US2374908A - Selective calling system - Google Patents

Description

3 Sheets-Sheet 1 ATTORNEY I M/VEIVTUR A. WEAVE A. WEAVER SELECTIVE CALLING SYSTEM Filed Aug. '28, 1942 y 1, 19454 A. WEAVER SELECTIVE CALLING SYSTEM Filed Aug. 28, 1942 3 Sheets-Sheet RNEV m R R. A w. A W

May 1, 1945. V A. WEAVER SELECTIVE CALLING SYSTEM Filed Aug. 28, 1942 5 Sheets-Sheet 3 m/vavron B WEA VER Patented May 1, 1945 UNITED STATES PATENT "OFFICE 2,374,908 SELECTIVE CALLING SYSTEM Allan Weaver, Port Washington, YL, assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application August 28, 1942, Serial No. 456,571,

' lSClaims. (01.178-2) Thisinvention relates to a selective calling system and particularly tosuch a system in which a plurality of stations to be selectively called are associated with a common signaling channel.

An object of the invention is to transmit selective station calling signals and telegraph message signals over the same communication channel.

Another object of the invention is to render the selective station call receiving apparatus unresponsive to telegraph message signals.

The invention features at the calling station ,a pulsing dial and a pulse divider circuit whereby only one signaling current'transition occurs on each pulsing cycle of the dial contacts.

The invention also featuresat eachof the selectively callable stations at call: responsive step-bystep selector which is disabled during intervals of idleness of the signalin channel and is also disabled during the transmission of telegraph siglittle on the channel and which becomes qualified to respond to selective calling signals in stepbystep manner under the control of timing apparatus which becomes effective only after a signal of'a predetermined character has beenimpressed upon the signaling channel for a predetermined interval.

In accordance with the preferred embodiment of the invention the system includes a principal or call initiating" station having station calling signalgeneratingapparatus and also having telegraph signal transmitting and receiving apparatus, and a plurality of subordinateor outlying station's having selective station call signal receiving apparatus and also having telegraph-signal receiving and transmitting apparatus; All of the stations are associated'with a closed loop type of signaling channel which has at least one source of signaling potential associated therewith.

At the principal station the selective station call signal generating apparatus comprises a system of relays controlled by a pulsing dial so as to impress markin and'spacing signals on the signaling channel at the rate of one transition from marking to spacing-or from spacing to marking for eachcomplete cycle of the pulsing contacts of the dial. The station also has telegraph signal transmitting contacts and the selector magnet of'aprinting telegraph receiving recorder associated with the signaling. channel for transmitting and receiving telegraph signals.

At each of the outlying or subordinate stations a signal responsive re1ay,.a set. of telegraph signal transmitting. contacts and-the selector magnet of a printing telegraph receiving recorder are associated with the signalingchannel The signal receivingrelay controls a.stepby-stepse1ectorand andfthe stepby-step selector at each of the .out-j lying stations is disabled. The disabling relay, when operated, is controlled by the signal receiving relay and has a slow-release characteristic so that it" will beheld energized by marking current on the signaling channel and willnot be released until there has been a spacing signalonthe channel of a duration longer than that of the longest spacing'interval normally occurring in telegraph signal transmission.

In the operation of the system an attendant at the principal station desiring to call one of the outlying stations operates a break key, which impresses a spacing'condition on the signaling channel, fora sufficient interval to release the selector disabling relays at all outlying stations. The attendant then transmits by means of the dial the calling code for the particular station and this code operates the step-by-step selectors at all of the outlying stations to advance the selectors, but'iat only one of the stations will the selector beadvanced' tosuch position that it will completethe circuit for a call indicator to inform an attendant at the particular outlying station I that telegraphic communication With maceration is desired.

However, upon the beginning of transmission of telegraph signals; such as when an attendant at the called station operates the telegraph signal transmitting contacts thereat to transmit char acters" representing an answereback, the short spacingi'mpulses which such signals will contain are effective: to cause the timing mechanism to operate the selector disabling relay at. that station andat all other stations.

For aco'mplete understanding of the invention, reierence mayybe had: to the following detailed description to be interpreted in the light alsocontrols atiming circuitincluding-a plurality of relays one-of which-isarranged to disable the step-by+step-selector.. a

In the idle-condition of'the apparatus follow of the accompanying drawings wherein:

latter" being represented symbolically;

Fig. 2 i's a circuit diagram showing" a third-subordinate station in full detail;

Figs. 3, 4 and 5 are circuit diagrams showing alternative arrangements of apparatus to be controlled by the step-by-step selector at a subordinate station; and

Fig. 6 is a diagrammatic view showing how Figs. 1, 2 and 3, Figs. 1, 2 and 4, and Figs. 1, 2 and 5 are to be interassociated to reveal the complete selective calling ystem provided with any of the three types of selector controlled apparatus.

Referring now to the drawings, and particularly to Fig. l, the broken line rectangle H designates the principal station of the system. From the station H signal transmission line conductors l2 and 93 extend out to the subordinate stations, and the line conductors l2 and I3 are interconnected at the station ll through a loop which includes break key I6, the normally closed upper pair of contacts of a dial key I'I, signaling battery i8, telegraph signal transmitting contacts 58 and the selector magnet 2| of a printing telegraph recorder, which may be of the type shown in Patent 1,745,633 granted December 23, 1924, I

to S. Mortion et al., or may be of the type shown in Patent 1,904,164 granted April 18', 1933, to S. Morton et al.

