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Encyclopedia > Timer
A simple digital timer. The internal components—including the circuit board with control chip and LED display, a battery, and a buzzer—are visible.
A simple digital timer. The internal components—including the circuit board with control chip and LED display, a battery, and a buzzer—are visible.

A timer is a specialized type of clock. A timer can be used to control the sequence of an event or process. Timers can be mechanical, electromechanical, digital, or even software, since most computers include digital timers of one kind or another. Image File history File linksMetadata Timer. ... Image File history File linksMetadata Timer. ... Close-up photo of one side of a motherboard PCB, showing conductive traces, vias and solder points for through-hole components on the opposite side. ... External links LEd Category: TeX ... Symbols representing a single Cell (top) and Battery (bottom), used in circuit diagrams. ... A buzzer or beeper is a signaling device, usually electronic, typically used in automobiles, household appliances such as a microwave oven, or game shows. ... A platform clock at Kings Cross railway station in London A clock is an instrument for measuring and indicating the time. ... Wind turbines The scientific definition of a machine is any device that transmits or modifies energy. ... In engineering, electromechanics combines electromagnetism and mechanics. ... A digital system is one that uses discrete values (often electrical voltages), especially those representable as binary numbers, or non-numeric symbols such as letters or icons, for input, processing, transmission, storage, or display, rather than a continuous spectrum of values (ie, as in an analog system). ... Computer software (or simply software) refers to one or more computer programs and data held in the storage of a computer for some purpose. ... The NASA Columbia Supercomputer. ...

Contents

Mechanical Timers

Early mechanical timers used typical clockwork mechanisms, such as an escapement and 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. Gear with escapment mechanism For other uses, see Clockwork (disambiguation). ... A simple escapement. ... Helical or coil springs designed for tension A spring is a flexible elastic object used to store mechanical energy. ... For a solid object moving through a fluid or gas, drag is the sum of all the aerodynamic or hydrodynamic forces in the direction of the external fluid flow. ...


More accurate mechanisms resemble small alarm clocks. The chief advantage is that they require not much battery/electricity and can be stored for long periods of time. The most widely-known application is to control ([explosives])


Electromechanical timers

Electromechanical timers have two types. A thermal type has a metal finger made of two metals with different rates of thermal expansion (steel and bronze are common). An electric current flows 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. In physics, thermal expansion is the tendency of matter to increase in volume or pressure when heated. ... The steel cable of a colliery winding tower. ... Assorted ancient Bronze castings found as part of a cache, probably intended for recycling. ... Electric current is the flow (movement) of electric charge. ... Turn signals (US English) or indicators (British English) are a set of lights on a vehicle (be it a car, truck/lorry, tractor, motorcycle, etc. ... Karl Benzs Velo model (1894) - entered into the first automobile race An automobile or motor car (usually shortened to just car) is a wheeled passenger vehicle that carries its own motor. ... Christmas lights (also sometimes called fairy lights, twinkle lights or holiday lights in the United States) are strands of electric lights used to decorate homes, public/commercial buildings and Christmas trees during the Christmas season. ...


Another type of electromechanical timer (a cam timer) uses a small synchronous AC motor turning a cam against a comb of switch contacts. 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. A cam timer is an electromechanical system for controlling a sequence of events automatically. ... City lights viewed in a motion blurred exposure. ... Rotating magnetic field as a sum of magnetic vectors from 3 phase coils An electric motor converts electrical energy into mechanical energy. ... monkey ... Electrical switches. ... Spur gears found on a piece of farm equipment A gear is a wheel with teeth around its circumference, the purpose of the teeth being to mesh with similar teeth on another mechanical device -- possibly another gear wheel -- so that force can be transmitted between the two devices in a... Front-loading washing machine. ... An electric clothes dryer A clothes dryer or tumble dryer is a major household appliance that is used to remove the residual moisture from a load of clothing and other textiles, generally shortly after they are cleaned in a washing machine. ... A Dishwasher A two drawer DishDrawer dishwasher. ...


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. Automotive style miniature relay A relay is an electrical switch that opens and closes under the control of another electrical circuit. ... A Soyuz rocket, at Baikonur launch pad. ... It has been suggested that Guided missile be merged into this article or section. ...


Digital Timers

Digital timers can achieve higher precision than mechanical timers because they are quartz clocks with special electronics. Integrated circuits have made digital logic so 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. A quartz clock A quartz clock is a timepiece that uses an electronic oscillator which is made up by a quartz crystal to keep precise time. ... Integrated circuit of Atmel Diopsis 740 System on Chip showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ... Digital circuits are electric circuits based on a number of discrete voltage levels. ... A router, an example of an embedded system. ... Russian Poljot Siberia model finished movement viewed through crystal back For other uses, see Watch (disambiguation). ...


However, most timers are now implemented in software. Modern controllers use a programmable logic controller rather 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. A router, an example of an embedded system. ... PLC & input/output arrangements A Programmable Logic Controller, PLC, or Programmable Controller is a digital computer used for automation of industrial processes, such as control of machinery on factory assembly lines. ... Ladder logic is a method of drawing electrical logic schematics. ...


Digital timers can also be used in safety device such as a Gas Timer.


Computer timers

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 interrupt the computer. In computing, an interrupt is an asynchronous signal from hardware or software indicating the need for attention. ...


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 amplifier to perform pulse width modulation). The term amplifier as used in this article can mean either a circuit (or stage) using a single active device or a complete system such as a packaged audio hi-fi amplifier. ... Pulse-width modulation of a signal or power source involves the modulation of its duty cycle to either convey information over a communications channel or control the amount of power sent to a load. ...


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. A router, an example of an embedded system. ...


See also

Look up timer in Wiktionary, the free dictionary.

Wikipedia does not have an article with this exact name. ... Wiktionary (a portmanteau of wiki and dictionary) is a multilingual, Web-based project to create a free content dictionary, available in over 150 languages. ... An intervalometer is a device to trigger exposures of a camera at a defined interval, most notably for time-lapse photography. ... In electronic instrumentation and signal processing, a time to digital converter (abbreviated TDC) is a device for converting a signal of sporadic pulses into a digital representation of their time indices. ...

External links


  Results from FactBites:
 
Timer - Wikipedia, the free encyclopedia (686 words)
Timers can be mechanical, electromechanical, digital, or even software, since most computers have clocks.
Early mechanical timers used typical clockwork mechanisms, such as an escapement and spring to regulate their speed.
Another type of electromechanical timer (a cam timer) uses a small synchronous AC motor turning a cam against a comb of switch contacts.
Timer (Java 2 Platform SE v1.4.2) (1512 words)
Creates a new timer whose associated thread may be specified to run as a daemon.
A deamon thread is called for if the timer will be used to schedule repeating "maintenance activities", which must be performed as long as the application is running, but should not prolong the lifetime of the application.
Note that calling this method from within the run method of a timer task that was invoked by this timer absolutely guarantees that the ongoing task execution is the last task execution that will ever be performed by this timer.
  More results at FactBites »

 
 

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