A touch switch is an electrical momentary or latching contact that is manually controlled by tapping it. It is used in many home power control applications for convenience. In industrial applications, touch switches are usually used with special considerations for safety.
Switches have been used for as long as electricity has been around. The principle involved is to make or break the electrical circuit. In high-current applications, a touch switch is used along with relays that further actuate higher capacity contacts. The touch-sensitive tactile sensor is very useful for safety switches, and there is stationary cutting equipment that is designed to stop almost instantly when human touch is sensed.
While electronic switches are popular due to their longer lifetime, ordinary switches that are frequently used have a shorter lifespan due to arcing, which gradually vaporizes the switch contacts. Electronic switches may use semiconductor circuits that require very little transient power across the switch. An open switch and a closed switch have no power dissipated in them. The transient power in an ordinary switch may be significant depending on the load. For instance, capacitive loads and cold resistive loads may cause large transient currents.
Capacitance touch switches use the additional capacitance of the switch user’s body. When a person touches this type of touch sensor, the increased capacitance is detected and the corresponding result is obtained. Elevator floor selectors are a common use for capacitance touch switches. With the lightest touch, a passenger is able to set the desired floor.
A resistance touch switch uses two electrodes to sense the resistance of a human finger as opposed to an open circuit. Its construction is similar to a raindrop detector. A decrease in resistance may produce a change in voltage level when compared to a reference. The result is a durable switch that will not wear out due to the very low current that is needed to detect a human finger.
Touch switches are used for security and safety applications. Doorknobs may be wired to sense if they have been touched. Light switches and dimmers may use touch switches for more convenience. A touch switch kit usually has an integrated circuit that has analog circuitry that senses the touch and then drives a semiconductor power switch or relay. The sensing circuit, if not probably designed, may have erratic operation when surge currents and interference from electrical loads are present.
