Introduction to three basic properties of terminal blocks_ Mechanical performance, environmental performance and electrical performance of wiring terminal

1、 Mechanical properties

As far as the connection function is concerned, the plugging force is an important mechanical property. The insertion force is divided into insertion force and pull-out force (pull-out force is also called separation force), and their requirements are different.

Another important mechanical property is the mechanical life of the connector. Mechanical life is actually a kind of durability index, which is called mechanical operation in the national standard gb5095. It takes one insertion and one pull-out as a cycle, and takes whether the connector can normally complete its connection function (such as contact resistance value) after the specified insertion and pull-out cycle as the evaluation basis. The plugging force and mechanical life of the connector are related to the contact structure (positive pressure), the coating quality of the contact part (sliding friction coefficient) and the dimensional accuracy (alignment) of the contact arrangement.

2、 Environmental performance

Common environmental properties include temperature resistance, humidity resistance, salt spray resistance, vibration resistance and impact resistance.

1. Temperature resistance: at present, the higher working temperature of the connector is 200? C (except for a few high-temperature special connectors), the lower temperature is -65? C。 When the connector works, the current generates heat at the contact point, resulting in temperature rise. Therefore, it is generally considered that the working temperature should be equal to the sum of ambient temperature and contact temperature. In some specifications, the allowable higher temperature rise of the connector under the rated working current is clearly specified.

2. Moisture resistance: moisture intrusion will affect the insulation performance of the connector and rust the metal parts. The constant damp heat test condition is that the relative humidity is 90%~95% (up to 98% according to the product specification), and the temperature is +40 ± 20? C. The test time is 96h according to the product regulations. The alternating damp heat test is more rigorous.

3. Salt spray resistance: when the connector works in the environment containing moisture and salt, the surface treatment layer of its metal structure and contact may produce electrochemical corrosion, affecting the physical and electrical properties of the connector. In order to evaluate the ability of electrical connectors to withstand this environment, salt spray test is specified. It is to hang the connector in a temperature controlled test box and spray the specified concentration of sodium chloride solution with compressed air to form a salt mist atmosphere. The exposure time is specified by the product specification, which is at least 48h.

4. Resistance to vibration and impact: resistance to vibration and impact is an important performance of electrical connectors, especially in special application environments such as aviation and aerospace, railway and highway transportation. It is an important index to test the robustness of mechanical structure and electrical contact reliability of electrical connectors. There are clear provisions in relevant test methods. The peak acceleration, duration and impulse waveform as well as the time of interruption of electrical continuity shall be specified in the impact test.

5. Other environmental properties: other environmental properties of the electrical connector include tightness (air leakage, liquid pressure), liquid immersion (anti habitation ability to specific liquid), low air pressure, etc.

3、 Electrical performance

The main electrical properties of the connector include contact resistance, insulation resistance and electrical strength.

1. Contact resistance: high quality electrical connectors should have low and stable contact resistance, and the contact resistance of the connector ranges from a few milliohms to tens of milliohms.

2. Insulation resistance: it is an index to measure the insulation performance between the connectors of electrical connectors and between the contact and the shell. Its order of magnitude ranges from hundreds of megaohms to hundreds of gigaohms.

3. Electrical strength: electrical strength, also known as voltage resistance and dielectric withstand voltage, is the ability to withstand rated test voltage between connector contacts or between contacts and housing.

4. Other electrical performance: electromagnetic interference leakage attenuation is to evaluate the electromagnetic interference shielding effect of the connector. Electromagnetic interference leakage attenuation is to evaluate the electromagnetic interference shielding effect of the connector. It is generally tested in the frequency range of 100mhz~10ghz. For RF coaxial connectors, there are also electrical indicators such as characteristic impedance, insertion loss, reflection coefficient and voltage standing wave ratio. Due to the development of digital technology, in order to connect and transmit high-speed digital pulse signals, a new type of connector, high-speed signal connector, has emerged. Accordingly, in terms of electrical performance, in addition to the characteristic impedance, some new electrical indicators have emerged, such as crosstalk, transmission delay and time delay.