| 摘要 |
PURPOSE:To detect the deterioration in a light emitting element, by detecting a pilot signal from both of an output of the light emitting element and an output of a circuit before photoelectric conversion, and comparing both the levels. CONSTITUTION:A pulse frequency modulating signal with a pilot signal inputted from a terminal 1 is converted into an optical signal via a pulse frequency reproducing circuit 2, a light emitting element driving signal 3 and a light emitting element 4 and outputted from a terminal 6. An optical signal of the element 4 is received at a photodetector 7, a pilot component only is selected at a BPF9 and detected at a detector 10. In the output of the circuit 2, the pilot component is selected at the BPF9' and detected at the detector 10. A differential amplifier 15 inputs the output of the detectors 10 and 10' and generates alarm when the output signal level of the element 4 is decreased. |
