Laser Rangefinder Laser Ranging Principle Laser ranging is a kind of distance measurement method in optical wave distance measurement. If light travels at speed c in the air, the time required for a round trip between A and B is t, then A, B The distance D between two points can be expressed as follows.
D=ct/2
In the formula:
D--distance between the two points A and B;
c - the speed at which light travels in the atmosphere;
t - The time required for the light to travel back and forth between A and B.
From the above equation, we can see that measuring the distance between A and B is actually measuring the time t of light propagation. According to different methods of measuring time, laser range finder can usually be divided into two types of pulse and phase measurement.
') Phase Laser Rangefinder')
The phase laser range finder uses the frequency of the radio wave band to modulate the amplitude of the laser beam and measure the phase delay generated by the reciprocating line of the modulated light. The distance represented by the phase delay is then converted according to the wavelength of the modulated light. That is, the indirect method is used to determine the time required for the light to travel back and forth, as shown in the figure.
Phase laser range finder is generally used in precision ranging. Because of its high precision, generally in the millimeter level, in order to effectively reflect the signal and limit the measurement target to a specific point that is commensurate with the accuracy of the instrument, this kind of range finder is equipped with a reflection called a cooperation target. mirror.
If the modulated light angular frequency is ω, and the phase delay generated by the round trip once at the distance D to be measured is φ, 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=1/2ct=1/2c·φ/ω=c/(4πf)(NπΔφ)
=c/4f(NΔN)=U(N)
In the formula:
φ--The total phase delay generated by the signal from the round trip line.
The angular frequency of the ω--modulated signal, ω=2πf.
U - unit length, the value is equal to 1/4 modulation wavelength N - the number of modulation half-wavelength included in the line.
The Δφ--signal round trip produces a phase delay less than π.
The ΔN--measured line contains less than half the wavelength of the modulated wave.
ΔN=φ/ω
Under a given modulation and standard atmospheric conditions, the frequency c/(4πf) is a constant. At this time, the measurement of the distance becomes a measurement of the number of half-wavelengths included in the measurement line and a measurement of the fractional part less than half the wavelength. Or φ, due to the development of modern precision machining technology and radio phase measurement technology, the measurement of φ has achieved high accuracy.
In order to measure the phase angle φ which is less than π, it can be measured by different methods. Usually the most widely used is the phase delay measurement and digital phase measurement. At present, the short-range laser distance meter uses the principle of digital phase measurement to obtain φ.
From the above, the phase laser range finder uses a laser beam with a continuous emission band to modulate the signal. In order to obtain a high accuracy of the distance measurement, a cooperation target needs to be configured. The current handheld laser range finder is a pulsed laser measurement. Another new distance meter in the distance meter is not only small in size, light in weight, but also adopts digital phase-sweep pulses to broaden the subdivision technology, can achieve millimeter-level accuracy without cooperation goal, and the measuring range has exceeded 100m, and can be quickly and accurately. Direct display distance. It is the latest type of length measurement standard instrument for short-range precision precision engineering measurement and house construction area measurement. The most widely used is the DISTO series of hand-held laser rangefinders produced by Leica.
Handheld laser range finder precautions DISTO and other hand-held laser range finders use lasers for distance measurement, and the pulsed laser beam is a monochromatic light source with very concentrated energy. Look straight ahead and do not use the telescope to observe the smooth reflective surface so as not to injure the human eye. Be sure to measure according to the safety instructions in the instrument manual. When measuring in the field, do not direct the emission port of the instrument to the sun so as not to burn the photosensor of the instrument.
D=ct/2
In the formula:
D--distance between the two points A and B;
c - the speed at which light travels in the atmosphere;
t - The time required for the light to travel back and forth between A and B.
From the above equation, we can see that measuring the distance between A and B is actually measuring the time t of light propagation. According to different methods of measuring time, laser range finder can usually be divided into two types of pulse and phase measurement.
') Phase Laser Rangefinder')
The phase laser range finder uses the frequency of the radio wave band to modulate the amplitude of the laser beam and measure the phase delay generated by the reciprocating line of the modulated light. The distance represented by the phase delay is then converted according to the wavelength of the modulated light. That is, the indirect method is used to determine the time required for the light to travel back and forth, as shown in the figure.
Phase laser range finder is generally used in precision ranging. Because of its high precision, generally in the millimeter level, in order to effectively reflect the signal and limit the measurement target to a specific point that is commensurate with the accuracy of the instrument, this kind of range finder is equipped with a reflection called a cooperation target. mirror.
If the modulated light angular frequency is ω, and the phase delay generated by the round trip once at the distance D to be measured is φ, 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=1/2ct=1/2c·φ/ω=c/(4πf)(NπΔφ)
=c/4f(NΔN)=U(N)
In the formula:
φ--The total phase delay generated by the signal from the round trip line.
The angular frequency of the ω--modulated signal, ω=2πf.
U - unit length, the value is equal to 1/4 modulation wavelength N - the number of modulation half-wavelength included in the line.
The Δφ--signal round trip produces a phase delay less than π.
The ΔN--measured line contains less than half the wavelength of the modulated wave.
ΔN=φ/ω
Under a given modulation and standard atmospheric conditions, the frequency c/(4πf) is a constant. At this time, the measurement of the distance becomes a measurement of the number of half-wavelengths included in the measurement line and a measurement of the fractional part less than half the wavelength. Or φ, due to the development of modern precision machining technology and radio phase measurement technology, the measurement of φ has achieved high accuracy.
In order to measure the phase angle φ which is less than π, it can be measured by different methods. Usually the most widely used is the phase delay measurement and digital phase measurement. At present, the short-range laser distance meter uses the principle of digital phase measurement to obtain φ.
From the above, the phase laser range finder uses a laser beam with a continuous emission band to modulate the signal. In order to obtain a high accuracy of the distance measurement, a cooperation target needs to be configured. The current handheld laser range finder is a pulsed laser measurement. Another new distance meter in the distance meter is not only small in size, light in weight, but also adopts digital phase-sweep pulses to broaden the subdivision technology, can achieve millimeter-level accuracy without cooperation goal, and the measuring range has exceeded 100m, and can be quickly and accurately. Direct display distance. It is the latest type of length measurement standard instrument for short-range precision precision engineering measurement and house construction area measurement. The most widely used is the DISTO series of hand-held laser rangefinders produced by Leica.
Handheld laser range finder precautions DISTO and other hand-held laser range finders use lasers for distance measurement, and the pulsed laser beam is a monochromatic light source with very concentrated energy. Look straight ahead and do not use the telescope to observe the smooth reflective surface so as not to injure the human eye. Be sure to measure according to the safety instructions in the instrument manual. When measuring in the field, do not direct the emission port of the instrument to the sun so as not to burn the photosensor of the instrument.
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