Contact resistance refers to the resistance generated between the contact surfaces of two electrical conductors. The existence of this resistance is due to imperfect contact on the contact surface, usually due to factors such as surface roughness, oxide layer, contamination, and differences in the conductivity of materials. Contact resistance is an important parameter in electrical engineering, especially in the design of electrical connections and switchgear. Its size directly affects the efficiency of current conduction and the performance of the equipment.

Where contact resistance occurs:

Contact resistance usually occurs at the contact points of various electrical connections, such as:

1. Plugs and sockets: In household appliances and electronic devices, the contact resistance between plugs and sockets may affect the normal operation of the equipment.

2. Switches and relays: At the contact surface of electrical switches and relays, changes in contact resistance may cause delayed response or failure of the equipment.

3. Battery connection: At the connection point between the battery and the device, an increase in contact resistance may cause a decrease in battery efficiency.

4. Cable joints: At the connection point of the cable, an increase in contact resistance may lead to a decrease in power transmission efficiency, or even overheating and damage.

How to test contact resistance?

There are many ways to test contact resistance. Here are some common test steps and equipment:

1. Use the four-probe method: The four-probe method is a common technique for testing contact resistance. This method uses four electrodes, two of which are used to apply current and the other two are used to measure voltage. By measuring the voltage and current, the contact resistance can be calculated using Ohm’s law (R=V/I).

2. Contact resistance tester: Dedicated contact resistance testers can provide accurate measurements. These instruments usually have automation functions that can quickly measure and record the value of contact resistance.

3. Thermistor method: This method calculates contact resistance by measuring the temperature change of the contact point. When the contact resistance increases, the heat generated by the contact point will also increase, causing the temperature to rise.

4. Frequency response method: By applying AC signals of different frequencies and observing the phase difference and amplitude changes of current and voltage, the characteristics of contact resistance can be derived.

Factors affecting contact resistance

The size of contact resistance is affected by many factors, including:

Surface condition: Whether the contact surface is smooth and clean will directly affect the size of the resistance. Large surface roughness or the presence of contaminants will increase contact resistance.

Contact pressure: The greater the pressure applied at the contact point, the lower the contact resistance will generally be. This is because greater pressure allows the contact surface to fit better and reduces irregularities in the contact area.

Material properties: Different materials have different electrical conductivities, and materials with better electrical conductivity (such as copper and silver) generally have lower contact resistance.

Environmental factors: Environmental factors such as temperature and humidity can also affect the measurement of contact resistance. In high temperature environments, the conductivity of metal materials may change, which affects the contact resistance.

Contact resistance is an important parameter that cannot be ignored in electrical connections. It directly affects the performance and reliability of the equipment. By understanding the definition, occurrence location and test methods of contact resistance, electrical equipment can be better designed and maintained to ensure its stable operation in various environments. With the advancement of technology, the test and control technology of contact resistance is also constantly developing, and in the future there may be more efficient and accurate methods to evaluate and optimize contact resistance.