Parameters and selection applications of aviation plugs

Aviation plugs are electromechanical components that connect electrical circuits. Therefore, the electrical parameters of the aviation plug itself are the first thing to consider when choosing an aviation plug. Correct selection and use of aviation plugs is an important aspect of ensuring circuit reliability.

　　Aviation plugs (hereinafter referred to as aviation plugs) are also called plug sockets. They are widely used in various electrical circuits and play the role of connecting or disconnecting circuits. Improving the reliability of aviation plugs is first the responsibility of the manufacturer. However, due to the wide variety of aviation plugs and their wide range of applications, the correct selection of aviation plugs is also an important aspect of improving the reliability of aviation plugs. Only through the joint efforts of manufacturers and users can the functions of aviation plugs be maximized.

　　There are different ways to classify aviation plugs. According to the frequency, there are high-frequency aviation plugs and low-frequency aviation plugs; according to the appearance, there are circular connectors; according to the purpose, there are 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). Table of Contents Electrical Parameters Requirements Safety Parameters 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 itself are the first thing to consider when choosing an aviation plug.

　　1: Rated voltage Rated voltage is also called working voltage, which mainly depends on the insulating material used in the aviation plug and the spacing between the contact pairs. Some components or devices may not be able to perform their functions when the voltage is lower than the rated voltage. The rated voltage of the aviation plug should actually be understood as the maximum working voltage recommended by the manufacturer. In principle, the aviation plug can work normally at a voltage lower than the rated voltage. The author tends to reasonably select the rated voltage according to the withstand voltage (electric strength) index of the aviation plug, the use environment, and the safety level requirements. In other words, the same withstand voltage index can be used with different maximum working voltages according to different use environments and safety requirements. This is also more in line with objective usage.

　　2: Rated current Rated current is also called working current. Like rated voltage, aviation plugs can generally work normally under the condition of lower than rated current. In the design process of aviation plugs, the rated current requirements are met through thermal design of aviation plugs, because when current flows through the contact pair, the contact pair will heat up due to the existence of conductor resistance and contact resistance. When the heat exceeds a certain limit, it will destroy the insulation of the aviation plug and soften the surface coating of the contact pair, causing failure. Therefore, to limit the rated current, in fact, to limit the temperature rise inside the aviation plug to not exceed the specified value of the design. The problem to be noted when choosing is: for multi-core aviation plugs, the rated current must be used at a reduced rate. This should be paid more attention to in high current situations. For example, the φ3.5mm contact pair is generally specified to have a rated current of 50A, but when it is 5-core, it must be used at a reduced rate of 33%, that is, the rated current of each core is only 38A. The more cores there are, the greater the reduction.

　　3: Contact resistance Contact resistance refers to the resistance generated by two contact conductors at the contact part. Two issues 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 resistance of the conductor. 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, it is necessary to pay attention to the conditions under which the given contact resistance index is tested, because the contact surface will be attached with an oxide layer, oil or other contaminants, and the surface of the two contact parts will produce film resistance. When the thickness of the film layer increases, the resistance increases rapidly, and the film layer becomes a poor conductor. However, the film layer will undergo mechanical breakdown under high contact pressure, or electrical breakdown under high voltage and high current. The contact pressure designed for some small-volume connectors is quite small, and the use occasions are only mA and mV levels. 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 for 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 down, the DC or AC peak value of the open circuit electromotive force of the test circuit 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 should choose aviation plugs with low-level contact resistance indicators.

　　4: Shielding In modern electrical and electronic equipment, the increasing density of components and their related functions have put forward strict restrictions on electromagnetic interference. Therefore, aviation plugs are often enclosed in metal shells to prevent internal electromagnetic energy from radiating or being interfered by external electromagnetic fields. At low frequencies, only magnetic materials can play a significant shielding role in 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 parameters

　　1: Insulation resistance Insulation resistance refers to the resistance value presented by applying voltage to the insulating part of the aviation plug, which causes leakage current inside or on the surface of the insulating part. It is mainly affected by factors such as insulation material, temperature, humidity, and contamination. The insulation resistance values ​​provided on the aviation plug samples are generally index values ​​under standard atmospheric conditions. Under certain environmental conditions, the insulation resistance values ​​will decrease to different degrees. In addition, pay attention to the test voltage value of the insulation resistance. According to the insulation resistance (MΩ) = voltage applied to the insulator (V) / leakage current (μA), different voltages are applied, and different results will be obtained. In the test of aviation plugs, the applied voltages are generally 10V, 100V, and 500V.

