Electromagnetic dot timer is a commonly used timing instrument. Based on the principle of electromagnetic induction, the oscillator is driven by alternating current to vibrate, which drives the point needle to contact with the paper tape to form a point trace. Because of the use of alternating current, the electromagnetic dot timer can generate periodically changing current, thus driving the oscillator to generate periodically changing vibration, so that the dot needle can generate uniform dots on the paper tape.
In contrast, the current of direct current is constant, so it can't generate periodic current, so it can't be used in electromagnetic dot timer. In addition, the voltage and current stability of direct current is poor, which is easily influenced by external factors, such as temperature and humidity, while the voltage and current stability of alternating current is good, which can ensure the accuracy and stability of electromagnetic dot timer.
In a word, the electromagnetic dot timer uses alternating current, because alternating current can generate periodically changing current, which drives the oscillator to generate periodically changing vibration, thus ensuring that the dot needle generates uniform dots on the paper tape.
Development history of alternating current
When electromagnetic induction was discovered, the method of generating alternating current was known. The early generators were invented by michael faraday, an Englishman, and Bo Piaorongsu, a Frenchman. 1882, British electrician James Gordon built a large two-phase alternator. Lord Kelvin and Sebastian Ferranti developed early alternators with frequencies ranging from 100 Hz to 300 Hz.
189 1 year, nikola tesla obtained the patent of high frequency alternator (15000Hz). 189 1 year later, power supply will be provided by multiphase alternator. Thereafter, the AC frequency of the alternator is usually designed between 16 Hz and 100 Hz, and it is used in conjunction with arc lamps, incandescent lamps or motors.
According to the law of electromagnetic induction, when the magnetic field around a conductor changes, an induced current will be generated in the conductor. Usually, the rotating magnet is called rotor, and the fixed group in the coil with conductor wound on the iron core is called stator. When it passes through a magnetic field, it generates an electric current. The basic machine that generates alternating current is called alternator.