Measuring resistance of less than 1 ohm
measuring less than 1 ohm accurately
Having some issues with the resistance of a db-25 cable, and need to compare the end to end resistance of several brands to find the lowest resistance.
Unfortunately when using most DVM's, the sub ohm accuracy and resolution is pretty poor.
Special sub ohm testers usually use a 4 connection meter. two leads apply a constant current, and two pick up the developed voltage.
I used my adjustable constant current lab supply, set to produce 1A CC.
This current through the sub ohm cable wires will develop 1V/ohm, so the cables actual resistance can be measured with 0.001ohm accuracy. The voltmeter will read 220mV for the 0.220 ohms.
Since the current is constant, and the current connections are separate from the measuring connections, the accuracy is very good.