US1859910A - Telephone system - Google Patents

Description

May 24, 1932. 1.5.1. BOWNE TELEPHONE SYSTEM Filed NOV. 28, 1931 I/QI/EA/TOR BYL. J BOWNE fikac A TTORNEV Patented May 24, 1932 UNITED STATES PATENT OFFICE LANGFOR-D BOWNE, OF HOWARD BEACH, NEW YORK, ASSIGNOR T'O BELL TELE- PHONE LABORATORIES,INCORPORATED, OF NEW' YORK, N. Y., A CORPORATION OF new YORK TELEPHONE svsrnm Application filed November 28, 1931. Serial No. 577,750.

This invention relates to. telephone systems and more particularly to the central ofiice equipment therefor. V

It has been the usual practice in telephone systems to provide, in connection with each subscribers line circuit terminating in a central oflice switchboard, a line relay which operates to close a circuit to a line lamp individual to the subscribers line when a subscriber makes a call. An auxiliary or pilot relay common toa group of subscribers lines is also provided to close a circuit to a pilot signal lamp whenever a call. is made by a subscriber in that particular group. Heretofore when efiorts have been made to dispense with the line relays by connecting the line lamp directly to the line in order to reduce the cost of the system, it has been found that the combined leakage currents in a group oi subscribersllines have been sufficient to cause operation of the pilot relay. Operation of thepilot relay by these line leakage currents results in the lighting of the pilot lamp and hence a false signals An object of the invention, therefore,'is to prevent. false operation of the auxiliaryor pilot relays from leakage currents in such subscribers line circuits having seriesline lamps. I

A teature .of the invention, whereby the foregoing object is attained resides in "con necting an individualresistance element or device, having the; characteristic of decreasing in resistance inv greater than directproportion to: an increase: in applied potential, in. parallel with each series line lamp and through the auxiliary or pilot relay common to group of lines to a source of electrical energy. Line leakages will cause insuflicient current throu-ghfthe devices and relay inse ries with them tooperatethe relay. .When a lamp is energizedby the-closingot its circuit, however, the potential drop across the resistance devices becomes great enough to cause its resistance decrease and a current sufficient to operate the. relay results.

More specifically a resistance device whose resistance decreases in greater than direct proportion to the applied potential acrossitsterminals, for example, an element of thyrite,

is connected between the ungr'ounded side of each subscribers line and the common auxiliary or pilot relay which, in turn, is connected to battery. The resistance of these devices prevents the flow of leakage currents through the relay. Upon the positive grounding of a linein response to the removal of the subscribers receiver from its switchhook', the line lamp, which is .also connected to the line, is lighted. The potential drop across the: hot lamp filament is impressed across the resistance device connected to the line and causes its resistance to decrease to a point where the current flow. is suflicient to operate the pilot relay.

To more completely describe this invention, reference will now be made to the drawing in which the invention is shown applied to a common battery manual telephone sys-- tem.

In the figure, 1, 2 and 3 represents three separate substations forming a group of substations terminating in a central ofiice switchboard 4. 5 represents the cord circuit for connecting a subscribers line to another subscribers line in the system and 6-represents an alarm system which-may be employed, for instance, as a night alarm to indicate an incoming call when a central operator is not in attendance at the board, or when there is no operator at the particular position in which the group of subscribers lines is located.

The operators telephone equipment and circuit associated with the cord circuit has not been shown in the drawing because the operation and utility of such equipment is well known and the showing of such equipment is not necessary to a ull understanding of this invention.

The subscribers line circuits 7, 8' and 9 of the substations 1, 2 and 3, respectively, terminate at the central otiice switchboard 4 in the respective jacks 10, 11 and 12. Connected directly to jack 10 is a line signal lamp 13 connected directly to jack 11 in line signal lamp 14 and likewise to jack 12 is connected line signal lamp 15. The line signal lamps13, 14 and 15 have a filament which increases in resistance with temperature orcurrent flow.

Tungsten filament lamps have this characteristic and may be used for these line lamps.

