Aviation plugs are electromechanical components that connect electrical circuits. Therefore, the electrical parameters of the aviation plug are the first issues to be considered when selecting the aviation plug. The correct selection and use of aviation plugs is an important aspect of ensuring circuit reliability.
Aviation plugs (hereinafter referred to as aviation plugs) can also be called plug sockets, and are widely used in various electrical circuits, playing a role of connecting or disconnecting circuits. Improving the reliability of aviation plugs is first and foremost the responsibility of manufacturers. However, due to the wide variety of aviation plugs and the wide range of applications, the correct choice of aviation plugs is also an important aspect of improving the reliability of aviation plugs. Only through the joint efforts of both the manufacturer and the user can the maximum function of the aviation plug be fully exerted.
There are different classification methods for aviation plugs. According to the frequency, there are high-frequency aviation plugs and low-frequency aviation plugs; according to the shape, there are circular connectors, according to the use: aviation plugs for cabinets, aviation plugs for audio equipment, power aviation plugs, special purpose aviation plugs, etc. The following mainly discusses the selection method of low-frequency aviation plugs (frequency below 3MHZ). Catalog electrical parameters require safety parameter classification application selection of terminal blocks
Electrical parameter requirements
Aviation plugs are electromechanical components that connect electrical circuits. Therefore, the electrical parameters of the aviation plug are the first issues to be considered when selecting the aviation plug.
1: Rated voltage Rated voltage, also known as working voltage, mainly depends on the insulation material used by the aviation plug and the distance between the contact pairs. Some components or devices may not be able to perform their proper functions when they are below their rated voltage. The rated voltage of the aviation plug should be understood as the highest working voltage recommended by the manufacturer. In principle, the aviation plug can work normally under the rated voltage. The author tends to choose the rated voltage reasonably according to the pressure resistance (electrical strength) index of the aviation plug, according to the use environment and safety level requirements. That is to say, the same withstand voltage index, according to different use environment and safety requirements, can use different maximum working voltage. This is more in line with objective usage.
2: Rated current Rated current is also called working current. As with the rated voltage, the aviation plug can work normally under the rated current. In the design process of the aviation plug, the thermal design of the aviation plug is used to meet the rated current requirements, because when current flows through the contact pair, due to the presence of conductor resistance and contact resistance, the contact pair will heat up. When its heat exceeds a certain limit, it will destroy the insulation of the aviation plug and form a contact to soften the surface coating, causing failure. Therefore, to limit the rated current, in fact, it is necessary to limit the temperature rise inside the aviation plug not to exceed the specified value of the design. The problem to be noted when selecting is that for multi-core aviation plugs, the rated current must be derated. This should be paid more attention to in the case of large currents. For example, the φ3.5mm contact pair is generally specified to have a rated current of 50A, but it needs to be derated by 33% when using 5 cores, that is, the rated current of each core is only 38A, the number of cores The more, the greater the derating.
3: Contact resistance Contact resistance refers to the resistance generated by the two contact conductors at the contact part. There are two issues to be noted when selecting. First, the contact resistance index of aviation plugs is actually the contact resistance, which includes contact resistance and contact resistance. Usually the conductor resistance is small, so the contact resistance is called contact resistance in many technical specifications. Second, in the circuit connecting small signals, pay attention to the conditions under which the contact resistance index is tested, because the contact surface will have an oxide layer, oil or other contaminants, and the film resistance will be produced on the surface of the two contacts . When the thickness of the film layer increases, the resistance increases rapidly, and the film layer becomes a poor conductor. However, the membrane layer will undergo mechanical breakdown under high contact pressure, or electrical breakdown under high voltage and large current. The contact pressure of some small-volume connector designs is quite small, and the use occasions are only mA and mV. The film resistance is not easy to be broken down, which may affect the transmission of electrical signals. In GB5095 "Basic test procedures and measurement methods for electromechanical components used in electrical equipment", one of the contact resistance test methods "contact resistance-millivolt method" stipulates that in order to prevent the insulation film on the contact from being broken, the open circuit electromotive force of the test circuit is tested The DC or AC peak value should not be greater than 20mV, and the DC or AC test current should not be greater than 100mA. In fact, this is a low-level contact resistance test method. Therefore, those who have this requirement choose the aviation plug with low-level contact resistance index.
4: Shielding In modern electrical and electronic equipment, the increasing density of components and related functions between them has imposed strict restrictions on electromagnetic interference. Therefore, the aviation plug is often closed with a metal shell to prevent the internal electromagnetic energy from being radiated or interfered by the external electromagnetic field. At low frequencies, only magnetic materials can significantly shield the magnetic field. At this time, there are certain regulations on the electrical continuity of the metal shell, that is, the shell contact resistance
Safety parameter
1: Insulation resistance Insulation resistance refers to the resistance value that appears when a voltage is applied to the insulation part of the aviation plug, so that a leakage current occurs in or on the surface of the insulation part. It is mainly affected by insulating materials, temperature, humidity, fouling and other factors. The insulation resistance values ​​provided on the aviation plug samples are generally the index values ​​under standard atmospheric conditions. Under certain environmental conditions, the insulation resistance values ​​will decrease to a lesser extent. Also pay attention to the test voltage value of the insulation resistance. Depending on the insulation resistance (MΩ) = the voltage (V) applied to the insulator / leakage current (μA), applying different voltages will have unused results. In the test of aviation plugs, the applied voltage is generally 10V, 100V, 500V three gears.
