What are the rangefinders?

What are the rangefinders?
Common rangefinders can be divided into short-range, medium-range and elevation rangefinders in terms of range;
From the modulation object used by the rangefinder, it can be divided into: photoelectric rangefinder and acoustic rangefinder.
Photoelectric range meter
According to the distance measurement method, the photoelectric distance meter is divided into two types: phase method distance meter and pulse distance meter [4].
The pulse rangefinder uses a beam of light to be emitted to the target object to measure the time that the target object reflects the light back to calculate the distance between the instrument and the target object. Because the laser has good directivity and a single wavelength, it is a photoelectric measurement. Rangers generally use lasers as the modulation object, so pulsed rangefinders are also commonly known as laser rangefinders.
The laser rangefinder using pulse method can reach a wide ranging range, which can be used for indoor and outdoor measurement. Its typical range is 3.5 meters to 2000 meters, and the high range laser rangefinder can reach 5000 Meters, military laser rangefinders can reach farther ranges. Because of the ability to measure long-distance measurement targets, in order to visually observe the range-finding target by the user, laser rangefinders generally have a telephoto system, which is also called a laser rangefinder telescope.
The accuracy of laser rangefinders mainly depends on the calculation accuracy of the time between laser emission and reception by the instrument. According to the technology and applications used, laser rangefinders can be divided into conventional laser rangefinders with an accuracy of about 1 meter ( Mainly used for outdoor sports, hunting, etc.) and high-precision laser rangefinders used in surveying and mapping, land surveying, construction, engineering applications, military and other occasions that require high accuracy.
The phase method rangefinder is a rangefinder that modulates the phase of the laser, and obtains the distance by measuring the phase difference of the reflected laser light. Due to the need to detect the reflected laser phase, the received signal needs to have a strong intensity. Considering the safety of the human eye, the telephoto system like a pulsed laser rangefinder cannot be used, and the range is small The typical range of distance measurement is 0.5mm to 150 meters. The general phase method laser rangefinder uses a 635-nanometer (visual red) laser as the debugging object. It is also commonly known as an infrared rangefinder, but in fact, the definition of laser is not based on The color is defined, and if the 635-nanometer laser rangefinder is directly irradiated to the human eye, it will cause irreversible damage. Please use and protect it correctly.

Acoustic Distance Meter
Acoustic distance measurement is an instrument that uses the reflection characteristics of sound waves to measure. Generally, ultrasonic waves are used as the modulation object, that is, ultrasonic rangefinders. The ultrasonic transmitter emits ultrasonic waves in a certain direction and starts timing at the same time as the transmission. The ultrasonic waves propagate in the air and return immediately when they encounter obstacles on the way. The ultrasonic receiver immediately interrupts and stops timing when the reflected waves are received. By continuously detecting the echoes reflected by obstacles encountered after the generated wave is emitted, the time difference T between the transmitted ultrasonic wave and the received echo is measured, and then the distance L is calculated.
Because the speed of ultrasonic propagation in the air is greatly affected by temperature, humidity, air pressure, etc., the measurement error is large, and the longer the ultrasonic wave length leads to a shorter propagation distance, so the general ultrasonic rangefinder has a shorter measurement distance , The measurement accuracy is relatively low. However, using the characteristics of fan propagation of ultrasonic waves, its detection range is larger than that of photoelectric rangefinders. It is widely used in safety protection, cable height measurement, obstacle detection and other fields in practical engineering.