Clock is one of the earliest objects invented by human beings, because it is necessary to measure the time interval continuously. Some natural time intervals (such as day, leap month and year) can be obtained by observation, and shorter time intervals need to use clocks. For thousands of years, the principle of timing equipment has also changed greatly. A sundial is the change of time by the shadow of an object on a plane. There are many instruments to calculate the time interval, including the most widely known hourglass.
The water clock matched with the sundial may be the earliest timing instrument. Europe invented the escapement in 1300, and later created the first mechanical clock, which can use oscillating timing equipment such as balance wheels.
Clockwork-driven clocks appeared in the15th century, and the watch industry began to develop in the15th century to16th century. 1656 invented the pendulum clock, so the accuracy of timing was further improved. At that time, navigation required the accuracy of time, which also promoted the reliability and accuracy of clocks and watches. The electronic clock was patented in 1840, and the development of electronics in the 20th century produced a clock with no mechanical movement at all.
At present, the timing element in a clock is a harmonic oscillator, an object that oscillates at a fixed precise frequency. The harmonic oscillator can be a simple pendulum, a tuning fork, a crystal or an electron oscillation when an atom emits microwave.
Analog clocks use hands and angles to represent time, while digital clocks use numbers to represent time. There are two kinds of time expressions: twelve-hour system and twenty-four-hour system. Most digital clocks use electronic equipment, liquid crystal, LED and vacuum fluorescent display to display the time. Clock function is also one of the standard functions of computers, mobile phones or tablets.
For convenience, distance, telephone or the needs of the blind, an auditory clock is used to tell the time by sound. In order to meet the needs of the blind, there are also clocks for the blind that can sense their own time by touching, some of which are similar to the traditional time, but by adjusting their design, they can directly touch the surface to know the time without affecting the timing function. Timing technology is also constantly developing.
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There are clocks in homes, offices and other places. Small devices such as watches can be worn on your wrist or body. Larger ones will be displayed in public places, such as railway stations or churches, and corners of computer monitors, mobile phones and portable media players.
Most digital computers rely on signals with a certain fixed frequency for synchronous processing, which is called clock signals? Some research projects are developing CPU with asynchronous circuit processing. Computers and other devices will also display date, year and other information, which is different from the clock signal, but it is also obtained by timing the clock signal. Some devices will have special real-time clock (RTC) chips.
The main purpose of the clock is to show the time, but it also has the following functions.
1. Time management: The clock can also give a warning sound at a specified time to remind users and help people manage time. This kind of clock is called an alarm clock. At first, the volume may be very low and gradually increase, or the sound may be interrupted for a period of time, and then the alarm sounds again after a few minutes.
2. Timing control: the clock can control some equipment that needs timing, such as central heating and video recorders. The clock in this application is usually called a timer. In addition, the sun tracking device and telescope frame need to adjust their positions or angles according to the rotation of the earth, and also need to cooperate with the information of the clock.
3. Navigation: Since the12nd century, maritime navigation needs precise latitude and longitude, and latitude can be known according to astronomical navigation, while longitude measurement needs precise time calculation. John harrison invented the navigation timepiece in the18th century. The noon cannon in Cape Town will sound at noon, which is convenient for the crew to correct the time.
4. Seismology: When judging the epicenter of an earthquake, a clock with at least four observers will be used to observe and record the arrival times of different seismic waves at different positions to detect the epicenter.