The dial key IT has a pair of normally open contacts, namely, the lower contacts shown in Fig. 1, through which a source of alternating current may be connected across the input terminals of a full wave rectifier 22 which provides at its output terminals a source of direct current. A filter condenser 23 is connected across the output terminals of rectifier 22 for filtering out the alternating current components at the output of the rectifier.

Upon the operation of the dial key I! the loop interconnecting the line conductors I2 and I3 is opened at the upper dial contacts and the source of alternating current is connected across the rectifier 22 at the lower dial contacts. When the rectifier 22 has been energized, a circuit may be traced from the right-hand output terminal of the rectifier through the single pair of pulsing contacts of dial 24, which contacts are closed when the dial is at rest, through the right-hand armature and back contact of a relay 26, righthand armature and back contact of a relay 2'! and winding of a relay 28 to the left-hand output terminal of the rectifier. Over this circuit the relay 28 becomes energized.

At its outer right-hand armature and front contact the relay 28 recloses the transmitting line loop which was opened at the upper contacts of the dial key l1. At its inner right-hand armature and front contact the relay 28 prepares an energizing circuit for the left-hand or operating winding of relay 26 in series with the winding of relay 28 but the operating winding of relay 26 is at this time short-circuited by the closed dial contacts so that the operating winding of relay 26 does not become energized. At its lefthand armature and back contact, relay 28 opens a circuit from the. right-hand output terminal of rectifier 22 through the left-hand armatureand back contact of relay 21, left-hand armature and back contact of relay 28 and resistor 29 to the left-hand output terminal of rectifier 22. Resistor 29 and th winding of relay 28 preferably have the same resistance value so that with either the winding of relay 28 or the resistor 29 connected across the output of rectifier 22, the drain on the rectifier will be the same. It is for this season that the relay 28 upon being energized disconnects resistor 29 from across the out,- put terminals of the rectifier 22.

The selective calling code signal generator is now in condition for the transmission of a calling signal by means of dial 24. However, in order to place the outlying stations in condition to respond properly to the selective station calling signals, it is necessary to impress a long spacing signal on the signaling lines' l2 and IE to perform operations which will be described later. The transmission of the long spacing signal may be accomplished by opening the break key I6. It is necessary to do this because although the upper contacts of the dial key I! impressed a spacing signal on the line conductors, the relay 28 became energized and immediately shunted the open dial key contacts by means of it outer right-hand armature and front contact so that the spacing signal thus briefly impressed upon the line conductors may not be of sufi'icient duration to accomplish the desired result at the outlying station.

Following the reclosure of the break key l6 to terminate the long spacing ignal, dial 24 is operated by rotating it in well-known manner to advance the dial to the position corresponding to the first digit of the calling code to be transmitted. The dial contacts 24 remain closed until I the dial is released to permit it to return to the normal position, during which return the calling code impulses are transmitted. The dial cone tacts open and reclose once for each element or unit of the digit so that if the digit i 8, for example, the dial contacts will open and close eight times whereas if the digit is 5, for example, the.dial contacts will open and close five times.

Upon the first opening of the dial contacts, the shunt across the operating winding of relay 26 is removed, so that the relay 26 become energized through its operating winding in series with the winding of relay 28 over a circuit previously traced. At its right-hand armature relay 26 transfers the dial contact connection from the armature of relay 2! through which relay 28 was originally energized and connects the now open dial contacts to one terminal of its holding winding, the other terminal of which is connected to the left-hand output terminal of rectifier 22, and also connects the dial contacts to one terminal of the winding of relay 21, the other terminal of which is connected through resistor 3| to the left-hand output terminal of rectifier 22.

At its left-hand armature and front contact the relay 26 connects a resistor 32 across the output terminals of rectifier 22 in shunt relation to the operating winding of relay 2'6 and the winding of relay 28, which are now in series, and

' whereas the placing of the operating winding of relay 26 in series with the winding of relay 28 tends to reduce the drain on the rectifier 22, the resistor 32 draws sufiicient additional current to hold the total drain on the rectifier at the same value as it was when resistor 29 or the Winding of relay 28 was connected across the rectifier. Since the relay 28 has remained energized, the loop across the line conductors l2 and I3 has remained closed so that no change has occurred in the condition of the line conductors as a result of the opening of the dial contacts.

Upon the first reclosure of the dial contacts the energizing circuits for the holding winding of relay 26 and for the winding of relay 2? are completed in parallel from the output terminals of rectifier 22. Thus the relay 26 remains energized and the relay 2! at its right-hand armature and back contact interrupts the energizing circuit for the operating Winding of relay 26 and for the Winding of relay 28. At it left-hand armature 2,3114, one:

and back contact; the relay- 21; opens the circuit for resistor: 29;. which: haspreviously been opened at the left-handarmature; and back: contact of relay ZB-so: thatthe. resistorifliwill not be ccnnected across the output of. rectifierZZ upon the releaseotrelayZB which theenergization of re lay 2'! has caused: Three conductive-paths are now connected across the output on the a rectifier 22, these bein the resistor 32' the: holdings/ind: ing' of relay 26-and the winding: of relay 2'! with the resistor 3.! in: series with-it. The-resistance:

