The "snap action switch" was invented by the American engineer Peter McGell in 1932. Five years later he founded the Microswitch company to manufacture his renamed switch. Microswitches are one of the most ubiquitous switches in the world. There are several in your home, several in your car and several more where you work. They detect movements of physical objects and signal this movement to an electrical circuit. They are used in security alarms, to detect objects on conveyor belts, to tell elevators where to stop and to let microwaves know when the door is closed.
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Place the switch where it will be activated by the movement you are interested in detecting. The placement of the switch often makes the difference between a system that works and one that does not. When used as part of a security system, micro switches should be placed near enough to doors and windows that they are activated if the door or window is opened, but not near enough that storms and trucks driving by will activate the switches. To stop a conveyor belt when products back up, the switch should be placed at a point where it is triggered before the products back up enough to be a problem, but not at a point that may be temporarily reached during normal operation.
Choose the type of switch lever that will give the best results. One of the key features of a micro switch is the switch lever -- the mechanism that translates physical movement into an electrical contact. Typically, this is a lever, although in some cases, such as the microswitch on a microwave door, it is a small nub. This lever comes in many forms. The lever may be a thin piece of metal to detect if a window or door is open. Many types of levers have rollers -- these are used for sensing objects moving along conveyor belts because you do not want something to jam the switch. There are even switch levers that fan out. These are used in vending machines to tell if a small object has fallen down a tube. You should choose the style that fits the job you are interested in.
Use the type of electrical switch that you need for the application. Micro switches can be single pole or double pole, meaning they can control one circuit or two circuits. They are also "normally open" or "normally closed." Normally open means that activating the switch closes a circuit, allowing current to flow. Normally closed means that activating the switch breaks a circuit, preventing current from flowing.
Tips and warnings
- For security circuits, a normally closed switch is used. Cutting the wires to this switch activates the system, because cutting the wire is the same as activating the switch.
- Because they interact with the constantly changing world, micro switches should be periodically checked. You want to use a microswitch to prevent a disaster, not use a disaster to detect a faulty micro switch.
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