The speed radar mainly uses the Doppler Effect principle: when the target approaches the radar antenna, the reflected signal frequency will be higher than the transmitter frequency; conversely, when the target is away from the antenna, the reflected signal frequency will be lower than the emission. Probability. In this way, the relative speed of the target and the radar can be calculated by changing the value of the frequency.
It has been widely used in industries such as police speeding test.
The principle of radar speed measurement is to apply the Doppler effect, that is, the effect of moving objects on the received electromagnetic waves with frequency shift. The radar speedometer obtains the moving speed of the measured object according to the calculation of the received reflected wave frequency shift. Therefore, it has the following characteristics: 1. The radar beam is larger than the irradiation surface of the laser beam (ray), so the radar speed is easy to capture the target without precise aiming.
2, radar speed measuring equipment can be installed on the patrol car, the detection of speed in the movement, is a very important part of the "mobile electronic police."
3. The radar fixed speed measurement error is ±1Km/h, and the motion measurement error is ±2Km/h, which can fully meet the requirements for traffic violation investigation.
4. The electromagnetic wave beam emitted by the radar has a certain opening angle, so the effective speed measuring distance is relatively close to the laser speed measurement, and the farthest speed measuring distance is 800M (for the big car).
5. The radar speedometer is moderately priced due to its mature technology. Therefore, it is very popular.
6. The opening angle of the radar speedometer's transmit beam is a very important technical indicator. The larger the opening angle, the more susceptible the speed measurement rate is; on the contrary, the impact is smaller.
Speedometer principle
A radar is a device that uses radio echoes to detect the direction and distance of a target. The radar is the transliteration of the word Radar in English. The word is abbreviated by the prefixes of Radio Detection And Ranging. It is the meaning of radio exploration and ranging. The world began to become familiar with radar. In the 1940 British Air War, 700 British fighters carrying radars defeated two thousand German bombers, thus rewriting history. After the Second World War, the radar began to have many peaceful uses. It can be used to detect storms in terms of weather forecasting; it can help pilots and airport air traffic controllers perform their tasks more efficiently in terms of aircraft navigation safety.
The principle of radar operation is very similar to that of sound waves. The only difference is that the wave used is a very high frequency radio wave, not sound waves. The radar transmitter is equivalent to the sound of the shouting sound, and emits a pulse similar to the shouting sound. The pointing antenna of the radar is like a microphone, so that the energy of the electric pulse can be concentrated in one direction. The receiver acts like a human ear to receive echoes of electrical pulses emitted by the radar transmitter.
The speed-measuring radar mainly uses the Doppler Effect principle: when the target approaches the radar antenna, the reflected signal frequency will be higher than the transmitter frequency; conversely, when the target is away from the antenna, the reflected signal frequency will be lower than the emission. Probability. In this way, the relative speed of the target and the radar can be calculated by changing the value of the frequency.
The English word for laser is Laser, which is abbreviated by the first letter of Light Amplification by Stimulated Emission of Radiation, which means that the amplification of light is achieved by excitation radiation. The light excited by the laser has the same photon size and direction of motion, so each beam has the same frequency, and a bundle of them is closely arranged, which are parallel to each other and make the whole beam It will not spread when it is launched far away. In the 1962 experiment, it was discovered that after a nearly 400,000-kilometer space journey, the laser light emitted from the Earth only projected a circle of about three kilometers in diameter on the surface of the moon! This characteristic makes the laser It is widely used in the processing of welding, cutting, engraving, and piercing, and in medicine (ophthalmology, dentistry, and tumor).
Speed ​​lasers are semiconductor lasers in solid state lasers. The laser speed measuring device uses an infrared semiconductor laser diode. The laser diode has several features that make it ideal for measuring speed:
1. A laser diode emits a very narrow beam of light from a small range that is precisely aimed at the target.
2. The laser diode switches the switch at an instant of less than one billionth of a second, greatly improving accuracy.
3. The laser diode has a very low emissivity, and its detector is very easy to receive accurate wavelengths; therefore, it can operate normally when there is strong sunlight during the day.
4. The laser diode emits only the infrared portion of the electromagnetic spectrum; the infrared system is invisible to the eye and does not affect the driver's attention.
The laser speed gun measures the speed of the infrared light wave transmission time. Since the speed of light is fixed, the time that the laser pulse is transmitted to the target and then folded back is proportional to the distance. By transmitting two pulses at regular intervals, two distances can be measured; dividing the difference between the two distances by the transmission time interval yields the target velocity. In theory, two pulses can be measured to measure the speed; in practice, in order to avoid errors, the general laser tachometer (gun) emits up to seven groups of pulse waves in an instant, and the average value is obtained by the least square method to calculate Target speed.
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