　　2: Withstand voltage Withstand voltage is the critical voltage that can be withstood by the mutually insulated parts of the contact pair or between the insulated part and the ground within a specified time, which is higher than the rated voltage without breakdown. It is mainly affected by the spacing and creepage distance of the contact pair, the geometry, the insulator material, the ambient temperature and humidity, and the atmospheric pressure.

　　3: Flammability Any aviation plug cannot work without electric current, which poses a risk of fire. Therefore, aviation plugs are not only required to prevent ignition, but also to be able to extinguish themselves in a short time once ignited or on fire. When selecting, pay attention to choosing aviation plugs that use flame-retardant, self-extinguishing insulating 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 structures, it is quite difficult to directly measure the contact pressure. Therefore, the contact pressure is often indirectly measured by the single-pin separation force. For circular pinhole contact pairs, a standard pin with a specified weight is usually used to test the ability of the female contact to hold the weight. Generally, the diameter of the standard pin is the lower limit of the diameter of the male contact, which is -5μm. The total separation force is generally twice the sum of the upper limits of the single-pin separation force. When the total separation force exceeds 50N, it is already quite difficult to plug and unplug manually. Of course, for some test equipment or some special requirements, zero plug-in and pull-out force aviation plugs, automatic shedding aviation plugs, etc. can be selected.

　　5: Mechanical life The mechanical life of an aviation plug refers to the plug-in life, which is usually specified as 500 to 1000 times. When this specified mechanical life is reached, the contact resistance, insulation resistance and withstand voltage of the aviation plug should 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 is obvious that the situation is different if it is used 500 times in 10 years and 500 times in 1 year. However, 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: analog signal transmission and digital signal transmission. Regardless of analog or digital signal connectors, their required functions should mainly protect the integrity of the transmitted voltage pulse signal, which should include the waveform of the pulse signal and its amplitude. Data signals differ from analog signals in pulse frequency, and their pulse transmission speed determines the maximum frequency of the protected pulse. The transmission speed of data pulses is much faster than some typical analog signals. The transmission speed of some pulses in the connector is close to one hundred billionth of a second. In today's microelectronics technology, connectors are usually treated as wires because the wavelength associated with such a fast-growing frequency is comparable to the size of the connector.

　　When an aviation plug or an interconnection system such as a cable assembly is used in high-speed data signal transmission, the corresponding description of the connector performance changes. The characteristic impedance that replaces the resistor and the crosstalk in the interconnection system become particularly important. Controlling the characteristic impedance of the connector has become a major trend of consciousness, and in cables, it is to control crosstalk. The reason why characteristic impedance has such an important position in connectors is that it is difficult to achieve complete uniformity in the geometric shape of resistors, and the connector size is very small, so the possibility of crosstalk must be minimized. In cables, the control of the geometry of the aviation plug is easier to achieve, and its characteristic impedance is also easy to control, but the length of the cable may cause potential crosstalk.

　　Selection of Terminal Blocks

　　How to select aviation plug terminals Connectors are electromechanical components that connect electrical circuits, so the electrical parameters of the connector itself are the first thing to consider when selecting a connector. 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 electrical circuits. Therefore, the electrical parameters of the connector itself are the first thing to consider when selecting a connector.

　　2. Rated voltage and current: Aviation plugs with the same withstand voltage index can use different maximum working voltages according to different use environments and safety requirements. To limit the rated current, in fact, the temperature rise inside the electrical connector must not exceed the specified value of the design. The issue to be noted when choosing is: For multi-core electrical connectors, the rated current must be reduced.

　　3. Installation method and appearance: The appearance of aviation plug terminals is ever-changing. Users mainly choose from the aspects of straight shape, curved shape, outer diameter of wire or cable, fixing requirements with the shell, volume, weight, whether to connect metal hose, etc. The electrical connector used on the panel should also be selected from the aspects of appearance, shape, color, etc.