PURPOSE: To prevent under-registration or over-registration of a subscriber's transmission by employing a reference circuit having the same electric characteristics as a counting register circuit, and a detection circuit, whereby faults in the counting register circuit can be detected at the time of a subscriber's transmission to thereby stop the subscriber's transmission.
CONSTITUTION: A reference circuit 9 having the same electric characteristics as a counting register circuit 3 is provided. When the counting register circuit 3 is connected to a marker 2, the condition of electric potential of the reference circuit 9 and that of the counting register circuit 3 are compared with each other by differential amplifiers DF1, DF2 in detection circuits 5, 6. Contact and disconnection in the counting register circuit 3 are detected by the detection circuits 5, 6., respectively. When contact or disconnection in the counting register circuit 3 is detected, a relay M is actuated so as to allw the marker 2 to discontinue the transmission connection. Since the detection of contact and disconnection in the counting register circuit 3 and the connection control of the marker 2 are concurrently carried out, faults in the counting register circuit 3 can be automatically carried out at the time of a subscriber's transmission without extending the holding time for the marker 2.
IIDA HARUHIRO
KARASAWA SADAO
TASHIRO YOSHINARI
