An aviation plug is an electromechanical component that connects electrical lines. Therefore, the electrical parameters of the aviation plug itself are the first considerations for selecting an aviation plug. Proper selection and use of aviation plugs is an important aspect of circuit reliability.
Aviation plugs (hereinafter referred to as aviation plugs) can also be called plug sockets, which are widely used in various electrical circuits and function as connecting or disconnecting circuits. Improving the reliability of aviation plugs is first and foremost the responsibility of the manufacturer. However, due to the wide variety of aviation plugs and a wide range of applications, the correct selection of aviation plugs is also an important aspect to improve 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 maximized.
Aviation plugs have different classification methods. 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 purpose: air 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 (with a frequency below 3MHZ). Catalog electrical parameters require safety parameter classification application terminal block selection
Electrical parameter requirements
An aviation plug is an electromechanical component that connects electrical lines. Therefore, the electrical parameters of the aviation plug itself are the first considerations for selecting an aviation plug.
1: Rated voltage Rated voltage, also known as operating voltage, depends mainly on the insulation material used in the aviation plug and the spacing between the contact pairs. Some components or devices may not perform their intended functions below their rated voltage. The rated voltage of an aviation plug is in fact understood to be the highest operating voltage recommended by the manufacturer. In principle, the aviation plug works well below the rated voltage. The author tends to use the rated voltage according to the use environment and safety level requirements according to the pressure (electrical strength) index of the aviation plug. That is to say, the same withstand voltage indicators, according to different use environments and safety requirements, can use different maximum working voltage. This is also in line with objective use.
2: Rated current Rated current is also called working current. As with the rated voltage, the aviation plug generally works normally at less than the rated current. In the design process of the aviation plug, the thermal current design of the aviation plug is used to meet the rated current requirement, because when there is a current flowing through the contact pair, the contact pair will generate heat due to the conductor resistance and the contact resistance. When the heat exceeds a certain limit, it will damage the insulation of the aviation plug and form a softening of the coating on the surface, causing malfunction. Therefore, to limit the rated current, in fact, to limit the temperature rise inside the aviation plug does not exceed the design specified value. The problem to be aware of 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 high current. For example, φ3.5mm contact pair generally has a rated current of 50A, but it should be derated by 33% when it is 5 cores, that is, the rated current per core is only 38A, the number of cores. The more you deduct, the greater the derating.
3: Contact resistance Contact resistance refers to the resistance generated by the two contact conductors in the contact portion. Two problems should be noted when selecting. First, the contact resistance index of the aviation plug is actually the contact resistance, which includes the contact resistance and the contact-to-conductor resistance. Usually the conductor resistance is small, so the contact pair resistance is called contact resistance in many technical specifications. Second, in the circuit connecting small signals, it should be noted under what conditions the contact resistance index is given, because the contact surface will be attached with oxide layer, oil stain or other contaminants, and the surface resistance of the two contact parts will be generated. . When the thickness of the film layer increases, the resistance rapidly increases, and the film layer becomes a poor conductor. However, the film may undergo mechanical breakdown under high contact pressure, or electrical breakdown may occur at high voltage and high current. The contact pressure of some small-volume connectors is quite small. In the case of mA and mV, the resistance of the film is not easily broken down, which may affect the transmission of electrical signals. One of the contact resistance test methods in GB5095 "Basic Test Procedures and Measurement Methods for Electromechanical Components for Electrical Equipment" "Contact Resistance - Millivolt Method" stipulates that the open circuit electromotive force of the test circuit is to prevent the insulation film on the contact from being broken down. The DC or AC peak should be no more than 20mV, and the DC or AC test current should be no more than 100mA. In fact, this is a test method for low-level contact resistance. Therefore, the selector with this requirement is chosen to use an aviation plug with a low-level contact resistance indicator.
4: Shielding In modern electrical and electronic equipment, the density of components and the associated functions between them are increasing, and strict limits are imposed on electromagnetic interference. Therefore, the aviation plug is often closed with a metal casing to prevent internal electromagnetic energy radiation or interference from external electromagnetic fields. At low frequencies, only magnetic materials can significantly shield the magnetic field. At this time, there is a certain regulation on the electrical continuity of the metal casing, that is, the casing contact resistance.