values of the holding. winding of relay; 2.6, of re-- sistor 3.1 and: the Winding of: relay. 2'!" in: series. and of resistor 32; ar suchtthat the aggregate resistance. of the three parallel path in theex be: apparent thatodd-numbered closures" of the ternal circuit of rectifier; 22: is equal to the re rupted so that this circuit willnot be; reestabs lished when relay 2-6 is released! At its left hand armature and. back. contact. the; relay 2!! again preparesv for" the connection of resistor 29 across the outputterminals of'the rectifier. the path now being open at the left hand armature and backcontact of relayzl. '5 l Upon; the second opening of the dial contactsthe energizing circuits. fonthe holding windin 3. opening}. ofthe" dial-i contactsrelays 26. and; 2 1.- are releasedzrandz the; direct energizing; circuit for. relays 2831s: preparedi. Upon; the fourth, closing of the: .dial! contacts; relay 28 becomes energized to restore: the-line: conductors; I 2 y and L3 to marking. the: foregoing. it will be apparent that onht'thaiclosune andmct. the: opening of the. dial contactsiis eifective to cause aline current transiftionbnr the: lineaconductors tizandg 31 v,Thus

there are only halfrasimany: line current transitime: as; dial: contact transitions; and: the system maybe; said? to: be a: pulse. divider. It' will also dial. contacts: change the. charactenof the signal on: the line from; that. which existed: beforeathe dial was; operated and: even-numbered dial. contact: closure restore the line condition to that which existed beforezthe dialswas operatedi. Ac.- cordingly; whenlan oddtnumber-isdialed the line condition will be different when the dial comes to rest from that whichyexisted-before the dial was operated": and when an even. number isdialed the line condition will be the same when the dial comes to rest as thatwhich existed before the dial' was operated; If a. calling signal consists of two digits and both areoddnumbers. ornboth are-even numbers; the' -line conductorswill be in n marking condition whenthe dial comes to rest after the transmissionof the-second digit, whereas if one only of the digits is an odd number, the line conductorswill be in the spacing condition when the diaireturn's to rest after the second digit.

Following thetransmission ofithe selective sta tion calling signal; which is not limitedto one or two digits but may=beofthree or four digits, de-

of relay 25 and for the winding of relayllsreinterruptedso that-these relays are released. right-hand armatures of. the: relays 26 and 21. again nrepare the direct energizingi circuit for: the relay 28 through thein right-handbook contacts but this energizing path is now interrupted at the open dial. contact. At its lefteh'andarma--. ture the relay zfi disconnects resistor iizafrom: across the output terminal of the rectifierrwhile at the left-hand armature and-back contact of: relay 21, resistor 29 is reconnectediacross the, output terminals of the rectifier" to mainta n con stant drain on the rectifier during-the nterval that none of the relays 25, 2''! or: 28' isenergizcd. The condition or line conductors; t2: and liihas o ee cha ed due; to the second} opening: of. the dial. contactsv because relay 28. has: remained: deenergized. i

Upon the second closing; of the dia'lacontacts the relay 28 becomes energized. over thefirst-described directenergizing; circuit andlrecloses the loop across the lineconductorsalll and I3; .The relay 28 also disconnects resistorzfi from. across the rectifier 3.2 and again: prepares for. the ene1.- gization ofthe operating w ndine of relay 2-55 inseries with the winding of relay 285. Thex opena-t ng winding of relay 25. is atthistime shunted by the now closed dialcontacts.

Upon the third openingsor the dial-contacts relay Zfibecomes energized inseriesiwith. relay 28: and again prepares for: the energization of its holding winding. and for, the energization of relay 21. Upon, the third clos ng of diatcontacts relay 2! becomes. energized. tofirelease-irelay 218 and relay 2'5 remains energized-through itsholding winding. Thus a second spacing signal is impressed upon the line conductors liiand {it due to. the release. of. relay 28. Upon: theifflurflfb pending upon the number of stations contained in the system; the-dialkeyx I1 is restored'to normal.' At its upper contacts the loop across the line conductorst7. and l 3-is reclosed and at'its lower contacts poweris disconnected from the rectifier 22 i so that all relays are releasedand the system is restored sc the-initial condition. From this-it will be apparent that the line conductors l2 and- [3 are aiwaysin markingcondition following the operation of dial key ll in preparation for the transmission" of a selective calling responsive relay 12* all inseries-at-station 36, then through selector magnet: 03; transmitting contactsMLand signal responsive-relay 46- allfinseries at: station a lland then through selector magnetdh transniittingcontacts 4B' and'signal responsive relayi-dilalliin series-at station 3B (Fit-:52), liiine conductor l3extends-on beyond station- 38 and may include the selector" magnets, transmitting contacts and signal responsive relays of' other stations and is: eventually interconn ected through a loop Witjhrline conductor 12 which n1aya]so-inelude selector-magnets;transmitting contacts and signal responsivc;relays of other-outlying or sub.- ordinaterstations;

ReierringLnow' particulanly to FigLlZythe-stw- 131011138: has awmotor 5i for: driving the printin'gl telegraph receiving recorder controlled by selector magnet 4! and also for operating transmitting contacts 48. Power is applied to motor 5| from a source of alternating current through a switch 52, the normal condition of which is open and. which is closed by an attendant when the station is to participate in intercormnunication with the principal station H. The stations 36 and 31 have. similar motors 53 and 54 controlled by switches 56 and 51, respectively. 1

Since the selector magnets and signal responsive relays are in series'with-the line conductors at all stations, these elements respond to and follow all signals, whether such signals are telegraph signals or selective station calling signals generated at the principal station II, or whether they are telegraph signals generated at any of the outlying or subordinate stations.

