What is the photoelectric range finder's method of determining distance?
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 measuring 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.
Photoelectric range finder structure
1. Instrument structure
The host is placed on the upper part of the theodolite through the connector, and the theodolite can be an ordinary optical theodolite or an electronic theodolite. By using the optical axis adjustment screw, the emission-receiver optical axis of the host and the collimation axis of the theodolite can be located in the same vertical plane. In addition, the height from the horizontal axis of the rangefinder to the horizontal axis of the theodolite is consistent with the height from the center of the target plate to the reflective prism, so that the line of sight of the theodolite aimed at the center of the target plate is parallel to the line of sight of the rangefinder aimed at the center of the reflective prism.
The reflective prism used for distance measurement with the main engine can be selected as a single prism (within 1500m) or a triangular prism (within 2500m) according to the distance.
2. The main technical indicators and functions of the instrument
The maximum range of the short-range infrared photoelectric rangefinder is 2500m, and the distance measurement accuracy can reach ± (3mm+2×10-6×D) (where D is the measured distance); the minimum reading is 1 mm; the instrument is equipped with automatic The light intensity adjustment device can also manually adjust the light intensity when measuring in complex environments; the temperature, air pressure and prism constant can be input to automatically correct the result; the vertical angle can be input to automatically calculate the horizontal distance and height difference; the distance can be preset Carry out alignment stakeout; if you input the station coordinates and elevation, it can automatically calculate the coordinates and elevation of the observation point. The distance measurement method includes normal measurement and tracking measurement. The time required for normal measurement is 3s, and the average value of several measurements can also be displayed; the time required for tracking measurement is 0.8s, and the distance measurement is automatically repeated at regular intervals.
