US2034017A - Multiconductor signaling system - Google Patents

Description

arch-17, 1936 c. E. BEACH 2,034,017

MULTICONDUCTOR S IGNALING SYSTEM Filed Jurie 27, 1952 2 Sheets-Sheet 1 Z0 4/6 /7 0 /6 A H9 m3- 7;; Wu

INVENTOR March 17, 1936. c. E. BEACH MULTIGONDUCTOR SIGNALING SYSTEM Filed June 27, 1952 2 Sheets-Sheet 2 INVENTO R Patented Mir. 17, 1936 UNITED STATES PATEN MULTICONDUCTOR SIGNALING SYSTEM Application June 2'7, 1932, Serial No. 619,405

14 Claims.

This invention relates to multi-conductor electric signaling systems; particularly systems in which facilities should be provided for response to signals formulated in two or more alternative current paths.

In my Patent No. 1,528,596, dated March 3, 1925, facilitiesv are disclosed for the energization of conductors of such systems through the utilization of a source of alternating current, either independently or in connection with the utilization of a source of direct current.

In my co-pending application, filed under date of November 5, 1931, Serial No. 573,151, there is disclosed a. signaling system having a normally closed current path energized from a rectified alternating current source; one of the alternating current tenninals being grounded; so that, in the event of a break in the normally closed path, a portion at one side or the other of the break may be energized with a half-wave rectified current by connecting such circuit portion to the ground. Furthermore, the system disclosed in said co-pending application is arranged so that grounding of the normal current path, when it is not broken, will result in alternating current flow in the ground path; incidentally tending to render dissimilar the succeeding ones of the rectified full-wave alternating current impulses in the normally closed path at respective sides of the ground.

Under certain operating conditions,-as, for example, when there is occasion for at times conducting telephonic communications through utilization of a circuit and current source which is also utilized for code signaling,-it is desirable to avoid application to such a circuit of an alternating current supply arranged pursuant to the teachings of either said prior patent or said copending application.

It is therefore an object of this invention to provide a signaling system operable from a source of continuous direct current, and having three or more conductors for association in various groups to provide a plurality of alternative current paths, and responsive devices associated with such conductors and such source in a relationship whereby breaks and closures between any two of such conductors will cause a suitable action of the responsive devices.

Another object of this invention is to provideimpairing the effectiveness of such signaling cir:

and

cuit for causing dependable response of the signal manifesting devices associated therewith.

Another object of this invention is to provide a signaling system comprising a circuit serially including central oflice manifesting and current 5 supply mechanism with a plurality of distributed initiating stations so that facilities will be provided, without alternative readjustments, for complete and correct manifestation at the central oflice of signals from all actuated initiating 10 stations, either when the conductors and apparatus of such system are in normal condition or when such conductors and apparatus are subjected to any of the following abnormal conditions; series circuit broken at any one or between 15 any two initiating stations; circuit grounded at any one or between any two initiating stations; wires crossed so as to shunt out any one, more or all initiating stations; broken ground connection at any initiating station or stations; concurrent signaling activity of any two initiating stations while the circuit is broken or grounded between such stations or at either one or both thereof; line wires crossed at opposite sides of one, more or all initiating stations and broken at any one point.

A still further object of this invention is to provide such a signaling system, in which there will be no objectionable current flow effect between the signaling circuit and an associated common return conductor, or the ground, due to capacitance therebetween.

An object of certain aspects of this invention is to provide such a signaling system which will accomplish such of the results just referred to as are needed for meeting special operating condi- "tions, without necessarily accomplishing all of such results. F

Other objects of this invention will be in part obvious and in part specifically set forth in the following specification.

Figure 1 is a diagrammatic representation of a signaling system embodying an aspect of this invention; 46

Fig. 1A is a simplified representation of the current paths of the system of Fig. 1.

Figs. 2, 3, 4, 5 and 6 are diagrammatic representations of portions of signaling systems similar to that of Fig. l, embodying other aspects of 50 this invention;

Fig. 7 is a detailed view of a compensating relay corresponding to the relays more diagrammatically indicated at K in Fig. 1 and at K in Fig. 2,

Fig. 8 shows a manner of connecting two or more compensating relays for cumulative effect.

Referring to the system of Fig. 1, the signal initiating stations A, B, C, D and E, each comprises facilities for at times effecting variations in the condition of an electric circuit, and in the relationship of such circuit to the ground or to some other common return conductor.

Examples of such facilities are diagrammatically indicated at stations A and C. Station A comprises the code signaling or pulsating contacts l6 and I1, and a contact 20 for at times connecting such contacts H5 and H to the ground CR. The contact ll nal wheel l8 in a manner usual to signaling stations of a type variously termed plain or interfering; in which the actuation of a starting handle causes a desired number of revolutions of a code signal wheel such as the wheel 18', with incidental signal formulation between respective sides of the line and the ground, irrespective of concurrent formulation of other signals. Station C comprises the code signaling or pulsating contacts PC and an emergency switch ES. Said contacts PC include the springs 62, 64, B1 and 68, operable by the arm 9| responsive to rotation of the code signal wheel l8, subject to control of electromagnetic mechanism represented by the magnet MM. Said switch ES comprises the springs 13 and 14 and the associated contactor 18, for at times connecting said springs 13 and M to one another and to the ground OR. The mechanism indicated at station C is, therefore, representative of a type of initiating station such as is frequently referred to as Perfect non-interference and succession.

A more detailed description of a signal initiating station such as indicated at C, embodying characteristics suitable for use in connection with this invention may be found in my co-pending application, Serial No. 573,150, filed November 5, 1931, to which reference is had, and in which reference characters similar to those herein employed denote mechanism corresponding to the contacts PC and the switch ES, and the parts thereof; however, this invention is suitable for use in connection with other forms of signaling stations which comprise facilities for effecting suitable variations in the condition of an electric circuit, and reference is herein made to my said co-pendin'g application merely as a means of conveniently illustrating one of a general type of signal initiating stations which may be employed in connection with this invention. In any event, it should be assumed that each of the stations A, B, C, D and E comprises mechanism whereby the wired or metallic circuit is normally maintained closed, but may be broken thereat, and whereby a common return conductor or the ground may be there conductively associated with the metallic circuit at certain times.

In constructing a signaling circuit in accordance with this invention, including a responsive instrument arranged and connected as the instrument EI of Fig. 1, if the initiating stations are of the so-called "Perfect non-interference and succession type having a ground connection rendered efiective only when the normal current path therethrough has remained shortcircuited or open for an extended time,-it is important that the mechanisms of such stations shall'be so arranged that the time which will elapse between the initial establishment of the ground connection and the first break incidental to signal formulation will not differ appreciably is operable by the code sigwhen line conductors from succeeding closures between line and ground incidental to the formulation of the signal. In other words, the manifestation of the code signal by an instrument such as EI may be objectionably distorted if some of the closures are appr'eciably longer than others, in the course of the formulation of code signals by making and breaking between line and ground while the normal current path remains closed. The reason for this will be hereinafter more fully explained.

Referring now to the so-called central station or ofiice equipment indicated within the boundary of the broken line CS, wherein the features which specially characterize this invention are more particularly found,--current supply mechanism is provided for applying a suitable electromotive force to the normally eifective or metallic circuit current path, and for applying a correspondingly suitable electromotive force between said path and the ground or other common return conductor. in the arrangement shown by Fig. 1, such current supply mechanism comprises the normally effective battery NB and its associated rectifier NR, together with the ground or common return path battery GB and its associated rectifier GR.

It will be apparent that primary battery cells may be employedrfor the batteries NB and GB, in which event the rectifiers NR and GR would not be required. It will the batteries NB and GB may be dispensed with, and the current supply obtained directly from the rectifiers NR and GR, in which event the signaling circuit current supply will be maintained only during effectivensss of the alternating current source associated with such rectifiers, and if there is a considerable capacity between the normally closed circuit and the earth, (as are comparatively large and are enclosed in a lead sheath) the charging current of the condenser thus formed may assume objectionable proportions, due to the pulsating character of the rectified alternating current.

Furthermore, it should be understood that various other forms of continuous direct current supply may be utilized in lieu of the batteries NB and GB. Thus, if either primary battery cells, or storage battery cells in association with rectifiers (such as the rectifiers NR and GR shown) are employed for the batteries NB and GR, all of the operating characteristics of the system will be maintained so long as such cells do not become unduly discharged, irrespective of interruptions of any alternating current supply utilized for charging the storage cells. On the other hand, if the ultimate current source is subject to interruption (as might be the case if energy from public service lines is exclusively relied upon) the operability of the system will be suspended in the event of interruption of such service, because of the absence of storage batteries or other equipment for maintaining the effectiveness of the current supply during interruptions of the normal'source.

