| 摘要 |
PURPOSE:To prevent breakdown of the whole system, by detecting abnormal oscillations of the modulator of the own station with a retrigable monostable multivibrator and separating the own station from the common transmission line. CONSTITUTION:Since an output (e1) of a modulator 4 becomes an intermittent wave when the modulator 4 is normal, an output (e2) of a retrigable monostable multivibrator 7 also alternately repeats ''0'' and ''1'', and a Zener diode ZD is maintained under a condition where no continuity is obtained because the charging charge of a condenser C is discharged by a transistor Tr1. Therefore, a relay L does not work, its contact R is maintained under a condition shown in the diagram, and data from a transmitter 2 are sent to a common transmission line (l) through a transformer T. On the other hand, when an abnormal oscillation occurs in the modulator 4, its output (e1) becomes a continuous wave, the output (e2) of the retrigable monostable multivibrator 7 becomes ''0'' level, and the transistor Tr1 is turned off. Therefore, the charging voltage of the condenser C rises to a level at which the diode ZD can obtain a continuity, and another transistor Tr2 is turned on. Then, the relay L works and its contact R is switched to the NC side. |
