Mechanical switches can be divided into two basic types. The first, commercial and appliance switches, are used in fairly clean environments such as offices or homes. They are not sealed and are generally used for light, low-current applications. The second type, industrial switches, actuate magnetic contactors and remote-operated controllers. These switches must be ruggedly constructed because they are frequently exposed to oil, solvents, chemicals, and dust. And their contacts must handle the high inrush current drawn by electromagnets in the controllers. Industrial switches are available in five basic types: standard duty, heavy duty, heavy-duty oiltight, miniature oiltight, and multilight-control oiltight. The terms standard duty and heavy duty are derived from the Standards for Industrial Control Equipment of Underwriters' Laboratories Inc. for normal current and inrush current. Manual switches can have one or a combination of switching actions. In momentary-action switches, the operator pushes (pushbutton or toggle) or twists (rotary) the actuating device and contacts move to transfer the circuits to the second set of contacts. When the actuating force is removed, the actuating device and the contacts return to the original position. When a maintained-action switch is actuated, the contacts move to transfer the circuits to the second set of contacts. No change takes place until the operator actuates the switch a second time. Then the circuit moves to another set of contacts or returns to the original position. Mechanical-bail switches have separate switching assemblies, which are interlocked so that actuation of one switch deactivates another. A capacitive touch switch consists of two conductive layers on opposite sides of an insulating material such as glass or a printed-circuit board. The conductive layers create a capacitance that decreases when a layer is touched. Interface circuitry converts the capacitance change into a usable switching action to drive logic systems or to switch analog
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Limit switches are electromechanical or solid state devices that require the physical contact of an object with the switch’s actuator to make the contacts change state.
Linear Limit Switches
Linear limit switches are electromechanical devices that require physical contact between a target object and switch activator to make the contacts change state.
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.
Thermostats and Thermal Switches
Thermostats and thermal switches are electro-mechanical on/off switches that are activated by temperature changes. They are typically used to control heating and cooling systems.
RF switches route radio frequency signals to particular waveguides.
Topics of Interest
Instrument and control switches are used to manage relatively large currents and voltages as found in operator panels at electrical utility substations. switches are used to manage relatively large...
For basic and plunger-actuated switches, this is stated as a range. The low limit indicates the smallest differential obtainable. For switches with leaf or lever actuators, the movement differential...
Ordinary electromechanical switches are not the only choices for applications demanding long life. To get a long-lived switch it is possible to use a photointerrupter in lieu of mechanical fixed and...
This chapter covers representative general-purpose relays used in the control circuits of most industrial, commercial, and consumer products. Relay names and terminology are in accordance with...
Mercury switches have long served as tilt sensors. Their operating principle Tilting the device past a threshold causes the conductive mercury to bridge between two conductors, thus making a...