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Sanity check for a cheap DVM

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bob prohaska
Guest

Sat Jun 23, 2018 1:45 am   



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

Phil Hobbs
Guest

Sat Jun 23, 2018 2:45 am   



On 06/22/18 20:12, bob prohaska wrote:
Quote:
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


Guest

Sat Jun 23, 2018 9:45 pm   



On Friday, June 22, 2018 at 8:12:38 PM UTC-4, bob prohaska wrote:
Quote:
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.

Dimitrij Klingbeil
Guest

Sun Jun 24, 2018 10:45 pm   



On 23.06.2018 03:01, Phil Hobbs wrote:
Quote:


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

Phil Hobbs
Guest

Sun Jun 24, 2018 11:45 pm   



On 06/24/18 17:22, Dimitrij Klingbeil wrote:
Quote:
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


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

Phil Allison
Guest

Mon Jun 25, 2018 3:45 am   



bob prohaska wrote:
Quote:


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.


Quote:
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.

Quote:

Thanks for reading, and any thoughts.


** Your cheap DVM is fine.


..... Phil

bob prohaska
Guest

Thu Jun 28, 2018 1:45 am   



Phil Allison <pallison49_at_gmail.com> wrote:
Quote:
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

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