The principle of phase photoelectric range finder
The working principle of the phase photoelectric range finder can be explained according to the block diagram shown in the figure.
The light wave (infrared light or laser) emitted by the light source enters the modulator and is modulated by the high-frequency ranging signal from the master oscillator (referred to as the master oscillator) to become an amplitude modulated wave. The amplitude-modulated wave enters the receiver through the external optical path and converges on the photoelectric device, and the optical signal is immediately converted into an electrical signal. This electrical signal is the demodulated high-frequency ranging signal after the AM wave travels back and forth to the survey line, and its phase has been delayed.
The high-frequency ranging signal and the high-frequency signal from the local oscillator (abbreviated as local oscillator) are photoelectrically mixed by the ranging signal mixer, and a low-frequency ranging signal is obtained after frequency-selective amplification, denoted by . The original phase delay of the high-frequency ranging signal is still preserved. In order to perform phase comparison, a part of the high-frequency ranging signal of the main oscillator is called the reference signal and the high-frequency signal of the local oscillator is sent to the reference signal mixer at the same time. After frequency selection and amplification, a low-frequency reference signal that can be used as a reference for phase comparison is obtained. It means that there is no phase delay as in the image because there is no round trip to and from the survey line. Therefore, the phase delay result of the ranging signal from and to the measuring line will be displayed on the display when the digital phase measuring technology is used for phase comparison with the phase device sent at the same time.
When a measuring ruler frequency is used, there is only the mantissa corresponding to the phase difference of less than one week on the display, and the number of whole feet corresponding to the number of full cycles exceeding one week cannot be known. For this reason, the phase rangefinder The two components of the main vibration and the local vibration also include a set of oscillation frequencies of the coarse scale, that is, the main vibration frequency and the local vibration frequency. As mentioned earlier, if the same measurement is made with the frequency of the coarse scale, the results of the fine scale and a set of coarse scales are combined to obtain the value of the entire distance to be measured.
