1) Thickness measurement with single laser displacement sensor

The measured object is placed on the measuring platform, the distance from the sensor to the surface of the platform is measured, and then the distance from the sensor to the surface of the measured object is measured, and the thickness is measured after calculation. It is required that there is no air gap between the measured object and the measuring platform, and the measured object is not lifted. These stringent requirements can only be fulfilled offline.

2) Thickness measurement with dual laser displacement sensors

Install a laser displacement sensor above and below the measured body, and the measured body thickness D=C-(A+B). Among them, C is the distance between the two sensors, A is the distance between the upper sensor and the measured object, and B is the distance between the lower sensor and the measured object. The advantage of this method for online thickness measurement is that the influence of the vibration of the measured body on the measurement results can be eliminated. But at the same time there are requirements for sensor installation and performance. The conditions for ensuring the accuracy of the measurement are that the two sensors emit beams that are coaxial and that the scans of the two sensors must be synchronized. Coaxial is achieved by installation, and synchronization depends on the selection of a laser sensor with a synchronization end.

4. Laser vibration measurement

It measures the vibration velocity of an object based on the Doppler principle. The Doppler principle means that if the wave source or the observer receiving the wave moves relative to the medium in which the wave propagates, the frequency measured by the observer depends not only on the frequency of vibration emitted by the wave source but also on the motion of the wave source or observer. The magnitude and direction of the velocity. The difference between the measured frequency and the frequency of the wave source is called the Doppler shift. When the vibration direction is consistent with the direction, the Dopp frequency shift is fd=v/λ, where v is the vibration velocity and λ is the wavelength. In the laser Doppler vibration velocity measuring instrument, due to the light round trip, fd = 2v/λ. This kind of vibrometer converts the vibration of the object into the corresponding Doppler frequency shift by the optical part during measurement, and converts the frequency shift into an electrical signal by the photodetector, and then sends it to the multi-channel after proper processing by the circuit part. The Doppler signal processor converts the Doppler-shifted signal into an electrical signal corresponding to the vibration velocity, which is finally recorded on a magnetic tape. This vibrometer uses a helium-neon laser with a wavelength of 6328 angstroms (┱), uses an acousto-optic modulator for optical frequency modulation, uses a quartz crystal oscillator and a power amplifier circuit as the driving source of the acousto-optic modulator, and uses a photomultiplier tube. For photoelectric detection, a frequency tracker is used to process the Doppler signal. Its advantages are that it is easy to use, does not require a fixed reference frame, does not affect the vibration of the object itself, and has a wide measurement frequency range, high precision and large dynamic range. The disadvantage is that the measurement process is greatly affected by other stray light.

5. Laser speed measurement

It is also a laser velocimetry method based on the Doppler principle. The laser Doppler rheometer is more commonly used, which can measure the wind tunnel airflow velocity, rocket fuel velocity, aircraft jet airflow velocity, atmospheric wind velocity and chemical reactions. particle size and convergence speed.

In summary, laser sensors are widely used. It can use the characteristics of high directivity, high monochromaticity and high brightness of lasers to achieve non-contact long-distance measurement. It can also be used for flaw detection and monitoring of atmospheric pollutants. Favored by many people, it is a very used technology. In-depth research may reveal more mysteries and benefit all walks of life.