At the station 38 the upper and lower contacts of the signal responsive relay 49, which are the marking and spacing contacts respectively, are connected to the positive and negative conductors BI and 62, respectively, of a power supply comprising a half wave rectifierincluding the upper anode and cathode of a discharge tube 63 connected so that the discharge path between the anode and cathode is between the positive conductor 6| and one side of a source of alternating current, the negative conductor 62 being connected directly to the other side of the source of alternating current. A filter condenser 65 is connected between conductors 5i and 62 for filtering out alternating components at the output of the rectifier. 'I'ne armature of signal responsive relay 4S is connected through a condenser 64 to one side of the operating magnet 66 of a step-bystep selector 6?. The other side of the magnet 65 is connected to the lower armature of a relay 68.

The step-by-step selector 5'! may be of the type shown in Patent 1,345,256 granted June 15, 1920, to J. C. Field and the disclosure of that patent is incorporated herein by reference as part of the present specification. Briefly, such a selector consists of a polar magnet having an armature which is rocked clockwise or counter-clockwise from a central or neutral position in response to polar impulses of .current. The armature is provided with an arm which operates a pawl mechanism for stepping a contact wheel or disc and the disc is advanced two steps for each full cycle of oscillation of the armature lever, by which is meant from the neutral position to one side, then to the opposite side and back to the neutral position. The contact wheel or disc is provided with selectively located pins which will be engaged by a check pawl controlled by the armature lever when the armature lever is momentarily permitted to be at rest in the neutral position after having been operated through a plurality of cycles or half cycles, and such pawl prevents the contactdisc or wheel from returning to normal position under the influence of its restoring spring. When a plurality of such selectors with difierently located stop pins respond to signals consisting of current reversals, a pause in the transmission of signals will cause those which have stop pins presented to their check pawls to be held in the positions to which they have been advanced, whereas all'selectors which have no stop pins in those positions will return to normal position under the influence of the disc restoring springs. When transmission of current reversals is resumed those discs which were held in advanced positions are further advanced from those positions, whereas in all of. the selectors the discs of which were restored to normal, those discs are again advanced from the normal position.

Step-by-step selectors of the type disclosed in the patent to Field are provided with contacts which are engaged by a contact arm carried by the step-by-step wheel or disc for the completion of electrical circuits. The electrical circuits are completed through the check pawl as a circuit element, 501 that as the contact arm comes into engagement with a contact, as it is being advanced step by step, an electrical circuit is not completed if the advance continues but only if there is a pause in the signal train which permits the check pawl to engage a stop pin and hold the disc or wheel in the position to which it has been advanced. When selectors of this type are employed in a system, all may have their electrical contacts in the same relative positions, such as in the eleventh, thirteenth, fifteenth and seventeenth steps. Taking the thirteenth step as an example, it is not necessary to send thirteen impulses in regular succession in order to cause the selector to reach that position. The selector may be provided with one or more stop pins intermediate the rest position and the thirteenth step whereby the thirteenth step may be reached by the transmission of sets of impulses which total thirteen, with a pause between each two sets of impulses. During the pause at the end of the first set of impulses, those selectors which have stop pins in the position to which the discs of all of the selectors have been advanced will be held and the discs of the remaining selectors will be restored to normal. In a two-digit system only one disc would be so held and all of the others would be returned. In a three-digit system, a plurality of discs would be held and the remainder would be restored to normal. Upon the resumption of transmission of impulses, all of the selector discs would again be advanced, some" from their initial positions and one or more fromits advanced position. At the end of the second group of impulses the disc of one selector closes an electrical circuit, if the system operates on a two-digit call, and all of the remaining discs return to their normal positions, with the exception that the second set of impulses may correspond to the first digit for some other selector in the system and the disc of that selector may beheld in its first digit position although it will close no electrical circuit in this position. Following the closure of the electrical circuit by the disc or wheel of the selector, the transmission of a single impulse will restore all of the selectors to normal. If the system is operable upon a three-digit call, a plurality of discs will be held at the end of the second set of impulses, the number being smaller than the number which were held at the end of the first set of impulses. At the end of the third set of impulses only one of the discs will have been advanced to a position to close an electrical circuit.

In the arrangement shown in Fig. 2, when the relay 68 is deenergized, which is the condition following the transmission of a long spacing signal preparatory to the transmission of selected station calling signals, as will be described later, one side of the operating magnet 66 of the stepby-step selectorfif! is connected to the negative conductor 82 of the direct current power supply and the other side of magnet 66 is connected through condenser 64 and through the armature and marking contact of relay 49 to the positive conductor 6| of the power supply. This causes the condenser fl to be charged positivelyon the side toward the-armature :of relay i9 and negatively on "the side toward magnet 66. When relay 49 goes to spacing, both sides of condenser 64 are now connected to the negative conductor B-Lpermitting condenser 64 to discharge through condenser is thus connected in parallel with resistor when :relay "If is sde'enengized.

For'the purpose of setting iorth the operation of the system of condensers associated with magnet "66 which roc'lrs the armature to one side. i i

If the relay E9 returns to mar-king before the discharging current has died out, condenser fi l will be recharged and the charging current will condenseriil liiniparallel with variableresistorzdh relay H, it will be assumed'tha't the lineicon doctors 12 and '13, having previously beenin marking condition, :have gone to rspacing condition as, Ifor example, lupon transmission of the first spacing iimpulse 10f 1a selectivecalling code. Relay 4:? goes to spacing and releases :relay l! which removes the lowtresistance shunt includ ing resistance 81 .from condenserrliziand connects Condenser :82 isrroi relatively large capacity and ahigh initial charging current flows lthrough:re--' sistor 18 3. This produces a relatively high p0 line cond'uetors m and I3 =arenot polar-inthe arrangementshown 'inFigs. 1 and 2 and there is no actual reversal of battery connection across the "magnet 66.

