| 摘要 |
879,174. Automatic exchange systems. SIEMENS & HALSKE A.G. Sept. 30, 1958 [Sept. 30, 1957; Feb. 5, 1958], No. 31216/58. Class 40 (4). Supervisory current flowing in a line is detected by a transistor connected across a resistor in the line. The arrangement enables current differences to be detected independently of voltage differences on the supervisory line. As shown in Fig. 1 links between the row wires of relay matrices F1, F2 have resistors R1 across which the emitter and base of a transistor T are connected. The collector circuit of T comprises a voltage limiter R2, R3, G1 connected to voltage sources U1, U2. With the link idle and no current flowing T is cut off and terminal a has the potential of source U2. When the link is busy T conducts in response to current in R1 and enables G1 to conduct so that terminal a rises to the potential of source U1. A single link or a group of links may be artificially busied by providing a relay which disconnects the source U2 and replaces it with source U1. The resistor R1 may be constituted by the holding coil of a cross-bar switch such as the dry reed switch described in Specification 797,913. When in shunt across a holding coil the transistor should be in series with a limiting resistor. |
