Optoelectric distance measuring apparatus with delay and zero cross detector

Claim 1

An optoelectric distance measuring apparatus, comprising: means for transmitting at least one light pulse toward a target, the transmitting means including a diode laser and the light pulse having a predetermined duration; means for receiving a portion of the at least one light pulse reflected from the target, the receiving means including a photodiode which converts the portion of the at least one light pulse received into an electrical pulse; a pulse amplifier connected to the photodiode, the pulse amplifier producing an output corresponding to the electrical pulse and having a predetermined output impedance; means for detecting when the portion of the at least one light pulse reflected from the target is received, the detecting means producing a stop signal and including: a delay line having a short-circuited end and another end which receives the output pulse; a threshold value and zero crossing detector connected to the delay line between the ends of the delay line at a predetermined distance from the short-circuited end in accordance with the predetermined duration; and a timer circuit for determining a time difference between a start of the at least one light pulse transmitted and the stop signal, wherein the delay line conducts the output pulse from its other end to its short-circuited end, the output pulse being reflected and inverted at the short-circuited end to form a copy pulse, the threshold value and zero crossing detector determining when a combination of the output pulse and the copy pulse crosses a predetermined threshold value and crosses a zero value, and the pulse amplifier's predetermined output impedance is selected so that the pulse amplifier does not reflect the output and copy pulses, and wherein the predetermined distance of the threshold value and zero crossing detector from the short-circuited end of the delay line is selected so that a delay between the output pulse and the copy pulse corresponds to substantially half of a width of the output pulse.