| 摘要 |
PURPOSE:To decide the disconnection of a circuit, by impressing the voltage varying in steps to a telephone circuit and receiving a charge/discharge current as an answer to measure the duration time. CONSTITUTION:A relay 23 is driven by a duration signal genrator 25 and a TR24 and impress the DC voltage to a cable core wire 1 and a telephone 2. The charge current waveforms 13 and 14 are shown in the figure when a communication circuit is normal, and only the waveform 13 is obtained when the wire 1 has disconnection. This disconnection is detected by a resistance 26 and a TR27, and a capacitor 28 generates the voltage proportional to the duration time of a detecting signal 9 at its terminal A TR31 conducts when the duration time exceeds the prescribed value to generate a normal detecting signal 11. Then the voltage proportiolnal to the time limit for decision of disconnection is generated at the termnal of a capacitor 32, and a field effect TR33 initializes the capacitor 32 with each above-mentioned prescribed time by the signal 11 to always have charging with a constant current. A TR36 decides no existence of the signal 11 when the output of a field effect TR34 is larger than the sum of voltages of a Zener diode 35 and its base-emitter voltage and then conducts to generate a disconnection detecting signal 19. |
