A Digital Low Resistance Ohmmeter or DLRO is used to measure the resistance of circuit breaker contacts, welded joints, terminal connections and other bonded surfaces. The resistance measurements are sensitive enough to detect very small changes in test samples. For example, they provide users with the ability to identify loose connections, corrosion or the presence of other contaminants.
A DLRO measures low resistances by passing a current through the test sample and measuring the voltage drop. Given the value of voltage and current, Ohm's Law (R=V/I) can then be used to calculate and display a value of resistance..
With a DLRO the resistance is automatically computed by a microprocessor and displayed on the LCD screen. Nominal currents used for this type of testing may vary anywhere from 10 Amps to 600 Amps depending on the application for which it is being used. DLRO's are normally use a 4 point measuring system. One pair of leads are used to inject current through the test specimen. Another pair of leads is connected inside of the current leads and is used to measure only the voltage across the test specimen. This ensures a more accurate measurement that does not include the resistance of the current leads. Many manufacturers of this type test equipment will offer test probes that combine a 4 point connection system into a single pair of probes.
Related electrical test equipment available for rent from Protec:
Editor’s Note: This post was originally published on March, 2011 and has been updated freshness, accuracy and comprehensiveness.