Common to the group of subscribers lines represented by the substations 1, 2 and 3 is pilot relay 16 which operates to close a circuit to pilot lamp 17 whenever a call comes in from a substation in the group. To prevent operatiou of the pilot relay 16 by leak- ,age currents in the lines of the group, the

resistance devices 18, 19 and 20 are provided. The resistance devices 18, 19 and 20 are connected to battery 21 through the winding of pilot relay 16 and have the characteristic of decreasing in resistance in greater than direct proportion to an increase in potential applied. Thyrite, for instance, has this characteristic and blocks of this material I have found are adaptable for the purpose. Resistancedevice 18 is connected directly to jack 10 and in shunt of line lamp 13, is connected to battery 21 through the winding of pilot relay 16. -Resistance device 19 is connected directly to jack 11 andin shunt of line lamp 14, is connected through the winding of pilot relay 16 to battery 21. Resistance device 20 is connected in shunt of line lamp 15 directly to jack 12 and through the winding of pilot relay 16 to battery 21.

Assuming that a call is made by the subscriber at substation 1; when the substation loop is closed by the subscriber lifting the receiver 22 off the book 23, the line lamp 13 at the central ofiice is lighted to indicate to the central oflice operator the incoming call. The circuit for energization of line lamp 13 is as follows: ground, battery 21, conductor 24, line lamp, 13, conductor 25, contact 26, ring contact of jack 10, conductor 27, left-hand side of inductance coil 28, switchhook 23, transmitter 29, conductor 30, tip contact of jack 10, contact 31 to ground. As the filament in the line lamp. 13 11eats up, the resistance of the lamp increases. WVith increase in the line lamp resistance, increased potential is applied to the resistance device 18 to cause operation of pilot relay 16. Resistance device 18', as has been said before, has the characteristic of decreasing in resistance in greater than direct proportion to an increase in potential applied. Therefore, as the potential applied increases, the resistance intlie device 18 decreases in greater than direct proportion to the increase in, potential applied. An increase incurrent flow to the pilot relay 16 takes place. The circuit for energization of pilot relay 16 may be traced as follows: ground, battery 21, conductor 32, winding of pilot relay 16, conductor 33, resistance device 18, conductor 25, contact 26, ring contact of jack 10, conductor 27, left-hand side of in ductance coil 28, switchhook 23, transmitter 29, conductor 30, tip contact of jack 10, contact 31 to ground.

'Pilot relay 16 upon becoming energized 3 closes a circuit to pilot lamp 17 which thereupon becomes lighted to indicate to an attendant at the switchboard an incoming call from one of the subscribers in that particular group.

When a central office operator answers a call by plugging into the jack of the calling line with the cord circuit 5, which in this instance would be jack 1(), the tip and ring contacts of jack 10 are separated from the contacts 26 and 31. This disconnects the line lamp 1.3 and the pilot relay 16 from the subscribers line circuit causing extinguishment of the line lamp 13 and deenergization of the pilot relay 16 with consequent opening of the circuit to the pilot lamp 17.

The alarm system 6 comprises an alarm signal 34, a source of energy therefor which may be, for instance, an alternating current generator 35 and a switch. 36. When the alarm system 6 is to be used to indicate an incoming call, switch 36 is closed. Closing of a subscribers loop circuit in the group served by the alarm system 6 will, in addition to causing lighting of the line lamp, energization of the pilot relay 16 andlighting of the pilot lamp 17 cause energization of the alarm relay 37. The circuit for the alarm relay 37 may be traced as follows; ground, battery 38. winding of alarm relay 37, conductor 39, pilot lamp 17, conductor 40, front contact and armature of pilot relay 16 to ground. Alarm relay 37 upon becoming energized will close the circuit of the alarmsystem 6. The alarm signal 34 is operated over the following circuit: alternating current generator 35, conductor 41, alarm signal 34, front contact and armature of alarm relay 37, conductor 42, closed switch 36 to the generator 35.

