Principles and applications of phased laser rangefinders
Phase-type laser rangefinder is the use of laser beam amplitude modulation and determination of modulated light to and from the line of measurement of the phase delay generated once, and then according to the wavelength of the modulated light, the conversion of the phase delay represented by the distance. That is, the indirect method of determining the time required by the light through the round-trip line measurement.
Phase-type laser rangefinders are generally used in precision ranging. Because of its high accuracy, generally millimetre-scale, in order to effectively reflect the signal, and make the determination of the target is limited to a specific point commensurate with the accuracy of the instrument, such rangefinders are configured with a mirror known as the co-operative target.
If the angular frequency of the modulated light is ω and the phase delay produced by one round trip over the distance to be measured D 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=1/2 ct=1/2 c-φ/ω=c/(4πf) (Nπ+Δφ)
=c/4f (N+ΔN)=U(N+)
Eq:
φ - the total phase delay produced by the signal travelling to and from the survey line once.
ω - angular frequency of the modulating signal, ω = 2πf.
U - unit length, the value is equal to 1/4 modulation wavelength
N - the number of modulating half-wavelengths contained in the measurement line.
Δφ - the part of the signal travelling to and from the line that produces a phase delay of less than π at a time.
ΔN - the fractional part of the modulating wave contained in the line that is less than half a wavelength.
ΔN=φ/ω
In the given modulation and standard atmospheric conditions, the frequency c / (4πf) is a constant, at this time the measurement of distance has become the measurement of the number of half-wavelengths contained in the measurement line and less than half a wavelength of the fractional part of the measurement of the measurement of the N or φ, due to the development of modern precision machining technology and radio phase measurement technology, the measurement of the φ has reached a high degree of accuracy.
In order to measure the phase angle φ of less than π, can be measured by different methods, usually the most widely used is the delayed phase measurement and digital phase measurement, short-range laser rangefinder are used to obtain the φ of the principle of digital phase measurement.
From the above mentioned general circumstances phase type laser rangefinder using continuous emission of laser beams with modulated signals, in order to obtain high precision ranging also need to configure the co-operation target, and the introduction of the hand-held laser rangefinder is a pulsed laser rangefinder and a new type of rangefinder, it is not only small in size and light in weight, but also the use of digital phase measurement pulse spreading interpolation technology, no need to co-operate with the target to achieve millimetre-level accuracy, the measuring range has more than 100m, and can quickly and accurately display the distance directly. Is a short-range precision precision engineering measurement, building area measurement in the latest type of length measurement standard apparatus. Now the most widely used is the DISTO series handheld laser rangefinder produced by leica.
