Re: Battery Voltages
From: mike (spamme0_at_juno.com)
Date: 07/28/04
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Date: Wed, 28 Jul 2004 13:12:40 -0700
Norm Dresner wrote:
> Back in the stone age when I built my Heathkit VTVM, its instructions were
> to "calibrate" it with a fresh Carbon-Zinc [about the only dry cells
> available back then] battery at [IIRC] 1.51V. I vaguely remember that a
> sample of a few such cells proved pretty consistent -- within a needle's
> width is my recollection. I just grabbed 10 Alkaline batteries of various
> sizes and ages from the bin in the basement and there's an overall variation
> of 100mv in their potentials [using a DVM which is only moderately reliable
> but has proven to give consistent short-term results]. Obviously these
> won't do as a "calibration" standard of any sort -- unless there's a known
> maximum voltage and even then the sampling may require more units than
> practical.
> Alkaline cells can't be used; could I go back to Carbon-Zinc?
> Are these really reliable or were we just lucky back then?
>
> What else is practical for a typical EE's home environment? Could I build a
> reasonably accurate chemical cell of any sort with stuff that the CPSC will
> allow me to keep in my house?
>
> Or am I going to have to bite the bullet and purchase something? Are there
> units available for rent?
>
> TIA
> Norm
>
There's an old saying, "a man with one watch always knows what time it
is. A man with two watches is never quite sure what time it is".
What are you really trying to do? You talk about accuracy and "old
heathkit vtvm with carbon-zinc battery calibration" in the same breath.
If you're doing commercial work, you must have current calibration
stickers. Not much way around that.
If you're just messing around, you'll probably find that a cheap 3.5
digit meter works just fine.
I've been doing this for 40 years. The only time I ever pulled out the
5.5 digit dvm was when I needed more digits and a Kelvin connection
to measure (relative) low ohms to find a short on a circuit board.
Sure, you can easily rent calibration standards, but you won't like the
price.
So, gather up a few resistors to exercise the ohms ranges.
Gather up some more resistors and a battery to exercise the current ranges.
Call up a local ham radio operator and ask to come over and compare
your meter against hers. If they don't have a decent meter, they'll
know someone who does.
If you're a working EE, you can likely find suitable reference
instruments at your place of employment.
Most accuracy requirements are greatly exaggerated.
mike
-- Return address is VALID. Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121 Bunch of stuff For Sale and Wanted at the link below. HP200LX 10MB + MODEM + LEATHER CASE Sony Digital Camera Compaq Aero floppy,ram,battery. FT-212RH 2-meter 45W transceiver. Toshiba & Compaq LiIon Batteries, Test Equipment 30pS pulser, Tektronix Concept Books, spot welding head... http://www.geocities.com/SiliconValley/Monitor/4710/
- Next message: Jonathan Kirwan: "Re: Battery Voltages"
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- In reply to: Norm Dresner: "Battery Voltages"
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