GB260214A - Improvements in automatic telephone substation instrument circuits - Google Patents

Abstract

260,214. Dicker, S. G. S., (Assignee of Pye, H. C.). Oct. 23, 1925, [Convention date ]. Automatic exchange systems.-Relates to common batterv anti-side-tone substation circuits and comprises several features illustrated in the three arrangements shown. In the first arrangement, Fig. 1, employing a direct-current receiver, the primary 13 of the induction coil is in series with both transmitter 7 and receiver 8, and the secondary 14 which is coupled and multipled to the primary so as to have an auto-transformer action is connected to the mid-point of the condenser 9 and bell 10. A third winding 12 of the induction coil in series with a condenser 11 acts as an artificial line to prevent the receiver 8 from being affected by the microphone 7. During impulsing, the transmitter 7, receiver 8 and winding 13 are short-circuited, winding 12 is directly shunted by condenser 11, whilst a circuit comprising condenser 9 in series with bell 10 shunted by coils 13, 14 in series is connected across the impulse contacts 3. This arrangement prevents the bell from responding to the impulses. The second arrangement, Fig. 4, for use, for example, in a cradletype instrument, is such that the microphone 7 and receiver 8 mounted as one unit can be connected to a second unit comprising bell, condenser, induction coil and number dial by a threeconductor cord. The connections of the various elements are re-arranged as shown, with the result that an alternative direct-current path exists across the conductors 2, 1 through dial 3, winding 12 and bell 10 to hold up the exchange apparatus in the event of a complete break at the microphone 7. During impulsing, the connection of condenser 11 across winding 14 reduces the inductive effect of winding 13 in the impulse circuit. In the third arrangement, Fig. 7, which employs a permanent magnet receiver 38, the microphone circuit includes only one winding 43 of the induction coil, the compensating circuit includes a second winding 42 and condenser 39, whilst the receiver is in series with the third winding 44 which is coupled to both windings 42, 43. During operation of the microphone, equal and opposite currents in the windings 42, 43 cause no effect to be produced in winding 44 and the receiver, but during reception the receiver is excited by current through windings 43, 44 whilst the current in winding 42 is opposed by current induced by winding 43. During impulsing, the microphone, receiver and winding 44 are directly short-circuited, and the impulse springs are shunted by a circuit comprising condenser 39 in series with bell 40 which is shunted by windings 42, 43. The shortcircuit across winding 44 reduces the inductive effect of winding 43 in the impulse circuit. Specification 177,130 is referred to.