| 摘要 |
PURPOSE:To discriminate the presence and the absence of line connection without providing a circuit monitoring those at the reception side, by using a current-voltage converter at the transmission side of a voltage signal. CONSTITUTION:The output side of a voltage signal generating source 5 in a transmitter 3 transmitting a voltage signal is provided with a current-voltage converter 6 of positive polarity and a current-voltage converter 7 of a negative polarity. When a transmitter at the reception side is connected, a high level voltage is caused depending on the polarity of a current flowing to the transmission line to the current-voltage converters 6 and 7, an output of an NOR circuit 8 is kept at low level. If the transmitter 4 at the reception side is opened due to open trasmission line or the like, no current flows to the current-voltage converters 6 and 7, the output of the NOR circuit 8 goes to high level, and an alarm signal is produced. |
