Principle of phase photoelectric rangefinder
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), becoming an amplitude-modulated wave. This amplitude modulation wave through the external optical path into the receiver, convergence in the photoelectric device, the optical signal is immediately converted into an electrical signal. This electrical signal is the amplitude modulated wave round-trip to the measurement line after demodulation of high quite ranging signal, its phase has been delayed.
This high-frequency ranging signal and the high-frequency signal from the local oscillator (referred to as the local oscillator) through the ranging signal mixer for photoelectric mixing, frequency selection and amplification to obtain a low-frequency ranging signal, expressed in. The original phase delay of the high-frequency ranging signal is still retained. In order to carry out than the phase, the main oscillation high-frequency ranging signal is part of the reference signal called with the high-frequency signal and the oscillation at the same time into the reference signal mixer, after frequency selection and amplification, get can be used as a reference than the phase of the reference signal of the low-frequency, said that, because there is no round-trip travel to the measurement line, so there is no elephant in the generation of that phase delay. Therefore, and at the same time feeding the phasor using digital phase measurement technology for phase comparison, in the display will show the results of ranging signal to and from the line of measurement of the phase delay.
When using a scale frequency, the display will only be less than a week of the phase difference in the corresponding distance tail number, more than a week of the number of full weeks of the corresponding distance measurement of the number of full feet can not be known, for this reason, phase rangefinder main oscillator and vibration of the two components also contains a set of coarse scale oscillation frequency, i.e., the frequency of the main oscillator and the oscillation frequency of the oscillator. As mentioned earlier, if the same measurements with the coarse measuring tape frequency, the fine measuring tape and a group of coarse measuring tape results combined, you can get the entire distance to be measured values.