Furthermore, if the batteries NB and GB are dispensed with and the current supply is obtained from the rectifiers NR and GR,conditions will not be favorable for telephonic communication over the exterior circuit, unless some means is utilized for rendering the otherwise pulsating rectified current practically continuous in character, as through utilization of some well-known form of filter. Correspondingly, in a system having a comparatively large electrostatic capacity between the normally closed line and the ground he further evident that or other common return conductor, or between a portion of such line situated at one side of one or more initiating stations and that at the other side of such station or stations, it is desirable that, if rectifiers are used, they be shunted by storage batteries as shown, or that other means he employed for correspondingly smoothing out the pulsations of the rectified alternating current, so as to avoid charging current flow of significant magntiude; other than such fiow as may be inevitable incidental to the breaks and closures of signal formulation.

If desired, a single battery may be utilized as indicated in Fig. 2, having one end terminals thereof connected to an end of the normal metallic circuit, and having the other end terminal thereof connected to the ground or other common return conductor CR; the remaining end of the normal metallic circuit being connected to such battery intermediate the end terminals thereof. If a battery utilized as indicated by Fig. 2 is of the storage type, both sections thereof may be charged from a single rectifier NR, as shown. Inasmuch, however, as the portion of such a battery situated between the terminals of the normal current path will ordinarily require application thereto of more energy than the portion associated only with the ground connection, through which there is normally little if any current flow, such last named portion may be partially shunted as by the resistor r. a

In lieu of the utilization of a single battery as indicated in Fig. 2, other forms of direct current potential sources may be utilized, as by employing well-known potentiometer connections, in which a two-conductor source is applied to the ends of the potentiometer resistance, one of the ends of such resistance being connected to an end of the metallic circuit and the other end of such resistance to the ground or other common return conductor; and the remaining end of the normal metallic circuit being connected intermediate the ends of the resistance.

For want of better terms, a current source embodying the combined characteristics of batteries NB and GB will, at times, be hereinafter referred to as a "divided potential source; and the extreme terminals of such a source will be referred to as the maximum potential terminals" and the remaining terminal will be designated as the intermediate terminal.

Referring again to Fig. 1,-a terminal t of the battery NB (indicated, for convenience, as the positive terminal thereof) is connected to external circuit terminal T" through conductor 2|, magnet winding 22 of line signal manifcs'ing'instrument LI, conductor 23, magnet winding 24 of supervisory relay F, conductors 25 and 25 to back contact 21 and thence through movable contact 28 of compensating relay K, with alternative path from conductor 25 through resistor 29 to said contact 28; thence through magnet winding 30 of said relay K, through conductor 3|, fixed resistance FR, conductor 32, adjustable resistance AR and conductor 33, to terminal T" of the 4|, the magnet winding 42 of manifesting instrument GI, resistor 43, and conductor 44 to conductor 44; and the other branch comprising the conductor 41' including the unilateral valve or rectifying unit IR" which is soconnected as to facilitate current flow away froin conductor 40,

the magnet winding 42 of manifesting instrument EI, and conductor 44" which joins conductor 44 of the first named branch at conductor 44', through which the path proceeds to terminal t of battery NB.

With the arrangement thus far described, it is evident that current flow through the conductor 40, in the direction induced by the electromotive force of the battery NB, will cause some current fiow through the winding 42 of instrument GI, due to the resistance of the rectifying unit IR and winding 42'. If the relationship between the resistance of the path through said unit and that through said winding 42 is such that the current flow under the condition just indicated through winding 42 is sufiicient as to adversely affect the operability of instrument GI, such current flow should be restricted by including a rectifying unit or asymmetric valve in series with the branch path through said winding 42, as, for example, the rectifying unit IR shown in conductor 4 l. f See also Fig. 3.)

If desired, a single unit unilateral valve assembly may be employed, embodying the charnals of such unit being connected to, respective conductors M and M, and an intermediate terminal of such unit being connected to the conductor 40.

In any event, the unilateral valve or rectifying equipment associated with the winding 42- of instrument GI of Fig. l, (as well as with the winding of a compensating relay, if one is associated with that side of the circuit, as relay K of Fig. 2),- should be so appliedv that the current flow through such winding or windings will be insuilicient to cause effective energization if in the direction induced by battery NB, but will be sufficient to cause effective energization if in the direction induced by battery GB.

The ground path battery GB is connected to the normally effective battery NB, in such polarity as to facilitate cooperation of said batteries at certain times, as hereinafter more fully pointed out; the negative terminal t of battery NB being shown as connected through conductor 45, winding 41 of ground supervisory relay 1 and conductor $9, with positive terminal t of battery GB; the negative terminal t of GB being associated through conductor 50 with the ground or other common return conductor CR.

The battery NB is connected with the charging rectifier NR through conductors 52 and 53;

and the battery GB is correspondingly connected with its charging rectifier GR through conductors 54 and 55. Rectifiers NR and GR are supplied by transformer secondary w.ndings 55 and 58, which are in turn excited by transformer primary windings 57 and 59, respectively.

The normally closed external circuit comprises the conductor 34 extending from central ofiice terminal T to station E, conductor extending from station E to station D; conductors 35, 31 and 38 correspondingly connecting stations D and C, C and B, and B and A, and conductor 39 extending from station A to central office terminal 'I".

As it may be assumed, for the purposes of this description, that the connections within the stations B, D and E are identical with that of either station A or that of station C,-only that of stations A and C will here be stated in detail.

acteristics of units IR and IR", the end termi- At station A, conductor 38 connects with contact I6, conductor 39 connects with contact I7, and conductor I9 connects contact 28 with the ground CR. Contact I1 is normally held in engagement with contact I6 by code wheel I8, but, while code wheel I8 is in its normal position, contact I6 is not raised high enough to bring it into engagement with contact. 28. During activity of the code wheel I8, each tooth thereof raises contacts I6 and IT to a point where contact I6 is brought into engagement with contact 28, so that during the impulses incident to en gagement of respective teeth of the code wheel I8 with the contact I1, current may freely pass from one to the other of conductors 38 and 39, or between either or both of such conductors and the ground or common return conductor I9. It will therefore be evident that during activity of a station, such as station A, incident to the engagement of each tooth of the signal wheel with the contact I I, the circuit will first be closed, then grounded as well as closed, and then broken as between the portions of the circuit at opposite sides of the box and between such portions and the ground.

At station C, conductor 36 connects with contacts 83 and 64, and conductor 31 connects with contacts 6| and 62. Contacts GI and 62 are normally connected with contacts 63 and 64 through shunting contact 8|. During activity of the code wheel I8, contact 8| is withdrawn so that, during closures between contacts 62 and 64 and contacts 81 and 68, respectively, current may pass from conductor 36,'through contacts 64 and 68, through non-interference magnet winding MM, through contacts 61 and 82 to conductor 31.

At times when contactor '18 engages contacts 73 and 14, the winding MM will be thereby shortcircuited, and current may then pass between I conductor 36, through contacts 64, 68 and 14, contactor I8, and the ground or common return conductor CR, and may correspondingly pass between conductor 37, through contacts 82, 61 and I3, and said contactor 18, and conductor CR.

The current path between conductor 36 and conductor 31 while contact 8| is separated from contacts GI and 63, as well as the current paths between respective ones of said conductors and ground CR, is dependent upon contacts 8'] and 68 being brought into engagement with contacts 62 and 64, respectively, regardless of the position of the contactor I8. Hence current will not flow through either conductor 36 or 31 at any time when contacts 8'! and 68 are away from contacts 82 and 64 incidental to the rotation of code wheel I8.

In practicing the aspect of this invention indicated by Fig. l, the current supply mechanism and the responsive instruments should be connected in a relationship substantially as there indicated, at least to the extent that responsive instruments, such as EI and GI with their respectively associated rectifiers IR and IR should be connected in parallel with one another and between one end of the external line and the terminal of the battery NB which is also connected to a terminal of the battery GB, and another manifesting instrument should be connected between the other end of the external line and the remaining terminal of battery NB.

Where service conditions are such that it is desirable that a special warning signal should be given in the event of rupture of the external circuit, suitable mechanism for such purpose should be connected for response to current flow through the normal path therefor; lay F, whose armature I8I tracted position by normal line circuit current flow, but whose armature moves into engagement with contact I82 upon interruption or reduction to more than a predetermined extent in normal current flow, to thereby establish a current path from battery I83 through bell I84, causing said bell to sound. correspondingly, if service conditions are such that it is desirable that a warning signal should be given in the event of more than a predetermined extent of impairment of the insulation between the line conductor and the ground, the relay 1 may be connected in the branch between the normal current path and the ground which includes the battery GB, the armature I85 of said relay being normally in retracted position but moving to attracted position whenever current fiow in the ground path exceeds a predetermined value, and thereupon engaging contact I88 to thereby establish a current path from battery I81 to cause bell I88 to sound.

