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 Laser Pointer Forums - Discuss Laser Pointers So my "1 Ohm" resistor measures .8 ohms...

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02-11-2008, 02:28 PM #1
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desslok
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So my "1 Ohm" resistor measures .8 ohms...

So should I divide by .8 when calculating ma? This is pretty big, a discrepency of 25%. So if I measure 250 mV, instead of it being 250 mA, it is actually 312.5 mA.

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02-11-2008, 02:41 PM #2
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rog8811
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Re: So my "1 Ohm" resistor measures .8 ohms...

Quote:
 "1 Ohm" resistor measures .8 ohms
What tolerance resistor is it? *BN/BK/GLD( 1 OHM )...Tol....Gold band indicates the resistor is within 5%, Silver = 10% and None = 20%.).
If it is a 3 band resistor it is within tol, if gold then suspect your meter.
Measure some other known resistors to check whether your meter reads repeatedly low or high...once that is sorted then we can see what recalculation is required, if any.

Regards rog8811

*Edit.... even if the meter is out on resistance it may be ok on voltage ranges, the easiest way I can think of checking is to see how close the ref voltage on the LM317 (if that is what you are using) is to 1.25v.
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02-11-2008, 02:58 PM #3
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desslok
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Re: So my "1 Ohm" resistor measures .8 ohms...

Well the meter was about \$350 (Fluke), the resistor was less than a dollar. I did have trouble even finding a 1 ohm resistor. Maybe I should just try to find a better quality 1 ohm resistor somewhere.

02-11-2008, 03:01 PM #4
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rog8811
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Re: So my "1 Ohm" resistor measures .8 ohms...

Quote:
 Well the meter was about \$350 (Fluke),
I would trust the meter
What tolerence was the resistor?

Regards rog8811
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02-11-2008, 03:10 PM #5
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desslok
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Re: So my "1 Ohm" resistor measures .8 ohms...

[quote=rog8811]
Quote:
 What tolerence was the resistor? Regards rog8811
Not sure. It's at home, i'm at work. I'll post later.

02-11-2008, 10:32 PM #6
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Re: So my "1 Ohm" resistor measures .8 ohms...

Measuring resistances in the order of 1 ohm or less is always tricky, no matter how expensive the meter (bar models with seperate sense wires). Usually you get a reading that is a bit too high due to the leads and contact resistance, but perhaps this is overcompensated for?

I have found resistors to be very accurate these days, even those rated 5% tolerance are rarely off by more than 1% in practice. You could have gotten a bad one ofcourse, but it's rare.

02-11-2008, 11:31 PM #7
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chimo
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Re: So my "1 Ohm" resistor measures .8 ohms...

Do you have a delta/relative function on the fluke to negate the lead resistance?

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