| 摘要 |
829,348. Telephone transmission systems. PHILIPS ELECTRICAL INDUSTRIES Ltd. March 19, 1957 [March 22, 1956], No. 8977/57. Class 40 (4). [Also in Group XL (c)] In an arrangement comprising two switching relays for switching in alternative transmission equipments, each switching relay has an auxiliary relay which in its unoperated state short-circuits its associated switching relay and in its operated state short-circuits the other auxiliary relay. As shown, Fig. 1, switching relays A and B serve to connect the carrier sources 1, 5 to the common circuit 4 and when unoperated to respective dummy loads 8, 12. Fig. 2 illustrates the timing of events, the broad end of an arrow denoting the closure of a front contact and the pointed end the closure of a back contact. Assume first that relays C and A are operated (the contacts of these relays are shown in the operated position) so that carrier source 1 is in use. To bring carrier source 5 into use switch 17 is operated short-circuiting C which opens its make contact c1 at time t2 thereby initiating the operation of relay D. When D opens its back contact d2 at time t8 it initiates the operation of relay B. When at time t3 C makes its back contact c2 it initiates the release of relay A. The interval between the making of the front contact b1 of B and the breaking of the front contact a1 of A (which is the time for which the supply to load 4 is interrupted) is seen to be t7-t4 which can be made very small by adjusting the operate and release times of relays A and B, which may be effected by adjusting resistances 9, 10, 13, 14. Change-over may be effected automatically on failure of the carrier supply in use. Thus, if carrier supply 1 is in use, when it fails relay E falls back, to open the circuit for C to initiate the change-over as previously described, and also to complete a circuit for the alarm 23. |
