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I want to have the knowledge about electronic distance meters(use infra-red light wave ), their's theory,element function and electronic scheme for example
In general, the IR beam intensity is modulated by a sine wave. The beam is reflected off a surface that is at the point being measured. The returned beam is detected and amplified. You end up with a sine wave with a phase shift compared to the transmitted one because of the time of flight to and from the target reflector. Ordinary electronic methods are used to measure the phase shift angle.
As an improvement to the system to reduce the errors caused by the phase shift measurement, a low frequency is first used. This is low enough that the phase shift is less than 360 degrees at the maximum possible range. This will give you a range reading with an error. Then a higher modulating frequency is used like 10x as much. The phase measurement error will cause 1/10 of the distance error. There will be several cycles of phase change between the reflecting target and the measuring device. This will give several possible ranges. The one that is closest to the lower modulating frequency range estimate is selected.
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