A rotary switch is a special switch that is used in electrical engineering to set switching states by means of a mechanical rotary movement. One or more circuits are switched on or off jointly by different contact arrangements in the form of a rotary movement that is triggered by the operator. In the case of a multi-pole rotary switch for low voltage , as shown in the figure opposite, the individual contact fields are arranged on a common axis; the contacts are moved together by the rotational movement of the axis.
Rotary switches are available in different, mostly very application-specific designs, such as single or multi-pole, with and without a stop, for certain switching sequences or for binary coding. Specific examples of rotary switches are:
- Rotary switches that are mechanically combined with a potentiometer on the rotary axis . This form can be found, for example, in some radio devices in which the on / off switch is combined as a rotary switch with the volume control (potentiometer).
- Single-pole rotary switches were mainly used as light switches in house installations until the middle of the 20th century , before they were largely replaced by the toggle switches that are common today . The expression "turn the light on or off", which comes from the times of kerosene lamps and gas lights , was adopted by the rotary switch in the era of electrification and is still used today, especially in southern Germany and Austria.
- Multipole rotary switches that have mechanically coded certain states or sequences of states and are used for configuration in electronic devices. Application examples are older television receivers from the 1960-1970s, in which the channel selector switch is implemented as a rotary switch. They are more convenient than DIP switches or jumpers for setting the addresses of bus-bound or wireless electronic assemblies and devices .
- In the field of energy technology for older electric rail vehicles : rotary switches for setting different travel speeds or drive powers
- Also in power engineering for switching transformer taps to automatically regulate the level of medium voltage in substations , motor-operated
- In measuring devices such as multimeters and older oscilloscopes , they are used to select calibrated measuring ranges
- Cam switch as main switch for manual switching of electrical consumers.
Depending on the shape of the contact, a distinction can be made between “wiping” and “breaking” contacts; In principle, this also applies to changeover switches . A "wiping contact" is a short circuit between two neighboring contacts with the slider during switching. In the opposite case, there is no such short circuit.
Many of the modular rotary switches, as shown in the illustration, are equipped with wiping contacts; interrupting behavior results from the omission and mechanical skipping of the intermediate contact. In power engineering, for switching transformer taps, such an intermediate contact is wired with power resistors the size of a bucket. On the other hand, wiping behavior is uncommon with toggle switches and fixed rotary switches. When designing the circuit, this may have to be taken into account to avoid hazards .