| 摘要 |
1302153 Automatic exchange equipment; D.C. signalling INTERNATIONAL STANDARD ELECTRIC CORP 19 April 1971 [21 April 1970] 27146/71 Headings H4K and H4R] A two-way D.C. signalling system includes units at each end of a junction each with a receiving relay and transmitting circuit connected to the junction so that when a signal is transmitted the receiving relay in that unit is short circuited. Since the signals, e.g. meter pulses, may be transmitted during a conversation an induction coil S couples the signal to both lines symmetrically. As shown an earth signal within junctor EU1 is applied at M and passes without delay through diode D1 and resistor R1 to coil S and lines L1, L2. The signal is also applied through diode D2 so that no signal can appear across relay ri which remains inoperative. In unit RE<SP>1</SP> the signal passes through coil S<SP>1</SP>, diode D<SP>1</SP> 3 and causes relay ri<SP>1</SP> to operate thus closing contact ri<SP>1</SP>l to apply an earth to junctor EU2 at E<SP>1</SP>. Similarly if a signal is transmitted in the opposite direction from junctor EU2 to junctor EU1 relay contact ri1 will be operated. In a modified system, Fig. 2 (not shown), an initial sizing signal is transmitted along one line of the line pair and an acknowledgment signal transmitted along the other line. Operation of additional relays in the signalling units in response to these signals connects the units as shown in Fig. 1 so that transmission along both lines is obtained. In this modified system faults on the loop will be indicated by non-receipt of one of these by signals. |
