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Snap Action, Limit Switches

Snap action or limit switches refer to a class of switches which use levers or plungers that actuate abruptly or ‘snap’ at the end of their range to open or close a switch contact. Their wide variety of configurations and actuation types make them an important electrical switch component of many applications.

Application Field

The robustness of snap action switches, together with their fast and repeatable response , makes them ideal for use in a variety of industrial and consumer products. Examples of the types of industries that primarily use snap action switches include automotive, food manufacturers, medical devices, security systems and access control systems. These applications require switches that need to regulate temperature, fuel level, door openings and fire alarms. The present snap action switch technology is so advanced that modern switches can be adjusted to a variety of set-points, from 0.1m/s to a few m/s over long travel ranges, depending on the application.

The versatility of snap action switches is such that it can also be used for something as mundane as a power window switch in a car or a switch in an elevator, and just as much in an airplane or machine tool. Furthermore, the cost of snap action switches vary greatly and can be tailored to fit the budget. Apart from these areas, snap action switches can also be used for monitoring any other activity that requires precise triggering during operation. The types of limit switches available today also cater to magnetic and inductive applications.

Working Principle

Snap action switches come in a variety of contact options, including reed contacts, open-frame contact with teflon coating, and solid-state switches. Miniature versions with designated features have been developed, making them useful in applications such as those found in medical devices. Despite the variety of designs, the working principle behind the operation of all snap action switches is the same.

The operation of the switch is based on the concept of mechanical overtravel. The switch’s plunger is held in place by a combination of spring pressure and manually applied pressure. When the force is increased past a certain point, a new equilibrium is triggered whereby the switch’s contacts either open or close, thus causing the switch to ‘snap’. This overtravel causes the switch contacts to keep the switch in the actuated state until the force needed to actuate the switch is once again applied.

The major advantage of using snap action switches is their relatively low cost and ability to switch rapidly. Furthermore, as these switches are normally used in systems that require precision functioning, they can be designed to operate with low current levels and thus do not need a separate relay or breaker. The versatility of the snap action switch and the fact that they can be used in a wide range of applications make them a preferred choice among manufacturers.