US2371972A - Signaling system - Google Patents

Description

March 20, 1945. A. s. MARTINS I ,9

SIGNALING SYSTEM Filed Feb. 22, 1944 FIG.

CURRENT TIME C URRE N 7' INVENTOR V A$.M AR77N$ ATTORNEY Patented Mar. 20, 1945.

-UNlT-ED I ST'ATES PATENT/OFFICE SIGNALING-SYSTEM Arthur S. Martins, Glendale, N. Y.',['assignor to -Bell Telephone Laboratories; I Incorporated,= I I I Ne'w'York, N. Y., a corporation of New York I Application February 22, 1944,; Serial No. 523,437 I H I oo1ain'1 (01. 179-16)} This invention relates to improvements I naling systems and particularly to means for preventing impulse surges from falsely actuatingsignal responsive relays. I I

.The objects of the invention are to obtain a; I

greater degree of reliability and certainty in' the operation of signal responsiverelays; to render these relays immune to surges; tov safeguard the relays from false operations; and to secure other improvements and advantagesin signaling systems. I I

In automatic telephone systems numerical switches of the conventional type, such as selectors and connectors, include impulse, relays which vibratorily respond to impulses transmitted by. the dial mechanism. Impulse relaysare also included in impulse-repeater circuits, as well as in acteristics: of the asymmetric resistance being such as .to allowcurrent in the normal direction 'tion, taken in connection with the accompanying but to substantially block out current in'the opposite direction, With this arrangementthe re- I verse current produced by the transient surges is limited to a safe value and as aconsequence the impulse relay responds with more reliabilityto the transmitted impulses. I

- This andother features of the, inventionwill be described in detail in the following specificadrawing in which:

- 'Fig. 1 illustrates graphically the current conditions in a typical impulse signaling circuit during a dialing; operation when an asymmetric resistance is not employed; I I

incomin and outgoingtrunk circuits of-automatic telephone systems. It often ,occurs,.par--v ticularly in connection with interoflice-trunkst wherein the primary windings of the Well-known repeating coil bridge are interposed serially .be-

tween the incoming line conductors and an impulse responsive relay and the bridge condenser,

that the impulse responsive relays are :falsely; actuated by transient surges" set up during the dialing operation. It has been found in'practice' that when the dial pulsing contacts open during an impulse cycle the current throughthe impulse relay windings decays to zero to release this relay r and then builds up in the opposite direction sufflciently to reoperate the relay fals ely.. The false reoperation of the impulse relay naturally results infalse operation of the switch, which in turn selects a wrong trunk or wrong. number,

7 thereby causing annoyance to the. calling/subscriber. n

.Various schemes have been proposed-forpreventing false operation of the impulse responsive relay among which is included that of connecting dry rectifiers across theprimary windings of the repeating coil. This prior arrangement, while it appearsto deal efiectively with surges arising atthe repeating coil, does not block outthe reversed current surges produced'by the condenser connected between the mid-taps of, therepeating coil. I I I According to the 'present invention false operationof the impulse responsive relay is prevented by inserting an asymmetric resistance, such as a I copper oxide rectifier, serially in circuit between the impulse responsive relay and the condenser,

and I I I Fig. 3 illustrates graphically the current condi nalin'g circuit in which anfasymmetric resistance is provided serially-between animpulse responsive relay and tions when an asymmetric resistance is employed,

' as in Fig. 2. I

7 Referring now, to Fig; 2 of the drawing, there is illustrated in schematic form a telephone circuit of the automatic type comprisingthe usual subscriber's dial 10, having impulse contacts H I connectedto line .conductorsl2, I3, which in turn are connected through conventional switches that are not shown since they are. not essential to the invention, to primary winding terminals [4, I5 respectively, of repeating coiiRC; It is to be understood that there may be'any number of ,switchesinserted between the dial ,lojand repeating coil RC, and that the subscribers dial I 0 may instead be part of an operators telephone setwithout affecting the invention. ,The secondary windings of repeating coil RC may be connected to a switch in the same oiiice or through trunks to a switch in a distant ofl'ice. These connections, however, are well known and have been omitted to simplify the drawing. I

. I To mid-taps 11, I8 of the primarywinding of repeating coil RC a condenser I9 is connected for talking transmission purposes and in parallel with condenser I9 is connected an impulse responsive relay 21 having an upper and lower I winding. An upper contact of this relay may bearranged to step a selector switch in th'e same ofilce or to repeat pulses to a distant ofiice. Be-

a repeating coil winding and condenser;

The operation of an impulse si naling circuit of the type schematically disclosed in Fig, 2 iswell' known and accordingly will be briefly-recited herein. The circuit is seized in the normal manner. by the subscriber lifting his; handset-(not after which impulse responsive relay 2i is actuated n a circuit that can be traced from positive pole of grounded battery through lower winding. of relay 2|, lower primary winding of repeating coil RC, over line conductor 13, through closed dial impulse contact ll, and b ack over line conductor l2 through upper 'primary'winding' 'of repeating coil RC, asymmetric resistance 22,

an'd thence to'negative pole of batterythrough the upper Winding of-relay2l. Upon actua- -tionof relay 2| the front contacts 'are' closed and the succeeding circuits (not shown) are prepared for reception of the transmitted impulses in the conventional manner.

