| 摘要 |
PURPOSE:To continue a call even if a power failure occurs during a call with a trunk line, by providing a nonlock type trunk button contact and a lock type trunk button contact with operates by manual operation and is held magnetically. CONSTITUTION:When the power failure monitoring circuit SUP of a main device MS detects a power failure, magnetic holding relays 1A, 2A... are all switched to trunk-line sides by the charging of the large-capacity capacitor of an unshown rectifying circuit. When there is trunk-line incoming during the power failure, an additionally provided bell sounds, and for reception by a subordinate set TEL1, a contact 1a1 and a contact 1a2 are already switched to trunk-line sides, so its handset is lifted and a lock type trunk-line button contact LK1 is pressed, forming a loop circuit for the call. In this state, when the power failure is recovered, the control circuit CONT of the main device sends polling signals to subordinate sets TEL1, TEL2... through a control signal line L. Since the TEL1 is still engaged with the trunk line, the contacts 1a1 and 1a2 of the magnetic holding relay 1A are held connected to the trunk line, and other subordinate sets are placed at no-trunk-line side through contacts. |
