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Choice of the electric connector

Time:2015-11-25 15:39:11 Browse:

Choice of the electric connector

Connector is electromechanical to connect with electric circuit. Therefore the technical parameter is primary factor to choose connector. To choose correctly and use for connector is important area to ensure reliable circuit. 

Introduction 

Electric Connector(Abbr. connector)also call connector,which is used for all kinds of electric circuit, it can connect and break off. To improve the reliability for connector is the responsibility. Therefore we choose connector correctly, which is one of the important aspects due to the variety connectors and widely applying.  Just manufacturer take effort together with user, it will achieve the function mostly. Connector has different classify method. According to the classification for different frequency, it has high frequency and low frequency connector; According to the different shape, it has round connector, rectangle connector; According to the range using, it has printing connector, connector for cabinet, connector for speaker, power connector and connector for special environment and so on. We just describe the choice method low frequency connector ( below frequency:3MHZ) as follow. 

Electric parameter 
Connector is critical component connecting to electric circuit. So the electric parameter is primary question to choose connector.
 
Rated Voltage 
Rated voltage also call working voltage, it largely depends on the continuous machine use insulation materials, contact on the amount of space between. The voltage for some component or device in lower than the rated voltage, may not be able to achieve its corresponding function. In principle, for the rated voltage for connector is lower than rated voltage, it work normally. I tend to under connector withstanding voltage (withstand) indicators, in accordance with the use of the environment, the security levels required for reasonable choice of rated voltage. In other words, the same withstand voltage index, depending on the use of environmental and safety requirement, you can use a different maximum working voltage. It is also more consistent with the objective being used.  
 
Rated Electric current 

Rated Current also name operation current. When the operation current is lower rated current, the connector can work normally like rated voltage. In the process of design for the connector, through to the connector's thermal design to meet the requirements of the rated current, because in contact on a current to flow, due to the presence of conductor and contact resistance, contacts will be hot. When the heat exceeds a certain limit, it will damage the insulation and softening of surface coating for the connector, causing failure. Therefore, we must be limit rated current; the fact that you have to restrict the internal temperature of the connector rise shall not exceed the value of design requirement. We note when choose is: on multiple-core connector, derating of rated current must be used. This high-current applications more attention, for example φ 3.5 mm exposure on general provisions, its rated current is 50A, but when the 5 core 33% derating, a core of rated current only 38A, cores, the greater the rate drops. Derating range can be found in table 1. 

Contact resistant 

Contact resistant indicates the resistant in the contact section of resistance between the two contact conductors. In the selection, pls take note of the two questions as follow: first, the index contacting resistant of the connector is in fact a contact-on-resistance, it includes contact resistant and contact exposure on the conductor. Usually the conductor resistance is smaller. Many technical specifications for contact resistance are called the contact resistance. Second, when we connect small signal circuit, the contact resistance is tested under what conditions, because the contact surfaces will schedule the oxide layer, grease and other contaminants, the surface of two contacts will occur the film resistors. In the film thickness is increased, the rapidly increasing resistance, is a poor conductor of film. However, the film in the high contact pressure mechanical breakdown occurs, or in high-voltage, high current electrical breakdown occurs. On some of the small size of the connector is designed for contact pressure is small, used only for the mA and mV-level, the film resistance to breakdown that could affect the signal transmission. In the electric equipment GB5095 electromechanical components basic test procedures and methods of measurement of one of the contact resistance measurement method "contact resistance — Millivolt method", in order to prevent contact with the insulation film breakdown, the test circuit of open-circuit voltage DC or AC peak should be no greater than 20mV, DC or AC test should be less than 100mA of current. In fact this is a low level of contact resistance of the test, the selection, chosen by the low level of contact resistance index of connectors.  
Shield 
In modern electrical and electronic equipment, density of components and related functions in growing on the EMI presented the strict restrictions. Therefore, the connectors with a metal shell are often closed to prevent internal electromagnetic energy radiation or external electromagnetic interference. Only in low-frequency magnetic materials can play a significant magnetic field shielding effect. At this point, the metal housing of electrical continuity has certain requirements, the contact resistance of the shell.

