Principles and applications of phase laser rangefinders
The phase laser rangefinder uses a laser beam to perform amplitude modulation and measures the phase delay caused by the modulated light traveling back and forth to the measurement line once, and then converts the distance represented by this phase delay based on the wavelength of the modulated light. That is, the indirect method is used to measure the time required for light to travel back and forth from the measuring line.
Phase laser rangefinders are generally used in precision distance measurement. Due to its high accuracy, generally millimeter level, in order to effectively reflect the signal and limit the measurement target to a specific point commensurate with the accuracy of the instrument, this rangefinder is equipped with a reflection called a cooperative target. mirror.
If the angular frequency of the modulated light is ω, and the phase delay generated by one round trip on the distance D to be measured is φ, then the corresponding time t can be expressed as:
t=φ/ω
Substituting this relationship into equation (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 produced by the signal traveling back and forth to the measuring line.
ω--The angular frequency of the modulated signal, ω=2πf.
U--Unit length, the value is equal to 1/4 modulation wavelength
N--The number of modulated half-wavelengths contained in the measuring line.
Δφ--The phase delay produced by the signal traveling back and forth to the measuring line is less than π.
ΔN--The fractional part of the modulated wave contained in the measuring line that is less than half the wavelength.
ΔN=φ/ω
Under given modulation and standard atmospheric conditions, the frequency c/(4πf) is a constant. At this time, the measurement of distance becomes the measurement of the number of half-wavelengths contained in the measuring 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 high accuracy.
In order to measure the phase angle φ that is less than π, different methods can be used to measure it. The most commonly used ones are delayed phase measurement and digital phase measurement. Short-range laser rangefinders all use the principle of digital phase measurement to obtain φ.
As mentioned above, in general, phase laser rangefinders use continuous emission of laser beams with modulated signals. In order to obtain high accuracy in ranging, it is necessary to configure a cooperative target. The handheld laser rangefinder launched is a pulse laser rangefinder. Another new rangefinder in the instrument. It is not only small in size and light in weight, but also adopts digital phase measurement pulse broadening and subdivision technology. It can achieve millimeter-level accuracy without a cooperative target. The measuring range has exceeded 100m, and it can quickly and accurately directly Display distance. It is the latest length measurement standard instrument for short-range precision precision engineering measurement and building area measurement. The most widely used one now is the DISTO series of handheld laser rangefinders produced by Leica.
