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Re: To our Guide and Pioneer, Steve Sage

To: Theo Smit <tsmit@shaw.ca>
Subject: Re: To our Guide and Pioneer, Steve Sage
From: Steve Laifman <SLaifman@socal.rr.com>
Date: Tue, 15 Jun 2004 10:50:47 -0700
Meter Good. Glasses bad?  Didn't see the tiny decimal point in the 
readout. Hell, this was the best $7 instrument the Chinese make.  So, 
divide readings by 10.  My abacus doesn't even have a decimal point.

I have a more expensive Triplet needle type that is older than you are, 
though. :-)  
Don't think they even make the batteries anymore.

I do have a Professional Digital Model, but it is hidden away (lost in 
the clutter) better than this one was, or it was "borrowed".  Maybe I'll 
find it, someday.

I am either going to have to spend more money, or be less trusting of 
bargain sales.  Maybe there is a $15 model from Malaysia? ;-)

Nice having you around to correct my errors.  Thanks.

Steve

Theo Smit wrote:

> Hi Steve,
> Better get new batteries for that multimeter, or else use it as ballast.
>
> No selfrespecting digital multimeter would ever give a reading as high 
> as 4 ohms with test leads shorted. I just repeated your tests on my 
> test arrangement here, with these results:
>
> The setup is a Flamethrower II coil with a 0.05 ohm, 1% accuracy power 
> resistor hooked up in series (that is so I can measure coil current 
> with a live ignition system running, by recording the voltage across 
> the resistor when the coil is charging, using an oscilloscope).
>
> Meter with test leads shorted: 0.3 ohms
> Meter connected across the 0.05 ohm resistor only: 0.3 ohms
> Meter connected across the coil only: 0.9 ohms
> Meter connected across a 1 ohm, 5% accuracy resistor (I use these in 
> the tach modules): 1.2 ohms.
> Meter connected across two 1 ohm resistors in parallel: 0.7 ohms.
> Meter connected across three 1 ohm resistors in parallel: 0.5 ohms
>
> So here, if we subtract the 0.3 ohm "zero reading" from all these 
> measurements, we end up with 0.6 ohms for the coil, 0.9 ohms for the 
> single resistor, 0.4 for the pair in parallel, and 0.2 ohms for the 
> three-resistor combination. If we assume a 0.1 ohm basic accuracy 
> (since that is the smallest digit it will tell me), we can see that 
> allowing for a 0.1 ohm offset, all the numbers come out pretty much 
> exactly as expected for the known resistances, and the coil then 
> measures at 0.6 ohms, plus or minus 0.1.
>
> Your resistance ratios may still be accurate, but the magnitudes are 
> off by about one order, and that will also affect the theoretical 
> power dissipated in the coil and/or resistor by a factor of 10.
>
> Theo
>
>

-- 
-----

Steve Laifman
Editor
http://www.TigersUnited.com





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