 

Safety Technical Parameter 

Insulation Resistant 
the insulation resistance is the insulation voltage of the connector part, so that the surface of the insulating part or on the surface, resulting in the leakage current and emerging resistance values. It is mainly affected by insulation, temperature, humidity, defaced. Connector sample provided by the insulation resistance values are generally at standard atmospheric condition index value, in some circumstances, the insulation resistance value would have unused. Note also the insulation resistance of the test voltage values. Depending on the insulation resistance (M Ω) = add insulation voltage (V)/leakage current (μ A) impose different voltage, there are no results. In connector of the test, the voltage is generally imposed 10V, 100V, 500V in third gear.
Withstand Voltage 
The pressure is on for insulating between or among insulation parts and grounding, at a specified time, the higher than the rated voltage and voltage breakdown phenomena of critical. It is mainly affected by exposure to spacing and creepage distance and geometric shapes, insulator materials as well as the ambient temperature and humidity, atmospheric pressure.
Inflammability 
Any connector at work are current, there is the risk of fire. Therefore, the connector requires not only prevent ignition, also called in the event of ignition and fire, it can in a short period of time. In the choice when the flame retardant, self-extinguishing insulation of electric connectors.

Mechanical Spec 

Single foot separation force and total separation force 
Connector contact pressure is an important indicator, it directly affects the contact resistance of the size and exposure on the amount of wear and tear. In most of the structure, the direct measurement of contact pressure, thus, often through one foot separation force to indirect measurement of contact pressure. Contact for circular holes, normally provided in the weight of the weight of standard pin to verify Yin contact holding weights, general standard pin diameter is Yang contact diameter lower-5 μ m. Total separation force is generally one foot separation force line of two times. Total separation force more than 50N, artificial-plug has been quite difficult. Of course, for some test equipment or special requirements of the occasion, choose zero insertion force connector, auto off connector, etc.

Mechanical Life 

Connector of the mechanical life means life, are usually required to plug is 500 ~ 1000 times. Provisions in this mechanical life, connector contact resistance, insulation resistance and voltage measurements should not exceed the prescribed value. strictly speaking, the mechanical life is a vague concept. Mechanical life time should have a certain relationship, 10 years out of 500 and 1 year used 500 times, it is clear that it is not the same. But there is no more economical, more scientific methods to measure.
The contact number and the preferred pinhole 
Firstly we can choose the contact number of contacts in accordance with the circuit, meanwhile we considerate the dimension of the connector and total force. The more contact number, the volume bigger, total force is also large.  In some reliability requirements, while the volume and permitting, you can use to contact on the parallel approach to improve the reliability of the connection. Connector plug, socket, pin (Yang contact) and Jack (vaginal contact) General Assembly are interchangeable. Actually used, according to the plug and socket at each end of the live situation to select. If you always live, the socket can choose to install Jack socket, because Jack socket, its live buried in the contacts, the human body easily crimps touch live contacts, relatively safe.
Vibration、impact、collision 
Mainly consider connector set frequency and acceleration under vibration, impact, collision contact electrical continuity. Contact for this dynamic stress situations occur instantaneously circuit breaker. Instantaneous fault time provided is generally 1 μ μ s, 10 s, 100 μ s, 1ms and 10ms. To note is how to tell if a contact on the occurrence of instantaneous fault failure. It is generally agreed that, when closed contact (contact) at both ends of the voltage drop over 50% of the electromotive force, can be found close contacts (contacts) to malfunction. That is whether happening instantaneous fault has two conditions: duration and voltage drop, and other.

Wiring method

Connectors are generally composed by plugs and socket-outlets, plugs, also known as the free end connectors, sockets, also called fixed connectors. By plugs, socket and plug in the competent and separation to connect and disconnect the circuit, and therefore produces a variety of plugs and socket connection. Circular connectors, mainly in the threaded connection, bayonet connection and billiard-style connection three ways. One of the most common threaded connections, it has the process simple, manufacturing a wide range of low cost, etc., but the connection is slow does not need to frequently swap and quick consecutive occasions. Billiard-is a way to connect the fastest one, it does not need to be rotated, with linear motion can make connections, separation and locking functionality. Because it belongs to a straight sliding connections, so it only applies to the total separation of the connector. Generally, the more common is in small connector.

Install method and Appearance

Connector installed prior to installation and backward installation, install fixed way rivets, screws, clips or connector itself fast locking pin, etc. Also have a plug and socket is a client-side connector is free, the so-called relay connectors. Connector shape-changing, mainly from straight, curved shape, the outer diameter of a wire or cable, and shell's fixed requirements, size, weight, whether you want connection metal vlexible hose etc, be selected on the Panel, use the connector also from beautiful, shape, color, etc., be selected.