The electromotive force of the battery NB should be such as will cause current of the desired strength to flow through the normally effective signaling current path. Such normal current flow should, pursuant to usual practices, be at least 50% in excess of the minimum current which will assure dependable response to intended signals of the normal line instrument LI as well as the emergency line instrument EI. It will be seen that in a system arranged as indicated in Fig. 1, the resistance of the normally effective current path will be the sum of the resistances of the magnet winding 22 of instrumentLL the magnet winding 24 of relay F, the magnet winding 38 of compensating relay K, the fixed resistance FR; such portion of adjustable resistance AR as may at the time be included in the circuit, the resistance of the exterior circuit comprising the conductors 34, 35, 36,31, 38 and 39 and the normally effective current paths within stations A, B, C, D and E, the resistance of the current path past the winding 42' and the rectifying unit IR" (as slightly reduced by the relatively high resistance connection afforded in parallel therewith because of the failure of the rectifier IR to fully block the flow of unintended current therethrough, which parallel path comprises the winding 42, resistor 43 and said rectifying unit IR) and whatever slight resistance there may be in the connections within the central ofltice, comprising conductors 2|, 23, 25, 26, 3|, 32, 33, 48 and 44.

as the supervisory reis maintained in at- The electromotive force of thebattery GB should be such as to provide current flow sufficient to assure efl'ective energization of the controlling magnet of instrument GI (with desired factor of safety), through an emergency path of maximum resistance which would ordinarily comprise the sum of the resistances of the winding 47 of supervisory relay 1, resistor 43, winding 42 of instrument GI, and rectifying unit IR (the resistance of the path past said resistor 43, winding 42 and unit IR being somewhat reduced by the relatively high resistance connection afforded in parallel therewith because of the failure of the rectifier IR" to fully block the flow of unintended current therethrough, which parallel path comprises the winding 42' and said rectifying unitIR"); together with the resistance of the external circuit comprising conductors 39, 38, 31, 36 and-35 as well as the resistance of the current paths normally effective through stations A, B, C and D; and the emergency signaling current path through station E, the resistance of the common return path, as from ground OR of station E to ground OR at the central oflice, and whatever resistance there may be in conductors within the central office such as 50, 49, 45, 44', 44, 4| and 40.

In determining the required electromotive force for battery GB, allowance should be made for whatever leakage will occur through rectifier IR", because of which the current flow through winding 42 may be somewhat reduced, although if a reasonably eflicient rectifying unit is employed such reduction may be barely appreciable. Allowance should also be made for such fall of potential as will result from the fact that the path from an active signaling station (say station E) through common return conductor CR from said station to and through conductor 50, battery GB, winding 41 and the other conductors of the current path to terminal t of battery NB, is traversed by the current flow through battery NB, and the path including conductor 34 to the active initiating station, as well as the current flow through the path including instrument GI and terminal T which paths are simultaneously effective in parallel one with the other.

Inasmuch as the fall of potential resultant from current flow through the ground path serves, under many emergency conditions, to decrease .the electromotive force available for causing current flow in a portion of the current path through signaling stations, it is very desirable that the resistance of the ground path be restricted to as low a value as circumstances permit. Otherwise, the current flow-resultant say, from an accidental ground-over the side of the circuit supplied by the batteries NB and GB acting in series, may cause so great a fall of potential in the ground path that the current flow in the portion of the circuit where caused by the potential of the battery GB (to the exclusion of the battery NB) will be insufficient, both for assuring signal formulation by positive non-interfering signaling stations of types heretofore used, and for causing dependable manifestation of such signals by a responsive instrument in such last named portion of the signaling circuit.

In a system in which the resistance of the external current path from the initiating station nearest to terminal 'I'" (as station E) to the station nearest terminal '1" (as station A) is such that there is likely to be an objectionable surge of current resulting from the cooperation of the electromotive forces of batteries GB and NB, when an emergency or common return connection is established at a station near terminal T (as station E) ,-compensating mechanism, such as is diagrammatically indicated at the relay K with its associated resistance 29, should be included in the current path which would be set up under circumstances such as those just referred to. This relay should be of type and adjustment such that its armature 28 will remain retracted so long as the current flow through its winding 30 remains below a predetermined value, continued current flow above which is deemed objectionable; but if such current flow is increased above that value, said armature will move, substantially instantaneously away from its normal or back stop 21, thus breaking the short circuit normally maintained around the resistance 29 prior to the time when current flow will have attained objectionable proportions.

In a system such as here contemplated, current flow attains a characteristic which, for want of a better term, will be hereinafter referred to as "detrimental force, when the combined effects of intensity and duration (1) cause heating of conductors, particularly-magnet windings, to such extent as to result in damage to or destruction of some conductor or its insulation; (2) cause disablement of the circuit due to melting of protective fuses; (3) cause development of magnetic flux such that armature retraction will occur only following current diminution of extent exceeding in detrimental degree that otherwise needful, and will not occur as promptly as following energization to not more than normal extent; (4) cause destruction of or damage to signal formulating contacts; and/or (5) cause damage to current supply mechanism.

In this connection, it should be remembered that the application of the available electromotive force to a current path of abnormally low resistance does not always irmnediately cause objectionable results. One of the reasons for this is that, due to the inductance of the electromagnet windings in a current path such as here under consideration, rise of current flow therein to full ultimate intensity is delayed by the inductance of such windings, and further delayed due to the effects of shortening the magnetic paths of such electromagnets, which shortening occurs incidental to movement of the associated armatures, (resultant to the attained excitation) to their attracted positions. Another reason is that detrimental heating of conductors, damage to current supply mechanism and detrimentally excessive excitation of electromagnet cores do not occur, even after attainment of maximum current flow, until after the conclusion of a brief but nevertheless appreciable time.

Furthermore, if the length of time during which abnormally great current flow may continue is in all instances less than so-called signaling closures, the code signaling contacts will never have occasion to act to break the circuit while such flow is occurring, and, therefore, will never be exposed to injury thereby.

For the foregoing reasons, compensating mechanism, such as the relay K, should be of such type that it will (1) act during the building up of current flow therein (as just explained) before such current flow has attained an intensity and maintained it for a time sufficient to cause injury, (2) act with increasing rapidity in proportion to greater rapidity of rate of increase of current flow, and (3) act with stability, 1. e., will not, after having rendered the compensating resistance effective, needlessly render it ineffective to thereby set up a so-called chattering" vibratory action, in the course of each cycle of which action the resistance will be rendered effective because the current flow is, for the moment, too great without it, and thereupon render it ineffective merely because of the diminution of current flow resultant from its having been rendered effective.

The resistance 29 should be of such value that the line current strength will be reduced, so long as said armature remains in attracted position, to a valuesuitably below that at which the armature of the relay was picked up. It is preferable that this relay further be of such type and adjustment that, when its armature has moved to attracted position, it will not thereafter drop away until the current flow therethrough is reduced to a value'appreciably below that to which such flow will be reduced responsive to inclusion of the resistance 29 in the current path through the winding 30 at a time when, without said resistance,

such current flow is at or about the value which causes the armature 28 to move to attracted position.

Physical characteristics and operative relationships of controlled resistances to associated current paths of relay structure or other current limiting devices (whether comprising a single de- "vice or a cascade of devices, as will be presently described in greater detail) will, for want of a better designation, be hereinafter referred to as stabilized or qualified asstabilizing.

For example, assuming that the battery NB has an electromotive force suitable for maintaining intended current flow in the normal metallic circuit, and that the battery GB has an electromotive force sufllcient to cause eflective energization of the electromagnet 42 of instrument GI in the event that a ground connection is established at the station through which there would be least current flow (which would doubtless be the station E of Fig. 1, if all ground connections are of substantially equal resistance) the compensating relay K and its associated resistance 29 may be omitted provided that the relative circuit resistances are such that, irrespective of which of the stations may have a ground connection established thereat, the current flow through battery NB, instrument LI, etc. would be insuflicient to be injurious to the current supply mechanism or conductors in that path, or to be in any way objectionable. If, on the other hand, the relative resistances of various circuit components are such that, under any such condition, the relatively high current flow for an appreciable length of time through the path indicated would be liable to attain detrimental force, one or more compensating relays, with their associated resistances should be supplied.

