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Linear limit switches are electromechanical devices that make the contacts change state when there is a physical contact between a target object and switch activator.
There are two basic types of linear limit switches viz. Momentary switches and contact switches.
Momentary or spring return switches return to their normal state as soon as the actuator passes its release point. On the other hand, maintained contact switches continue to remain in their triggered position even after the actuator is released, and can be reset only by further mechanical action of the operating head. Most of the linear limit switches have a rugged design, and therefore are suitable for a various industrial applications. But as these devices contain mechanical parts, they undergo abrasion after some time. However, linear limit switches are slower than non-contact switches, like proximity sensors and photoelectric sensors. Common triggering methods include pushbuttons, plungers, standard levers, roller leavers, and adjustable levers. Top-mounted devices position the actuator on the top of the limit switch. Side-mounted devices locate the actuation mechanism on the side.
Selecting linear limit switches
Linear switches are selected based on pole-and-throw specifications.
Single pole, single throw (SPST) switches are also known as "single pole" switches. They have two terminals, and they make or break the connection of a single conductor in a single branch circuit.
Single pole, double throw (SPDT) switches are also known as "three-way switches" as they have three terminals and are used in pairs. They make or break the connection of a single conductor with either of two other single conductors.
Double pole, single throw (DPST) switches have six terminals and are available in either momentary or maintained contact versions. They make or break the connection of two circuit conductors in a single branch circuit and usually have four terminals. Double pole, double throw (DPDT) switches make or break the connection of two conductors in two separate circuits. Most DPDT. Special throw types with more than two poles are designed to split loads into separate circuits.
Specification for linear limit switches
Electrical specifications includes:
- Maximum current rating
- Maximum AC voltage rating
- Maximum DC voltage rating
In addition when triggered, Normally open (NO) contacts close, and when triggered gain, Normally closed (NC) contacts open.
Mechanical specifications include:
-Actuating force, pre-travel, total travel, and operating temperature.
Actuating force is the force required to move the switch actuator to the operating or trip position. Pre-travel is the distance the actuator moves from the free or rest position to the operating position. Total travel is the total physical movement of the switch from the resting position to the actuation point. Operating temperatures is the temperature range over which switches are designed to operate.
Application
- linear limit switch are used in transistor-transistor logic (TTL)
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