Typical method of contact resistance test

The four-wire (Kelvin) DC voltage drop is a typical method used by micro-ohmmeters for contact resistance testing. It can ensure more accurate measurement by eliminating its own contact resistance and the resistance of the test leads.

• The contact resistance test uses two current connections for injection, and two potential leads for voltage drop measurement; the voltage cable must be as close as possible to the connection to be tested and always in the circuit formed by the connected current leads.

• From the voltage drop measurement, the micro-ohms controlled by the microprocessor calculates the contact resistance, and at the same time eliminates the error that may occur due to the thermal EMF effect in the connection (thermo EMF is the small thermocouple voltage generated when two different metals are connected together) They will be added to the total voltage drop measured. If they are not subtracted from the measurement by different methods (polarity inversion and averaging, direct measurement of thermal EMF amplitude, etc.), they will introduce errors in the contact resistance test.

• If a low resistance reading is obtained when using a low current test circuit breaker contact resistance, it is recommended to retest the contact with a higher current. Why would we benefit from higher current? Higher currents will be able to overcome connection problems and oxidation on the terminals, where lower currents may produce false (higher) readings under these conditions.

In contact resistance testing, it is very important to maintain consistent measurement conditions to be able to compare with previous and future results of trend analysis. Therefore, when performing regular measurements, the contact resistance test must be performed at the same location, using the same test lead (always use the calibration cable provided by the manufacturer), and under the same conditions, so that you can know when to perform bonding, connection, and welding Or the device will become unsafe.