The four-wire (Kelvin) DC voltage drop method is widely used for accurate contact resistance testing in micro-ohmmeters. This technique minimizes errors by isolating the measurement from the internal resistance of test leads and connectors.
Testing Process:
- The test setup requires two current leads to inject current and two potential leads to measure the voltage drop across the contact points.
- The voltage leads should be attached close to the contacts, inside the circuit formed by the current leads, ensuring a precise reading.
The microprocessor of the micro-ohmmeter calculates the contact resistance from the voltage drop, adjusting for potential errors from thermal EMF effects. These thermocouple voltages, generated when metals join, can distort readings. To counteract this, the device may use polarity reversal, averaging, or direct measurement of thermal EMF, ensuring these effects are effectively removed from the measurement.
Best Practices for Consistent Results
Higher Currents for More Reliable Readings: If low current yields high readings, it’s recommended to re-test at a higher current to overcome potential surface oxidation or minor connection issues. Higher currents generally offer more reliable readings in such cases.
Maintaining Consistency for Trend Analysis: To ensure accuracy across multiple tests, keep all conditions the same each time, such as using calibrated cables from the manufacturer and maintaining the same test positions. This consistency is crucial for monitoring changes in resistance over time, helping to identify when a joint, connection, or device may need maintenance.
These steps ensure accurate, reliable data, contributing to improved safety and maintenance planning.
EZT's Contact resistance tester TEHL Series outputs DC 600A/400A/200A/100A current to test the contact resistance of circuit breaker or high current cable contacts. It is designed according to IEC62271. The main application of the tester is the measurement of circuit breaker contact resistance.
Nov 13,2024