The armature of signal 'responsivegrelay lfdisl conne'ctedlthrough "conductors H, 1'2 "and '13 to 3 the upper armature of "relay 68 which, beingassumed to be released at this time, engages its back contact, from which a circuit extends through resistor T4, shunted by a condenser '75, conductor 1'6, Winding ofrelay -71 and conductor power 18 to the negative conductor 62 of the supply. Overtime circuit just "traced the relay tential difference across resistor 83 which is (also impressed across condenser '34. condenserm becomesccharged,thechargingcurrentand therefore lthewpotential difference "across :resistor '83 decreases and the potential :difference across condenser 84 correspondingly"decreases. If the .relay ll .:sh:o1ild remain :rleased :under the control of zzrelayrfis zuntil condenser "82 becomes :iully charged, the :fiow :of current ithroughiresistor 83 willrceaserand the potentialadiiference "acrosscc'on denser :84 ibe reduce'd ito zzero.

:Ilhe'tront icontact which the lower arma ture of :relay 11.1 is :engagealdlelwhen .the relay is energized, is connected by conductor :86 to the grid of an :electrom'd'ischarge tube .81. Before M will follow-the "operation of the armature of signal responsive relay '49, whether "that relay is following rapid telegraph signals or 'theslower selective station calling signals generated by the dial controlled pulse divider circuit in Fig, 1, the relayl'l being energized when the armature of' relay 49 engages the marking contact and being deenergized when "the armature of relay 69 engages the spacing contactfThe function of condenser T5 is to accelerate the operation of relay 77. A resistor 19 {having approximately the same resistancevalue as the aggregate of resistor M "and the winding of relay '11 in seriesis .cfonnecterl between positive power supply conductor BI and the armature of relay 49 through conductor 1! :to provide a drain on the power sup ply when the armature 'of relay 49 engages the the llower armature \oflrelay :11! engages its :iront contact, the arid :ofltulbe 18! sis at the potential :of

the negativelpower supply conductor 6-2 by virtue of its connection to that conductor through a resistor 88, and the cathode of tube 8 7 is more positive than th :grid loy virtue =of the potential difference across a resistor BEl in a circuitT-rom the, negative power supply conductor 62, lower back contact an-d :armature of a relay 9 Icondujotors 92 and 93, resistors 89 :andpll l to the positive power supply conductor '6 the cathod of tube 8 bei1rg-connected"tothepoint of interconnection "LOT resistors -89 and 94. Upon the engagement of {the lower arm'ature of relay "H with its front contact, which occurs when a marking impulse is impressed upon the line conductors spacing contact, whichiis connected tonegative 1 power supply conductor "62, substantially equal to "the drain through resistor '14 and the Wi-riding of relay 1'! when the armature of relay 49 engages themarking contact. When the latter.

condition of the relay 4'9 exists, the resistor ill is short-circuited by the armature and marking contact. a j y The upper armature of relay 2.! is connected :to positive power supply conductor Bil through a resistor '81 and the upper front contactLi-s connected to thesame conductor through a condenser =82. The upper from contact is .also connected .to the lower back contact and to one terminal of a variable resistor 8'3, the other terminal of which isconnected to the negative power supply conductor "51. it willhelapparent from an examination of Fig. .2 that when relay "H is de energized condenser'lli is connected in series with variable resistor d3 across the power supply conductors El and 6'1 and condenser '82wil1nbeeome charged.

When relay "I? is energized condenser 8.2 will be discharged through resistor 8 I. The'lowerg'armature of relay 1'! is connected through condenser 34' to negative power supply conductor 62 and the der which the tube is rendered conductive will.

t2 and f3, as for "example at the beginning of y a marking signal following the 'firstspacin'g signal 'o'f the selectedsta'tion calling code, "thepo tential of the grid of tube "81 is raised by the po tential difference across condenser 84. This potential will be smaller in magnitude the longer the intervalduring which charging-current fiowed to condenser 82 and the constants or the circuit-are-"such that insufficient potential difference appears across'condenser 84 atthe end of a spacing impulse of a selective calling code to render tube 81 conductive. Accordingly, tube 8 remains 'nomcondu'ctiye during the reception of "a selective calling code and the circmnstances unbe described later. During the reception of the selected calling code, the selector discs of the selectors are .ad-V vanced step by Step at all stations and it will be assumedtliat the received code causes thesjel'ector disc at "thestation shown in Fig. 2 to advance its contact arm to "engagement with contact 101.

The check vpavvl I02 *o'ftheselector, whichgem gages and holds the "disc in the position to which it has been advanced, is connected to the negative power *supply conductor 62 so that it comp-letes a circuit from that conductor 'tm'ough the contact disc and contactann of the selector to contact IIJI and from there through conductor I63, and assuming that the selector controlled system shown in Fig. 3 is associated with the station shown in Fig. 2, through conductor 363, conductor I64, winding of relay I66, resistor It! and conductor ms to a positive power supply conductor I69 which derives its positive potential from the cathode of the lower diode section of tube 63, the anode of which is connected to the same side of the alternating current source as the anode of the upper diode section. From this it will be apparent that the negative power supply conductor 62 is common to the separate positive power supply conductors 6I and I89. A filter condenser II! is connected between positive power supply conductor I69 and negative conductor 62.

