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

1、 Mechanical properties

As far as the connection function is concerned, the insertion and extraction force is an important mechanical property. Insertion and pull-out 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 durability index, which is called mechanical operation in the national standard GB5095. It takes one insertion and one extraction as a cycle, and takes whether the connector can normally complete its connection function (such as contact resistance value) after the specified insertion and extraction cycle as the judgment basis. The insertion and removal 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: the current 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 is working, the current generates heat at the contact point, causing temperature rise. Therefore, it is generally believed that the working temperature should be equal to the sum of the ambient temperature and the contact temperature. In some specifications, the allowable higher temperature rise of the connector at the rated operating current is clearly specified.

2. Moisture resistance: moisture intrusion will affect the insulation performance of the connector and rust 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 less than 96h according to product regulations. The alternating damp heat test is more rigorous.

3. Salt fog resistance: when the connector is working in an environment containing moisture and salt, the surface treatment layer of its metal structures and contacts may produce electrochemical corrosion, which will affect the physical and electrical performance of the connector. In order to evaluate the ability of electrical connectors to withstand this environment, a salt spray test is specified. The connector is suspended in the temperature controlled test box, and the sodium chloride solution of specified concentration is sprayed with compressed air to form a salt fog atmosphere. The exposure time is specified by the product specification, which is at least 48h.

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

5. Other environmental properties: according to the use requirements, other environmental properties of electrical connectors include sealing (air leakage, liquid pressure), liquid impregnation (resistance to specific liquids), low air pressure, etc.

3、 Electrical performance

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

1. Contact resistance: high-quality electrical connector should have low and stable contact resistance, and the contact resistance of connector varies from several milliohms to tens of milliohms.

2. Insulation resistance: an index to measure the insulation performance between connectors of electrical connectors and between contacts and enclosures, with the order of magnitude ranging from hundreds of megohms to thousands of megohms.

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

4. Other electrical properties: EMI leakage attenuation is used to evaluate the electromagnetic interference shielding effect of the connector, and EMI leakage attenuation is used to evaluate the electromagnetic interference shielding effect of the connector, which 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, namely high-speed signal connector, has emerged. Accordingly, in terms of electrical performance, in addition to characteristic impedance, there are also some new electrical indicators, such as crosstalk, transmission delay and time delay.