How to Select Rotary Limit Switches

Rotary limit switches use physically-actuated levers to rotate a shaft and operate the contacts in a switch, making them change state. Most products feature a rugged design and are suitable for factory and/or industrial applications; however, because these switches contain mechanical parts, they wear over time. Typically, rotary limit switches are slower than noncontact, electrical devices such as proximity sensors and photoelectric sensors.

Types of Rotary Limit Switches

There are three types of rotary limit switches: momentary, maintained contact, and positive opening.

• Momentary switches or spring return switches return to their normal state as soon as the actuator passes its release point.
• Maintained contact switches remain in the triggered position after the actuator is released and are reset only by further mechanical action of the operating head.
• Positive opening switches remain in the activated position even in the event of mechanical failure such as the breakage of a spring or contact weld.

Common actuation methods include standard rollers, offset rollers, adjustable rollers, fork lever rollers, wide rollers, rods or wire, loops, and wobble-type springs. Top-mounted devices position the actuator on the top of the limit switch. Side-mounted devices locate the actuation mechanism on the side.

Product and Performance Specifications

Rotary limit switches vary in terms of electrical specifications, movement specifications, mechanical specifications, connection options, actuator direction, and normal state.

Electrical specifications include maximum current rating, maximum AC voltage rating, maximum DC voltage rating, and transistor-transistor logic (TTL) compatibility. Pre-travel distance, total travel, movement differential, operating force, minimum return force, and repeatability are important movement specifications.

Mechanical specifications include minimum mechanical life and minimum electrical life. Both amounts are measured as measured in number of cycles.

Connection options for rotary limit switches consist of integral cables, solder terminals, screw terminals, and spade terminals. Actuators move in either a clockwise or counterclockwise direction. Electromechanical and solid-state switches are commonly available. Normally open (NO) contacts close when actuated. Normally closed (NC) contacts open when actuated.

Features and Approvals

Rotary limit switches are available with a variety of features. These include self-cleaning switch contacts, safety pulls or guards, and rotating heads. Some products are rated for harsh environments, or are enclosed within a NEMA-rated housing that can be accessed via a conduit.

Organizations such as Underwriters Laboratories (UL) and the Canadian Standards Association (CSA) provide certifications and approvals.

References

YouTube Video – GF4C Testing Rotary Gear Limit Switches

Grainger – Limit Switch

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