As already indicated, the resistance brought into effective relationship with the circuit through the movement of the armature of its compensating relay to attracted position, should not be so great that, if brought into the circuit at a time when the current flow is otherwise barely sufllcient to cause effective: energization of the magnet, such current flow will be thereby reduced below the desired normal operating value. If, however, the circuit characteristics are such that the inclusion of resistance sufiicient to prevent current rise to an extent which would be injurious or objectionable during establishment of a current path of minimum resistance would reduce the current flow to an objectionable extent if included in another current path, the resistance of which was such that, without inclusion of some compensating resistance the current flow therethrough would be injuriously or objectionably great,two or more relays should be arranged for inclusion of required resistance in a series of steps, whereby resistance will be added to prevent current rise injurious or objectionable in extent, while assuring that the amount of resistance thus added under any given condition will be insufllcient to objectionably reduce the current flow. A plurality of relays connected in accordance with Fig. 8 will accomplish the results just indicated.

In certain systems it may be found that objecti'onably high current flow will occur when the emergency current path is established at certain stations due to the external circuit being of exceptionally high resistance, in the sense that the resistance of that circuit between the initiating station nearest the terminal thereof corresponding to terminal T 0! Fig.1 (as station A) and the station farthest therefrom in said circuit (as station E) greatly exceeds the resistance of the magnet winding 42 of instrument GI, (taken with the added resistor 43, if used); because of which the current flow when the circuit is grounded at station A and the circuit is broken between such station and terminal T will be excessive, (it being of course assumed that the electromotive force of battery GB is suificient to assure adequate current flow through said winding 42 when the circuit is grounded at station E, without being broken) In such cases, the resistor 43 should be replaced or supplemented by a compensating relay, such as the relay K of Fig. 2, having'a suitable resistance 48 controlled thereby and for operation corresponding to that of relay K hereinbefore more fully described.

It should be understood that the representations employed in Figs. 1 and 2 of the compensating relays K and K are merely diagrammatically suggestive in form. In order to satisfactorily assure action of such relays such as will provide best results under certain operating conditions frequently met with in practical service, it has been found desirable that the armatures of such controlling relays should be permitted to move a substantial distance from their retracted positions before effecting interruption of the normal shunt around their associated resistances; or that movement of such armatures shall effect alteration of the relationship of the electromagnet winding; to the circuit, so that movement of the armature toward attracted position will render the magnet subject to stronger energization during current flow in the associated circuit of a given intensity, or that a combination of both of such expedients be employed.

An improved type of relay embodying a construction particularly suited for accomplishing the results just indicated is shown in Fig. 7, in which the armature I28 is movable between a back stop I21 and a front stop Hi1, and a movable contact 28 extends in the path of movement of said armature towards its stop I01; said contact 28 normally resting against a stationary contact 21. The relationship of these parts should be such that when said armature has moved away from its back stop I21 it will engage said contact 28 and move it away from contact 21 just before the movement of said armature is arrested by stop I01.

There should be such relationship between the associated resistance and the current strengths at which the armature will be picked up when retracted and will be permitted to drop away when in attracted position; as well as between the foregoing and the resistances of various portions of the circuit with which the relay is to be associated and the desired limits of maximum and minimum current strengths therein,--that the armature will leave its fully retracted position in which the magnet is shunted by its shunting resistance, if one is provided, as by resistance I08 of Fig-7, only when current flow exceeds a strength predetermined as the maximum it is desirable to permit in the circuit. That the compensating resistance (as the resistance 29) should bear such relation to the circuit resistance that when it is eifectively included in the circuit at a time when the circuit resistance otherwise effective would permit current flow of such strength as to cause the armature to move from fully retracted to attracted position; such inclusion of this compensating resistance will cause substantial decrease in the strength of current flow in the circuit, but

' the magnet of this relay will (through shortening the air gap and/or through having opened the shunt around the magnet winding) be enabled to retain the armature in attracted position notwithstanding diminution of current flow in the circuit resultant from such inclusion of the compensating resistance.

In the event that operating condition are such that it is desirable to restrict fluctuations in line current strength within closer limis than is practicable through use of single compensating relays applied as indicated in Figs. 1 and/or 2, as

might be the case in the event that the external line resistance is high in comparison with the resistance of the total normal circuit, especially if signal initiating stations are situated in the circuit, so close to the respective external line terminals that there is little if any resistance between such terminals and such stations;-such compensating relays should be arranged in groups of two or more, either at a location corresponding to that of relay K of Fig. l, to that of relay K of Fig. 2 or to those of both relays K and K in respective sides of the same line,-and the connection between the relays in each of such groups of relays should be arranged as indicated by Fig. 8.

Reference to this figure will show that the winding of magnet 30 of the left-hand relay is so connected as to be constantly responsive to the circuit, as is the case of the relays K and K of Figs. 1 and 2. However, the winding of the electromagnet of the righhhand relay of Fig. 8 is serially included in the current path through the compensating resistance 29 of the left-hand relay, so that when the armature of the left hand relay picks up and thereby positively includes its associated resistance 29, such action will also positively include the magnet 30 of the right-hand relay, in the current path of the portion of the circuit associated therewith.

If more than two relays are provided, the magnet winding of one of them should be directly connected in the line, as in the case of the winding of magnet 30 of the left-hand relay of Fig. 8. the winding of the magnet of a second relay should be associated with the resistance as of such first relay as indicated in Fig. 8, and the.

magnet winding of the third relay should be correspondingly associated with the resistance 29 of the second relay; additional relays being correspondingly connected so that the winding of each relay (except that of the first one of the series) is serially connected with the compensating resistance of another relay, to be rendered responsive to the circuit only after such other compensating resistance has been effectively included therein.

With an arrangement such as that just indicated, it is evident that if all of the relays are set to pick up at a given current strength,-- whenever the line current strength exceeds such setting, one of the relays will pick up (the one always directly responsive to the circuit, as in the instance of the left-hand relay of Fig. 8) and if the inclusion in the circuit current path of the compensating resistance associated with that relay results in decreasing the line current strength to a value less than the pick up value of the second relay, the armature of the second relay will remain in retracted position, although its winding will be connected in responsive relationship to the circuit. If, however. the current flow in the associated portion of the signaling circuit remains above that at which the second'relay will pick up, after the inclusion in the path of such current flow of the resistance associated with the first relay,the armature of the second relay will pick up and thus cause its associated resistance to be efiectively included in such circuit current path. Obviously, if there are more than two relays, the picking up of arma tures of additional relays will correspondingly follow, in rapid sequence, until the effect of the sum of the associated compensating resistances thus effectively included in the circuit current path has been suflicient to prevent current flow in excess of that required to cause the picking up of the armature of the next relay of the series (unless all of such relays have already picked up).

In a signaling system comprising a number of box circuits, each such as that indicated by Fig. 1, a single ground current path battery GB may be utilized in common by all of such circuits. the conductors corresponding to wire 49 of Fig. 1 of each such other circuits being connected to terminal t of such common battery GB, as through conductor 5i.

The operationof a signaling system such as that shown by Fig. 1 is as follows:

Under normal conditions, current flows from terminal t of battery NB, throughconductor 2|, magnet winding 22, conductor 23, magnet wind ing 24, conductors 25 and 28, shunting contacts 21 and 28 or relay K, winding 30 of said relay. conductor 3!, fixed resistance FR, conductor 32. adjustable resistance AR, conductor 33, tcrml' nal T". conductor 34. station E, conductor 35. station I), conductor 88, contacts 63, 8| and 6 of station C, thence through conductor 31, through station B, through conductor 38, through contacts i8 and H or station A, conductor 3!). terminal T, conductor 40, rectifier IR" (aside from a negligible current flow in parallel with said rectifier, through conductor 4!, magnet winding 42 and resistance 43) thence through conductor 4|, magnet 42, conductor 44", and conductor 44 to terminal t of battery NB.

As a result of such current flow, the electromagnets 22 and 42' of instruments LI and EL respectively. and the magnet 24 of supervisory relay F will be effectively energized. Said instruments LI and E1 will thereby be conditioned for response to any interruption in such normal current flow, and armature ml of relay F will be held in attracted position, thereby silencing bell I04. The electromagnet 42 of instrument GI will not be effectively energized, however, as nearly all of the line current will be shunted around said relay through rectifying unit IR" and magnet 42' of instrument EI.

Inasmuch as the ground or common return connections are normally open at the initiating stations A, B, C, D and E, and the external circuit is normally insulated therefrom, there will be no current flow from battery GB, and the magnet 41 of supervisory relay I will therefore be deenergized, and its armature I05 will be retracted, thus breaking the current path through bell Hi8.

