| 摘要 |
PROBLEM TO BE SOLVED: To adjust the optical axis more accurately and securely by allowing a photodetection part to detect the quantity of light from a light transmission part to output a photodetection signal indicating the photodetection quantity to a synchronous line and allowing the light transmission part to receive the photodetection signal from the synchronous line to output the photodetection quantity. SOLUTION: A photodetection part control circuit 3 once judging a fire from the quantity of light received by a photodetecting element 12 in synchronism with synchronizing pulses and inputted through a photodetecting amplifier circuit 14 and a sample holding circuit 15 turns on a fire signal output switching element 4 to turn on a fire pilot lamp 5 and also inform of the fire a receiver connected to terminals T1 and T2 through fire signal lines. When the synchronizing pulses are sent from the photodetection part side, a voltage detection circuit detects them and a light transmission part control circuit tuns on the electrified pilot lamp switching element with a prescribed pattern and supplies the electric power to the electrified pilot lamp, which blinks, so that the light transmission part side emits light.
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