Principle and Process of Laser Range Finder Measuring
Measuring Principle and Method of Laser Range Finder
1. What is the principle of using infrared ranging or laser ranging?
The principle of ranging can basically be attributed to measuring the time required for light to go back and forth to the target, and then calculate the distance D through the speed of light c=299792458m/s and the atmospheric refractive index n. Because it is difficult to measure time directly, it is usually to measure the phase of continuous wave, which is called phase measuring range finder. Of course, there are also pulsed rangefinders.
It should be noted that phase measurement does not measure the phase of infrared or laser, but the phase of the signal modulated on infrared or laser. The construction industry has a handheld laser distance meter for house surveying that works on the same principle.
2. Must the plane of the measured object be perpendicular to the light?
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Usually precision distance measurement requires the cooperation of a total reflection prism, while the rangefinder used for house measurement directly measures with smooth wall reflection, mainly because the distance is relatively short and the signal strength of the light reflected back is large enough. It can be known from this that it must be vertical, otherwise the return signal is too weak and the distance cannot be obtained.
3. Is it possible if the plane of the measured object is diffuse reflection?
It is usually possible. In actual engineering, a thin plastic plate is used as a reflective surface to solve the problem of serious diffuse reflection.
4. Ultrasonic ranging accuracy is relatively low.
Use of ppm in Measurement
1mm+1ppm is the abbreviation of 1mm+1ppm×D (kilometer), which reflects the nominal ranging accuracy of the total station or rangefinder. in:
1mm represents the fixed error of the instrument, which is mainly caused by the measurement error, centering error, and phase measurement error of the instrument plus constant. The fixed error has nothing to do with the measured distance. That is, no matter how far the measured actual distance is, the total station will have a fixed error not greater than this value.
1ppm×Dkm represents the proportional error, where 1 is the proportional error coefficient, which is mainly caused by the instrument frequency error and the atmospheric refractive index error. ppm means parts per million (a few), and D is the distance value actually measured by the total station or rangefinder, in kilometers. As the actual measurement distance changes, the proportional error part of the instrument also changes proportionally. For example, when the distance is 1 km, the scale error is 1mm.
For a total station or rangefinder with a ranging accuracy of 1mm+1ppm, when the measured distance is 1km, the ranging accuracy of the instrument is 1mm+1ppm×1(km)=2mm, that is to say, the total The distance of the station instrument is 1 km, and the maximum ranging error is not more than 2mm.
3 seconds is the time for ranging
