What Is Contact Resistance?

The resistance that appears between conductors is called contact resistance. The contact resistance is generally required below 10-20 mohm. Some switches require below 100-500uohm. Some circuits are sensitive to changes in contact resistance. It should be noted that the contact resistance of the switch is the maximum value of the allowed contact resistance of the switch during several contacts.

Contact resistance

Correct

Observe the surface of the connector contacts under the microscope, although the gold plating is very smooth, you can still observe 5-10

In summary, the real contact resistance should consist of the following parts

In addition to using the milliohm meter, volt-amperometry can also be used.

It is mainly affected by factors such as contact material, positive pressure, surface condition, use voltage and current.

1) Contact resistance1 ) Low battery

It is considered that the contact film will have mechanical breakdown under high contact pressure or electrical breakdown under high voltage and high current. For some small-volume connectors, the contact pressure is quite small, and the application is only mV or mA. The film resistance is not easy to be broken down, which may affect the transmission of electrical signals. Therefore, the national standard GJB1217-91 electrical connector test method specifies two test methods. That is, low-level contact resistance test method and contact resistance test method. The purpose of the low-level contact resistance test is to evaluate the contact resistance characteristics of the contact under the condition that the voltage and current of the non-conductive oxide film that does not change the physical contact surface can be changed. The applied open-circuit test voltage does not exceed 20mV, and the test current should be limited to 100mA. The performance at this level is sufficient to meet the performance of the contact interface under low-level electrical excitation. The purpose of the contact resistance test is to measure the resistance between the ends of a pair of mating contacts that pass a specified current or between the contact and the measuring gauge, and this specified current is much larger than the former, usually specified as 1A.

2) Contact resistance 2) Single hole separation force

To ensure reliable mating contact of the contacts, maintaining a stable positive pressure is key. Positive pressure is a direct indicator of contact pressure and significantly affects contact resistance. However, since the positive pressure of the mated state of the contact is difficult to measure, it is generally used to measure the single-hole separation force of the contact in the mated state from static to moving to characterize the contact between the pin and the socket. Generally, the separation force requirements specified by the technical conditions of electrical connectors are determined experimentally, and the theoretical value can be expressed by the following formula.

F = FN ·

Where FN is the positive pressure and is the friction coefficient.

Because the separation force is restricted by both the positive pressure and the coefficient of friction. Therefore, it must not be considered that the separation force is large, and the contact is reliable in the case of large positive pressure. With the improvement of the precision of the production of contact parts and the quality of the surface coating, the reliable contact can be guaranteed by controlling the separation force at an appropriate level. In practice, the author found that the separation force of a single hole is too small, which may cause a momentary signal interruption when subjected to a vibration shock load. It is more effective to measure the contact reliability than to measure the contact resistance by measuring the separation force of a single hole. Because in the actual inspection, the contact resistance parts rarely fail, and the single-hole separation force is too low, and the contact resistance is often still qualified.

3) Contact resistance 3) Inspection

In many practical applications, automobiles, motorcycles, trains, power machinery, automation instruments, and aviation, aerospace, and marine military connectors are often used in dynamic vibration environments. The experiment proves that just checking the static contact resistance is qualified, and it can not guarantee the reliable contact in dynamic environment. Often, connectors with qualified contact resistance still experience instantaneous power failures when subjected to simulated environmental tests such as vibration, shock, and centrifugation. Therefore, for some connectors with high reliability requirements, many designers have proposed that it is best to perform 100% dynamic vibration tests to assess contact reliability. Japanese company NECO has introduced a small desktop electric shaker for use with the continuity tester, which has been successfully applied to the contact reliability inspection of many civilian wiring harnesses.