| 摘要 |
PURPOSE:To prevent a malfunction due to dark discharge, etc. by inputting an output of an ultraviolet detecting tube to the first and second pulse width stretching circuits, and controlling an output signal of the first stretching circuit by a signal of the second stretching circuit. CONSTITUTION:An output A of an ultraviolet detecting tube 2 for detecting a flame by a discharge phenomenon is provided to the first pulse width stretching circuit 4, a signal B is obtained, electric charge is charged and stored by an integration circuit 5, its value is compared with a set value, and a flame detecting signal is outputted from a switching circuit 6. On the other hand, the output A is provided to the second pulse width stretching circuit 7 for stretching a shorter time than the stretching circuit 4, and the charged electric charge of the integration circuit 5 is discharged by a cancelling circuit 8. Accordingly, it is possible to prevent a malfunction due to discharge which is not caused by ultraviolet rays of a flame, for instance, when no discharge is generated after the detecting tube 2 has repeated discharge, when concentrated discharge is executed at an interval of time, etc., and its reliability can be elevated. |