If, now, say at the initiating station C, contact 8| is withdrawn from contacts SI and 63 and code wheel I8 is rotated,-the current path just traced will be alternately broken and closed, thereby causing intended response of instruments LI and EI, and causing bell I04 to sound.

While the normal current path just traced is 18 is brought into engagement with its associated contacts 13 and I4, and the code wheel I8, is rotated,-even if the contact 8| has not been withdrawn from the contacts 8| and 83 and/or there is a short-circuit around the active station (as would be the case were conductors 36 and 31 accidentally connected or crossed when station C was active) the signal of such station will nevertheless be responded to by instruments GI and EI because of reversal of direction of current flow through the portion of the normal circuit including these instruments, due to establishment of an emergency path as follows: from terminal i of battery GB, through conductor 49, winding 41 of supervisory relay 1, conductor 45 to terminal t of battery NB, from whence there are two current paths effective to the active station, one of which paths does not directly affect the response of instruments GI and EI as it traverses battery NB, winding of instrument LI and conductor 34, but the other path comprises conductors 44' and 44, resistor 43, winding 42 of instrument GI, conductor 4| and rectifier IR (around which resistor and winding there may at most be a slight leakage current through rectifying unit IR", efiective energization of magnet 42' being therefore terminated), thence through conductor 40, terminal T. conductors 38, etc., and inactive stations to contact 62 of the active station, thence through said contact, the associated contact 13 and conductor 18 to common return conductor OR at such station, and through the earth to CR at the central station and thence through conductor to terminal t of battery GB. The resultant current flow through the path last described will cause effective energization of supervisory relay f, the armature I85 thereof will thereupon engage its associated contact I06 and cause bell I 08 to sound, the previous efiective energization of the agnet 42' of instrument EI will be terminated, and the magnet 42 of instrument GI will become effectively energized. Thereafter, the rotation .of the code wheel l8 of the active station will cause such current path to be alternately broken and closed between contacts 82 and 61, (and correspondingly between contacts 64 and 68) thereby causing intended response of instruments EI and GI.

If, in the system of Fig. 1, the circuit is broken to the right of an active station (as would be the case were the conductor 34 ruptured) the code signal of such station would nevertheless be responded to by the instrument GI, due to the formulation of such signal in the portion of the emergency current path comprising the second described one of those just referred to.

If, on the other hand, the normal current path were broken to the left of an active station, (as in the event of rupture of conductor 39) the signal of such active station would be responded to by instrument LI through the current path established by such an active station, which includes both the batteries NB and GB acting in series, as well as said instrument LI. Decrease of the resistance in the signaling current path incidental to activity of station E, in the course of which the emergency current path was established as just referred to, would tend to cause the line current strength to increase above normal to an extent suflicient to cause effective energization of the magnet 30 of compensating relay K; so that the armature 28 of such'relay would a move to attracted position and thus break the 'normal current path situated in Fig. 1 to emergency current path thereby established will exclude the resistance of that portion of the left of station E, which portion includes conductors 35, 38, 31, 38 and 39, as well as the resistance of the path through instrument EI.

It will, therefore, be evident that application of the electromotive force of the batteries NB and GB (acting in series) to this current path of greatly decreased resistance, will tend to cause the line current strength to rapidly increase above normal. When, in the course of such increase, eifective energization of the magnet of compensating relay K is thus effected, the armature of said relay will move away from its back stop contact I21 (see Fig. 7) and thereby cause marked acceleration in its speed of move-- provided,the resistances 28, 29 of such relays will be consecutively included in the newly established current path, in rapid succession. If more than two such relays are provided, their respective resistances and magnet windings willbe correspondingly included in rapid succession, thus arresting and limiting the extent of the increase in current strength due to such signal closures.

Upon occurrence of each of the circuit interruptions following such respective signaling closures, the armature or armatures of the compensating relay orrelays will move to retracted position, and there remain until thenext succeeding closure; whereupon, as current flow builds up at the commencement of each such closure, the compensating relay or relays will act insofar as.may be necessary to arrest the building up of current flow, and/or to cause reductions therein, well in advance of the action of the formulating mechanism to terminate the closure, and before any condition has developed whereby there will occur damage to or destruction of insulation or conductors (including magnet windings, current supply mechanism, resistances and fuses) or whereby electromagnetic flux will build up to a density so great as to be inimical to einciency and dependable operation.

From the foregoing it will be apparent that should the external circuit be broken, and a station at one side of the break or the other be short-circuited, the signal of such station will be received by the appropriate one of the responsive instruments, over a current path the same as would be in effect were the line broken but such station not shortcircuited. For example, if the conductor 31 was ruptured, signals from stations A and B would be responded to by instrument GI and signals from station C, D or E would be responded to by instrument LI, irrespective of the whether the conductors leading to such stations were short-circuited.

Furthermore, if the entire external circuit was shounted out, as by an accidental connection between conductors 34 and 39, or the connection of a jumper wire between terminals-T and T",instrument GI would respond to any one of the initiating stations the same as if such station was individually short-circuited or shunted out; and compensating relay K (if used) would act to suitably limit the extent of resultant increase in line current strength.

It will be still further evident that should the external circuit be broken (as by the rupture of conductor 31) if signaling stations are concurrently or simultaneously operated at opposite sides of such break (as, for example, stations A and C) the signal of one of such stations will be responded to by instrument GI and the signal of the other of such stations by the instrument LI; and the responses to such respective signals will be as clear and complete as if but one or the other were acting alone.

Should a connection be established between the external circuit and the ground, through a comparatively high resistance, a condition might be thereby developed such that neither the instrument LI nor the instrument GI would be caused to respond to the operation of a station situated in the circuit between such connection and the terminal T, if the mechanism of such station was of a type similar to that indicated at station C. For example, assuming that such a high resistance connection is established at X between conductor 36 and the earth, the resistance of such connection being such that if the circuit is broken to the left thereof (as at station C), the current flow through such accidental leakage would be sufficient to prevent response of the instrument LI to the resultant partial interruption of the circuit at station C. Nevertheless, the current flow through station C might well be of sufficient magnitude to cause effective energization of its magnet MM, so that its contactor 18 would not be released and the ground connection at such station would not become effective; In such an event, it is evident that the instrument LI would not respond to the operation of station C, and it is further evident that the instrument GI would not respond thereto because such current flow as was maintained in the portion of the circuit situated at the left of the accidental ground leakage would not be in such direction as to cause response of the instrument GI.

In a system having stations with characteristics just indicated, and having operating conditions such as to permit development of such a high resistance leakage path, an instrument such as EI should be provided to assure response to signals under conditions such as just indicated, as this instrument is so associated with the circuit that it will respond to breaks and closures of current flow in the normal direction.

Where the conditions of service are such that provision need not be made for development of high resistance ground leaks, the instrument EI need not be used, as either the instrument LI or the instrument GI will then respond to all signals.

Furthermore, if the mechanism at the signaling stations is of a type such that a ground connection is established incident to every closure in the course of the formulation of all signals (irrespective of the normally closed circuit being unbroken other than incidental to the formulation of the signal, as is the case when station mechanism such as shown at station A is used) the instrument EI will not be needed. For example, assuming the'existence of an accidental ground leak X such as would prevent response of either the instrument LI or the instrument GI to mechanism such as that at station C,-if mechanism such as that indicated at station A is operated, each closure to ground incidental to the formulation of the signal thereat will cause response of instrument GI irrespective of the extent of leakage to ground, as at X.

In connection with the description of the mechanism at station C, it has hereinbefore been mentioned that it is desirable that the mechanism employed at signaling stations shall be so arranged that there will be substantial uniformity in the duration of all closures between line and ground (as when a short-circuited initiating station is formulating a signal between line and ground). If such isnot the case, the operation of a short-circuited initiating station may result as follows Assuming that initiating station C of Fig. 1 is short-circuited, and, after being set in motion, applies its ground connection through movement of the contactor- 18 into engagement with the contacts 13 and 14 at a stage in the rotation of the wheel [8 such that the first break of the signal will not occur until a time has elapsed much greater than that during subsequent closures of the signal,-upon the ground connection being thus rendered effective, the current flow through conductors 39, 40 and 44 will cease to be in the direction induced by the normal battery NB and, instead, will be in the opposite direction asv induced by the ground battery GB. Such reversal in direction of current flow will cause deenergization of the electromagnet 42 of instrument EI, and will cause energization of the electromagnet 42 of instrument GI. When the current path thus established is then broken (as by the opening of the contacts 62-61 and 64-68) the magnet 42 of instrument GI will be deenergized.

