Principle Analysis of Distance Meter and Temperature and Humidity Monitoring
Laser range finders generally use two methods to measure distance: pulse method and phase method. The process of pulse method ranging is as follows: the laser emitted by the range finder is reflected by the measured object and then received by the range finder, and the range finder records the time of the laser back and forth at the same time. Half of the product of the speed of light and the round-trip time is the distance between the rangefinder and the measured object. The accuracy of distance measurement by pulse method is generally around +/- 1 meter. In addition, the measurement blind zone of this type of rangefinder is generally about 15 meters.
Laser distance measurement is a method of distance measurement in light wave distance measurement. If light travels in the air at speed c and takes time t to go back and forth between two points A and B, then the distance D between points A and B can be used as follows express.
D=ct/2
In the formula:
D——the distance between two points A and B of the station;
c——the speed of light propagating in the atmosphere;
t——The time required for light to go back and forth between A and B once.
It can be seen from the above formula that to measure the distance of A and B is actually to measure the time t of light propagation. According to the different methods of measuring time, laser range finders can usually be divided into two types of measurement: pulse type and phase type.
Phase Laser Range Finder
The phase laser rangefinder uses the frequency of the radio band to modulate the amplitude of the laser beam and measure the phase delay generated by the modulated light going back and forth to the survey line once, and then convert 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 on the distance to be measured D 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, the most widely used ones are delay phase measurement and digital phase measurement. At present, short-range laser rangefinders use the principle of digital phase measurement to obtain φ.
Generally speaking, the phase-type laser rangefinder uses a laser beam with a modulated signal to continuously emit. In order to obtain a high-precision distance measurement, a cooperative target needs to be configured. However, the current handheld laser rangefinder is a pulsed laser rangefinder. Another new type of rangefinder in the rangefinder, 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 Displays the distance directly. It is the latest standard length measurement instrument in short-range precision precision engineering measurement and building area measurement.
