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 the light to travel to and from the target, and then calculate the distance D through the speed of light c = 299792458m/s and the atmospheric refraction coefficient n. Because it is difficult to measure time directly, it is usually to measure the phase of the continuous wave, which is called a phase-measuring rangefinder. Of course, there are also pulsed rangefinders, typically WILD's DI-3000

It should be noted that the phase measurement does not measure the phase of the infrared or laser, but measures the phase of the signal modulated on the infrared or laser. The construction industry has a handheld laser rangefinder for house measurements that works the same way.

2. Must the plane of the object to be measured be perpendicular to the light?

Usually, precise ranging requires the cooperation of a total reflection prism, and the rangefinder used for house measurement is directly measured by reflection from a smooth wall, mainly because the distance is relatively close, and the signal strength of the reflected light is large enough. It can be known from this that it must be vertical, otherwise the return signal is too weak and the precise distance cannot be obtained.

3. Is it OK if the plane of the measured object is diffuse reflection?

Usually it is also possible. In practical projects, a thin plastic plate will be used as a reflective surface to solve the problem of serious diffuse reflection.

4. The accuracy of ultrasonic ranging is relatively low, and it is rarely used now.