How to Select Rotary Switches

Rotary switches move in a circle and can stop in several positions. They are used to control many different circuits or select different valves for one circuit with a single switch. These devices have some advantages over other switches since turning the actuator can turn circuits on or off depending on the position and many different actuation positions are possible. Rotary switches can also be designed to have many contacts happening at once on a single switch position. While rotary switches can be found on many types of industrial equipment, they can also be found in consumer equipment such as in a car for adjusting things like fan speed. Rotary switches are becoming less common since complex switching operations are being done with digital equipment such as touchscreens. Mechanical rotary switches are still used however, especially in equipment where a computer failure could be a safety issue. Image Credit: Omega Engineering

Rotary switches have a rotating spindle. The rotors are on a spindle and each rotor has an arm projecting outward that can make contact with a terminal when the switch is in a certain position. Depending on the number of rotors, the switch can have dozens of different positions and each one can be attached to a particular circuit.

^{Parts of a rotary switch. Image Credit: Doctronics.co.uk}

In order to put the rotary switch in the proper position, a detent mechanism is used. This mechanism makes the switch "click" into position and stay in place until enough force is applied, preventing the switch from turning freely and being put in the wrong setting accidentally. A detent uses a wheel with notches or grooves cut into it and attached to the rotor. When the wheel reaches the correct position a spring-loaded ball bearing or piece of spring steel pressing against the wheel presses into the groove holding it into place.

Important physical switch specifications to consider when selecting a rotary switch include mechanical life, number of poles, angle between positions, number of decks, number of poles per deck, and switch frame.

^{Multi-deck (left) and Single deck (right) rotary switch Image Credit: Elma}

Number of poles per deck- The number of poles per deck is the number of separate circuits that can be activated through a rotary switch per deck. The output connections are usually called ways instead of throws. The construction of the switch provides a total of 12 ways but there may be 1, 2, 3, or 4 poles. The rotating contact will channel the signal from the pole to the output terminals. The number of terminals required determines how many positions a switch will have.

Stop Style

Rotary switches with an adjustable or continuous stop are commonly available. The stop style should be selected based on the need of the application.

Adjustable stops give the user the option to stop when desired. Adjustable stops allow the user to take a 12-position switch and adjust it to have any number of positions between 2 and 12. This stop should be used for low volume requirements.

Continuous stops, also known as no stops, do not have any stop positions on the rotary switch.

Fixed stops have the stop positions come fixed from the manufacturer and are not changeable by the user. They are better for volume production requirements so the user does not have to adjust the switch.

For more information on Rotary Switches please read IHS GlobalSpec's How to Select Rotary Switches guide.