CALCULATION FOR THE DETECTION OF TRANSITIONAL LANGUAGES AND PROCEDURES FOR THE TRANSMISSION AND TEST OF A RAILWAY SPEAKER

摘要

PCT No. PCT/GB91/00409 Sec. 371 Date Sep. 11, 1992 Sec. 102(e) Date Sep. 11, 1992 PCT Filed Mar. 15, 1991 PCT Pub. No. WO91/14330 PCT Pub. Date Sep. 19, 1991.A telephone circuit is provided for distinguishing between a normal incoming telephone call and a test telephone call. When the telephone is polled from a central station to cause it to undergo a self-test routine, a ringing signal is used which consists of a series of three ringing signals each lasting less than a predetermined time. Consequently, when such a ringing signal is received, a relay remains open so that there is no audible ringing tone. The system thus enables a testing routine to be carried out by the telephone without causing the telephone to ring.