| 摘要 |
PURPOSE:To accurately grasp that the leading or trailing end of an object reaches a preset reference position by sampling the electric signals, which are obtained by a photoelectric detector, every preset time and by comparing the resultant difference with a threshold value. CONSTITUTION:The irradiating light 2 emanating from a heated metal 1 being conveyed is converted by a photoelectric converter 5 into electric signals, which are sampled by means of first and second samplers 6 and 6' having different half sampling periods so that the difference inbetween may be obtained by a differential amplifier 7. Before the object 1 enters a detecting portion, a threshold value is determined, and this value is compared by a comparating amplifier 11 with the differential signals from the amplifier 7. Thus, it is possible to accurately grasp the instant, when the differential signals exceed the threshold value, as the instant when the leading or trailing end of the object 1 crosses the field 8 of the converter 5. |
