| 摘要 |
PURPOSE:To avoid inconvenience that the test using a test signal gives a good result while the operation using a control signal shows a fault by using a signal equal to the control signal but opposite in the order of transmission as the test signal. CONSTITUTION:A transmitter side is provided with a tone oscillator 3-1 oscillating a frequency f1 and an oscllator 3-2 oscillating a frequency f2 and when a control signal transmission switch 1 is turned on, the said tone frequencies are transmitted in the order of the f1 and f2 from a transmission section 4. In case of the test, the order of transmission is reversed and the frequencies are transmitted in the order of the f2 and f1. Detection sections 6-1, 6-2 provided to the receiver side detect each transmitted tone frequency and gives an output to a discriminating circuit 7. The discriminating circuit 7 discriminates whether the order of transmission is f1, f2 or f2, f1, and in case of the former order, a control signal is outputted from an output circuit 8. Further, when the order is f2, f1, after the test signal is detected and no test signal is detected within the set time of a timer 9, then it is discriminated as a fault and an alarm signal is outputted from an output circuit 10. |
