Patent GB-190314363-A (GB)
Title: Improvements in Telephone Call Recording Systems
Filed: 1903-06-27
Granted: 1904-06-27
Abstract: 14,363. Lake, H. H., [Automatic Telephone Meter Co.]. June 27. Telephone systems; telephone calls.-Relates to telephone-call metering-devices, and is described with reference to a central-battery exchange system. The metering system is such that the call is recorded only on the meter of the calling- subscriber, and no record is made if the desired connection is not established, or if the subscriber is cut off before the conversation is finished. In the arrangement shown in Fig. 1, the meters are situated at the subscribers' stations, but they may be placed at the exchange. The meter is a polarized instrument, which is set in readiness for making the record by the current which flows in the line when the receiver is lifted to make a call. The record is not actually effected until the desired connection is established and the called subscriber has lifted his receiver from the hook, when, by means of a pole-changing switch at the exchange, the line current is reversed and the meter actuated. The pole-changer consists of a switch a adapted to be thrown over by means of an electromagnet b against the tension of a controlling spring. In order for the switch to be actuated it is, however, necessary for both the electromagnets d<10>, d<20> to be energized, as they control two independent detents d<12>, d<22> which normally lock the switch against movement. The electromagnet b is energized as soon as either plug is inserted in a jack in response to a call, the circuit comprising the battery A, electromagnet b, conductor 1<c> (or 1<B>), supervisory lamp l<1> (or l<2>), plug terminal n, jack socket n<2>, conductors n<20>, n<21>, and earth. The electromagnets d<10>, d<20> are placed in the existing circuits commonly employed to shunt and extinguish the supervisory lamps. When the plug is inserted in the jack of the calling-subscriber, the electromagnet c is energized, the circuit being as follows :-Battery A, conductors 1, c', switch a, conductors c<3>, c<3> to the tip side B of the line, returning through the subscriber's station (the receiver being off the hook), the sleeve side C of the line, conductor c<4>, electromagnet c, conductors c<5>, c<6>, switch a, conductor c<7>, and earth. The armature 1g being attracted, the electromagnet d<0> is thrown in shunt with the supervisory lamp l<1> and the detent d<12> attracted. The other electromagnet d<20> is not energized until the other plug has been inserted in the called subscriber's jack and he has lifted his receiver from the hook. When this has been done, circuits are closed precisely similar to that just described, and the electromagnet d<20> is thrown in shunt with the supervisory lamp l<2>. Both detents being thus withdrawn, the switch a is thrown over and the battery connections reversed with respect to the tip aud sleeve sides of the lines, the meter at the calling subscriber's station then making the record. The meter is shown in Fig. 2. The coil e is connected through conductors 3,4, 5, 6 as a shunt to the transmitter, thus offering no impedance to the speaking-currents. The core e' is pivoted at e'‹, and plays between the polepieces f, f<2> of a permanent magnet f<3>. The core normally adheres to the pole-piece f, but is thrown over against the pole-piece f<2> when the call is made, returning to the pole-piece f when the calling-subscriber responds. A lever e<3> is pivoted at e' and connected with the core e<2> at e<30>. When the core moves towards the left, the lever e<3> rocks the pawl g through the medium of a link e<5> and bellcrank lever e<6>. A lever i pivoted at i' bears a guard-piece i' and an armature i<3> co-acting with the upper end of the core e<2>. The armature i<3> is not attracted to the core as rapidly as the core itself moves relatively to the permanent magnet, and the guard-piece i<4> consequently prevents engagement of the pawl g with the wheel h during the right-hand movement of the pawl g, the detent s being, however, withdrawn. When the current is reversed, the armature i<3> remains adherent to the core e', and the pawl g turns the wheel h of the meter through the space of one tooth. As long as the conversation continues, the armature i<3> remains attracted. If, therefore, the operator at the exchange removes the plug before the calling- subscriber has hung up his receiver, the current reversal which ensues moves both pawl and wheel, and cancels the registration. To ensure that the pawl shall in no circumstances leave the wheel until the receiver is hung up, a gravity locking- catch o is provided to detain the tail end i<6> of the lever i. The catch is released when the highresistance electromagnet p is energized. This electromagnet is in a circuit 6, 14, and is shortcircuited until the receiver is hung on its hook. An automatic switch r, comp:rising a vessel holding a small quantity of mercury, may be secured to the lever i and included in the circuit of the electromagnet p. The automatic switch breaks the circuit of the electromagnet p as soon as the catch o has been actuated, and so prevents waste of current. The catch o and electromagnet p can be dispensed with if a dash-pot is provided to prevent rapid movements of the lever i. When the meters are located at the exchange, the coil e is doubly wound, each winding being a shunt to a resistance in one of the line wires.