This eliminates the need for a photocell (which may be repeatedly triggered on and off by the light which it operates) or for repeatedly re-setting a regular timer for seasonal changes in the length of day or for daylight-saving time. Combining the two allows a light to come on at sundown and go off at midnight, for example.Īn astronomical (or astronomic) timer calculates dawn and dusk times for each day of the year based on the latitude and longitude (or just north/central/south and time zone on more cheaply made ones), and the day of the year (month and date), programmed by the user upon installation in addition to the usual time of day, except in the case of GPS enabled astronomic timers wherein all programming is fully automatic. Timers may do other processing or have sensors for example, a timer may switch on lights only during hours of darkness, using a seasonal algorithm or light sensor. Likewise, a coffee maker may turn itself on early in the morning in time for awakening residents to have fresh coffee already brewed for them. A timer for an unattended slow cooker may switch on automatically at a time and for a period suitable to have food ready at mealtime. A cyclical timer switches equipment both on and off at preset times over a period, then repeats the cycle the period is usually 24 hours or 7 days.įor example, a central heating timer may supply heat for a specified period during the morning and evening every weekday, and all day on weekends. A countdown time switch switches power, usually off, after a preset time. The timer may switch equipment on, off, or both, at a preset time or times, after a preset interval, or cyclically. The mechanism may be mechanical (e.g., clockwork rarely used nowadays), electromechanical (e.g., a slowly rotating geared motor that mechanically operates switches) or electronic, with semiconductor timing circuitry and switching devices and no moving parts. They are intended to allow viewers to watch as they fall asleep. The setting is usually made either from the remote control of the device or the device's menu. It may be built into power circuits (as with a central heating or water heater timer), plugged into a wall outlet with equipment plugged into the timer instead of directly into the power point or built into equipment.Ī sleep timer is a function on many modern televisions and other electronic devices that shuts off the power after a preset amount of time. The switch may be connected to an electric circuit operating from mains power, including via a relay or contactor or low voltage, including battery-operated equipment in vehicles. Intermatic introduced its first time switch in 1945, which was used for "electric signs, store window lighting, apartment hall lights, stokers, and oil and gas burners." A consumer version was added in 1952. A simple 24-hour cyclical electromechanical time switch with a French CEE 7/5 socketĪ time switch (also called a timer switch, or simply timer) is a timer that operates an electric switch controlled by the timing mechanism.
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