| 摘要 |
PURPOSE:To dispense with the cable between a light emitter and a light receiver and to prevent erroneous operation due to the light from the other light emitter, by emitting pulse like light from each light emitter while detecting the pulse like signal peculiar to the corresponding light emitter in each light receiver. CONSTITUTION:Light emitting LEDs 8(8-1-8-n) and light receivers each having a photo-transistor HTR11 respectively opposed to said LEDs 8 are arranged in parallel in an alarm region and, when either one of light is blocked, an alarm is generated to perform a facial alarm. In this case, a signal generator 6 generating a different pulse signal at constant intervals is provided and each pulse signal is imparted to each LED8 while specific pulse like light is emitted from each LED8. In addition, means 13, 14 for detecting the pulse signal peculiar to the light emitter corresponding to each light receiver are provided and an alarm signal is generated when there is no detection output. |
