Push button switch is a common type of component in our daily life, whether it is industrial instrumentation, medical equipment, anti-theft machines, electronic amusement equipment, household appliances, office automation machines and automobiles, airplanes, ships, computer keyboards, digital converters, children’s toys and industrial automation Systems, even the operating systems of cutting-edge aerospace technology and military installations, have buttons in all electronic products. Today, the editor will talk to you about the specific content of many common sense issues related to buttons.
The structure, function and symbol of push button switch
- The function of the push button switches are mainly used in electronic equipment to turn on or off the power source and change the power circuit to change the working condition of the machine. For example, the frequency band and frequency of the communication machine are changed, the channel of the TV receiver is changed, the function of the tape recorder is changed, the range of the measuring instrument is changed, and the control of various power circuits, etc.
- Structural characteristics of the switch. A large part of the button is composed of the outer shell, insulating sheet, handle, contact, lead device, reset key spring (self-locking device), and fasteners. Among them, the shell and insulating sheet are made of ABS engineering plastic and insulating bake-lite; the handle, reset key spring, and fastener are made of metal; the material of the lead device is mostly copper alloy; the contact for the button Generally, silver-copper alloy or sterling silver is used.
3 The graphic symbol (circuit symbol and symbol picture) of the button in the power circuit is shown in Figure 1. Among them, the symbol picture was expressed by “K” in the past (the button switch also used “AN”), and the new regulations use or “” XS” expression.
Types of push button switch
①Press pole type, which can include single pole switch, double pole switch and three pole switch button. When the switch is pressed or toggled, the movable contact is connected (or disconnected) with the stationary contact, thereby making or breaking the circuit. Since the single-pole unit switch button has only one movable contact and one stationary contact, only one circuit can be made or cut. The single-pole two-position switch can choose to switch on (or off) one of the two circuits; the double-pole two-position switch can turn on or off two independent circuits at the same time; the effect of the other pole switches can be based on this analogy.
②The action means of pressing the switch button, including key-off, direct-dial switch button, lever-off, DIP switch, push-pull switch button, and rotary-off, etc.
③The structural advantages of the push switch can include straight key switch, touch switch, push button switch, slide switch, boat switch button, button switch, piano key switch button, key switch button and band switch and so on.
④ According to the control method, it can include proximity switch, timing switch, infrared photoelectric switch, Hall switch, human infrared sensor switch, magnetic switch, etc. The switch button type is not only a row type, it is not unique. The important thing is to specify which switch button to choose, not only from the technical requirements of the circuit, but also from the aesthetics of the panel layout of the whole machine and the efficiency of use.
The key basic parameters of the push button switch
- Contact resistance: When the push button switch is turned on normally, the resistance value between the “contact pair” (two contacts) conductors is called the contact resistance. The value needs to be as small as possible. Its value has different specifications according to the working requirements of the circuit and the structure type of the switch. For example, the normal contact resistance of small ceramic band switches and tact switches exceeds 0.01Ω, and the power switch exceeds 0.02 Ω, the general switch button is below 0.02Ω.
- Contact capacity: refers to the function that the contacts can pass current. Some switch buttons also have certain requirements for the nature of the load at the same time as the current capacity is specified. For example, when the contact without inductive load is working in a circuit with inductive parameters, the current rating should be reduced accordingly.
- Withstand voltage: also called electric strength, its meaning usually refers to the voltage that can be withstood between the conductors of the switch buttons that are not in contact. The points and contacts should ensure that a pair of contacts will not break down when they are broken. The technical standards of various switch buttons have standardized the value of their rated working voltage. The withstand voltage of the normal switch button is at least 100V. The power supply (mains) switch button needs to exceed 500V (AC, 50Hz).
- Insulation resistance: The resistance between the conductors of the switch buttons that are not in contact is called insulation resistance. The larger the value, the better, more than 100MΩ. More is needed for good quality switch buttons.
- Duration and safety and reliability: Duration usually refers to the efficient number of tasks (the number of times of use) that the switch button can work under normal conditions. Usually 10,000 to 50,000 times are required. The wear-resistant switch can reach 1 million times, some toggle switches can reach 40 million times, and the tact switch can be as high as 1 to 200 million times. Safety and reliability usually refer to contact with trustworthiness and no malfunction in the process of work tasks. In ordinary electronic production, maintenance and electronic product design, when selecting and exchanging switch buttons, in addition to the model or shape, it is no problem to pay attention to each item of AC voltage, rated current and contact resistance in terms of specifications.