Upon; actuation of dial'.l0,*whereby the'impulsecontact H is opened and closed intermittently, relay 2-|- responds vibratorilythereto and operates the switches (not shown) 'inthe well-knownmanner;

To ascertain the transient efiectuponimpulse relay 2| during dial pulsing vibrating elements VI V2, V3 of aconventional oscillograph, such as that disclosed in- A. M. Curtis Patent 1,907,745 of May -9,' 1933, were temporarily inserted inthe upper winding, lower front contact,"and lower back contact circuits, respectively, of relay 2|. Oscillogra'rns of the current variations inthese circuits were then obtained f or bothconditions, that is, without use of the asymmetric resistance 22 and then with 'thisasymmetric resistance," as showngraphically in Fi'gssl an'd=3. l

' Referringnow'to Fig. 1, which is'a graph ofan oscillog'rarihic record taken of the pulsing operationof'impulse relay" 2l whenan asymmetric resistance was not'employed in the circuitgcurve Vl represents the current throughthe upper winding of' relay 2|, curve-V2'-represl3l1ts the current through the lower'relay make contact and curve V3 represents the current through the lower relay break contact. It is readily seenthat 'curve's V2 andVS depict'the operating and releasing periods of relayl22 inresponse to the-closing and open ng operations of dial impulse contact I. With the pulsing contact ll closed, relay'22 isenergized andits lower make contact is closed, consequently,

- as indicated by the curves, current flows throughvibrating elements V1,: V2 only, the leften'd of curve V3 for the lower break contact being represented as of zero current. In curve Vl' the-point A" represents the instant-the pulsing contact ll was opened, point B represents-the instant the pulsing contact ll 'was reclosecl, and point C represents the reopening of the contact H for starting another pulse cycle, theinterval A-'-C therefore; representingone complete: impulsing cycle. .In curve V2, point 1) indicates the release of relay 2 l, which corresponds to thein'stant at which the relay current is passing through its zero value points EtoF indicate the interval through which the reversed current is of "sufllcieht' "mag- 15,. shown) from the mounting support (not shown)' 7 nitude to falsely reoperate relay 2i; and point G indicates the reoperatlon of relay 2| following the closure of impulse contact H, as at point B of curve Vl. In curve V3 points H--J and K- -L respectively indicate separated portions of the release period of relay 2|, that is, the periods during which the lower back contact is closed, while the interval between points .J and .K indicates the periodcdurin-g which the unwanted reversed current is effective to open the lower back contact.

An inspection of the curves VI, V2, V3 of Fig. 1 will therefore reveal that upon opening contact 1 l the-current in the winding of relay :2! falls on to a zero value, at which time the lower make contact is-openediand the lower break contact is closed, and then continues to build up in the reverse direction sufliciently to falsely reopen the lower-break contact and shortly thereafter to reclose the lower make contact. This false reoperation of relay 2| continues until the value of the reversed current is insuificient to energize the relay further after which the lower'make contact opens and the lower break contact closes.

The false reoperation of relay '2! appears to be caused particularly by condenser I9, the circuit proximity of relay 2! to condenser l9 also being a contributing factor. It is well known that,when alcontact, such as pulsing contact H, is opened in a circuit containing inductive elements, the current persists thereafter for a short interval of time, the current in this instance chargingcondenser l9. The accumulated charge on condenser t9 raiseslts'potential above that of the battery so that upon discharge thereofthe current reverses sand surges through a local circuit includingrelay 2| which-ialselyreoperates due to the magnitude 'ofth'e'surgev This circuit can be traced from the lower terminal-of condenser 19 through lower winding of relay 2|, positive and negative poles =01 battery, and thence to the upper terminal of condenser IBthrough upper winding of relay 2!.

Applicant has found that, by inserting an asymmetric resistance 22 in the above-traced condenser l9-relay 2! circuit with the resistance 22 .properly poled, the reversed current surges were efiectively blocked. The efiectiveness of applicants invention is readily apparent in Fig. 3, which is agraphof an oscillographic record taken of the pulsing operation of impulsing relay 2| con- 22,-=as shown in Fig. 2. The same character references are employed in Fig; 3 as in-Fig. 1 to identify the-same curves and the various points thereon wherever-they are repeated. From curve VI, it 'w-ill' b'e seen thatthere is very little, if any,- reversedlcurrent to falsely actuate relay 2 I. This is further borne out by-curves V2 and V3, whereon the interval between points D and G indicates a continuousopen-period for the lower make con- -tact and the interval between points H an L indicates a continuous closed period for the lower break 'contact of relay 2 l While-this invention has been shown and described in accordance with the preferred embodL ment merely for the purpose of illustration, it is,

of course, understood that various modifications may be made and that the features thereof may b'e-appliedto many other and widely varied'fields without departing from the scopeoi the invention as "defined in the appended claims;

