| 摘要 |
PURPOSE:To prevent malfunctions of a monitoring circuit even when a very little electric current flows to the primary winding of the transformer, by providing a capacitor of a small capacity between the midpoints of the transformer. CONSTITUTION:A capacitor C attenuates a transient voltage which is produced when a very little electric current flowing to the primary winding W of a transformer Tr is interrupted by the contact (r) of a relay R which intermittently operates while a call signal is sent. As a result, the change in the electric potential of a midpoint N2 due to the intermitting of the contact (r) is reduced to such an extent that a monitoring circuit S does not make any malfunctions. When a called subscriber responses, a ring trip is performed, and the relay R stops the intermittent operation, the capacitor C2 having a small capacity is connected in parallel with another capacitor C1 connecting midpoints N1 and N2 of the transformer TR, and therefore, a talking condition which is almost the same as before can be offered to subscribers. |