When in answer to an incoming call the operator at the central station plugs into the jack of the calling substation with the cord circuit 5, answering supervisory lamp 43 is lighted. The circuit for lighting of the answering supervisory lamp 43 may be traced as follows: ground, battery 44, conductor 45, answering supervisory lamp 43, conductor 46. resistance 47, sleeve contact 48 of the answering plug 49, sleeve 50 of the jack of the calling line to ground. \Vhen the answering plug 49 is fully inserted into the jack of the calling line, answering supervisory relay 51 becomes energized and causes shunting of the answering supervisory lamp 43. Answering supervisory relay 51 remains energized until the calling subscriber opens the subscribers line circuit again. The circuit for energizati on of the answering supervisoryrelay 51 is as follows: common battery 52, lower left-hand winding of repeating coil winding of answering supervisory relay 51, ring contact of the answering plug 49, ring contact of the jack of the calling subscribers line circuit, through the calling subscribers loop, tip contact of the jack of the calling subscribers line circuit, tip contact of. the answering plug 49, upper left-hand winding of the repeating coil 53, to the other side of the common battery 52. When the answering supervisoryrelay 51 is energized, the answering supervisory lamp 43 is shunted by way of the front contact and armature of answering supervisory relay 51 and resistance 54. The current flow through-the lamp 43 is thereby reducedto such. an extent as to cause extinguishment of the lamp. Opening of, the subscribers loop circuit will cause deenergization of answering supervisory relay 51 and removal of the shunt from the answering supervisory lamp 43' The lamp 43 will then again be. lightedto indicate to the operator at the central office that the calling subscribers'loop-circuit has been opened and the call hasbeen'terminated. The calling end of the-cord circuit has been shown as including a calling supervisory relay 55, a calling supervisory lamp 56 and the calling plug 57. A' jack 58. representing a subscribers line circuit terminating in the central office switchboardhas. also been included in the drawing. The jack 58represents the termination in the central oiiice switchboard of the line circuit of a called line. Insertion'of the calling plug 57 into the jack 58of the called line will result in lighting of the calling. supervisory lamp 56. The circuit for the calling supervisory lamp 56' is as follows: ground, battery 59, conductor .60, calling supervisory lamp 56, conductor 61, resistance v62, sleeve contact 63 of calling plug5'Z, sleeve 64 of jack58 toground. The called partyupon answering will cause closing of the calledsubscribers loop circuit and energization of the calling supervisory relay 55. Thecalling supervisory relay upon being energized will place a shunt around the calling supervisory lamp 56. When the called party opens the loop circuit of the called line, the calling supervisory relay 55 will be deenergized, the shunt around the callinv supervisory lamp will be removed and the calling supervisory lamp 56 will be lighted again to indicate to the operator at the central otlice that the called subscriber no longer desires the called connection.

The equipment at substations 2 and 3 is identical with that shown in substation 1 and requires no further description. The resistance device 19 connected through the contact 65 to the ring contact of jack 11 of the subscribers line circuit from substation 2 prevents leakage current in the substatien line from affecting the pilot relay 16. Likewise the resistance block 20 which is connected through contact 66 to the ring contact of jack 12 of the subscribers line circuit from substation 3 and through the winding of pilot relay 16 to the battery 21 prevents leakage current in the substation line circuitfrom substation 3 from affecting the pilot relay 16.

- If the loop circuit of substation 2 is closed, the line lamp 14 is lighted. The resistance --in the line lamp 14 increases and increased potential is applied to the resistance device 19. The resistance in the device 19 decreases in greater than direct proportion to the increased potential applied and the current flow through the pilot relay 16 increases to such an extent as to cause operation of the pilot relay 16. Pilot relay 16 in operating closes the circuit of pilot lamp 17. The lighting of the pilot lamp 17 indicates an incoming call in the group of subscribers lines served by the pilot relay 16 and the lighting of the line lamp 14 indicates that the call has come in from substation 2.

A call coming in from substation 3 causes lighting of the line lamp 15, increase in the resistance in this lamp, a decrease inresistance in the resistance device 20, and opera? tion of the pilot relay 16.