Upon th energization of relay I65, a holding circuit is completed from the negative power supply conductor 62 over conductor II2, conductor 3I2 in Fig. 3, normally closed key BIS, conductor 3M, conductor I I4, front contact, lower armature and winding of relay I06, resistor I61 and conductor I08 to the positive power supply conductor I09. The selector disc contact arm leaves the contact IBI upon receipt of the next signal transition, thereby interrupting the energizing circuit of relay I06. However, the relay has already established its holding circuit, and remains energized until that circuit is released. The relay I66 also completes a circuit from one terminal of the secondary-winding of a buzzer operating transformer I I6, the primary of which is connected across the source of alternating current, over conductor II'I, conductor 3I'I, buzzer 3I8, conductor 3I9, conductor II9, front contact and upper armature of relay I66, conductor I2I, conductor 32I, and conductor I22 to the other terminal of the secondary of transformer H6. The operation of buzzer 3I8 indicates to an attendant at the station shown in Fig. 2 that intercommunication between the principal station II shown in Fig. 1 and the subordinate station 38 shown in Fig. 2 is desired. Accordingly, the attendant momentarily opens key 3I3 to release relay I66, thereby stopping the operation of buzzer 3I8, and closes switch 52 to start the operating motor 51 for the printing telegraph receiver and recorder at station 38. The attendant at the station 38 in Fig. 2 may thereupon operate transmitting contacts 48 by mean of keyboard control mechanism shown in the Morton patents hereinbefore identified to transmit permutation code telegraph signals over line conductors I2 and I3 indicative of the fact that the station 38 is in condition to receive and transmit telegraph signals. Since the selected station call has caused the buzzer at station 38 in Fig. 2 only to operate, the operating motors for the telegraph recorders and transmitters at all other outlying stations should be idle and only the principal station II and the subordinate station 38 will be operative to transmit and record telegraph message material.

Since the permutation code telegraph signals involve spacing impulses which are much shorter than the spacing impulses of the selective station calling codes, the armature of the signal responsive relay 49 which follows the permutation code signals will engage its spacing contact for very much shorter intervals than it did during the reception of the selective station calling code, and relay 11 will be released for correspondingly shorter intervals. The charging current for condenser 32 flowing through resistor 83 during these short intervals will be relatively high and will produce a correspondingly high voltage across condenser 84 so that when the lower armature of relay 'I'I engages its front contact followin the first short spacing signal impressed upon the line conductorsIZ and I3, the potential of the grid of tube Bl will be made sufiiciently positive with respect to the cathode to render tube 81 conductive. The space discharge path of tube 81 extends from positive power supply conductor 6I through the winding of a relay I26, conductors I21 and I28, anode to cathode discharge space of tube 81, conductor I29, resistor 89, conductors 93 and 92 and lower armature and back contact of relay ill to negative power supply conductor 62. The relay I26 will become energized over this circuit and will remain energized through a holding circuit from positive power supply conductor 6i through the winding, lower armature and front contact of relay I26 and resistor I3I to the negative power supply conductor 62. At its upper armature and. front contact the relay I26 prepares an energizing circuit for the relays 68 and ill in series which may be traced from the negative power supply conductor 62 over conductor I32, winding of relay 9|, conductor I33, winding of relay 68, resistor I34, conductor I36, upper armature and front contact of relay I26 and conductors I2 and "II to the armature of signal responsive relay 49. Upon engagement of the armature of relay 49 with its marking contact following the spacing signal interval in which tube 81 was actuated, the circuit just traced is completed to the positive power supply terminal 6| and. relays 68 and Ill become energized.

At its upper armature the relay 68 interrupts the circuit from its back contact through the winding of relay TI to negative power supply conductor 62 and establishes a circuit through its front contact, resistor I34, winding of relay 68, conductor I33, winding of relay 9| and conductor I32 to negative power supply conductor 62, thus establishing a holding circuit for the relays 68 and 9|. This holding circuit derives its positive power supply connection through the armature of relay 49 which oscillates in response to the signals impressed upon line conductors I2 and I3 but relays 68 and BI have slow-release characteristics which are sufiiciently slow that they will not release during the longest spacing interval normally occurring in permutation code signals but will release in response only to long spacing signals, such as may be impressed upon the line conductors by break key I6 at station I I. At its lower armature the relay 68 disconnects operating magnet 66 of the step-by-step selector 61 from the negative power supply conductor 62 so that the magnet will be prevented from attempting to operate the selector in response to the permutation code signals which signal responsive relay 49 follows, thereby estopping false and undesired operation of the step-by-step selector.

With relay 9| energized the positive power supply conductor 6| is connected over the outer upper armature and front contact to the lower armature of relay I26 which is connected to the winding of that armature, thus short circuiting the winding and releasing the relay I26. At its lower armature relay 9! interrupts the connection from the negative power supply conductor 62 to the cathode of discharge tube 8'! thus preventing the further flow of discharge current through that tube. The inner upper armature of relay BI, is connected through resistor MI and glow lamp I42 to the positive power supply will be completed from negative power supply conductor 62 through check pawl I02 and the selector disc contact arm, conductors I59 and 459, winding of relay 40!, resistor 408, conductor 409 to positive power supply conductor I09 whereby relay 40I will be energized to interrupt the holding circuit for relays I41 and I06 which will release, thereby interrupting at two points the controlling circuit for remotely controllable device 453.

