Two methods for measuring distance: pulse method and phase method principle
A rangefinder is a tool for measuring length or distance, and can be combined with angle measuring equipment or modules to measure parameters such as angle and area. There are many forms of rangefinders, usually a long cylindrical structure consisting of an objective lens, an eyepiece, a display device (which can be built-in), a battery, and other components.
Laser rangefinders can also emit multiple laser pulses to determine whether an object is moving away or close to the light source through the Doppler effect.
Principles of rangefinder
Laser rangefinders generally use two methods to measure distance: pulse method and phase method. The process of pulse ranging is as follows: the laser emitted by the rangefinder is reflected by the measured object and then received by the rangefinder, which simultaneously records the time of the laser traveling back and forth. Half of the product of the speed of light and round-trip time is the distance between the rangefinder and the object being measured. The accuracy of pulse method for measuring distance is generally around+/-1 meters. In addition, the measurement blind spot of this type of rangefinder is generally around 15 meters.
Laser ranging is a distance measurement method in optical wave ranging. If light propagates in the air at a speed of c and A If the time required for a round trip between two points B is t, then A The distance D between two points B can be expressed as follows.
D=ct/2
In the formula:
D - Test site A B distance between two points;
The speed of light propagation in the atmosphere;
T-optical round-trip A The time required for one time.
As can be seen from the above equation, to measure A The distance B actually measures the time t of light propagation. According to different measurement methods, laser rangefinders can usually be divided into two measurement forms: pulse and phase.
Phase type laser rangefinder
A phase laser rangefinder is a device that uses the frequency of the radio band to modulate the amplitude of the laser beam and measure the phase delay generated by the modulated light traveling back and forth to the measuring line. Based on the wavelength of the modulated light, the distance represented by this phase delay is then converted. The indirect method is used to determine the time required for light to travel back and forth through the measuring line, as shown in the figure.
Phase laser rangefinders are generally used in precision ranging. Due to its high accuracy, usually in the millimeter range, in order to effectively reflect signals and limit the measured target to a specific point that is proportional to the instrument's accuracy, this type of rangefinder is equipped with a reflector called a cooperative target.
