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20to20
diyAudio Member

Join Date: Jun 2010
Location: W-S, NC
Quote:
 Meter lead resistance won't have any impact for a voltage measurement across a sense resistor wired in to the cathode circuit :-)
Ya, the voltage measurement is not where the error starts. It's in determining the resistance value. If you check the resistor and it "reads" 1R, the meter leads are adding anything from .1 -.3 R which means the real resistor value is .7 -.9. My Fluke 77 will read .1 -.2 R in the autoranging mode between leads, on a good day. So .05/.8 = .0625 instead of .05. Whereas .5/9.8 = .051.

Last edited by 20to20; 13th September 2012 at 02:16 AM.

 13th September 2012, 03:15 AM #32 trobbins   diyAudio Member     Join Date: Feb 2009 Location: Melbourne, Oz Yes, trying to read a 1 ohm resistor with a typical fluke is asking for question marks on accuracy. Even using a DC supply and a current meter and a voltage meter still needs meters with good resolution and accuracy. I take a backward step and use a new modern commercial resistor, with the view that anything from 1% to 5% tolerance is likely to give me more confidence than trying to make a 'measurement' of the resistors resistance value.
20to20
diyAudio Member

Join Date: Jun 2010
Location: W-S, NC
Quote:
 Originally Posted by trobbins Yes, trying to read a 1 ohm resistor with a typical fluke is asking for question marks on accuracy. Even using a DC supply and a current meter and a voltage meter still needs meters with good resolution and accuracy.
I think having the Fluke read my meter lead resistance is added accuracy. It's just that there is no "0" adjust possible as in many analog meters. I have three sets of meter leads from different quality meters I've purchased and they all have different resistances.

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