It will be understood that remotely controllable device 453 may have some other function than controlling motor switch 52 and it may be desired that such other operation be initiated and terminated before telegraphic communication begins, in which case such operation may be terminated under the control of the attendant at station I I, after the operation has been in process of performance for a suitable interval, by the transmission of the necessary selective calling code for advancing the selector disc contact arm to contact I58 before the transmission of telegraph signals has been started and therefore before selector I58 has been disabled. For example, the operation to be performed might be the completion of a buzzer circuit for notifying the attendant at station 38 to operate motor switch 52 manually. Instead of having the disablement of the buzzer controlled locally at station 38 as in Fig. 3, the buzzer could be released by the release of relays I41 and I06 under the control of relay 4IlI after it had been permitted to operate for an interval which the attendant at station II considered adequate.

When a subordinate station is equipped with selector controlled apparatus as shown in Fig. 5, the operation of two remotely controllable devices may be selectively initiated and terminated. For this purpose, a conductive path extends from selector contact I! over conductors I03, 503 and I46 to the winding of relay I41, and when the selector disc contact arm is advanced into engagement with contact IOI the energizingcircuit for relay I41 will be completed. 'The lower armature of relay I41 completes a holding circuit over conductors I49,;549, 5I2 and H2 to negative power supply conductor 62. I'he upper armature and front contact of relay I41 complete an operating circuit for a remotely controllable device 50I, over conductors I52 and 552 to one terminal of device 56I and over conductors I54 and 554 to the other terminal of that device.

From the contact I56 a conductive path extends over conductors I51, 551 and I04 over which the energizing circuit for relay I06 may be completed. The lower armature of relay I06 completes a holding circuit over conductors I I4, 5I4, 5| 2 and M2 to negative power supply conductor 62. The upper armature of relay I06 completes an operating circuit for a remotely controllable device 502 over conductors H9 and 5| 9 to one terminal of device 502 and over conductors I2I and 52I to the other terminal of device 562.

For releasing relay I41 to terminate the operation of remotely controllable device 50!, contact I58 of selector 61 is connected over conductors I59, 559 and I6I to the positive terminal of the winding of relay I41, and when the selector disc contact arm is advanced by appropriate selective calling signals into engagement with contact I58, a circuit is completed from the negative power supply conductor 62 in shunt relation to the holding circuit for relay I41, whereby the relay is released to terminate the operation of remotely controllable device 50I. Similarly a contact I62 of selector 61 is connected through conductors I63, 563 and I64 to the positive terminal of relay I06, so that when the selector disc contact arm is advanced into engagement with contact I52 the holding circuit for relay I06 is shunted by a direct connection to the negative power supply conductor 62, relay I66 is released and the operation of selectively controllable device 502 is terminated.

It will be understood that other outlying stations in the system, such as the stations 3'6 and 31 shown in Fig. 1, are identical with the station shown in Fig. 2 and will have, in addition to the step-by-step selectors 58 and 59 at the stations 36 and 31, respectively, electron discharge tube and relay systems for controlling the conditioning and disablement of the selectors. It will also be understood that such other stations may be equipped with selector controlled apparatus according to Fig. 3, Fig. 4 or Fig. 5 as desired.

Although particular embodiments of the invention have been shown in the drawings and described in the foregoing specification, it will be understood that the invention is not limited to such specific embodiments but is capable of modification and rearrangement without departing from the spirit of the invention and within the scope of the appended claims.

What is claimed is:

1. In a selective station calling system, a first station including means for transmitting rapid telegraph signals and means for transmitting slower station calling signals, a second station including a relay responsive to both of said types of signals, a selector mechanism controlled by said relay, a slow-release relay energizable to disable said selector mechanism and releasable in response to a long spacing signal to restore said selector mechanism to operative condition, and means operable in response to rapid telegraph signals for operating said slow-release relay.

2. In a selective station calling system, a first station including means for transmitting rapid telegraph signals and means for transmitting slower station calling signals, a second station including a relay responsive to both of said types of signals, a selector mechanism controlled by said relay, a slow-release relay operable to disable said selector and releasable to restore said selector to operative condition, a timing relay operable by said signal responsive relay, and means controlled by said timing relay in response to rapid telegraph signals for operating said slow-release relay.

3. In a selective station calling system, a first station including means for transmitting rapid telegraph signals and means for transmitting slower station calling signals, a second station including a relay responsive to both types of signals, a selector mechanism controlled by said relay, a slow-release relay energizable to disable said selector and releasable to restore said selector to operative condition, a timing relay controlled by station including means for transmitting rapid telegraph signals and means for transmitting slower station calling signals, a second station including a relay responsive to both of said types of signals, a selector controlled by said relay, a

slow-release relay energizable t disable said selector and releasable to restore said selector to operative condition, a timing relay controlled by said signal responsive relay, timing means controlled by said timing relay, a normally non-conductive discharge tube rendered conductive bysaid timing means, and means controlledby said discharge tube for operating said slow-release relay.

5. In a selective station call-ing system, a first station including means for transmitting rapid telegraph signals and means for transmitting slower station calling signals, a second station ineluding a relay responsive to both of said types of signals, a selector controlled by said relay, a slow-release relay energizable to disable said selector and releasable to restore the selector to operative condition, a timing relay controlled by said signal responsive relay, timing means including a i normally non-conductive electron discharge tube controlled by said timing relay in response to rapid telegraph signals for rendering said tube conductive, and a relay operable by said tube for energizing said slow-release relay.

