Application and Theory of Phase Laser Range Finder
The phase laser rangefinder uses the amplitude modulation of the laser beam to measure the phase delay generated by the modulated light going back and forth to the survey line once, and then converts the distance represented by the phase delay according to the wavelength of the modulated light. That is, the indirect method is used to measure the time required for the light to travel through the survey line.
Phase laser rangefinders are generally used in precision distance measurement. Due to its high precision, generally at the millimeter level, in order to effectively reflect the signal and limit the measured target to a specific point commensurate with the accuracy of the instrument, this rangefinder is equipped with a reflector called a cooperative target. mirror.
If the angular frequency of the modulated light is ω, and the phase delay generated by one round trip over the distance D to be measured is φ, then the corresponding time t can be expressed as:
t=φ/ω
Substituting this relationship into (3-6) the distance D can be expressed as
D=1/2 ct=1/2 c·φ/ω=c/(4πf) (Nπ+Δφ)
=c/4f (N+ΔN)=U(N+)
In the formula:
φ——The total phase delay generated by the signal going back and forth to the measuring line once.
ω——The angular frequency of the modulating signal, ω=2πf.
U——unit length, the value is equal to 1/4 modulation wavelength
N——The number of modulated half-wavelengths included in the survey line.
Δφ——The portion of the phase delay less than π generated by the signal going back and forth to the measuring line once.
ΔN——The fractional part of the modulation wave contained in the survey line that is less than half the wavelength.
ΔN=φ/ω
Under the given modulation and standard atmospheric conditions, the frequency c/(4πf) is a constant. At this time, the measurement of the distance becomes the measurement of the number of half-wavelengths contained in the survey line and the measurement of the fractional part less than half-wavelength, that is, N Or φ, due to the development of modern precision machining technology and radio phase measurement technology, the measurement of φ has reached a very high accuracy.
In order to measure the phase angle φ that is less than π, different methods can be used to measure it. Usually, delay phase measurement and digital phase measurement are the most widely used. Short-range laser range finders use the principle of digital phase measurement to obtain φ.
Generally speaking, the phase laser range finder uses a laser beam with a modulated signal to continuously emit. In order to obtain a high-precision range measurement, a cooperative target needs to be configured. The handheld laser range finder is a pulsed laser range finder. Another new type of rangefinder in the instrument, it is not only small in size and light in weight, but also uses digital phase measurement pulse broadening and subdivision technology, which can achieve millimeter-level accuracy without the need for a cooperative target. The measuring range has exceeded 100m, and it can quickly and accurately directly Show distance. It is the latest standard length measurement instrument in short-range precision precision engineering measurement and building area measurement. The most widely used is the DISTO series handheld laser rangefinder produced by Leica Company.
