Metals have a very low resistance of a few microOhms. This information is used to diagnose problems in joined or welded metals. A weakened or corroded joint will increase the resistance of the junction. Ordinary Ohmmeters do not have the capability to measure very low resistances on joined metals. In order to effectively measure low resistances, a digital low resistance Ohmmeter should be used.
Ordinary Ohmmeters do not have the capacity to measure very low resistance and therefore use a different method of measuring. It sends out a low test voltage on one probe and the other probe receives the residual current. The current that was able to pass through indicates the resistance of the test sample. For low resistances, this method is not applicable because low resistances will allow the full test voltage to flow and give false results. A better method is to apply a high test current on the sample and measure the voltage drop across it. The voltage drop serves as a reference and the resistance is then calculated using Ohm’s law. A DLRO uses this method and its microprocessor automates the calculations of the results.