Principle of operation
The laser sensor works by firing a laser pulse from a laser emitting diode at a target. The laser light is scattered in all directions after being reflected by the target. Part of the scattered light is returned to the sensor receiver, which is received by the optical system and imaged on the avalanche photodiode. The avalanche photodiode is an optical sensor with internal amplification so that it can detect extremely weak light signals and convert them into corresponding electrical signals. A common type of sensor is the laser distance sensor, which determines the distance to a target by recording and processing the time elapsed from when the light pulse is emitted to when it returns to be received. Laser sensors must be extremely accurate in determining the transmission time because the speed of light is so fast.
For example, the speed of light is about 3*10^8m/s, and to achieve a resolution of 1mm, the electronic circuitry of a transmission time ranging sensor must be able to discriminate between the following very short times: 0.001m/(3*10^8m/s)=3ps
To discriminate between the times of 3ps is an excessively high demand on electronics, and is too expensive to realize. But today's laser range sensors cleverly sidestep this obstacle by utilizing a simple statistical principle, the law of averages, to achieve a resolution of 1mm with a guaranteed response time.
Laser displacement sensor advantages and disadvantages:
Next, I would like to introduce the advantages and disadvantages of laser displacement sensors, first of all, I would like to say is the advantages of laser displacement sensing, because the laser's straight line performance is very good, in the flat place to measure a thing whether displacement occurs, it is a very large accuracy, but for the life of the present, the building site Many factors are subject to external interference, so it is not possible to be so idealized, at the same time, the laser generated device is relatively complex, and laser displacement sensor it is also relatively large, so that the laser displacement sensor it is applied to the scope of application and some of the application of the conditions are very demanding.
Main Functions
Laser Length Measurement
Precision measurement of length is one of the key technologies in the precision machinery manufacturing industry and optical processing industry. Modern length measurement is mostly carried out by using the interference phenomenon of light waves, and its accuracy mainly depends on the goodness of the monochromaticity of light. Laser is the most ideal light source, which is 100,000 times purer than the best monochromatic light source (krypton-86 lamp). Therefore, the laser length measurement range is large, high precision. By the principle of optics, the maximum measurable length of monochromatic light L and wavelength λ and spectral line width δ relationship between L = λ / δ. Krypton - 86 lamps can be measured at a maximum length of 38.5 cm, for the longer objects need to be measured in sections to reduce the accuracy. If a helium-neon gas laser is used, the maximum length can be measured in tens of kilometers. General measurement of length within a few meters, the accuracy of up to 0.1 microns.
Laser ranging
It's the same principle and radio radar, the laser will be fired at the target, measure its round-trip time, and then multiplied by the speed of light that is to get the round-trip distance. Ranging by radar sensors in the laser has a high directionality, high monochromaticity and high power and other advantages, these for measuring distance, determine the target location, improve the signal-to-noise ratio of the receiving system, to ensure the accuracy of the measurement is very critical, so the laser rangefinder is increasingly being attached importance. Developed on the basis of laser rangefinder LIDAR not only can measure the distance, but also can measure the target orientation, transport speed and acceleration, etc., has been successfully used for artificial satellite ranging and tracking, such as the use of ruby lasers LIDAR, ranging range of 500 ~ 2000 kilometers, the error is only a few meters. Not long ago, the R & D center of the real still have developed the LDM series of ranging sensors, can be measured in thousands of meters within the range of accuracy can reach the micron level. Often use ruby laser, neodymium glass laser, carbon dioxide laser and gallium arsenide laser as a laser rangefinder light source.
Laser vibration measurement
It is based on the Doppler principle to measure the vibration speed of an object. Doppler principle means: if the wave source or the observer receiving the wave relative to the propagation of the wave medium and movement, then the frequency measured by the observer depends not only on the frequency of vibration emitted by the wave source and also depends on the magnitude and direction of the speed of movement of the wave source or the observer. The difference between the measured frequency and the frequency of the source is called the Doppler shift. In the vibration direction and the direction of the Doppler shift fd = v / λ, where v is the vibration speed, λ is the wavelength. In the laser Doppler vibration velocity measurement instrument, because of the light round-trip reason, fd = 2v/λ. This vibration meter in the measurement by the optical part of the object vibration will be converted into the corresponding Doppler shift, and by the optical detector will be converted into an electrical signal, and then by the circuitry part of the appropriate processing to the Doppler signal processor will be converted into a Doppler shift signal with the vibration velocity corresponding to the electrical signal, and finally Recorded on magnetic tape. This vibrometer using a wavelength of 6328 ? (┱) of the HeNe laser, with the acousto-optic modulator for optical frequency modulation, with a quartz crystal oscillator plus power amplifier circuit as the acousto-optic modulator drive source, photomultiplier tubes for photoelectric detection, the frequency tracker to deal with Doppler signals. Its advantages are easy to use, does not require a fixed reference system, does not affect the vibration of the object itself, wide frequency range of measurement, high accuracy, and large dynamic range. The disadvantage is that the measurement process is greatly affected by other stray light.
Laser velocimetry
It is also based on the Doppler principle of a laser velocimetry method, with more laser Doppler flow meter (see laser flow meter), which can measure the speed of the wind tunnel air velocity, the rocket fuel flow rate, the aircraft jet stream flow velocity, the atmospheric wind speed and the size of the particles in the chemical reaction and the speed of convergence and so on.