| 摘要 |
PURPOSE:To perform easy and secure detection by providing a threshold level and resetting all circuits after a break of a main signal is detected. CONSTITUTION:A main signal break detecting circuit 7 consists of an integration circuit 71 which is connected to the output of a band-stop filter 2', a comparing circuit 72 which when receiving the output of a flip-flop 64, compares a DC level received at intervals of 4ms from the integration circuit 71 with a level received previously and held and outputs a large level as a threshold level, a level detecting circuit 73 which detects whether the output signal of the band- stop filter 2' is lower than the threshold level or not, a break decision time limiting circuit 74 which starts time limiting operation with the output of the level detecting circuit 73, and output a logical value '1' normally and outputs a logical value '0' after the time limit, and a gate circuit 75 which ANDs this logical output with the output of an AND circuit 52. The flip-flop 64 is reset with the output of a resetting time limiting circuit 63. |
