-5.0-NOPB/LM4040BIZ-5.0-NOPB-ND/363989> If you're okay with surface mount stuff, 78 cents will get you a 4.096V +- 0.1% reference, <https://www.digikey.com/product-detail/en/microchip-technology/MCP1501T-40E-CHY/MCP1501T-40E-CHYCT-ND/5844637> For about $5 you can get 5V +- 0.01%: <https://www.digikey.com/product-detail/en/maxim-integrated/MAX6126AASA50/MAX6126AASA50-ND/1867179> 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
On Friday, June 22, 2018 at 8:12:38 PM UTC-4, bob prohaska wrote:
> 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 > http://data.energizer.com/pdfs/cr2032.pdf, 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
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.
On 23.06.2018 03:01, Phil Hobbs wrote:
> > For about $5 you can get 5V +- 0.01%: >
<https://www.digikey.com/product-detail/en/maxim-integrated/MAX6126AASA50/MAX6126AASA50-ND/1867179>
>
For $28 you can get a reference in this class, fully assembled into a battery operated module, trimmed and calibrated. See http://www.voltagestandard.com/Home_Page_JO2U.html 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
On 06/24/18 17:22, Dimitrij Klingbeil wrote:
> On 23.06.2018 03:01, Phil Hobbs wrote: >> >> For about $5 you can get 5V +- 0.01%: >>
<https://www.digikey.com/product-detail/en/maxim-integrated/MAX6126AASA50/MAX6126AASA50-ND/1867179>
>> >> > > For $28 you can get a reference in this class, fully assembled into > a battery operated module, trimmed and calibrated. > > See&nbsp;&nbsp; http://www.voltagestandard.com/Home_Page_JO2U.html > > 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
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
bob prohaska wrote:
> > > 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 > http://data.energizer.com/pdfs/cr2032.pdf, which shows ~2.95 V with a > 15 kohm load. >
** 3.25V open cct is normal IME, that data sheet is miseading.
> I've noticed that brand-new alkaline D cells seem to measure around > 1.65 volts and credited it to improved battery chemistry.
** Also normal, been like that for decades.
> > Thanks for reading, and any thoughts. >
** Your cheap DVM is fine. .... Phil
Phil Allison <pallison49@gmail.com> wrote:
> bob prohaska wrote: >> >> >> 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 >> http://data.energizer.com/pdfs/cr2032.pdf, which shows ~2.95 V with a >> 15 kohm load. >> > > ** 3.25V open cct is normal IME, that data sheet is miseading. > > >> I've noticed that brand-new alkaline D cells seem to measure around >> 1.65 volts and credited it to improved battery chemistry. > > > ** Also normal, been like that for decades. > >> >> Thanks for reading, and any thoughts. >> > > ** Your cheap DVM is fine.
That's a relief, sort of. The trouble in question is then more complicated than a bum wallwart. Thank you very much! bob prohaska