2: Withstand voltage is the critical voltage between the mutually insulated parts of the contact pairs or between the insulated parts and the ground, which can withstand higher than the rated voltage within a specified time without breakdown. It is mainly affected by contact on the spacing and creepage distance and geometry, insulator material, ambient temperature and humidity, and atmospheric pressure.
3: Combustibility Any aviation plug can't be separated from the current when it is working, and there is a danger of fire. Therefore, the aviation plug is required not only to prevent ignition, but also to self-extinguish in a short time once it is ignited and caught fire. When choosing, pay attention to choose the aviation plug with flame retardant, self-extinguishing insulating material.
4: Mechanical parameters The contact pressure in the aviation plug is an important indicator, which directly affects the size of the contact resistance and the amount of contact pair wear. In most structures, it is quite difficult to directly measure the contact pressure. Therefore, the contact pressure is often measured indirectly through the separation force of one foot. For circular pinhole contact pairs, the standard pin with a specified weight is usually used to check the ability of the female contact to hold the weight. The diameter of the standard pin is the lower limit of the diameter of the male contact -5μm. The total separation force is generally twice the sum of the single-leg separation forces on the line. When the total separation force exceeds 50N, it is quite difficult to insert and remove manually. Of course, for some test equipment or occasions with special requirements, you can choose to use zero plug force aviation plug, automatic fall off aviation plug and so on.
5: Mechanical life The mechanical life of aviation plugs refers to the life of plugging and unplugging, which is usually specified as 500 to 1000 times. When the specified mechanical life is reached, the contact resistance, insulation resistance and withstand voltage of the aviation plug shall not exceed the specified values. Strictly speaking, the current mechanical life is a vague concept. The mechanical life should have a certain relationship with time. It takes 500 times in 10 years and 500 times in 1 year. Obviously, the situation is different. It's just that there is no more economical and scientific way to measure it.
Classification application
Signal transmission aviation plug: Signal transmission can be divided into two categories: simulation signal transmission and digital signal transmission. Regardless of the analog or digital signal connector, the required functions should mainly protect the integrity of the transmitted voltage pulse signal, which should include the pulse signal waveform and its amplitude. The data signal is different from the simulation signal in pulse frequency. The pulse transmission speed determines the maximum frequency of the protected pulse. The data pulse transmission speed is much faster than some typical simulation signals. Some pulses are in the connector. The transmission speed is close to the range of one hundred billionth of a second. In the field of microelectronics technology today, the connector is usually regarded as a wire, because the wavelength associated with such a fast-growing frequency can be comparable to the connector size.
When an aviation plug or an interconnected system such as a cable assembly is used in high-speed data signal transmission, the corresponding description of the connector's performance changes. Instead of the characteristic impedance of the resistor and the crosstalk in the interconnected system, it becomes particularly important. Controlling the characteristic impedance of the connector has become a major trend of consciousness, which is to control crosstalk in the cable. The characteristic impedance has such an important position in the connector, because the geometric shape of the resistor is difficult to be completely unified, and the size of the connector is very small, the possibility of crosstalk must be minimized. In the cable, the control of the geometry of the aviation plug is relatively easy to achieve, and its characteristic impedance is also easy to control, but the length of the cable will likely cause potential crosstalk.
Terminal selection
Selection method of aviation plug connection terminal The connector is an electromechanical component that connects the electrical circuit, so the electrical parameter of the connector itself is the first consideration when selecting the connector. The correct selection and use of electrical connectors is an important aspect of ensuring circuit reliability.
1. Electrical parameter requirements: The connector is an electromechanical component that connects the electrical circuit. Therefore, the electrical parameters of the connector itself are the first consideration when selecting the connector.
2. Rated voltage and current: the same withstand voltage index of aviation plugs, according to different use environment and safety requirements, different maximum working voltages can be used. To limit the rated current, in fact, it is necessary to limit the temperature rise inside the electrical connector to not exceed the specified value of the design. The problem to be noted when choosing is that for multi-core electrical connectors, the rated current must be derated.
3. Installation method and shape: The shape of the aviation plug terminal is ever-changing. The users are mainly from straight, bent, the outer diameter of the wire or cable and the fixing requirements with the shell, volume, weight, whether it is necessary to connect the metal hose To choose, the electrical connectors used on the panel must also be selected from the aspects of appearance, shape, color and so on.
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