| 摘要 |
<p>PURPOSE:To avoid erroneous information due to the incidence of a slight external ray by setting a threshold value for judging the reception of a dummy gate lower than a threshold value level for judging the reception of a gate. CONSTITUTION:An external received ray 1 sufficiently longer than a received reflecting ray is received 2 to input the signal to a level judging circuit 6 so that the judging level 4 is judged as a threshold value. When system noises N are overlapping each other, a detecting signal 8 is inputted to a gate circuit 12, and upon receiving a gate pulse 10 synchronized with the transmission of the signal 8 and pulse laser beam a gate passage signal 14 is sent. On the other hand, a level judging circuit 7 sets a judging level 5 lower than the level 4 by a noise level to a threshold value and judges a signal 3 having overlapping noises N to output a detecting signal 9. A dummy gate circuit 13 gates the signal 9 by a dummy gate pulse 11 to send a gate passage signal 15 which did not appear in the reflected ray reception. A judging circuit 16 discriminates an effect of external rays on the basis of the signal 15 to restrain the occurrence of erroneous alarm without outputting a judging signal 17.</p> |
