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Snap Action, Limit Switches

Snap action limit switches are electromechanical control devices used in a variety of applications to detect physical events or conditions and to switch electrical circuits. They feature a robust design and provide reliable switching with minimum hysteresis, repeatability and bounce characteristics. A snap action limit switch has a switch actuator that is actuated when the mechanism is moved to its end position. Upon actuation, the switch contacts move from their open/closed state and remain in that updated state until actuated again.

Applications of snap action limit switches range from simple mechanical on-off operation to the detection of product movement in high speed assembly lines. They are most commonly used to detect and actuate the following events:

• Product sensing and counting.
• Lamp and LED indication.
• Various automation control and sequencing applications.
• Control of pumps and motors.
• Relay and contactor switching.

Snap action limit switches are available in a variety of shapes, sizes, and mechanical designs to fit whatever application they are being used for. The most common types of snap action limit switches are those with 1) a through-hole mounting and a plunger or roller style actuator and 2) a surface mount type with a momentary or latching actuator. The through-hole type is generally used to detect product movement and has the ability to handle large volumes and heavy loads. The surface mount type is often used in light industrial applications, such as sensing the opening or closing of machines or equipment.

The mechanism of a snap action limit switch works by having an actuator arm, which when pressed up against an end stop creates a mechanical force. This force actuates a switch element, which recalls the contacts between the two poles which open or close the circuit. When released, the actuator components spring back to their operating positions and close the circuit again. Depending on the design, the actuator may reset either at the midpoint, or when the lever is manually returned to its start position.

In addition to the two types of actuators, there are also various contact types and methods of resetting. The most common contact types are single pole/double throw, double pole/double throw, and double pole/single throw. The most common reset methods are self-resetting, manual resetting, and latching contacts. The reset method is generally determined by the application the switch is being used for and the number of operators. Self-resetting is the most common type and only requires a single operator to reset the contacts.

In conclusion, snap action limit switches are versatile electromechanical control devices used in numerous applications to detect physical events or conditions and switch electrical circuits. There are several different types and contact arrangements to fit different applications and the design of the switch itself is fairly simple. Snap action limit switches provide reliable switching with minimum hysteresis, repeatability, and bounce characteristics, making them a cost-effective solution for a variety of applications.