Ambient Condition 

Environmental parameters mainly include environmental temperature, humidity, temperature, atmospheric pressure and the most corrosive environment.
Environmental Temperature
Connector in the use and storage, transportation to the environment on the properties have a significant effect, therefore, must be based on actual environmental conditions to choose the corresponding connector. Ambient temperature at the connector of metal materials and insulation materials determines the connectors working environment temperature. The usual environment temperature:-55 ~ 100℃ special occasion may require higher.
Humidity 
humidity greater than 80%, is due to electric shock. Damp environment caused by water vapor in the insulator surface absorption and diffusion, the insulation resistance is reduced to M Ω level, long-term in high humidity environment, causing physical deformation, decomposition, to escape the resultant, respiration and electrolysis, corrosion and cracks. In particular in the connectors to external devices, often considered wet, water permeability and pollution of environment conditions, this case should use sealed connectors. For water tight and dust-tight connectors generally use GB4208 of enclosures.
Temperature change gatheringly 
Humidity test is to simulate the use of seasonal connector device in a cold environment into the warm environment of actual usage, or simulate spacecraft, drastic changes in ambient temperature probes. Temperature progression may cause cracking or insulating material.
Temperature progression may cause cracking or insulating material. 
In the thin air of altitude, plastic discharge gas pollution exposure on the trend of increased Corona, pressure reduce, the circuit short-circuit. In the high-altitude reaches a certain value, the plastic properties. Therefore at high altitudes when using non-sealed connector, you must use the Derating. In low pressure recommended voltage Derating factor are shown in table 2.
Corrosive Environment 
According to the different using environment corrosive, select corresponding metal, plastic, cladding material structure connector, like using of connector in salt, if no anticorrosive metal surface, it have its function worsen. In the concentration environment of S02, it’s not suitable for using silver plating on the connector. In the hot flashes, the molds are also important issues.
 

Termination Method 

Termination method indicates the connecting method for connector and cable. Properly select termination method and using termination is one of important aspect to use and choose connector. 
Welding 
The most common welding is solder. Solder connection to the most important thing is that the solder material and are welded surface should be formed metal continuity. Therefore, the connector, it is important to solderability. The most common welding coating of the connector is Tin alloys, silver, and gold. Reed contact on common welding end lug, red eye lug and gap lug: pinhole-contact on common drilled arc welding end gaps. Reed contact on common welding end lug, red eye lug and gap lug: pinhole-contact on common drilled arc welding end gaps.

 Pressure Welding 

Crimping is provided for the metal in the compresses and within the limits of displacement and conductor connect to contact on a technology. Good crimp connections can produce metal welds, conductor and contact materials symmetric deformation. This connection is similar to a cold welding connection, get good mechanical strength and electrical continuity. It can withstand even extreme environmental conditions. Is generally considered proper crimp connections than solder good, particularly in high-current applications must use the Terminal. Crimping pliers for to be used for the crimping or automatic, semi-automatic crimping machines. According to the wire section, correct choice contact cans on the wire. It should be noted that crimp connection is permanent connection, can only be used once.

 Wire Wrapping 

Wire Wrapping is directly wound lead on the winding pillar for contact connector with pien. Wire Wrapping, under wire tension control of winding, indentation and fixed in the next column of contacts around the edges and corners, to form tight contacts. Pick wire has several requirements: wire diameter from the nominal value should be in the range 0.25mm ~ 1.0mm; wire diameter not greater than 0.5mm, conductor material elongation rate of not less than 15%; wire diameter greater than 0.5mm, conductor material elongation rate of not less than 20%. Pick wire has several requirements: wire diameter from the nominal value should be in the range 0.25mm ~ 1.0mm; wire diameter not greater than 0.5mm, conductor material elongation rate of not less than 15%; wire diameter greater than 0.5mm, conductor material elongation rate of not less than 20%.

Prick connection

Prick connection is also known as the insulation displacement connection that is managed by the United States during the 1960s the invention of a novel end technology, with high reliability, low cost, ease of use, etc., are already widely used in various connectors for printed circuit board. It applies to the ribbon cable connection. The connection is not needed for stripped cable, depending on the connector's "U"-shaped tip contact Reed into insulating layer, so that the cable conductor slide into the Groove contact Reed and clamping residents, allowing cable and connectors Reed formed between the electrical connectivity. It only takes a simple tool, but you must use the cable provided wire gauge.

Screw Connection

Screw connection with screw-terminal connection, it is necessary to pay attention to allow the connection wires-the largest and smallest cross sections and different screw allows maximum tightening torque.
concluding remarks 
As above discourse the method of the choice for connector from electric parameter, safety parameter, mechanical parameter, environment factor and termination method, but because of the variety of connectors, the above exposition instance, some views may not necessarily correct and comprehensive. I hope the connector's production plant and use the factory to pay attention to the choice and use of the connector.
 
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