How a Low Ohm Resistance Measurement Can Help Find Issues in Conductors and Bonded Metals

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The measurement of low resistance is performed to check if a device is still within its optimum resistance range. Protective device and relay contacts are some of the components often tested for resistance problems. These components are exposed to vibration, corrosion, electrical and thermal stress. Ideally, the contact points should have a resistance of a few microOhms to ensure maximum transfer of power. However, when the contacts degrade due to environmental and operating condition factors, they may reach a critical degrading factor until they fail to operate properly.

When the resistance of relay or circuit breaker contacts increase due to carbon deposition, corrosion and other contaminants, the contact points may heat up during operation. This can cause further degradation of the components and lead to eventual failure.

To measure low resistance, a digital low resistance Ohmmeter or DLRO is used. This device uses a Double Kelvin Bridge input to be able to measure resistance of conductors without the test leads affecting the reading. It often has 4 leads, 2 current and 2 potential probes. The current probes apply current across the sample that is being tested while the potential probes measure the drop of voltage. The measured voltage drop is used by the device’s microprocessor to calculate the resistance. Most modern microOhmmeters today have the current and potential probes combined, reducing the number of leads needed. Normally, a current of 10 A is applied to the sample being tested to be able to measure resistance from 0.1 μΩ up to 2000 Ω.

Aside from measuring low resistance on electrical facilities, a microOhmmeter can also be used on various facilities like in mining, telecommunications, UPS, refineries, chemical plants, aircraft and automotive. Measuring extremely low resistance allows engineers to determine if two metal parts are properly bonded together. The resistance of a bonded joint can tell if it is still structurally sound. If a bonded joint is weakened or corroded, the resistance of the joint increases.

Protec Equipment Resources is a trusted source of microOhmmeters and other electrical test equipment. You can choose from a wide selection of diagnostic devices from trusted brands like Megger, Siemens, GE, ABB, Fluke and HV Diagnostics. You can rent, lease or buy the test equipment you need. Give our application experts a call at 1-866-352-5550 to request for a quotation and for more information about our equipment acquisition services.