Snap action micro switches are one of the smallest switches available for high capacity industrial applications. A miniature snap-action button, often referred to as a micro switch or simply a micro lever, is an electronic switch that is activated by little manual force, via a turning-point mechanism, at the point where its contact with a surface or substrate can be located. These switches provide excellent facility in the production industry but are increasingly being used in home applications too. For instance, these switches are commonly found on digital watches, calculators and desk clocks. While these small switches are not overly complex, they are extremely convenient, allowing you to switch off an area, open a cabinet door or switch on and off a light without having to actually open or close the cabinet door or pull the plug!
A snap action micro switch works by the movement of a contact plate across a pair of contacts. The plate is simply two plates, a larger flat one and a smaller round one with prongs on it. The contact plate moves up and down a metallic path or rail, while the contacts in the switch or the actuator move up and down on the same path or rail. The mechanical energy that is required to operate the switch is stored in a small spring that responds to the movement of the actuator. The spring then exerts a pressure on the switch, activating it and switching it on or off.
In some variants of Snap Action Micro Switch, the actuator may be a simple spring or can incorporate other springs. A small hole is cut in the lower edge of the plastic surface to allow access to the actuator; the cut is stapled to the side of the component and a cover is then placed over the hole to protect it from moisture and dust. A thin layer of insulating material such as silicon rubber or an inert gas is then put over the actuator so that only a very small amount of heat generated by the switch is absorbed. The heat generated by the micro switch increases its resistance to cooling, so that when the plastic surface is exposed to air, the insulator shrinks back a little bit. As more time is taken to switch the actuator on or off, the amount of heat generated also increases. This causes the micro switch to reach a saturation point at which it cannot further increase its resistance.
Due to their simplicity, snap action micro switches are generally smaller than most other types of micro switches and have less mechanical energy storage than most types of switches. For this reason they are used in miniature electric circuits where smaller electric circuits are required. Some well known electrical accessory manufacturers such as STP have begun to use micro switches in certain applications. STP has also started using micro switches as part of their universal serial bus (USB) connectors. These switches have a very small footprint and are therefore easy to attach and remove from a USB connector.
The switching elements inside these micro switches consist of a pair of conductors. One of the two required contacts is soldered to a female contact connector while the other contact is connected to the male contact connector. Once the female contact connector is attached to the actuator body, the male connector is pushed through a hole in the base series designed for operating temperatures up to 150 degrees Celsius. The spring clip, which holds the springs in place, can then be fed through a hole in the cover of the box and leads to a thin metallic spacer.
The micro switch is designed so that when the switch is closed the spring clips form a U-shape around the top of the box. The opening at the top of the box allows the spring to push against the metal spacer and push the door open. When the switch is open the metal spacer pulls the door shut. At the end of the adaptor there is a small hole for the wires to pass through and the spring clips hold the springs in place. The snap action is operated by a small motor which moves the actuator along the U-shape when the button is activated.
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