A timer is a specialized type of clock. Circadian Locomotor Output Cycles Kaput, or Clock is a gene which encodes proteins regulating Circadian rhythm. 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. A machine is any device that uses Energy to perform some activity In Engineering, electromechanics combines the Sciences of Electromagnetism of Electrical engineering and mechanics. A digital system uses discrete (discontinuous values usually but not always Symbolized Numerically (hence called "digital" to represent information for A computer is a Machine that manipulates data according to a list of instructions.
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Mechanical Timers
Early mechanical timers used typical clockwork mechanisms, such as an escapement and spring to regulate their speed. A clockwork is the inner workings of either a mechanical Clock or a device that operates in a similar fashion In Mechanical watches and Clocks an escapement is a device which converts continuous rotational motion into an oscillating or back and forth motion A spring is a flexible elastic object used to store mechanical Energy. Inaccurate, cheap mechanisms use a flat beater that spins against air resistance. In Fluid dynamics, drag (sometimes called fluid resistance) is the force that resists the movement of a Solid object through a Fluid (a 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. A time bomb (or timebomb time-bomb) is an Improvised explosive device with a Timer so that it can be set to Detonate any time
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). Thermal Expansion is the tendency of matter to change in Volume in response to a change in temperature Steel is an Alloy consisting mostly of Iron, with a Carbon content between 0 Bronze is any of a broad range of Copper alloys, usually with Tin as the main additive but sometimes with other elements such as Phosphorus An electric current flows through this finger, and heats it. Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. 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. Christmas lights (also sometimes called fairy lights, twinkle lights or holiday lights in the United States are strands of Electric lights used
Another type of electromechanical timer (a cam timer) uses a small synchronous AC motor turning a cam against a comb of switch contacts. A cam timer is an Electromechanical system for controlling a sequence of events automatically An alternating current ( AC) is an Electric current whose direction reverses cyclically as opposed to Direct current, whose direction remains constant An electric motor uses Electrical energy to produce Mechanical energy. A cam is a projecting part of a rotating Wheel or shaft that strikes a Lever at one or more points on its circular path A switch is a mechanical device used to connect and disconnect an electric Circuit at will 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. This is the page for mechanical Gears For other uses see Gear (disambiguation For the gear-like device used to drive a roller chain see Sprocket The most common application of this timer now is in washers, driers and dishwashers. A washing machine, or washer, is a machine designed to clean Laundry, such as Clothing, Towels and sheets The term is mostly applied A clothes dryer or tumble dryer is a household appliance that is used to remove the moisture from a load of Clothing and other Textiles, generally A dishwasher is a mechanical device for cleaning dishes and eating utensils They can be found in Restaurants and private homes 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. A relay is an electrical Switch that opens and closes under the control of another Electrical circuit. 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. A rocket or rocket vehicle is a Missile, Aircraft or other Vehicle which obtains Thrust by the reaction of the A missile (see also pronunciation differences) is a self-propelled explosive Projectile used as a weapon towards a target
Digital Timers
Digital timers can achieve higher precision than mechanical timers because they are quartz clocks with special electronics. A quartz clock is a Clock that uses an Electronic oscillator that is regulated by a Quartz crystal to keep time Integrated circuits have made digital logic so inexpensive that an electronic digital timer is now less expensive than many mechanical and electromechanical timers. Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside Digital electronics are Electronics systems that use Digital signals Digital electronics are representations of Boolean algebra also see Individual timers are implemented as a simple single-chip computer system, similar to a watch. An embedded system is a special-purpose Computer system designed to perform one or a few dedicated functions often with Real-time computing constraints A watch is a timepiece that is made to be worn on a person The term now usually refers to a wristwatch, which is worn on the wrist with a strap or Bracelet. Watch technology is used in these devices.
However, most timers are now implemented in software. An embedded system is a special-purpose Computer system designed to perform one or a few dedicated functions often with Real-time computing constraints Modern controllers use a programmable logic controller rather than a box full of electromechanical parts. A programmable logic controller ( PLC) or programmable controller is a Digital computer used for Automation of industrial processes such as The logic is usually designed as if it were relays, using a special computer language called ladder logic. Ladder logic is a philosophy of drawing electrical logic schematics 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 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 indicating the need for attention or a synchronous event in software indicating the need for a change
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). An electronic amplifier is a device for increasing the power and/or Amplitude of a signal. Pulse-width modulation (PWM of a signal or power source involves the Modulation of its Duty cycle, to either convey information over a
Embedded systems often use a hardware timer to implement a list of software timers. An embedded system is a special-purpose Computer system designed to perform one or a few dedicated functions often with Real-time computing constraints 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.
- See also: Programmable Interval Timer and High Precision Event Timer
See also
External links
- Timer Management in Embedded Systems
- Stopwatch Timer
- Online Stopwatch Timer from eben tools
- Interval Timer for Fitness
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