Testing for low resistance is made possible with a digital low resistance ohmmeter (DLRO), or micro ohmmeter. A DLRO test produces complex measurements that are key when judging electrical equipment for performance and resistance. ATEC carries DLRO units from leading manufacturers such as Megger and AEMC.
What is a DLRO (Digital Low Resistance Ohmmeter)?
Also called a micro ohmmeter or ductor, these devices measure the contact resistance of a variety of facility electrical systems, like switch and circuit breakers, aircraft frame bonds, rail and pipeline bonds, and more.
Measuring low resistance of these electrical systems is crucial to identifying which resistance elements have accelerated to speeds that are beyond the accepted values. If certain elements of an electrical device or piece of equipment move too quickly, the flow of the device is interrupted, which will alter the amount of current being drawn and cause a circuit to short. A test will reveal if there is a low resistance measurement present, which typically falls below 1.000 ohm.
Benefits of DLRO Testing
Low resistance measurements performed by a DLRO are necessary to prevent long-term damage and energy waste.
With every electrical device, long-term degradation will impede proper usage. Factors like the working environment, climate, or even regular usage can damage electrical components.
Unexpected resistance is one of the clearest signs of degradation or damage. The increased resistance can prevent the flow of current and cause the device to overheat and fail. It's important to use a DLRO when troubleshooting a malfunctioning electrical device because a standard multimeter could show no issue with the resistance, reading at 0 ohms. Able to test currents from 0.5 mA to 600 A, the micro ohmmeter can find harmful resistance that's undetectable by other equipment.
DLROs can reduce energy costs by locating these issues. An unexpected resistance may cause the device's energy consumption to increase to compensate for the lost current.
How to Conduct a DLRO Test / Ductor Test
These devices work by sourcing a known DC current and measuring the resulting voltage drop across the contacts, allowing the unit to calculate resistance internally using Ohm's Law.
Testing can be very simple, even for inexperienced users. Simply connect the DLRO test leads to the opposite ends of the Device Under Test (DUT) and begin the test with the push of a button. The only minor complications in a DLRO test can come when choosing a test method or measurement:
Two-Wire Measurements
The easiest DLRO test uses two-wire measurements. Only involving two test leads, this method is often used for general testing. Factors like contact probe resistance can slightly affect result accuracy, so a two-wire measurement is preferred for readings above 10 ohms.
Three-Wire Measurements
A three-wire measurement adds an extra test lead as a guard and is reserved for high-resistance testing. A three-wire test is best for measurements greater than 10 megohms.
Four-Wire Measurements
The most accurate test method, four-wire measurements, gets rid of all resistances which could affect results. Using two current leads and two potential leads, the four-wire test can measure resistances that are less than 10 ohms. The lack of contact resistance delivers low resistance results free of any errors.