A Brief Discussion on the Principle and Usage of Laser Rangefinders
① Principles of Infrared Ranging or Laser Ranging The ranging principle can basically be summarized as measuring the time it takes for light to travel to the target and back, then calculating the distance D using the speed of light \(c=299792458\,\text{m/s}\) and the atmospheric refractive index n. Since direct time measurement is difficult, continuous-wave phase measurement is commonly adopted; instruments using this method are called phase-shift rangefinders. There are also pulse rangefinders, with the DI-3000 from WILD being a typical example.
It should be noted that phase-shift ranging does not measure the phase of infrared light or laser itself, but the phase of the signal modulated onto the infrared or laser beam. Handheld laser rangefinders used for building measurements in the construction industry operate on this same principle.
② The Plane of the Measured Object Must Be Perpendicular to the Light Beam Precision ranging usually requires a retroreflector prism. Rangefinders for housing measurement perform measurements via reflection off smooth walls. This is mainly because the measuring distance is relatively short, and the reflected light signal is strong enough. From this we know that the surface must be perpendicular; otherwise, the returned signal will be too weak to obtain an accurate distance.
③ Diffuse Reflection from the Measured Object Plane Is Acceptable This is generally feasible. In practical engineering, thin plastic sheets are used as reflective surfaces to mitigate severe diffuse reflection.
④ Ultrasonic ranging has relatively low accuracy and is less widely used.
⑤ Laser rangefinders can achieve an error as low as 1 mm, making them suitable for various high-precision measurement applications.
