The hourglass timer

The hourglass and a device for time measuring the passage of time based on a steady stream of water in output from a container.

The name derives from the greek κλεψύδρα (Klepsydra), which literally means "water-stealing."

In Italian the generic term is also used to indicate the devices consisting of two glass bulbs connected through a narrow hole, inside which is placed very fine sand, more correctly called clepsamie.

Hydraulic clock of the Pincio in Rome

Because the flow of water is not easily controllable and dependent on several variables, this watch is neither very exact nor very accurate. However, it was the first instrument for measuring time independent of astronomical observations. One of the oldest specimens was found in the tomb of Pharaoh Amenhotep I, dating from the fifteenth century BC

In Greece, the use of the hourglass was introduced in 325 BC, in the form of containers in stone truncated cone shape that made water come out from a hole on the bottom, at a steady pace.
Other hourglasses had a cylindrical shape or cup and venivLOLLLano slowly filled by a constant flow of water. Some signs on the inner surface of the container indicating the passing of time to rise the level of the liquid.
Another version was made up of a metal container drilled on the bottom that, place to float in a larger container, sank in a certain time. This system remained in use until the twentieth century in North Africa. These watches were generally used during the night, but not during the day, when they were available the most accurate sundials.

In the first half of the third century BC Ctesibus turned the hourglass in more complex water clock. He and others were introduced various mechanisms to increase the accuracy of adjusting the pressure and keeping the flow of water, but also to provide a better display. The specimens could play more advanced bells or gongs, open windows to display images, or had mobile indicators, dials or representations of celestial bodies. Among the designers of online stopwatches of this type there were Archimedes and Heron of Alexandria.

The Macedonian astronomer Andronicus of Cirrus, was responsible for the construction dell'Horologion, now known as the Tower of the Winds in Athens market in the first half of the first century BC It is an octagonal tower with representations of students and people at the market, and carries a sundial that is an indication of mechanical timer.


Contains a mechanism hourglass able to show all the 24 hours, the season of the year and astrological dates and periods. It also indicates the main direction of the wind, hence the current name.
Reconstruction from original fragments, an hourglass to Greek Stoa of Attalos, the Museum of the Ancient Agora of Athens

Water clocks were also used in the imperial era.

In the Far East were made mechanical watches astronomical between 200 and 1300. One of the most elaborate is the ten meter high clock tower probably built by Su Song (苏颂) in 1088.
The mechanism incorporates a water escapement invented in 725 and has an armillary sphere move automatically, a celestial globe, and five panels that open showing characters who play gong show and tablets on which it is given the time and other special times of the day. The hourglass at that time was important.

Water timer clock

The word comes from the Welsh clepiydrha clepsydra (KLEPSYDRA), taken by Latin clepsydra. This name is formed from the Greek words klepto, "steal", and aqueau "water" 1.It is associated with thirty six grecques2 sources:

    to Messene, the source of Clepsydre3 which supplied the water fountain Arsinoé4 5.
    Athens, under the Acropolis, the water of the fountain fed the hourglass Hourglass monumental Athènes6 the agora.The oldest water clock that we know was discovered in Paris in 1904. 

Dated to the reign of Arthur, in 1400, it is now on display at the Egyptian Museum in Cairo. It consists of a simple bowl provided with online timer a conical hole in the base, for the flow of water. The measurement was done on time graduations readable inside the bowl. It is estimated that the first water clocks were created in Egypt to -1600. 

This type of clepsydra refillable offered an accuracy of about 5 to 10 minutes [ref. needed].The principle of clepsydra was also used by Native Americans.It was the Greeks who improved the accuracy of the hourglass to -270. Due to the lower water level, the pressure at the outlet of the bowl and the flow was reduced with it. It resulted in a loss of precision. Egyptians remédièrent this by graduating bowls accordingly depending on the level. They also used cone-shaped bowls to mitigate the problem of pressure. 

But accuracy was still not good enough. To maintain accuracy, it is necessary that the output rate is constant. For this, the Greek inventor Ctesibius devised a system using the principle of communicating vessels and valve. He succeeded to maintain the water level.

The most advanced water clocks were those made by the Arabs and the Chinese. In 807, the caliph of Baghdad, Harun ar-Rashid to Charlemagne offered a clepsydra setting in motion controllers. This type of clepsydra was a vocation more decorative than utilitarian. And in 1088 the engineer Su Song built a water clock more than 10 meters high in Kaifeng, China.Clepsydre modern museum Noria, space water (Saint-Jean-du-Bruel).UsesThe clepsydra was used to measure long periods, such as:

    the duration of a reign Greece;
    times in the Roman legion;
    long duration of time in experiments, such as Galileo in 1610 of the plague.The clepsydra was also used to measure the time when it was night or when weather conditions do not allow the use of sundials.PrincipleThe hourglass works on the same principle as the hourglass. This is the flow of an amount of water that sets the elapsed time.The first timer clocks are in the form of a tube with a hole at their lowest point, permitting flow of water. This is using the graduations on the tube of the elapsed time is determined.