Such action will be repeated, as a result of each of the succeeding closures incident to the formulation of the code signal of the active station. Upon each ensuing deenergization of the magnet 42' of instrument EI, such instrument will act to manifest a signal stroke. The same will be true of instrument GI.

It is evident that because the'instrument EI would respond to closures of the ground current path, instead of breaks, the first response would, under the condition just described, precede the first break by an interval greater than that which would occur between the responses to succeeding closures and the ensuing breaks; so that, if the code signal of the active station was 35, the manifestations of instruments EI and GI would be spaced as follows:

(E1) s eeve *we aeeee On the other hand, if all closures are of substantially the same duration, although the stroke (E1) coop cacao (GI) one emcee In the first instance, the signal as given by instrument EI would be likely to be interpreted as 1- -25, while in second instance it would clearly be 35.

It should be noted that the electromotive forces of batteries NE and GB need not be identical. But, in any event, such resistances as are permanently in the respective sides of the circuit, (such as that of winding 22 added to that of winding 24, fixed resistance FR and adjustable resistance AR, with compensating relay winding 30 and resistance 29, if used, in the right-hand side of the line; and winding 42, resistance 43 and/or compensating relay K. and resistance 43', if used, in the left-hand side of the line) should be proportioned to suitably limit current flow under various conditions, as hereinbefore more fully explained.

It should also be noted that the instruments in the left-hand side of the line (such as GI) may be arranged for response to higher or lower current strength than those in the right-hand side of the line (such as LI).

Thus, for example, in a system in which the initiating stations are equipped with non-interference magnets intended for use in a circuit having the usual normal line current of 0.100 ampere, the central ofiice instruments in the right-hand side of the line and the associated resistances should be arranged and proportioned to provide a normal operating current on the order of such 0.100 ampere. On the other hand, if the mechanism at such initiating stations does not depend for intended operation upon effective energization of a non-interference magnet when operating over the emergency path (as is true with the station mechanisms hereinbefore referred to and indicated in Fig. 1), the instruments in the left-hand side of the line (such as GI) might be arranged for operation at a different current strength, for example, 0.020, 0.050 or 0.075 ampere. If, however, a responsive instrument such as E1 is provided, it should be arranged to act in response to current strengths substantially corresponding to, or somewhat below, those to which instrument LI will respond, irrespective of the operating characteristics of the instrument such as GI.

If the instrument such as GI is suited for operation at reduced current strength, the sum of the resistances of 42 and 43 (and/or 30 and 48 of compensating relay K if used) may be substantially higher, and the electromotive force of battery GB may be lower.

If desired, a responsive instrument may be included in the common return or ground connection at the central oflice, as indicated at CRI in Fig. 3; and such an instrument would not respond to signals received over the normal current path, but would correctly respond with either instrument LI or GI (as the case might be) in the event of a signal being received over either side of a broken line or from a shunted out station. However, should the external circuit be broken, and stations be concurrently active at opposite sides of the break, an instrument connected as CRI would respond to all impulses of both of such signals, and this would be likely to prove objectionable under certain operating conditions. Furthermore, an instrument connected as CRI would be responsive to current flow resultant from surges of potential between the circuit and ground such, for example, as those likely to be experienced during electrical storms. As is well understood by those skilled in this art, instruments responsive to current flow in the central oflice ground connection of a signaling circuit which is otherwise ungrounded, are likely to be caused to give signal manifestations upon an objectionably large number of cocasions. when instruments connected such a LI, GI and EI would remain inactive. In instances in which such external circuits are not subject to externally produced potential surges between circuit conductor and the 'earth, or under other operating conditions, an instrument connected as CRI might be considered advantageous, inasmuch as it would enable the attendant to more readily differentiate between signals received over the normal circuit and those received over an emergency current path.

Fig. 3 also shows an alternative arrangement of current supply, in which a battery RB is connected in opposing series with the battery NB; so that the electromotive force of the battery NB should be such that it will maintain the desired normal current strength through the entire normal signaling path, notwithstanding the counter-electromotive force of the battery RB.

With a current source arranged as indicated in Fig. 3, the battery NB may consist of either primary or secondary cells and/or a rectifier such as the rectifier NR of Fig. l. The current source RB should preferably consist of storage cells, but may consist of a rectifier connected in corresponding polarity and shunted by a suitable resistance 65 as indicated in Fig. 5. In any event such source RB should provide an electromotive force sufilcient to cause effective energization of the controlling magnets of instruments such as GI and CRI whenever any portion of the external circuit having unbroken connection with terminal T is connected with the common return conductor or ground;

The arrangement of Fig. 3 is not suited to all operating conditions, but may be used where, the resistance of the external circuit is low in comparison with that of one side and the other of the circuit inside of the central ofiice, and where the resistance of the ground or other common return conductor between. all stations and the central office is dependably maintained at a suitably low value. Unless conditions such as those just referred toare favorable, the dependability of response of instrument GI to signals received over an emergency pathparticularly those from a shunted out boxis distinctly less in a system arranged as indicated in Fig. 3 than in a system arranged according to Fig. 1 or 2.

The arrangement of Fig. 4 utilizes batteries such as NB and RB of Fig. 3 together with a battery in the central ofiice common return conductor such as GB of Fig. 1. It would appear that, aside perhaps from some exceptional operating condition, the arrangement of "Fig. 4 would be less advantageous than that of Fig. 1, on account of the higher electromotive force required for battery N3 in order to overcome the counterelectromotive force of battery RB.

The arrangement of current supply in Fig. 5 is substantially identical with that of Fig. 4, except that rectifiers NR, RR and GR. are utilized in lieu of the batteries NB, RB and GB respectively. In the instances of both Figs. 4 and 5,

greater detail with reference to Fig. 1, other than in the differing respects already explained.

Fig. 6 shows an aspect of this invention pursuant to which its desired objects may be attained in systems having a comparatively low resistance external line and in which it may be confidently assured that the resistance from the various initiating stations to the central oifice, through the ground or common return conductor will at all times be suitably restricted.

Pursuant to this aspect of this invention, the battery NB has terminal t thereof connected through conductor 2| to one end of winding 22 of instrument LI, and the other end of said winding is connected by conductor 23 to an'external circuit terminal corresponding to T. of Fig. 1, through desired relays and resistances (as, for example, in accordance with Fig. 1), and said terminal i is also connected through conductor 89 to one end of a winding 81 of instrument G1, the other end of which winding is connected to terminal T of the external circuit through conductor 48.

Terminal t of current source NB is connected to common return conductor or ground CR, and is also connected through conductor 44" to one end of a second winding 88 of instrument GI, the other end of which winding is connected with an end of winding 81 to conductor 48.

Windings 81 and 88 are so applied and connected that, under normal circuit conditions, one winding substantially neutralizes the other, and so that the current flow from terminal t through conductor 89, winding 81, winding 88 and conductor 44" will not cause effective energization of the electromagnet of said instrument GI; but in the event that the winding 88 is short-circuited or by-passed by a shunt of low resistance, the current flow through winding 81 will cause efiective energization of the controlling magnet of said instrument GI.

From the foregoing it will be apparent that if an initiating station, such as the station C of Fig. 1, is connected between conductor 23 and terminal T' of Fig. 6,operation of such station under normal circuit conditions (with contactor 18 withdrawn from contacts 13 and 14) will cause response of instrument LI, through breaking and closing the current path therethrough. Operation of such station will cause like response of said instrument LI in the event of a break in the circuit between such station and terminal T, and will cause operation of instrument GI in the event the circuit is broken between said station and conductor 23 as well as in the event that such stat-ion is short-circuited and the circuit is otherwise in normal condition.

If operating conditions are such that the ground or common return conductor resistance may be so great as to impair reliability of or prevent response of instrument GI, through failure to sufiiciently deenergize magnet 88 incident to closures between the external circuit and the ground when the external circuit is not broken, dependable operability may be insured by inclusion in the conductor 50 of a supplemental current source such, for example, as the sources GB or GR indicated in Figs. 1, 2, 4 or 5. The potential of such supplemental current source need merely be sufiicient to assure diversion of line current flow through the ground or common re turn connection, and thereby eiiect a sufiicient degree of deenergization of the Winding 88.

For want of better designations, instruments associated with unilateral valves, embodying polarized electro-magnets, or otherwise conditioned for functional response to current flow in but one direction, may be referred to as "biased; and instruments connected or constructed for response to current flow in either direction as unbiased.

