A timer is a specialized type of
clock. A timer can be used to control the sequence of an event or process. Whereas a stopwatchcounts upwards from zero for measuring elapsed time, a timercounts down from a specified time interval, like a sand clock.
Timers can be mechanical,
electromechanical, digital, or even software, since most computers include digital timers of one kind or another.
Early mechanical timers used typical
clockworkmechanisms, such as an escapementand spring to regulate their speed. Inaccurate, cheap mechanisms use a flat beater that spins against air resistance. Mechanical egg-timers are usually of this type.
More accurate mechanisms resemble small alarm clocks. The chief advantage is that they require little battery/electrical power, and can be stored for long periods of time. The most widely-known application is to control explosives.
Electromechanical timers have two types. A thermal type has a metal finger made of two metals with different rates of
thermal expansion( steeland bronzeare common). An electric currentflows through this finger, and heats it. One side expands less than the other, and an electrical contact on the end of the finger moves away from an electrical switch contact, or makes a contact (both types exist). The most common use of this type is now in the "flasher" units that flash turn signals in automobiles, or sometimes in Christmas lights.
Another type of electromechanical timer (a
cam timer) uses a small synchronous AC motor turning a camagainst a comb of switchcontacts. The AC motor is turned at an accurate rate by the alternating current, which power companies carefully regulate. Gears slow this motor down to the desired rate, and turn the cam. The most common application of this timer now is in washers, driers and dishwashers. This type of timer often has a friction clutch between the gear train and the cam, so that the cam can be turned to reset the time.
Electromechanical timers survive in these applications because mechanical switch contacts are still less expensive than the semiconductor devices needed to control powerful lights, motors and heaters.
In the past these electromechanical timers were often combined with electrical
relays to create electro-mechanical controllers. Electromechanical timers reached a high state of development in the 1950s and 60s because of their extensive use in aerospace and weapons systems. Programmable electromechanical timers controlled launch sequence events in early rockets and ballistic missiles.
Digital timers can achieve higher precision than mechanical timers because they are
quartz clocks with special electronics. Integrated circuits have made digital logicso inexpensive that an electronic digital timer is now less expensive than many mechanical and electromechanical timers. Individual timers are implemented as a simple single-chip computer system, similar to a watch. Watch technology is used in these devices.
However, most timers are now implemented in software. Modern controllers use a
programmable logic controllerrather than a box full of electromechanical parts. The logic is usually designed as if it were relays, using a special computer language called ladder logic. In PLCs, timers are usually simulated by the software built into the controller. Each timer is just an entry in a table maintained by the software.
Digital timers can also be used in safety device such as a
Most computer systems have one to sixteen electronic timers. These are usually just digital counters that are set to a number by software, and then count down to zero. When they reach zero, they
Another common form of timer is a number that is compared to a counter. This is somewhat harder to program, but can be used to measure events or control motors (using a class D digital
electronic amplifierto perform pulse width modulation). Embedded systems often use a hardware timer to implement a list of software timers. Basically, the hardware timer is set to expire at the time of the next software timer of a list of software timers. The hardware timer's interrupt software handles the house-keeping of notifying the rest of the software, finding the next software timer to expire, and resetting the hardware timer to the next software timer's expiration.
Timer software applications can be found in a number of modern items like
mobile phones or digital watches.
Time to digital converter
* [http://www.speedbagforum.com/timer Interval Timer for Fitness]
* [http://www.ebentools.com/ebentools/onlinetimer/ Online Stopwatch Timer from eben tools]
* [http://www.easysurf.cc:80/stimer.htm Stopwatch Timer]
* [http://www.eventhelix.com/RealtimeMantra/Patterns/TimerManagementDesignPatterns.htm Timer Management in Embedded Systems]
Wikimedia Foundation. 2010.
Look at other dictionaries:
TiMER — Solicita una imagen para este artículo. Título TiMER Ficha técnica … Wikipedia Español
timer — ► NOUN 1) an automatic mechanism for activating a device at a preset time. 2) a person or device that records the amount of time taken by a process or activity. 3) indicating how many times someone has done something: a first timer … English terms dictionary
Timer — Tim er, n. 1. A timekeeper; especially, a watch by which small intervals of time can be measured; a kind of stop watch. It is used for timing the speed of horses, machinery, etc. [1913 Webster] 2. (Internal combustion Engines) In electric… … The Collaborative International Dictionary of English
timer — / taimə/, it. / taimer/ s. ingl. [der. di (to ) time regolare, misurare, determinare il tempo ], usato in ital. al masch. [dispositivo a orologeria che regola il funzionamento di un apparecchio] ▶◀ contaminuti, Ⓣ (tecnol.) cronoscopio,… … Enciclopedia Italiana
timer — /ˈtaimer, ingl. ˈtaɪmə(r)/ [vc. ingl., da time «tempo»] s. m. inv. temporizzatore, contatore □ cronometro, cronografo, contasecondi … Sinonimi e Contrari. Terza edizione
timer — (izg. tàjmer) m DEFINICIJA 1. uređaj za mjerenje, reguliranje ili bilježenje vremena 2. inform. digitalni ugrađeni sat u računalu ETIMOLOGIJA vidi time … Hrvatski jezični portal
timer — [tīm′ər] n. 1. a) TIMEKEEPER b) STOPWATCH ☆ 2. in internal combustion engines, any part or system designed to control the timing of the spark in the cylinder 3. any of various devices for timing, or automatically starting and stopping at… … English World dictionary
Timer — Zeitgeber * * * Ti|mer 〈[taıme(r)] m. 3〉 1. Zeitmesser, Zeitschaltuhr, z. B. an einem Videorekorder 2. Terminkalender, Zeitplaner [engl.] * * * Ti|mer [ ta̮imɐ ], der; s, [engl. timer, zu: to time, ↑ timen]: 1. elektronischer Zeitmesser, der… … Universal-Lexikon
Timer — Als Timer (engl. für Zeitmesser) oder Zeitgeber im engeren Sinne bezeichnet man in der technischen Informatik und der Elektronik einen Steuerbaustein, der zur Realisierung der unterschiedlichsten zeitbezogenen Funktionen sowie in Zählern… … Deutsch Wikipedia
Timer — Cette page d’homonymie répertorie les différents sujets et articles partageant un même nom. Timer, du mot anglais time signifiant le temps, peut faire référence à : une minuterie ; Timer, anglicisme utilisé par les plongeurs… … Wikipédia en Français