Safety parameter
1: Insulation resistance Insulation resistance is a resistance value which is exerted by applying a voltage to an insulating portion of an aviation plug to cause a leakage current in or on the surface of the insulating portion. It is mainly affected by insulation materials, temperature, humidity, and fouling. 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 ​​may be reduced to a lesser extent. Also pay attention to the test voltage value of the insulation resistance. According to the insulation resistance (MΩ) = voltage (V) / leakage current (μA) applied to the insulator, different voltages are applied, and there is an unnecessary result. In the test of the aviation plug, the applied voltage is generally 10V, 100V, 500V third gear.
2: Withstand voltage is the critical voltage between the mutually insulated parts of the contact pair or between the insulated part and the ground, which can withstand higher than the rated voltage within a specified time without causing breakdown. It is primarily affected by contact versus spacing and creepage distance and geometry, insulator material as well as ambient temperature and humidity, and atmospheric pressure.
3: Flammability Any aviation plug can't be insulated from current when working, which poses a risk of fire. Therefore, the aviation plug is required not only to prevent ignition, but also to extinguish itself in a short time once it is ignited and ignited. When choosing, pay attention to the choice of aviation plugs with flame-retardant and self-extinguishing insulation materials.
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 wear of the contact pair. In most configurations, direct measurement of contact pressure is quite difficult. Therefore, the contact pressure is often measured indirectly by the separation force of one foot. For circular pinhole contact pairs, the standard pin with a specified weight is usually used to verify the ability of the female contact to hold the weight. Generally, the diameter of the standard pin is the lower limit of the male contact diameter of -5 μm. The total separation force is generally twice the sum of the single-leg separation forces. When the total separation force exceeds 50N, manual insertion and removal has been quite difficult. Of course, for some test equipment or some special requirements, you can use the zero plug force aviation plug, automatically drop off the aviation plug and so on.
5: Mechanical life The mechanical life of the aviation plug refers to the plug life, usually specified as 500 ~ 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. Mechanical life should have a certain relationship with time, 500 out of 10 years and 500 times in 1 year, obviously the situation is different. However, there is currently no more economical and scientific method to measure.
Classification application
Signal transmission aviation plugs: Signal transmission can be divided into two categories: analog signal transmission and digital signal transmission. Regardless of the analog or digital signal connector, its required function should primarily protect the integrity of the transmitted voltage pulse signal, which should include the waveform of the pulse signal and its amplitude. The data signal is different from the simulated signal at the 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 transfer speed is close to the range of one billionth of a second. In today's microelectronics field, the connector is usually treated as a wire because the wavelength associated with increasing the frequency is comparable to that of the connector. size.
When an aviation plug or an interconnected system such as a cable assembly is used for high speed data signal transmission, the corresponding description of the connector's performance changes. It is especially important to replace the characteristic impedance of the resistor and the crosstalk in the interconnected system. Controlling the characteristic impedance of the connector becomes a major trend, and crosstalk is controlled in the cable. The characteristic impedance is so important in the connector that the geometry of the resistor is difficult to achieve completely uniform, and the connector size is small, and the possibility of crosstalk must be minimized. In the cable, the control of the geometry of the aviation plug is easier to implement, and its characteristic impedance is also easy to control, but the length of the cable may cause potential crosstalk.
Terminal block selection
Selection method of aviation plug terminal The connector is an electromechanical component that connects the electrical circuit, so the electrical parameters of the connector itself are the first considerations for selecting the connector. Proper selection and use of electrical connectors is an important aspect of 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 considerations for selecting a connector.
2. Rated voltage and current: The same withstand voltage indicators of aviation plugs, according to different use environments and safety requirements, different maximum working voltages can be used. To limit the rated current, in fact limit the temperature rise inside the electrical connector does not exceed the design specified value. The problem to be aware of when selecting 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 user mainly from the straight shape, the curved shape, the outer diameter of the wire or cable and the fixing requirements of the outer casing, the volume, the weight, whether the metal hose needs to be connected, etc. To choose, the electrical connectors used on the panel should be selected from the aspects of aesthetics, shape, color and so on.
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