The effect of differences in relationship, within the circuit, of responsive instruments to active initiating stations may be illustrated by examples asfollows:

Unbiased responsive instruments may be included in the signaling circuit at any point, and will there respond to all signals the formulation of which is accomplished merely by effectively breaking and closing the normal signaling current path; that is, without utilization of the ground or other common return path. On the other hand, during emergency operating conditions in which the ground or common return path is utilized, the ability of such an instrument to correctly respond to code signals will be effected by the position in the circuit of the active initiating station with relation to the instrument so included, as well as such bias, if any, 'as may be imparted to the instrument for response to current flow in one direction or the other.

Correct response of an unbiased instrument to signal formulation which involves utilization of the ground or common return path, will be assured only in the event that there is an effective current path from the active initiating station through such responsive instrument to the ungrounded terminal of the normal current path battery (as terminal t of battery NB in Fig. 1) and hence that the active initiating station is situated in the circuit between such instrument and the grounded terminal of the normal current path battery (as terminal t of battery NB in Fig. 1). Thus, if the current path from the active station to the ungrounded terminal of the normal battery is broken, it is obvious that a responsive instrument in that path will not act.

On the other hand, if such an unbiased rcsponsive instrument is included in the signaling circuit between an active station and the ground-. ed terminal of the normal battery (for example,

in conductor 39 of Fig. 1) such instrument willcorrectly respond to the signal of any station situated in the circuit between it and the ungrounded terminal of the normal battery only in the event that the circuit stands broken between such active station and such ungrounded terminal (provided, of course, that the'circuit is not broken between the active station and the grounded terminal).

In other words, it should be understood that not only would such an instrument which is so located fail to respond to an active station if the circuit was broken between such station and the grounded terminal of the normal battery, but the response of such instrument would be likely to be confused and unintelligible if the active station was effectively breaking and closing the connection between respective sides of the circuit and the ground. The reason for this may be explained as follows: Assuming that an unbiased instrument was serially included in conductor 39, 48 or M of Fig. 1, and that a station having mechanism such as indicated at station A was operated; during the ungrounded portion of each resultant closure, current would flow through such instrument in the direction induced by the normal battery, thus causing energization .of the controlling magnet of such instrument. Then, when the ground connection-was closed, current flow would momentarily cease incidental to reversal, and such instrument would thereupcnact as in response to current cessation from any other cause, and its magnet would thereupon be reenergized in response to current flow induced "therethrough in the opposite direction by the bat- (Extra instrument) t I i F The result would be the same wherever the instrument was connected in the circuit, so long as it was between the active station and the grounded terminal of the normal battery, as, for example, if it was connected in conductor 35, 36, 3'! or 38 when station E of Fig. 1 was acting, if

the mechanism thereat was such as is indicated at station A.

The action of a correspondingly situated unbiased instrument in response to signal formulation between an unbroken circuit and the ground (as in the instance of a short-circuited station) would be correspondingly unsatisfactory; irrespective of whether the mechanism of the station had functional characteristics such as that shown at station A or station C.

If additional biased responsive instruments such as EI or GI are connected in the circuit, the response of such instruments will correspond to that already described for the instruments EI and GI shown, as to initiating stations situated in the circuit between such instruments and the ungrounded terminal of the normal battery; but instruments having the functional characteristics of instrument GI will not respond to initiating stations situated in the circuit between such instruments and the grounded terminal of the normal battery.

While certain specific embodiments of this invention are shown in the accompanying drawings and hereinbefore described in considerable detail, it should be understood that this is illustrative only, and for the purpose of making clear the nature and objects of this invention, and that the invention is not regarded as being limited to these details, nor to any of them, except insofar as such limitations are included within the terms of the claims, in which it is intended to cover all of the generic and specific features of the invention hereindescribed and all statements of the scope thereof, which, as a matter of language, might be said to fall therebetween.

I claim:

1. In a signaling system, the combination of central ofiice and external elements, said central office elements comprising unidirectional current supply means, a current limiting device including an electromagnet, code signal responsive devices one of which is biased for response to current flow in one direction only, and interconnecting conductors, said external elements comprising initiating stations each including means for formulating code signals in a normally closed path and for establishing a connection between said path and a channel normally independent of such path, together with conductors providing a normal path serially connecting said initiating stations and having the path ends at said central omce and providing a ground or common return path with associated parallel channels from respective stations; said central office interconnecting conductors providing a first and a second connection for linking said supply means with the respective ends of said normally closed external path, said limiting device operatively associated with said second connection, said first connection having said biased signal responsive device associated therewith for response to current flow in a predetermined one direction, another of said signaling devices connected for response to current flow in said second connection, said central ofifice conductors also providing a third connection for linking said supply means withsaid external ground or common return path; said current supply means of such character as to apply an electromotive force between said first and second connections suitable for assuring current flow through said connections and said normal path of non-detrimental force and of strength adequate for causing response of said signal devices to code signals formulated in said path, and to apply an electromotive force between said third and second connections such as will result in current flow of detrimental force upon establishment of current paths therebetween of least resistance incidental to establishment of any possible path between said normal path and said ground or common return path, said current supply means further of such character as to cause current flow through said first connection resultant from. establishment of a current path therefrom to said second connection of direction to cause response of said biased device and establishment of a current path between said first and third connections will result in current flow of opposite direction, said current limiting device characterized by means rendered efiective only responsive to energization of its associated magnet such as results from current flow exceeding, to a predetermined extent, that resultant from normal closure of said external closed path, for limiting current flow to non-detrimental force through said second connection.

2. In central office equipment for a signaling system comprising an external ground or common return conductor and an external normally closed path for serial connection of code signal initiating stations-the combination of current supply mechanism having three terminals to-' gether with means for urging unidirectional current flow from a first to a second one of said terminals and from said first to the third of said terminals as well as from said second to said third terminal, two stabilized current limiting devices each including an electromagnet, code signal responsive devices one of which is biased for response to current flow in one direction only,

a first connection from said second terminal and a second connection from one of the other of said terminals, said first and. second connections for association with the respective ends of such an external path, said limiting devices operatively associated with said connections, respectively, said first connection having said biased signal responsive device associated therewith for response to current flow in a predetermined direction,another of said signal responsive devices connected for response to current flow in said second connection, and a third connection from the remaining one of said supply mechanism terminals for association with said external conductor; said current supply'mechanism of such character as to apply an electromotive force between said first and second connections suitable for assuring current flow through an intended normal path of non-detrimental force and of strength adequate for causing response of said signal devices to code signal formulation, and to apply electromotive forces between said third connection and respective ones of said first and second connections such as would result in current flow of detrimental force upon establishment of current paths therebetween of least resistance incidental to establishment of any possible path between such a ground or common return conductor, said current supply mechanism further of such character as to cause current fiow through said first connection resultant from establishment of a current path therefrom to said first connection of direction to cause response of said biased device and establishment of a current path between said first and second connections will result in such current flow of opposite direction, each of said .current limiting devices characterized by means rendered effective only responsive to energization of its associated magnet such as results from current flow exceeding, to a predetermined extent, that of said signal-device-response-assuring-strength, for limiting current fiow to non-detrimental force through the connections with which said current limiting devices are respectively associated, each of said current limiting devices also characterized by means, including its electromagnet, for continuing operative conditioning of its said electromagnet notwithstanding such current flow limitation.

3. In central ofi'ice equipment for a signaling system comprising an external ground or common return conductor and an external normally closed path for serial connection of code signal initiating stations,-the combination of unidirectional current supply mechanism having three terminals together with means for urging unidirectional current fiow from a first to a second one of said terminals and from said first to the third of said terminals as well as from said second to said third terminal, two current limiting devices each including an electromagnet, code signal responsive devices one of which is biased for response to current fiow in one direction only, a first connection from said second terminal and a second connection from one-of the other of said terminals, said first and second connections for association with the respective ends of such an external path, said limiting devices operatively associated with said connections, respectively, said first connection having said biased signal responsive device associated therewith for reponse to current fiow in a predetermined direction, another of said signal responsive devices connected for response to current flow in said second connection, and a third connection from the remaining one of said supply mechanism terminals for association with said external conductor; said current supply mechanism of a character for applying an electromotive force between said first and second connections suitable for assuring current flow through an intended normal path of non-detrimental force and of strength adequate for causing response of said signal devices to code signal formulation, and to apply electromotive forces between said third connection and respective ones of said first and second connections adequate for causing current flow of detrimental force upon establishment of current paths therebetween of least resistance incidental to establishment of any possible path between such an external normally closed path and such a ground or common return conductor, said current supply mechanism further of a character for causing current flow through said first connection resultant from establishment of a current path therefrom to said third connection of direction for causing response of said biased device and of a character for causing current flow of opposite direction from establishment of a current path between said first and second connections, each of said current limiting devices characterized by means rendered effective only responsive to energization of its associated magnet such as results from current flow exceeding, to a predetermined extent, that of said signal-device-response-assuring-strength, for limiting current flow non-detrimental force through the connections with which said current limiting devices are respectively associated,

