Introduction to the distance measuring principle of photoelectric range finder
According to the method of measuring time t, the photoelectric rangefinder is divided into the pulse ranging method of direct measurement of time and the phase ranging method of indirect measurement of time. A high-precision range finder generally adopts a phase type.
The distance measuring principle of the phase photoelectric range finder is: after the light emitted by the light source passes through the modulator, it becomes a modulated light whose light intensity changes with the high frequency signal. The distance is calculated by measuring the phase difference φ of the modulated light traveling back and forth over the distance to be measured.
The phase method is equivalent to using a "light ruler" instead of a steel ruler to measure the distance, and λ/2 is the length of the light ruler.
In the phase range finder, the phase meter can only measure the mantissa ΔN of the phase difference, but cannot measure the number N of the entire period, so it cannot measure the distance greater than the optical ruler. In order to expand the measurement range, a longer ruler should be selected. In order to solve the contradiction between expanding the measurement range and ensuring accuracy, two modulation frequencies are generally used on the short-range range finder, that is, two kinds of light rulers. For example: long optical ruler (called thick ruler) f1=150kHz, λ1/2=1 000m, used to expand the measuring range, measuring hundreds of meters, ten meters and meters; short optical ruler (called fine ruler) f2=15MHz, λ2/2=10m, used to ensure accuracy, measure meters, decimeters, centimeters and millimeters.
Laser rangefinders are widely used in terrain surveying, battlefield surveying, tanks, airplanes, ships and artillery for distance measurement of targets, and for measuring the height of clouds, airplanes, missiles and artificial satellites. It is an important technical equipment to improve the accuracy of high tanks, aircraft, ships and artillery. Due to the continuous reduction in the price of laser range finders, laser range finders have gradually begun to be used in industry, which can be widely used in industrial measurement and control, mines, ports and other fields.
