Guide to Selecting Rotary Switches: Types, Features, Applications

The rotating switch is a device that moves in a circle and stops at various positions. The rotary switch is used to control many different circuits by using a single switch. As opposed than other switches, these devices have the advantage that turning the actuator can turn the circuit on or off depending on the position, and they can be actuated in a variety of positions. In a single switch position, a rotary switch can also be designed so that a large number of contacts can occur at the same time. It is common for rotary switches to be found on industrial equipment, as well as consumer equipment, such as cars, for adjusting fan speeds. Due to the use of digital equipment like touchscreens for complex switching operations, rotary switches are becoming less common. Nevertheless, mechanical rotary switches are still used on equipment where a computer failure could pose a safety threat.

In rotary switches, the rotors are mounted on a rotating spindle. Each rotor has an arm projecting outward that contacts a terminal when the switch is in a certain position. A switch can have up to dozens of different positions, and each position can be connected to a different circuit, depending on the number of rotors.

The rotary switch is placed in the proper position using a detent mechanism. It prevents the switch from spinning freely and being accidentally set to the wrong setting by making it "click" into place and staying in place until enough force is applied. A detent uses a wheel with notches or grooves cut into it and attached to the rotor. As soon as the wheel reaches the correct position, a spring-loaded ball bearing or piece of spring steel presses into the groove, securing it there. 

The mechanical life of rotary switches is the maximum. Electrical life expectancy is usually less than mechanical life, so please check with the manufacturer.

A switch's number of poles is the number of separate circuits that can be activated at any one time. The term "pole" describes the number of separate circuits controlled by the switch; it is the common or input terminal. It is important to note that the number of circuits controlled determines the number of switch contacts, which, in turn, determines the number of poles needed to make or break the contacts. A typical switch has between one and four poles. Three types of switches are commonly used: single pole (SP), double pole (DP), and triple pole (3P). In the image, the switch is connected to three separate circuits and has three contacts.

In rotary switches, the angle between positions determines the number of positions. For example, a four-position rotary switch has an angle of throw of 90°. For a 100-position rotary switch, the angle of throw is 3.6°.

There are two basic kinds of rotary switches: single-deck and multi-deck. Each one consists of a round plate with an arrangement of contacts. The maximum number of decks that can be attached to a common, actuated shaft is the number of decks. There are several circuits that can be controlled at the same time with a single deck rotary switch. With a multi-deck rotary switch, several circuits can be controlled at once.

Basically, the number of poles per deck refers to the number of separate circuits that can be activated by a rotary switch in a deck. The output connections are generally referred to as ways instead of throws. 12 ways are provided by the switch construction, but one, two, three, or four poles can be used. Signals are channeled from the poles to the output terminals by the rotating contact. The number of terminals determines the number of positions in a switch.

In addition to open frame switches, enclosed switches are also available. The open frame switches have visible moving parts that enable self-cleaning contact systems, ensuring reliable operation. There are more custom contact configurations available and the sections can be purchased separately. While enclosed frames do not show the internal parts, they offer more protection against dust and contamination. Comparatively, they are less expensive and more compact than open frames.

 

• Maximum current rating - The maximum nominal or nameplate current capacity that a switch will carry with the contacts in a closed position. Current carrying capacity is measured in amps. A switch with the contacts closed has no arc, and the carrying capacity is higher.
• Maximum AC voltage rating - The maximum AC voltage capacity of a device.
• Maximum DC voltage rating - The maximum DC voltage capacity of a device.

 

Switch Contact Material

   

Stop Style

   

Contact Style

   

Specifications for Actuators

 

• Bare Shaft Actuator: The shaft in this configuration lacks a knob but can be optionally notched to accommodate diverse knob arrangements.
• Knobbed Shaft: This type of actuator features an integrated knob on the shaft for easy operation.
• Flush Actuator: The actuator is designed to be flush with the switch body, eliminating any projection above the surface. It usually requires a screwdriver for activation.
• Keylock: Actuation is achieved through a key or other secure, tamper-proof mechanism, enhancing security and control.

 

Actuator Attributes

 

• Actuator Detents: These mechanical devices secure the switch in a specific position once the actuating force is withdrawn.
• Integral Potentiometers: As part of the assembly, these components include a potentiometer. Linear potentiometers generate resistance output that adjusts based on the movement or position of a slider or wiper.
• Guarded Positions: Changing switch position necessitates a distinct action, like pushing or pulling the shaft.
• Tease-Proof Mechanisms: These mechanisms prevent rotary switches from lingering between positions after the force is removed.
• Keylocking Toggles: Employed to avert unintentional power shutdowns or unauthorized manipulation, these toggles feature an open slot instead of the traditional toggle. This design permits the insertion of a key that can be toggled upward (ON) or downward (OFF).
• Actuator Material: The material constituting the actuator, be it the switch or its knob, may comprise plastic, thermoplastic, or metal substances.

 

Switch Features

 

• Dustproof Capability: Exhibits resistance to dust infiltration, ensuring reliable operation even in dusty environments.
• Momentary On Functionality: When positively loaded or actuated, the switch maintains its position only for the duration of the action. Upon release, it returns to the unloaded position. Rotary switches with a momentary-on feature can hold a position during positive loading or actuation.
• Configurable Coded Outputs: The switch's output can be customized to provide coded output formats, such as Binary Coded Decimal (BCD) or Octal.
• Weather Resistance and Waterproofing: Achieves hermetic sealing to prevent moisture penetration, making the switch weather resistant and waterproof.
• Self-Cleaning Wiping Contacts: Characterized by low resistance and a self-cleaning attribute. The wiping action during operation helps counter mechanical wear.
• Operational Temperature Range: Specifies the temperature span within which the device must function effectively.
• Binary Coded Decimal (BCD) Output: A specific output format that represents decimal numbers in binary form.
• Octal Outputs: Outputs structured in octal format, facilitating efficient data representation and communication.