6. In a selective station calling system,a first station including means for transmitting rapid telegraph signals and means for transmitting slower station calling signals, a second. station including a relay responsive to both of said types of signals, a selector controlled by said relay, a slow-release relay energizable to disable said selector andreleasable .to restore said selector to operative condition, a timing relay controlled by said signal responsive relay, timing means include ing a normally non-conductive electron discharge tube controlled by said timing relay for rendering said tube conductive inresponse to rapid telegraph signals, a relay operable by saiddischarge tube for energizing said slow-release relay, means controlled by the relay operated by said tube for establishing its own holding circuit, a relay ener sizable concurrently with said slow-release relay, and means controlled by said concurrently energizable relay for disabling said holding circuit.

7. In a selective station calling system, a first station including means for transmitting rapid telegraph signals and means for transmitting slower station calling" signals, a second station including a relay responsive to both of said types of signals, a selector controlled by said relay, a slow-release relay energizable to disable said se lector and releasable to restore said selector to operable condition, a timin relay operable by said signal responsive relay, timing means including a normally non-conductive electron discharge tube controlled by said timing relay in. response to rapid telegraph signals for rendering said tube conductive, a relay controlled by said tube for energizing said slow-release relay, and a relay energizable concurrently with said slow-release said tube for energizing said slow-release relay,

a relay energizable concurrently with said slow-. release relay,;and an indicating instrumentality controlled by said concurrently operable relay so as to operate according to one characteristic when'said relay is energized and according to another characteristicwhen said relay is released. l i

i 9. In a selective station calling system, a first station including means for transmitting rapid telegraph signals and means for transmitting slower station calling signals, a second station including a relay responsive to both of said types of signals, a selector mechanism controlled by said relay, a slow-release relay energizable to disable said selector and releasable to restore said selector to operative condition, means controlled by said signal responsive relay in response torapid telegraph signals for energizing said slow-release relay, an indicator lamp, a source of operating current for said lamp, and means associated with said slow-release relay for connecting said lamp to said source of current steadily when said slow-release relay is released and forconnecting said lamp to said source of current through and under the control of said signal responsive relay when said slow-release relay is energized whereby the operation ofsaid lamp corresponds to theoperation of said signal responsive relay.

10; In a communication system, a first station including means for transmitting rapid telegraph signals and means for transmitting slower station calling ignals, a second station including a relay responsive to both of said types of signals, a signal responsive selector mechanism controlled by said relay, a slow-release relay energizable to disable said selector mechanism and releasable to restore said selector mechanism to operative condition, said slow-release relay having a releasing time longer than spacing intervals normally occurring in said rapid telegraph signals, means controlled by said signal responsive relay in response to rapid telegraph signals for completing the energizing circuit of said slow-release relay, and means associated with said slow-release relay for establishing a holding circuit therefor through the armature of said signal responsive relay to the marking contact whereby said slow-release relay is released only upon response of said signal responsive relay to a continuous spacing signal of a duration at least as long as the release time of said slow-release relay.

11. In a selective station calling system, a

' first station including means for transmitting rapid telegraph signals andmeans for transmitting slower station calling signals, a second station including a relay responsive to both of said types of signals, a, selector controlled by said relay, a slow-release relay energizable to disable said selector and releasable to restore said selector to operable condition, a condenser having a resistor in series therewith, said condenser being chargeable through said resistor and dischargeable independently of said resistor under the control of said signal responsive relay,

discharge tube controlled by said timing relay to render said tube conductive in response to rapid telegraph signals, a relay controlled by a second condenser chargeable in accordance with the current through said resistor, 9, nornals, and a relay operable by said tube for 'energizing said slow-release relay.

12. In a selective station calling system, a station having means for transmitting rapid telegraph signals .and slower station calling signals, a station having a relay responsive to both types of signals, a slow-release relay having a holding circuit releasably by said signal responsive relay, a selector mechanism operable by said signal responsive relay through a back contact of said slow-release relay, and means responsive to rapid telegraph signal operation of said signal responsive relay and unresponsive to slower station calling signal operation of said signal responsive relay for energizing said slowrelease raly whereby to disable said selector mechanism.

13. In a selective station calling system, a station having means for transmitting rapid telegraph signals and slowerstation calling signals, a station having a relay responsive to both types of signals, a slow-release relay having a holding circuit including an armature and front contact thereof and the armature and marking contact of said signal responsive relay, a selector mechanism operable by said signal responsive relay through an armature and back contact of said slow-release relay, and means responsive to rapid telegraph signal operation of said sign-a1 responsive relay and unresponsive to slower station calling signal operation of said signal responsive relay for energizing said slow-release relay whereby to disable said selector mechanism.

14. In a selective station calling system, a station having means for transmitting rapid telegraph signals and slower station calling signals, a station having a relay responsive to both types of signals, a selector mechanism controllable by said signal responsive relay, a relay energizable to disable said selector mechanism and releasable to restore said selector mechanism to operability, a direct current relay operable by said signal responsive relay, means controlled by said direct current relay vfor accumulating electrical potentials in inverse relation to the duration of pulses received by said signal responsive relay, and mean operable .by an .accumulated potential corresponding to a received pulse of shortlduration for causing said disabling relay to be energized.

15.. In a selective station calling system, a station having means for transmitting rapid telegraph signals and slower station calling signals, a station having a relay .responsive to both types of signals, a selector mechanism controllable by said signal responsive relay, a relay energizable to disable said selector mechanism and releasable to restore said selector mechanism to operability, a direct current relay operable by said signal responsive relay, a resistance and condenser network associated with the contacts of said direct current relay, and means controlled by a condenser ,of said network upon rapid operation of said relay in response to rapid telegraph signal operation of said signal respons sive relay for energizing said disabling relay.

ALLAN WEAVER.

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