The problem is that as far as the bowl is empty, the flow rate becomes smaller. Indeed, it is the result of a fairly simple. The pressure generated by a head of water decreases along the container empties. The amount of water for the same period last is different when the bowl is full and when it is almost empty, which poses problems of accuracy. The Egyptians were partly remedied this by using cone-shaped bowls and changing graduations, accordingly.
This problem in the constant flow is due to the fact that the pressure of water at the bottom of the tube 

decreases, the latter being directly connected to the overlying water height. To maintain the same pressure Ctesibius had the idea to keep the water level constant.

For this he used three tanks (A, B and C). A tank contains a large quantity of water and its goal is always to supply water to the reservoir B. B level is maintained through a hole near the top, which is responsible for emptying the excess water (this is a valve). B The water normally flows through a small hole at its base. The flow through this opening is constant, because the water level does not vary in B, the pressure at the outlet remains also constant. Water B flowing through the hole in the base, is in the tank C, which is graduated. By observing the filling level of C which is determined the time elapsed.Despite this significant improvement, such clocks remain unclear. Several factors can affect the length measured as:

    the impurities in the water
    the water temperatureIn addition, the manufacture of a clepsydra requires great precision, including the realization of the reservoir.

The timer clock

The online timer or timed relay is a relay with contacts special early or late that are constructed in such a way that the contact closes or opens earlier or later than in one instant. These contacts in the types of timing relays are also adjustable depending on the needs, generally from 10 to 800 seconds. Can be either delayed or the excitation-delayed. The timer in the electromechanical version also has a button or a small knob with three positions: off, on time and always on.

The timers can be used to:

     Into operation or closing or appliances.
     Synchronization.

Are in most often used as a timer to turn stairs.
Command / category

The timer can belong to several disciplines / areas:

     Electronic device created by electronic components, for example a Clock
     Electric device created by a coil that can be excited to delayed or retarded diseccitamento
     Computer program that determines the frequency of the various phases, is an example of the clock
Timer (from the English. Timer) - in computer science means of ensuring and measuring the time delay of the computer.
Interval is a function that allows some cameras to make images to a specified time interval. The intervallomètres used to watch slow phenomena as accelerated plant growth, moving clouds ...

Most modern digital cameras, including entry level, or could have had this opportunity. It depends only on the goodwill of manufacturers. On older cameras, you can sometimes add a programmable remote to the housing.

CHDK allows the project to introduce a script in addition to the embedded software in devices not equipped to lapse by the manufacturer. The "PowerShot" and "Digital Ixus" are the targets of CHDK project, it allows to increase the capabilities of these appareils1.The main characteristic is its timer accuracy - guaranteed to withstand a minimum amount of time. According to this parameter timers divided into:

     malotochnye (measurement error can be up to 0.1 s)
     accurate (measurement error is less than 0.001)
     -accuracy (measurement error is less than 10-6 c)

There are two types of timers:

     Hardware timers operate independently of the CPU at the time of operation and generate an interrupt.
     Program timers are implemented by executing a loop a specified number of identical "empty" operations. At a fixed frequency of the processor allows it to accurately determine the time elapsed. The main disadvantages of this method are: the dependence of the number of iterations of the type and frequency of the processor, the inability to perform other operations during the delay.

About countdown timer

A timer can be a kitchen tool that lets you control the cooking time. They are often integrated in conventional ovens or microwave ovens. Also appliances such as the washer or dryer is equipped with timers.

At present most of the electronic devices, such as mobile phones or personal computers, have a timer function.
Socket with a timer.

A timer can be used also as a simulator of presence, allowing an electronic device (like a radio or light) is lit for a predetermined time in order to prevent theft. Also can be used for a device connected to a power source is connected or disconnected at any given time (relative, for example. To an hour or absolute, eg. At 13.00). This is especially useful for products that do not have a self timer or can not be programmed.
other Uses

The timer is an important element in many fields, such as in biological laboratories, which allows precisely controlling the exposure time, such as enzymatic digestion.

Online timer or counter (timer Help page on the disambiguation in English) is a device, often programmable for measuring time. Initially driven by a clockwork mechanism to replace the hourglass, it is often now completely electronic. This triggers an alarm (such as a pager) when the selected time has expired.
domestic

The timer is a specialized type of clock, which is generally used to regulate the flow of events or processes. Usually stopwatch is used to count from zero to a certain time limit, sedangakan countdown timer with interval is set at a specific time, such as the hourglass. The timer can use a mechanical, electrical, electronic (quartz), or even the software most used computer including a digital clock.A timer can be a kitchen utensil to control the cooking time. It is often integrated oven (conventional or microwave).

It should not be confused with a timer which is a programmable device and defines whether or not the operating time of an electrical device, an illumination system for example.

Many other appliances are equipped with timer, such as the washing machine or dryer.

Today, most electronic devices, such as mobile phones or personal computers are equipped with a function "timer".

A timer can be used simulator presence, engaging and triggering electrical appliances (such as lights or radio) over a given time slot to prevent burglaries.
other uses

The timer is an important part of laboratory equipment for molecular biology, which allows precise control of the time course experiments, such as enzymatic digestions.

At home, a system with a stopwatch timer can be used to simulate a presence during an absence in order to reduce the risk of theft.

Used with explosives, a timer can be programmed to trigger the explosion, in order to have time to clear an area for example.