Commonly used rangefinders can be divided into short-range, medium-range and elevation rangefinders.
From the perspective of the modulation object used by the range finder, it can be divided into a photoelectric range finder and an acoustic range finder.
1. Photoelectric range finder
According to the ranging method, the photoelectric range finder is divided into a phase range finder and a pulse range finder.
Pulse rangefinders use a beam of light emitted at a target object to measure the time it takes for the target object to reflect light, thereby calculating the distance between the instrument and the target object.
Due to the good directionality and single wavelength of the laser, the photoelectric range finder generally uses the laser as the tuning object, so the pulse range finder is also called the laser range finder.
The laser rangefinder using the pulse method can reach a wide range 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 the laser rangefinder can reach 5000 meters, and the laser ranging distance can reach even longer. Because laser rangefinders have the ability to measure targets at long distances, laser rangefinders usually have a telescope system, also known as a laser rangefinder telescope.
The accuracy of the laser range finder mainly depends on the calculation accuracy of the instrument to calculate the time between the laser sending and receiving. According to the 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 occasions application.
The phase method range finder is a range finder that modulates the phase of the laser light and obtains the distance by measuring the phase difference of the reflected laser light. Since the phase of the reflected laser light needs to be detected, the received signal needs to have a strong intensity. Considering the safety of human eyes, telescope systems such as pulsed laser rangefinders cannot be used, and the distance is small. Typical ranging ranges are 0.5mm to 150m. Generally, the phase method laser range finder uses 635nm (visually red) as the debugging object, and the laser is also commonly known as the infrared range finder, but in fact the definition of the laser is not defined by the color. If the 635nm laser rangefinder is directly irradiated to the human eye, it will cause irreversible damage. Please use and protect it properly.
Acoustic range finder
It is an instrument that uses the reflection characteristics of sound waves for measurement. Usually, ultrasonic waves are used as the modulation object, that is, ultrasonic range finders. Ultrasonic waves emit ultrasonic waves in a certain direction and start timing at the same time. When ultrasonic waves travel through the air, when they encounter obstacles on the way, they return immediately. When the ultrasonic wave receives the reflected wave, it will be interrupted immediately and stop timing. By continuously detecting the echo reflected by the obstacle after the generated wave is emitted, the time difference between the emitted ultrasonic wave and the received echo is measured, and then the distance L is calculated.
Because the propagation speed of ultrasonic waves in the air is greatly affected by temperature, humidity and air pressure, the measurement error is relatively large, and the ultrasonic wave length is longer and the propagation distance is shorter. Therefore, the measurement distance of ultrasonic waves is generally shorter and the measurement accuracy is lower.