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Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
Using that circuit with a highly inductive resistor (coil of wire) might not be the best idea, due to the pulsed output... IMHO, the best way to do it is to take a 1a source and clip it to the load. Then take your volt meter set to the mv scale, and touch it directly to the coil (not to the current source). This method has automatic zero adjustment, and the sensitivity is limited only by you imagination (with a 1a source you get a 1mv/.001ohm, minimal part count, and you don't have to worry about the connection resistance. If you need better resolution than the milliohm use a bigger supply, or more sensitive meter. The 1a source could be made with a 5v supply and a 5ohm resistor, as long as you are measuring only small resistances. If you want to measure resistances much greater than a few tenths of an ohm you should use a real constant current source, like the 317 circuit posted by kell.
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Measuring very low resistances