What is claimed is: i 1. In-a signaling system, a line,=an impulse transmitting-device at-one'end ofsaid line;-a repeating coil at the-other end of said line; a relay responsive to impulse transmitted by'said device,

nected in circuit with an asymmetric resistance a signaling circuit comprising said line and device and windings of said repeating coil and relay, a

2. In a signaling system, a line, an impulse sender at one end of said line, a repeating coil at the other end of said line, an impulse relay responsive to impulses transmitted by said sender, a signaling circuit comprisingsaid line and sender and windings of said repeating coil and relay, a condenser at mid-taps ofthe primary windings of said repeating coil, and an asymmetric resistance serially interposed between-a winding of said relay and said condenser, said relay being so polarized by said asymmetric resistance as to be responsive only to closures of said impulse send'er.

3. In a signaling system, a line, an impulse transmitting device connected to one end of said line, a repeating coil connected to the other end of saidline, an impulse relay responsive to said I device, a signaling circuit including said line and device and windings of said repeating coil andrelay, a condenser bridged across said relay wind+ ings, and a rectifier connected serially with said I condenser and a winding of said relay for 'pre I venting false operation of said impulse responsive relay.

4. In a signaling system, a line, a dialing device connected to one end of said line, a repeating coil connected to the other end of said line, an impulse relay vibratorily. responsive to impulses transmitted by said device, a signaling circuit including said line and device and windings of said repeating coil and relay, a condenser bridged across said relay windings for passing voice frequency currents, and a copper oxide rectifier connected serially with said condenser and a winding of said relay for preventing false operation of said im pulse responsive relay.

j.;5. Ir-i a signaling system, a line, an impulse .-;tr,ansmitter connected to one end of said line, a repeating coil conductively connected to the other end 'of said line, an impulse relay vibratorily responsive to impulses transmitted by said device, a signaling circuit comprising said line and device and windings of said repeating coil and relay,

the primary windings of said repeating coil and the windings of said relay being serially interconnected, a condenser bridged across said relay windings, and a copper oxide rectifier connected serially with said condenser, and each winding of said relay for preventing false operation of said impulse responsive relay. I

6. In a signaling system, a line, a dial at one end of the line for transmitting current'impulses, a repeating coil at the other end of said line, an

impulse relay responsive to said current impulses,

said repeating coil having a primary winding split into two sections in which the outer ends thereof are connected with said line and the inner ends thereof are connected with windings of said relay, a condenser connected to said inner ends of said repeating coil windings, and an asymmetric the mid-tam of said primary winding; an impulse sender in one of said sections for alternately opening and closing said line; a relay responsive to said impulse sender; 'a source of direct current; a circuit comprising said source, relay, pri mary winding, and said impulse sender; and an asymmetric resistance connected serially between said relay and the mid-taps of said primary winding for preventing false operation of said relay.

8. In a signaling system, a line, an impulse sender, a repeating coil including a primary winding conductively connected to said line, a condenser disposed'at. the mid-taps of said winding, said repeating coil and condenser being "adapted for talking transmission purposes, an

impulse responsive relay also connected to the mid-taps of said primary winding, a source of direct current for energizing said relay with normal current therethrough in a definite direction while said line is closed; said relay being deener-' gized when said line is opened-by said impulse sender, and an asymmetric resistance included serially between said relay and the mid-taps of said primary winding for preventing transient current produced at the opening of said line from falsely reoperating said relay, said transient current beingv of' a direction opposite to that of the normal current.

9. In combination, a line, a repeating coil having a primary winding and a secondary winding,

an impulse relay having two windings, one pole of battery connected to one of said relay windings and the other pole of battery connected to the other relay winding, the windings of said relay I being connected to the mid-taps of said primary winding, a condenser also connected to the midtaps of said primary winding, an impulse transmitter for closing and opening an impulsing circuit through said primary winding to cause said relay to energize and deenergize therewith, said impulse transmitter also causing said condenser to charge and discharge through the relay windings, and an asymmetric resistance serially connected with one of-said'relay windings and a midtap of said primary winding, whereby' the condenser discharge' through said relay windings is rendered ineifective.

10. In combination, animpulse circuit comprising, a line, an impulse sender, a primary winding of a repeating coil having separated mid-taps, an impulse relay having two windings, a battery,

all elements of said circuit being connected in series, a condenser connected to the mid-taps of said primary winding, said condenser also being bridged across said relay windings, and an asymmetric resistance in series with one of said relay windings and said condenser.

ARTHUR a. marine.

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