Brief introduction to the function and characteristics of phase range finder
Under the given modulation and standard atmospheric conditions, the frequency c/(4πf) is a constant, at this time, the distance measurement becomes the measurement of the number of half-wavelength contained in the survey line and the measurement of the fractional part less than half-wavelength, that is, the measurement of N or φ. Due to the development of modern precision machining technology and radio phase measurement technology, the measurement of φ has reached a high accuracy.
In order to measure the phase angle φ less than π, different methods can be used to measure it. Usually, delayed phase measurement and digital phase measurement are the most widely used. At present, short-range laser rangefinders all use digital phase measurement principle to obtain φ.
As mentioned above, in general, phase laser ranging uses continuous emission of laser beams with modulated signals, and in order to achieve high ranging accuracy, it is necessary to configure cooperative targets. At present, the hand-held laser rangefinder is another new type of pulse laser rangefinder, which is not only small in size and light in weight, but also adopts digital phase-measuring pulse broadening subdivision technology, which can achieve millimeter-level accuracy without cooperative targets, and the ranging distance has exceeded 100m, and can directly display the distance quickly and accurately.
Classification of electromagnetic wave rangefinder
1. According to the ranging principle, it can be divided into pulse rangefinder and phase rangefinder. The former is an optical pulse emitted by a pulse generator, and the distance can be obtained by using the number of pulses in the time interval of the pulse traveling back and forth on the survey line, such as a laser moon detector and a laser satellite rangefinder. The latter is a continuous sine modulated wave emitted by a range finder, and the phase shift generated by the modulated wave propagating back and forth on the survey line is measured to find the distance, such as laser range finder and infrared range finder. The instrument using phase method for ranging has short range and high accuracy, and is often used in geodetic survey.
2. According to the carrier, the electromagnetic wave in the microwave section or the light wave as the carrier is called microwave rangefinder or photoelectric rangefinder respectively. Photoelectric rangefinders which use laser or infrared light as carrier are called laser rangefinders or infrared rangefinders respectively. The infrared range finder uses the fluorescence developed by gallium arsenide light-emitting diode as the carrier source, and the intensity of the emitted infrared can change with the intensity of the injected electric signal. Therefore, it has the dual functions of carrier source and modulator. Gallium arsenide light-emitting diodes are small in size, high in brightness, low in power consumption, long in life and continuous in light emission, so infrared rangefinders are widely used. Electromagnetic wave range finder has the advantages of high precision, rapid operation and little influence by climate and terrain.
