An introduction to the types of rangefinder and how they work
Common rangefinders can be divided into short range, medium range, and elevation rangefinders in terms of range;
From the modulation objects used by rangefinders, they can be divided into photoelectric rangefinders and acoustic rangefinders.
Photoelectric rangefinder
Optoelectronic rangefinders are divided into two types based on ranging methods: phase method rangefinders and pulse rangefinders.
Pulse rangefinder is a device that uses a beam of light emitted from a target object to measure the time it takes for the target object to reflect the light back, thereby calculating the distance between the instrument and the target object. Due to the good directionality and single wavelength of the laser, it is generally used as a modulation object in optoelectronic rangefinders. Therefore, pulse rangefinders are commonly known as laser rangefinders.
Laser rangefinders using pulse method can achieve a wider range and can be used for indoor and outdoor measurements. The typical range is 3.5 to 2000 meters, while high range laser rangefinders can reach up to 5000 meters. Laser rangefinders for military purposes can reach even longer ranges. Due to the ability to measure distant targets, laser rangefinders generally have a telescopic system, also known as a laser rangefinder telescope, in order to visually observe the ranging target by the user. Figure 1 is a typical diagram of a three tube laser rangefinder telescope.
The accuracy of laser rangefinders mainly depends on the accuracy of the instrument's calculation of the time between laser emission and reception. According to the technology and application situation 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, land measurement, construction, engineering applications, military and other occasions with high precision requirements.
Phase method rangefinder is a rangefinder that modulates the phase of the laser and obtains distance by measuring the phase difference of the reflected laser. Due to the need to detect the phase of the reflected laser, it is necessary to receive a signal with strong intensity. Considering the safety of the human eye, the pulse laser rangefinder cannot be used as a telescopic system, and the range is small. The typical range for ranging is 0.5mm to 150 meters. Generally, the phase laser rangefinder uses a 635 nanometer (visually red) laser as the debugging object, also known as an infrared rangefinder. However, the definition of laser is not defined by color. If a 635 nanometer laser rangefinder is directly irradiated on the human eye, it will cause irreversible damage. Readers are advised to use and protect it correctly.
Acoustic rangefinder
Acoustic distance measurement is an instrument that uses the reflection characteristics of sound waves for measurement. Generally, ultrasonic waves are used as modulation objects, that is, ultrasonic distance meters. The ultrasonic transmitter emits ultrasonic waves in a certain direction and starts timing at the same time. The ultrasonic waves propagate in the air and immediately return when encountering obstacles. The ultrasonic receiver immediately interrupts timing upon receiving reflected waves. By continuously detecting the echo reflected by obstacles after wave emission, the time difference T between transmitting ultrasonic waves and receiving echoes is measured, and then the distance L is calculated.
Due to the significant influence of temperature, humidity, air pressure, and other factors on the propagation speed of ultrasonic waves in the air, measurement errors are large. Additionally, due to the longer wavelength of ultrasonic waves, the propagation distance is shorter, resulting in lower measurement accuracy for general ultrasonic rangefinders. However, due to the fan-shaped propagation of ultrasound, its detection range is larger than that of photoelectric rangefinders, and it is widely used in practical engineering such as safety protection, cable height measurement, and obstacle detection.
