Practical tips

Something about rangefinder

  • Thursday, 10 October 2019
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Range finder is a tool for measuring length or distance, and it can measure angle, area and other parameters with angle measuring equipment or module. Range finder has many forms, usually a long cylinder, which consists of objective lens, eyepiece, display device (built-in), battery and so on.

Laser rangefinders can also emit multiple laser pulses to determine whether an object is far from or near the light source by Doppler effect.


Classification

The common rangefinders of rangefinders can be divided into short range, medium range and elevation rangefinders.

From the modulation object adopted by the range finder, it can be divided into photoelectric range finder and acoustic range finder.


Photoelectric rangefinder

According to the method of ranging, the photoelectric range finder can be divided into two types: phase range finder and pulse range finder.

Pulse range finder uses a beam of light to emit to the target object to measure the time when the target reflects the light back, thus calculating the distance between the instrument and the target. Because the laser has good directivity and a single wavelength, it is generally used as a modulation object in the photoelectric range finder, so the pulse range finder is also commonly known as the laser range finder.


Laser Rangefinder Based on pulse method can reach a wide range, which can be used for indoor and outdoor measurements. Its typical range range is 3.5 m to 2000 m. Laser rangefinder with high range can reach 5000 m. Laser rangefinder for military purposes can reach a longer range. Because of its ability to measure long-range targets, laser rangefinders generally have a telescope system, also known as laser rangefinder telescopes, in order to make the rangefinder objects visually observed by users.

The accuracy of laser rangefinder mainly depends on the accuracy of calculating the time between laser sending and receiving. According to the technology and application occasions, laser rangefinder can be divided into conventional laser rangefinder (mainly used for outdoor sports, hunting, etc.) with accuracy of about 1 meter and high precision occasions such as surveying and mapping, land survey, building, engineering application, military and so on. High precision laser range finder.

Phase method rangefinder is a range finder which adjusts the phase of laser and obtains the distance by measuring the phase difference of reflected laser. Because of the need to phase the reflected laser phase, the received signal needs strong intensity. Considering the safety of human eyes, we can not use the same telescope system as the pulse laser rangefinder, and the range is small. The typical range of ranging is 0.5mm to 150 meters. The general phase method laser rangefinder uses 635 nanometers (vision is red) laser as its measurement range. The debugging object is also known as infrared range finder, but in fact, the definition of laser is not defined by color. If the 635 nanometer laser range finder is directly irradiated on the human eye, it will cause irreversible damage. Readers are requested to use and protect it correctly.


Acoustic rangefinder


Acoustic rangefinder is an instrument which uses the reflection characteristics of acoustic wave to measure. Ultrasound is generally used as the modulation object, that is, the ultrasonic ranging instrument. Ultrasound transmitter transmits ultrasound in a certain direction. At the same time, it starts timing. Ultrasound spreads in the air. When it encounters obstacles on the way, it returns immediately. When the ultrasonic receiver receives the reflected wave, it immediately interrupts the timing. By continuously detecting the echoes reflected by obstacles after the generated waves are emitted, the time difference T between transmitting and receiving the echoes is measured, and then the distance L is calculated.

Because the speed of ultrasonic propagation in the air is greatly affected by temperature, humidity and air pressure, the measurement error is large, and because of the long wavelength of ultrasound, the propagation distance is short, so the measurement distance of the general ultrasonic rangefinder is relatively short, and the measurement accuracy is relatively low. However, the detection range of ultrasonic wave is larger than that of optoelectronic range finder, which is widely used in safety protection, cable height measurement, obstacle detection and other fields in practical engineering.

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