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Common rangefinders can be divided into short-range rangefinders, medium-range rangefinders, and height rangefinders.
From the modulation object used by the rangefinder, they can be divided into optoelectronic rangefinders and acoustic rangefinders.
- Optoelectronic rangefinder According to the ranging method, optoelectronic rangefinders are divided into phase-shift rangefinders and pulse rangefinders.
Pulse rangefinders use the light beam emitted to the target object to measure the time it takes for the light beam to reflect back, and then calculate the distance between the instrument and the target object.
Due to the good directionality and single wavelength of lasers, optoelectronic rangefinders usually use lasers as the modulation object, so pulse rangefinders are also called laser rangefinders.
Laser rangefinders using the pulse method can achieve a wide range of measurement distances, and can be used for indoor and outdoor measurements. The typical laser ranging range is between 3.5 meters and 2000 meters. The ranging height of laser rangefinders can reach 5000 meters, and the ranging distance can even be further. Due to the ability of laser rangefinders to measure distant targets, they are usually equipped with a telescope system, also known as a laser rangefinding telescope.
The accuracy of laser rangefinders mainly depends on the accuracy of the instrument’s calculation of the time between the emission and reception of the laser. According to technology and application, laser rangefinders can be divided into traditional rangefinders and laser rangefinders with an accuracy of about 1 meter (mainly used for outdoor sports, etc.). High-precision laser rangefinders are used in military and other high-precision applications.
Phase-shift rangefinders are rangefinders that obtain distance by measuring the phase difference of the reflected laser light. Since the reflected laser light phase needs to be detected, the received signal needs to have a relatively strong intensity. Considering eye safety, it is not possible to use a telescope system like a pulse laser rangefinder, so the ranging distance is relatively short. The typical ranging range is from 0.5mm to 150m. Generally, phase-shift laser rangefinders use 635nm (visible red) as the modulation object, and are also commonly called infrared rangefinders, but the definition of laser is not limited to color. If directly exposed to the human eye, a 635nm laser rangefinder can cause irreversible damage, so please use it with caution and take protective measures.
- Acoustic rangefinder The instrument that measures using the reflection characteristics of sound waves usually uses ultrasound as the modulation object, that is, the ultrasonic rangefinder. The ultrasonic rangefinder emits ultrasound in a certain direction and starts timing at the same time. When the ultrasound propagates in the air and encounters an obstacle, it will immediately reflect back. When the reflected wave is received, the timing is immediately stopped. By continuously detecting the echo that returns after the emission of the ultrasound, the time difference between the emission of the ultrasound and the reception of the echo is measured, and the distance L is calculated.
Due to the relatively large influence of temperature, humidity and air pressure on the propagation speed of ultrasound in the air, the measurement error is relatively large, and the wavelength of ultrasound is relatively long and the propagation distance is relatively short. Therefore, the measurement distance of ultrasonic ranging is generally shorter, and the measurement accuracy is also relatively low.