david.nelson(at)pobox.com
Guest
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 Posted: Mon Aug 17, 2009 3:00 pm Post subject: VOM Troubles - Datapoint |
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I measured 7.2 uA for my Fluke 87.
/\/elson
~~ Lately my memory seems to be like a steel trap .... without any spring. ~~
On Mon, 17 Aug 2009, David E. Nelson wrote:
| Quote: |
<david.nelson(at)pobox.com>
I've a Fluke 87 so I'll check it out this PM and report back.
/\/elson
~~ Lately my memory seems to be like a steel trap .... without any spring.
~~
On Mon, 17 Aug 2009, Robert L. Nuckolls, III wrote:
> At 05:25 PM 8/16/2009, you wrote:
>
> <pinetownd(at)volcano.net>
>
> I have a Fluke model 87 digital VOM (Volt-Ohm-Milliammeter) that has
> just started discharging the internal 9 volt battery in less than a month
> while it is turned OFF. I've had this
> meter for 15 years and used it throughout building my airplane, as
> well as various hobbies before that, so I guess I got my money's worth out
> of it, but I'm puzzled.
>
>
> Great instrument. I've had one since they came
> on the market.
>
> Using another meter, I measured about 10 microamps current out of the
> Fluke's internal 9 volt transistor radio battery while it's turned OFF. If
> a 9 volt transistor radio battery
> holds 0.5 amp-hours, then with 10 microamps, the battery should last
> 50,000 hours. But the last two batteries lasted about a month each. They
> test good before I put them in and
> have an expiration date of 2013.
>
>
> Emacs!
>
> A Duracell 9v has published performance data as shown
> above. The smallest discharge curve is for 2 ma
> so with a end of life voltage of say 7 volts, yes
> the device should deliver 500 mAh of service at
> 2 mA and MORE at still smaller drains. The internal
> resistance of the battery becomes less significant
> as current demands drop . . .
>
> First, is my arithmetic correct? I think a milliamp is 0.001 amps
> and a microamp is 0.000001 amps. I think a 10 microamp current through a
> half amp-hour battery would take 50,000
> hours to deplete the battery.
>
>
> Yup, that's about right.
>
>
> Second, did I read my digital VOM correctly? Using a nice German BBC
> VOM, set on the 2 milliamp scale, it reads .009. Using a cheap Harbor
> Freight digital VOM, set on the 200
> microamp scale, it reads 09.5.
>
>
> The interpretation of your observations seems
> correct.
>
>
> You can see that something is wrong, either with my math or the way
> I'm reading the scale on the VOMs. Or maybe the Duracell fairies are
> sneaking in and sucking all the juice out
> of my batteries?
>
> I talked to Fluke customer support and he said there was no published
> spec on the current draw from the battery while it was turned off and
> couldn't say if mine was bad or not. My
> model 87 isn't supported anymore and he wanted me to buy the new
> version.
>
>
> My model 87 is 100 miles away right now
> but I'll be back in that shop tomorrow or
> Wednesday. I'll duplicate your experiment
> so we can compare results. In the mean time,
> perhaps someone else here on the List has
> a model 87 Fluke and can do their own
> investigation.
>
> Bob . . .
>
> ---------------------------------------
> ( . . . a long habit of not thinking )
> ( a thing wrong, gives it a superficial )
> ( appearance of being right . . . )
> ( )
> ( -Thomas Paine 1776- )
> ---------------------------------------
>
>
>
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