4. In central oflice equipment for a signaling system comprising an external ground or common return conductor and an external normally closed path for serial connection of code signal initiating stations,the combination of unidirectional current supply mechanism having three terminals together with means for urging unidirectional current flow from a first to a second one of said terminals and from said first to the third of said terminals as well as from said second to said third terminal, a current limiting device including an electro-magnet, code signal responsive devices one of which is biased for response to current fiow in one direction only, a first connection from said second terminal and a second connection from one of the other of said terminals, said first and second connections for association with the respective ends of such an external path, said limiting device operatively associated with said second connection, said first connection having said biased signal responsive device associated therewith for response to current flow in a predetermined direction, another of said signal responsive devices connected for response to current flow in said second connection, and a third connection from the remaining one of said supply mechanism terminals for association with said external conductor; said current supply mechanism of a character for applying an electromotive force between said first and second connections suitable for assuring current flow through an intended normal path of non-detrimental force andof strength adequate for causing response of said signal devices to code signal formulation and for applying an electromotive force between said second and third connections adequate for causing current flow of detrimental force upon establishment of a current path therebetween of least resistance incidental to establishment of any possible path between such an external normally closed path and such a ground or common return conductor, aid current supply mechanism further of su character for causing current flow through said first connection resultant from establishment of a current path therefrom to said third connection of direction for causing response of said biased device andof a character for causing current flow of opposite direction from establishment of a current path between said first and second connections, said current limiting device characterized by means rendered effective only responsive to energization of its associated magnet such as results from current flow exceeding, to a predetermined extent, that of said signal-device-response-assuring-strength, for limiting current flow to non-detrimental force through said second connection.

5. 11128. signaling system-the combination of unidirectional current supply mechanism, conductors and code signal initiating stations whereby a normal current path and a plurality of emergency current paths of diverse characteristics may be established for causing current flow in one of the conductors forming part of said normal path in one direction during establishment of said normal path only and in the opposite direction during establishment of a certain one or more of said emergency paths and whereby another of said conductors which forms part of said normal path will also form part of each of the remainder of said emergency paths and will be excluded from said certain one or more of said emergency paths, in combination with signal instruments one of which is associated with said first named conductor and biased for response only to current flow therethrough in said opposite direction and another of said instruments is responsive only to current flow in said other conductor.

6. In a signaling system-the combination of 7 code signal initiating stations, unidirectional ourrent supply mechanism and conductors associating said stations and mechanism to provide a normal current path serially connecting said stations and to provide for establishment at respective stations of emergency current paths, each of one or more of said emergency paths including a certain one of those conductors which form part of said normal path whereby current flow in said conductor will be in one direction during establishment of said normal path only and in the opposite direction during the establishment of any of said one or more emergency paths, signal responsive instruments in parallel paths serially connected with said conductor, and means opposing current flow in one.direction through one of said instruments and facilitating such current flow around such instrument and through the other of said instruments while facilitating current flow in the opposite direction through said first named instrument and opposing such current flow around said first named instrument through said other instrument.

7. In a signaling system,-the combination of code signal initiating stations, unidirectional current supply mechanism and conductors associating said stations and mechanism to provide a normal current path serially connecting said stations and to provide for establishment at respective stations of emergency current paths, each of one or more of said emergency paths including a certain one of those conductors which form part of said normal path, and to provide current flow in saidconductor in one direction during estabany of said one or more emergency paths, code signal responsive mechanism having a winding serially connected with said conductor, and means for diverting current flow of said first named direction around said winding.

8. In a signaling system-the combination of code signal initiating stations, unidirectional current supply mechanism and conductors associating said stations and mechanism to provide a normal current path serially connecting said stations and to provide for establishment at respective stations of emergency current paths, each of one or more of said emergency paths including a certain one of those conductors which form part of said normal path, and to provide current flow in said conductor in one direction during establishment of said normal path only and in the opposite direction during the establishment of any of said one or more emergency paths, code signal responsive mechanism having a winding serially connected with said conductor, and means opposing current flow through said winding in said first named direction and facil itating such current flow around said winding while facilitating current flow in said opposite direction through said winding,and opposing current flow around said Winding:

9. In a signaling system,-the combination of code signal initiating stations, unidirectional current supply mechanism and conductors associating said stations and mechanism to provide a normal current path serially connecting said stations and to provide for establishment at respective stations of emergency current paths, each of one or more of said emergency paths including a certain one of those conductors which form part of said normal path, and to provide current flow in said conductor in one direction during establishment of said normal path only and in the opposite direction during the establishment of any of said one or more emergency paths, and code signal responsive mechanism associated with said conductor and biased for response only to current flow therethrough in said opposite direction.

10. In a signaling system, the combination of code signal initiating stations, two current supply sources and conductors associating said stations and sources to provide a normal current path serially connecting said stations and supplied by one only of said sources and to provide for establishment at respective stations of emergency current paths a certain one or more of which emergency paths supplied only by the other of said sources and each including a certain one of those conductors which form part of said normal path and in which conductor a characteristic of current flow supplied by one of said sources difiers from that supplied by the other source and code signal responsive mechanism associated with said conductor and biased for response only to current flow therethrough of the character supplied by said other source.

11. In central oflice equipment for a signaling system comprising a ground or common return conductor and a'normally closed path for serial connection of code signal initiating stations-the combination of current supply mechanism having a pair of maximum electromotive force terminals and an interjacent terminal together with means for urging unidirectional current flow from one to the other terminal of said pair and from said one terminal to said interjacent terminal as well as from said interjacent terminal to said other terminal, signal responsive instruments one of which is associated with one of said pair of terminals for connection between such terminal and one end of such a path, another of said signal instruments forming a connection one end of which connection is applied to said interjacent terminal and the other end of which is for application to the remaining end of such a path, and means for rendering said second named instrument responsive only to current flow through said connection in the direction resultant from establishment of a connection between said interjacent terminal and the remaining terminal of said pair, said remaining terminal for connection to such a ground or common return conductor.

12. In central oifice equipment for a signaling system comprising a ground or common return conductor and a normally closed path for serial connection of code signal initiating stations,the combination of current supply mechanism having a pair of maximum electromotive force terminals and an interjacent terminal together with means for urging unidirectional current flow from one to the other terminal of said pair and from said one terminal to said interjacent terminal as well as from said interjacent terminal to said other terminal, one of said pair of terminals for connection to one end of such a path and the other for connection to such a ground or common return conductor, a signal responsive instrument having an electromagnet winding one end of which is connected to said interjacent terminal and the other end of which is for connection to the remaining end of such a path, and means for rendering said instrument responsive only to current flow in the direction urged by the electronictive force between said interjacent terminal and said ground or common return conductor connected terminal.

13. A signaling system having current supply mechanism, conductors and code signal initiating stations whereby current paths of diverse characteristics may be established each including a certain one of said conductors, and having the characteristics effective upon establishment of one of said paths for precluding current flow of detrimental force therethrough and characteristics effective upon establishment of another of said paths for permitting flow of such force,--in combination with means for association with said conductor to limit current flow to non-detrimental force therethrough during establishment of a path having characteristics such as those of the aforesaid other path, an electromagnet the winding of which is responsively associated with said conductor, an armature for said magnet, a

stabilizing current path for association in parallel with said winding during retracted positioning of said armature and of resistance relative to that of said winding such that current flow through said conductor will be effective for causing movement of said armature from retracted to attracted position only when the strength of such current flow exceeds, at least to a predetermined extent, that which results from the establishment of the first named one of said paths, and means rendered efiective in the course of movement of said armature from retracted to attracted position for stabilizing the action there-. of by interrupting said parallel path and thereafter for effecting aforesaid association of said first named means with said conductor.

14. A signaling system having current supply mechanism, conductors and code signal initiating stations whereby current paths of diverse characteristics may be established each including a certain one of said conductors, and having characteristics effective upon establishment of one of said paths for precluding current flow of detrimental force therethrough and the characteristics effective upon establishment of another of said paths for permitting flow of such force,-in combination with means conditionable for limiting current flow to non-detrimental force during establishment of the aforesaid other path, and means including an electromagnet for so conditioning said means only responsive to current flow therethrough greater than that which results from establishment of the first named one of said paths.

7 CLARENCE E. BEACH.

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