Patent ID: 7821618

Claim:
A method for light propagation time measurement, comprising the steps: sending a first light signal that is clocked by a clock pulse control from at least one transmitter into at least one light path via a reflecting object to at least one receiver for detecting a change of the first light signal in consequence of the approach, presence and/or distancing of the reflecting object, receiving the first light signal coming from the at least one light path by means of the at least one receiver, determining a received signal in consequence of the first light signal at the receiver, transmitting a second signal that is clocked by the clock pulse control and which appears without the at least one light path or via a path which is known in regard to its distance, comparing the received signal from the light path with the second signal in a clocked manner for producing a comparison value at the output of at least one comparator , detecting in a clocked manner a clock pulse alternation signal (TW) occurring at a clock pulse alternation and corresponding to the light propagation time between the received signal from the at least one light path and the second signal, determining an amplitude difference value by comparison of the clock pulse alternation signals between the signal received from the at least one light path and the second signal in the comparator, changing the amplitude difference value by means of a phase shifter in changing a phase delay of the phase of the received signal and of the second signal until the amplitude difference value is minimal, evaluating the phase delay of the phase shifter occurring at the minimum amplitude difference value for a determination of the light propagation time, wherein the received signal from the at least one light path is compared with the second signal in a clocked manner for producing a comparison value at the output of a first comparator which is used for the control of the amplitude values of at least one of the transmitted signal or the second signal in such a way that the received signal and the second signal are of the same magnitude at least at inputs of the first comparator, wherein the detecting in a clocked manner the clock pulse alternation signal is effected when the magnitude of the signal received from the at least one light path and the second signal have been controlled such as to be of equal magnitude at the inputs of the first comparator, and wherein the determining the amplitude difference value by comparison of the clock pulse alternation signals between the signal received from the light path and the second signal is effected in a further comparator.