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Reduced resistance of resistor
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Twoflower:
Oh, sorry, I missed the follow up question.

To measure low resistance resistors you can use better equipment of course. For better accuracy they use 4-Wire measurement methods (one set of wires apply the current while the second pair is used to measure the voltage across).

Or you do this using a bench supply as you suggested. Which comes with its own problems. As for example the power supply must be stable driving such high currents at low voltages (e.g. 1V with 1.78A). And you might do the voltage/current measurements with external meters (at least for cheaper supplies I don't trust the current readings untested). Ideal would be two meters. One for the voltage over the resistor (connected direct at the resistor leads) and one for current. This way you have the same setup like the 4-wire setup mentioned above. But again: You need to take cate about the accuracies of your meter. For example many meters lack a 2A range, so you have to use a 20A (or 10A) range. Which gets problematic with the +/-n digit error. Especially if you have only a low digit meter.

In general: Low resistance measurements ain't not easy if you want to get good and reliable results. Unless you have the right tools.
engrguy42:
Thanks, but my big question was regarding multimeter resistance accuracy down in the range of the OP's resistor (ie, 0.56 ohms), and specifically what can be expected with his reading of 0.7 ohms. If the spec'd accuracy of the meter is 5 digits, does that mean the 0.7 reading can be off by +/- 0.5 ohms?
Twoflower:
Argh, that was on page one. Sorry.

But your assumptions are right. Mainly the +/-n digits kill you in this case (+/-0.5Ohms in this case). And your calculations are right. The +/-m% ain't adding much (about +/-0.05Ohm). So the total value is 0.7Ohm +/-0.55Ohm. Which gives a total range of 0.15...1.25Ohm. Which is a huge error +/-467% if my math didn't fail me.

One digit more in resolution would gain much in the accuracy here.
engrguy42:

--- Quote from: Twoflower on April 12, 2020, 02:04:52 pm ---Argh, that was on page one. Sorry.

But your assumptions are right. Mainly the +/-n digits kill you in this case (+/-0.5Ohms in this case). And your calculations are right. The +/-m% ain't adding much (about +/-0.05Ohm). So the total value is 0.7Ohm +/-0.55Ohm. Which gives a total range of 0.15...1.25Ohm. Which is a huge error +/-467% if my math didn't fail me.

One digit more in resolution would gain much in the accuracy here.

--- End quote ---


Cool, thanks. I was kinda addressing what you mentioned about the possible disparity between the OP's measurement of 0.7 for a 0.56 ohm resistor, and your response that it might be due to multimeter lead resistance. Seemed to me that it was more likely due to the poor meter accuracy at those levels. 
Twoflower:
I haven't had looked up the accuracy of the meter itself. I should have done that, especially as I saw only one valid digit. So you had the right answer about the discrepancy of the reading.  :-+

Somehow I drop such one digit measurements mentally and never think about it except how do I get a valid measurement. And then one can easily fall into the next problem. Like the mentioned contact and lead resistance.
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