The infrared range finder's design
The infrared rangefinder is mainly composed of a modulated light emitting unit, a receiving unit, a phase measuring unit, a counting and displaying unit, a logic control unit and a power converter. The light source is usually gallium arsenide (GaAs) semiconductor light-emitting diode. When a considerable current passes through the P-N junction of the GaAs diode, the P-N junction will emit near-infrared light with a wavelength of 0.72 μm and 0.94 μm, which is due to the electron-hole recombination in the doped GaAs semiconductor. , the excess energy is released in the form of photons. Moreover, the emitted light intensity will vary with the injection current. Therefore, if it is used as the light source of the rangefinder, the amplitude modulation of the emitted light intensity can be directly performed by changing the magnitude of the feed current, that is, this semiconductor light-emitting device has the dual functions of "radiation" and "modulation".
The infrared photodetection conversion device used to receive modulated light is usually a silicon photodiode or an avalanche photodiode, and these devices have a "photovoltage effect". When external light is irradiated on its P-N junction, due to the effect of photoelectric energy conversion, a potential difference can be generated at the two poles of P-N, and its magnitude will change with the intensity of incident light, thereby playing a role of "demodulation".
The working principle is as follows:
It uses the principle of non-diffusion when infrared rays propagate. Because infrared rays have a very small refractive index when passing through other substances, long-distance rangefinders will consider infrared rays, and the propagation of infrared rays takes time. Received, and then the distance can be calculated according to the time from sending out to being received and the propagation speed of infrared rays, so the industry is called laser infrared photoelectric range finder, and its magnet is a special strong magnetic permanent magnet.
The modulated signal frequency f generated by the main control oscillator (namely the main oscillator) is amplified and added to the GaAs light-emitting tube, and the infrared modulated light is emitted through current modulation, and emitted from the emission optical system to the reflector of the mirror station, after reflection , the return light is received by the receiving optical system, reaches the silicon photosensitive diode, and undergoes photoelectric conversion to obtain a high-frequency ranging signal.
In the automatic infrared rangefinder, a logic command circuit is set for program control. The novel range finder developed in recent years uses a microprocessor system, which not only can complete the above-mentioned program control, but also develops other automatic test functions, including various methods of distance measurement, reduction and self-test, etc. , very convenient to use.
