| 摘要 |
1,083,532. Automatic exchange apparatus. INTERNATIONAL STANDARD ELECTRIC CORPORATION. May 13, 1966 [May 17, 1965], No. 21298/66. Heading H4K. The duplicated portions of a control circuit for a telephone exchange are switched into service alternately by means of the circuit illustrated which forms part of one of the control circuit portions. A bi-stable 12 switches its associated control portion in and out of service. Monostable circuits 2a and 2b, in the O condition when at rest, gate the 1 condition of bi-stable 3a so as to set bi-stable 12 to its 1 condition by clock pulses 7. The pulse setting 12 also sets 2a and resets the bi-stable corresponding to 12 in the other duplicate portion of the control circuit so as to switch it out of service. When monostable 2a falls back, having reset 3a and set 3b, the set state of 3b is gated to set monostable 2b. The time constant of 2b is made longer than 2a so that 2b is reset from the associated duplicate portion, where a circuit identical to that illustrated exists, before it resets itself supposing that the circuits are functioning normally. The pulses gated over 6b to set 2b, and the pulses gated over 6a to set 2a, are applied to an alarm circuit AL which operates in the absence of the pulses. |
