Introduction to the distance measuring principle of photoelectric rangefinders
Optical rangefinders are classified according to the way of determining the time t into the pulse ranging method which determines the time directly and the phase ranging method which determines the time indirectly. High-precision rangefinders generally use the phase type.
Phase-type photoelectric rangefinder distance measurement principle is: the light emitted by the light source through the modulator, the light intensity with the high-frequency signal changes in the modulated light. By measuring the modulated light in the distance to be measured back and forth propagation of the phase difference φ to solve the distance.
Phase method distance measurement is equivalent to the "light ruler" instead of a steel ruler to measure the distance, and λ / 2 for the length of the light ruler.
Phase type rangefinder, the phase meter can only measure the phase difference of the tail number ΔN, can not measure the whole cycle number N, so the distance is greater than the optical ruler can not be determined. In order to expand the measuring range, a longer optical ruler should be selected. In order to solve the contradiction between expanding the range and ensuring accuracy, short-range rangefinders generally use two modulation frequencies, that is, two kinds of light ruler. For example: long light ruler (known as coarse ruler) f1 = 150kHz, λ1/2 = 1,000m, used to expand the range, the determination of 100 metres, ten metres and metres; short light ruler (known as fine ruler) f2 = 15MHz, λ2/2 = 10m, used to ensure accuracy, the determination of metres, decimetres, centimetres and millimetres.