The normal low resistance of each line lamp allows operation of the line lamp when a subscribcrs loop circuit served by the line lamp is'closed. The normal high resistance of each of the resistance devices 18, 19 and 20 prevents operation of the pilot relay 16' by leakage current in a subscribers line circuit. Each resistance device, therefore, blocks oil from the pilot relay 16 any leakage current in the particular subscribers line circuit to which the block is connected. The pilot relay 16, therefore, cannot be operated by leakage current in any particular subscribers line circuit, nor by combined leakage cur rents from the group of subscribers line circuits served by the pilot relay. I

WVhile elements of thyrite have been suggested for the resistance devices 18, 19 andQO and tungsten for the filaments of the line lamps 13, 14 and 15, other devices or materials having the same relative resistance characteristics described, may be used in place thereof without departing from the spirit of this invention. I

What is claimed is:

1. A telephone system comprising a substation, a central station, aglinecircuit connecting said stations, a line signal connected to said line circuit, and a source of energizing current, a relay connected to said source of current and said linecircuit in parallel with said line signal, and a resistance element connected in series with said'relay to protect the relay against operation byleak age currents'in said line circuit. 7 2. A telephone systemcomprising a substation, a central station, a line circuit connecting said stations, a line signal connected to said line circuit, and a. source of energizing current, a relay connected to said source of current and said line circuit in parallel with said line signal, and a .resistance device connected inv series Wltll'Sal'd relay to protect the relay against operation by leakage currents in said line circuit.

3. A telephone system comprising substations, a central station, line circuits connecting the substations and the central station, a source of energizing current for the system, a line lamp connected to each line circuit and said source of current, a relay common to a group of substations, and a resistance element connected to each substation line and to said source of current through said relay to protect said relay against operation by leakage currents in said line circuits.

4. A telephone system comprising substations, a central station, line circuits connecting the substations and the central station, a source of energizing current for the system, a line lamp connected to each line circuit and said source of current, a relay common to a group of substations, and a resistance device connected to each substation line and to'sai'd source of current through said relay to protect said relay against operation by leakage currents in' said line circuits. 5. A telephone system comprising substations, a central station, line-circuits connecting the substations to the central station, a source of energy forthe system, a line lamp connected to each line circuit and to the source of energy, a relay common to a group of line circuits connected to the source of energy and to each line circuit-in the group, and an element of resistance material connected to each line circuit in the group and in series with said common relay to prevent operation of said relay by leakage currents in the line circuits, each of said line lamps having a filament, the resistance of which increases with current flow to the lamp, and eachof said elements of resistance material having the characteristic of decreasing in resistance in greater than direct proportion to an increase in applied potential, each element of resistance material being in parallel with the corresponding line lamp and permitting increase in current flow around the line lamp and through said common relay when the line lamp resistance increases.

6. A telephone system comprising substations, a central station, line circuits connecting the substations to the central station, a source of energy for the system, a line lamp connected to each line circuit and to the source of energy, a relay common to a group of line circuits connected to the source of energy and to each line circuit in the group, and a resistance device connected to each line circuit in the group and in series with said common relay to prevent operation of said relay by leakage currents in the line circuits, each of said line lamps having a filament, the resistance of which increases withvcurrent flow to the lamp, and each of said devices having the characteristic of decreasing in resistance in greater than direct proportion to an increase in applied potential, each device being in parallel with the corresponding line lamp and permitting increasein current flow around the line lamp 7 and through said common relay when the line lamp resistance increases.

7. A telephone system comprising a group of substations, a central station, line circuits connecting the substations to the central station, a source of energy for the system, a relay common to the group of substations connected to the source of energy and to each line circuit in the group, a tungsten filament line lamp connected to each line circuit and to the source of energy in shunt of said common relay, and a resistance block connected to each line circuit in parallel with a corresponding tungsten filament lamp and connected to the source of energy through the winding of said common relay, said resistance block having the characteristic of decreasing in resistance in greater than direct proportionto an increase in applied potential, said resistance block preventing operation of said common relay by leakage currents in the lines but allowing operation of said common relay when the resistance in a line lamp increases.

8. In a telephone system including a group of line circuits, a source of energy for the system and a relay common to the group, an element of resistance material connected to each line circuit and to the source of energy through the winding of the common relay to prevent operation of the common relay by leakage currents in the lines, said element of resistance material having the character istic of decreasing in resistance in greater than direct proportion to an increase in applied potential and permitting operation of said common relay when a line circuit is closed. V

In witness whereof, I hereunto subscribe my name this 25th day of November, 1931.

LANGFORD J. BOWNE. M

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