| 摘要 |
PURPOSE:To improve reliability by detecting the abnormality of a transmitter definitely with a simple circuit constitution by providing a circiut which detects as an an output pulse width a dissidence period of the input pulse signal and output pulse signal of the transmitter. CONSTITUTION:Received signal (a) and transmitted signal (b) are inputted to re- trigger monostable multivibrators MM1 and MM2, whose outputs (c) and (d) are inputted to exclusive OR circuit EXR, where a period of dissidence between both signals (c) and (d) is detected. In case abnormal that signals (a) and (b) of the transmitter differ, the dissidence output width of EXR becomes larger where a fault occurs, there is dissidence output (f) at the fall of monostable multivibrator MM3, and output (q) of FF is inverted into a low level; and then change-over relay 15 is reset (h) via driver inverter INV and photocoupler PC to output a pulse-string signal through by-pass line 16, so that the transmitter will be disconnected from transmission line 5. |
