The principle and application of phase laser rangefinder
The phase laser rangefinder uses a laser beam to modulate the amplitude and measure the phase delay generated by the modulated light traveling back and forth to the measuring line, and then converts the distance represented by this phase delay based on the wavelength of the modulated light. The indirect method is used to determine the time required for light to travel back and forth through the measuring line.
Phase laser rangefinders are generally used in precision ranging. Due to its high accuracy, usually at the millimeter level, in order to effectively reflect the signal and limit the measured target to a specific point that is proportional to the instrument's accuracy, this type of rangefinder is equipped with a reflector called a cooperative target.
If the modulation angle frequency is ω， The phase delay generated by a 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 the distance D of equation (3-6) can be expressed as
D=1/2 ct=1/2 c· φ/ω= C/(4 π f) (N π+ Δφ)
=C/4f (N+ Δ N) =U (N+)
In the equation:
φ—— The total phase delay generated by a signal traveling back and forth to the line.
ω—— The angular frequency of the modulated signal, ω= 2 π f.
U - Unit length, numerical value equal to 1/4 modulation wavelength
N - The number of modulated half wavelengths included in the measurement line.
Δφ—— The signal generates a phase delay of less than π in one round trip to the measuring line.
Δ N - The fractional part of the modulation wave contained in the measuring line that is less than half the wavelength.
Δ N= φ/ω
Under given modulation and standard atmospheric conditions, the frequency c/(4 π f) is a constant, and the measurement of distance becomes the measurement of the number of half wavelengths included in the measuring line and the measurement of fractional parts less than half wavelengths, i.e. N or φ， Due to the development of modern precision machining technology and radio phase measurement technology φ The measurement has achieved high accuracy.
In order to measure the phase angle of less than π φ， Different methods can be used for measurement, and the most commonly used methods are delay phase measurement and digital phase measurement. Short range laser rangefinders use the principle of digital phase measurement to obtain φ。
As mentioned above, in general, phase laser rangefinders use a continuous laser beam with modulated signals. In order to achieve high ranging accuracy, cooperative targets need to be configured. The handheld laser rangefinders introduced are another new type of rangefinders among pulse laser rangefinders, which not only have small size and light weight, but also use digital phase measurement pulse broadening and subdivision technology. Without the need for cooperative targets, millimeter level accuracy can be achieved, and the measurement range has exceeded 100m, And it can quickly and accurately display the distance directly. It is the latest type of length measurement standard instrument in short-range precision engineering measurement and building area measurement. The most widely used is the DISTO series handheld laser rangefinder produced by Leica Company.
