redbelly said:
How inaccurate are we talking about? I would think it's better than
the 1% of a precision resistor. If most meters are worse than that,
I'm surprised.
Mark
Hi, Mark. A Fluke 77 (typical handheld DMM) can be typically expected
to get around 1% measurement accuracy for resistors over a couple
hundred ohms.
However, current shunt resistors are typically in the low ohm or
milliohm range, and it's practically impossible to measure these
accurately without a Kelvin measurement.
If you have a precision wirewound resistor (0.1% 100 ohm) and a stable
variable DC power supply, you can make a fairly accurate Kelvin
measurement with that Fluke 77 by setting the voltage to allow a
precise current to flow through both the precision wirewound and the
resistor under test. You can then accurately measure the voltage
across the test resistor, inferring the resistance to the precision of
the 100 ohm resistor and the accuracy of the meter. If you're using a
Fluke 77 on the 200mV range and an 0.1% resistor, you might be looking
at 0.2% tolerance on your measurement.
Of course, if you have a bench DMM with built-in Kelvin measurements
(as I guess you do), that makes your job a lot easier, as you said.
Cheers
Chris