PURPOSE: To prevent malfunction occurring when a relay circuit for loop monitoring is connected by charging and discharging the capacitor of a call signal detecting circuit to the same potential between lines of the relay circuit for loop monitoring.
CONSTITUTION: A relay RAA operates when a relay RA is in operation to connect lines to the sides of resistances R3 and R4. When a relay TM is in operation and the relay RA is released, charges in the capacitor C3 of the call signal detecting circuit of a COT are absorbed by a power source -48V through resistances R3 and R4. Therefore, the potential difference between both contacts raa1 and raa2 at both ends of a malfunction preventing circuit encircled with a broken line is equal to the potential difference across the capacitor C3. Then when the relay RA is released to release the relay RAA, the malfunction preventing circuit is disconnected to connect a loop monitoring relay A to the line. The resistance of both windings of a relay A is equal to the resistances R3 and R4. Therefore, neither charging nor discharging current due to the charges of the capacitor C3 is generated by the connection of the relay A, which never malfunctions.
FUJI KATSUAKI
KATOU KIYOUKO
