. The telephone system of the British post office. A practical handbook . means of a pair of cords. A condenser is included in the ring-off circuitat the intermediate office, so that alternating currents only affect theapparatus. Thus the primary battery signalling between the terminaloffices does not affect the intermediate one. To call this office, the terminal tgd tntermediate Stations upon Tfunk Lines. oflSces rings with the red button. The disengaged side is cut off by removingthe peg, thus connecting up a polarised indicator relay and permanentcurrents. The circuit is then entered by mea
. The telephone system of the British post office. A practical handbook . means of a pair of cords. A condenser is included in the ring-off circuitat the intermediate office, so that alternating currents only affect theapparatus. Thus the primary battery signalling between the terminaloffices does not affect the intermediate one. To call this office, the terminal tgd tntermediate Stations upon Tfunk Lines. oflSces rings with the red button. The disengaged side is cut off by removingthe peg, thus connecting up a polarised indicator relay and permanentcurrents. The circuit is then entered by means of the speaking key. Thisvirtually divides the circuit into two. The disengaged side is joined up to thepermanent current relay, and thus the terminal office is not disturbed. Anycall would be received upon the relay and would then be answered by theintermediate office pegging into the second switch-spring. Now when theintermediate office connects a subscriber the condenser is short-circuited byinserting a solid brass plug in the special switch-spring. Thus when the. Figure 145. terminal office removes the peg the exchange galvanometer is deflected. Inorder to receive calls a magneto bell is joined in parallel with the self-restoringindicator and exchange galvanometer. If the intermediate office wishes to enter the circuit to speak to one of theterminal offices it is necessary to first ascertain whether the circuit is inserting the brass peg the exchange galvanometer is directly joined the circuit is disengaged the permanent currents deflect the not, no deflection is observed, and in the latter case the peg is left in, andthe circuit is entered upon the conclusion of the conversation, when thepermanent currents are restored. The whole arrangement is indicated in Figure ;, where the circuit is Single Wire Trunks. 191 shewn in the normal condition. Obviously, if the exchange galvanometerwere left directly in the circuit, both the termina
Size: 1244px × 2009px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjecttelepho, bookyear1901
