The measurement begins with the continuous emission of an infrared signal by an infrared light emitting diode onto a target object. The emitted IR ray is reflected by the object and the reflection is detected by a special photocell sensitive to infrared rays. The photocell (located next to the IR transmitter), the reflection point and the IR transmitter are arranged triangularly to each other. The determination of the distance can - depending on the measuring device - be divided into two different evaluation methods, based on triangulation or time.
Variant one is based on the principle of triangulation. The light falling back from the reflection point is focused by a lens located in front of the photocell. The result is a focused IR beam whose point of impact on the photodiode gives information about the angle of incidence. The infrared range finder calculates the distance to the object based on the angle of incidence. In this case, the IR evaluation depends on the incident light intensity. This type of infrared distance measurement is used, for example, in national surveying and mapping.
In variant two, the transit time from the emission of the IR signal to the detection of the reflection is determined. By the known distance between sensor and receiver, as well as by the speed of the IR rays stored in the device in combination with the determined time, the distance between the two points can be determined. Fields of application range from hunting to vehicle parking assistance, for example.