GB294095A - Improvements in or relating to party-line telephone systems - Google Patents

Abstract

294,095. Hasler Akt.-Ges. vorm. Telegraphenwerkstõtte von G. Hasler. July 16, 1927, [Convention date]. Manual exchange party-line systems. - In a party-line system employing step-by-step selectors S, calling and clearing signals to the exchange operator are controlled by a differential relay DR which is operated over earth connections at a substation when a call is initiated and when the subscriber hangs up. The operation of key RT by a calling subscriber completes a circuit from earth over normal contact 1 of the selector S, relay RA, lead a, and upper windings of relay DR which energizes and completes circuits for relay B and call lamp AL. Relay B locks over contacts of relay C1, lights busy lamp BL and connects the lower windings of relay DR to lead b. The windings of relay DR are thus energized in series over leads a, b, and selectors S and busy signals Bz at all the substations, and relay DR being differentially wound releases. The relays RA which control the speaking and ringing circuits are disconnected at selector contacts 1 at all other substations, thus preventing any interference with the call. Relay RA at the calling station, however, remains operated over its own contacts. When the answering plug As is inserted, sleeve relay C1 operates, releases relay B and lamps AL, and energizes relay C2. If the wanted party is on the same line, plug Ws is inserted into jack WK whereby relay W is energized over the ring circuit and the dial J is connected in series over leads a, b with selector windings S. The operation of the dial causes the selector at the wanted station to close at its contacts 2 the circuit of relay RA. The plug Ws is then withdrawn and ringing-current from the cord-circuit associated with plug As passes over contacts of relay RA to the wanted party's bell. The lifting of the receiver connects it to line and connects up the local-battery microphone M. When the two parties hang up, an earth connection over contact 6 of the switch hook unbalances relay DR which again operates and energizes relay B, which opens a loop to give supervision at the cord circuit. When plug As is withdrawn, relay C1 releases and disconnects C2, which however is slow to release so that a circuit is closed for relay W which releases relays B, DR, RA and selectors S.