? At 89C51 store's 17 pages or technical coefficient rate is generally .258%, and its speed is very fast, that is, it can turn about 3 times per second.
In p>1876, the British surgeon Soga obtained a patent for a timing device to control the switch of a gas street lamp. It uses a mechanical clock to drive a switch to control the gas valve. At first, it was wound once a week. After the clock was used in 1918, it was not necessary to wind it.
with the improvement of living standards, the use of timers is becoming more and more extensive. For example, the timing control of water boilers and water heaters, with a high-power timer, can be turned on and off at regular intervals to achieve energy-saving, safe and healthy use.
Timer.
The hourglass or water leak was the earliest timing tool used by human beings, but after the birth and development of clocks and watches, people began to try to use this brand-new timing tool to improve the timer to achieve the purpose of accurately controlling time.
Timer is really an amazing invention, which makes a lot of work that needs people to control time much easier. People even used timers in the military, making time bombs and time detonators. Many household appliances are equipped with timers to control the switch or working time.
On-delay timer: On-delay timer is the most common and basic timer in various PLCs, which is called SD timer in SIEMENS PLC.
OFF-delay timer: this timer has no delay effect when the input cONdition is on, and only produces delay effect when the input condition is off. In SIEMENS PLC, it is called SF timer.