US2384938A - Signaling system - Google Patents

Description

Se t. 18, 1945. c. E. I OMAX SIGNALING SYSTEM 5 Sheets-Sheet l Original Filed April 26, 1941 m2 7 1 mu QH mma 3 3 8E T 5 I E 33 8 m 5 02 m 5572 f .m: umwm Jmw IN V EN TOR. CLARENCE E. LOMAX M WM,

ATTORNEYS Sept. 18, 1945-. c. E. LOMAX SIGNALING SYSTEM 3 Sheets-Sheet 3 Original Filed April 26, 1941 o2 8m @8331? $16 8 m E j fl fb 6528 Ed m m5 um T $5 in 2m Q Q Q u T b N E n @3 mm om 3 5MB $004k hmmE IN VEN TOR. CLARENCE E. LOMAX ATTORN EY S Patented Sept. 18, 1945 SIGNALING SYSTEM Clarence E. Lomax, Chicago, Ill., assignor to Antomatic Electric Laboratories, Inc., a corporation of Delaware Original application April 26, 1941, Serial No.

390,595, now Patent No. 2,335,524, dated November 30, 1943. Divided and this application November 23, 19442, Serial No. 466,568 1 6 Claims.

The present invention relates to improvements in paging systems and has for one of its objects the provision of an improved signaling system in which the regular branch telephone exchange facilities of a hospital, for example, may be used in conjunction with improved paging equipment to provide a vehicle whereby any person attached to the hospitalstafi may be quickly summoned from any point in the hospital. This application is a division of copending application Serial No. 390,595, filed April 26, 1941, now Patent No. 2,335,524, granted November 30, 1943. i

It is another object of the invention to provide a system of the character described which is simple in arrangement, is positive and reliable in its operation to displa indications designating a large number of persons, and may easily be controlled to display a paging indication on the display board of the system.

It is a further object of the invention to provide a system of the character described wherein the regular automatic switching equipment of the branch exchange is utilized in setting up indications for display by the indicators of the display boards.

It is a further object of the invention to provide a system of the character described, wherein the indications designating a plurality of difi'erent persons who are being concurrentlypaged over the system are sequentially displayed by the display board indicators.

According to another object ofthe invention, each indication posted on the display board is automatically eliminated from the display sequence when a connection is set up through the telephone switching equipment for the purpose of answering the indication. V

It is still another object of the invention to provide a system of the character described, wherein the sequential display of the different in dications is arrested when the number of indications set up for display falls below a predetermined number. v

In the illustrated embodiment of the invention, paging and answering connectors are provided which may be seized through the outlet contacts of the selector switches conventionally included in the automatic switchin equipment of the branch exchange. The paging connectors each have a plurality of different settings which individually correspond to different indications designating difierent persons who maybe paged over the system, and each thereof may be selectively operated to the setting corresponding to any desired person, through operation of the calling or signal transmitting device conventionally provided at each of the branch exchange telephone substations. Display boards are provided on each floor of the hospital, and

each display board is equipped with indicators in the form of signal lamps. These lamps, when energized in different combinations, produce difierent indications, each of which designates a particular person. The signal lamps are selectively controlled in accordance with the settings of operated ones of the paging connectors. More specifically, a display sequence switch is provided which is controlled from the paging connectors and functions to cause the indications set up in these connectors sequentially to be displayed by the display board indicator lamps. This sequence switch only operates when more than one indication is set up for display. If a single indication is set up in one of the paging connectors for display on the display boards, it is continuously displayed.

As indicated above, the paging connectors are also utilized to establish answering connections over which a person being paged may communicatewith the substation from which he is called. To this end, answer trunks are provided which connect the corresponding outlet contacts of all of the paging and answering connectors. By virtoe of this arrangement, a called person may, by dialing a predetermined answer number, arbitrarily assigned to him and to him alone, route a connection through an idle one of the answering connectors to the answer trunk which has been seized by the paging gonnector through which his pagin indication was set up on the display boards. Each paging connector is also equipped with apparatusfor. eliminating an indication set up therethrough from the display sequence exhibited by the display boards when a talking circuit is established therethrough. The novel features believed to be characteristic of the invention are set forthwith particularity in the appended claims. The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specification taken in connection with the accompanying drawings in which Figs. 1, 2 and 3, when combined in the manner illustrated in Fig. 4, illustrate a portion of the equipment provided in a system embodying the features of the invention briefly outlined above.

Referring now more particularly to the drawings, the system there illustrated comprises a plurality of display boards which are individual to tact field are divided into ten levels of ten each, and each of the five banks has associated therewith one of the five wipers Ill to I15, inclusive. For the purpose of elevating these wipers to a position opposite a desired contact level, and then rotating the same into engagement with a selected contact set of the selected level, Vertical and rotary magnets I80 and I 8| are included in "the switching mechanism. The mechanism further comprises a release magnet I82 which, when energized, permits the wiper carriage structure to designating the different doctors who play he paged over the system. Preferably, the lamps of" the different rows are of different color in order to facilitate the reading ot the different indications. For example, the lamps oftheupper row may be white while the lamps of the lower row may be red. It will be understood that additional rows of lamps may be provided if the hum ber of difierent indications which the board is required to display is exceptionall-ylarge. The display boards provided ontheother floors of the hospital are identical inarrangement with the displayboard t8 individual to the first floor. As indicated by the multiple conductors appearing at the base of the rectangle designating the display board I8, the correspondin lamps of the various display boards are arranged to be enersized in parallel, so that identical indications are concurrently displayed by all of the boards. For the purpose of directly controlling the energization oftheselamps, a set of displa-ycon-trol relays t9 is provided. With the illustrated system are rangern-en-t, facilities are available for paging a maggimum ofone hundred doc-tors. If the entire capacity ofthe system is to be used, one hundred display control relays, eachhaving differently wired contacts, are provided. For convenience in explaining the operation of the system, however, onlytwo of these relays, R380 and R390, have been illustrated in the drawings;

In accordance with conventional practice, the hospital is equipped-withbra-nch exchange telephone facilities, which are illustrated asbeing ofthe automatic type. These facilities include the substation lines to and H which respectively EX- tendto the substations A andB; line switches l2 and t3 individual to the lines it! and l t; apluralityof selector switches; of which the two switches ht and W are schematically illustrated, and a plurality of groups of connector switches, not shown. The line switches are individual to the various substation linesof the hospital and each thereof hasaccess to aportion orall of the selector switches. These line switches may beof any desired commercial type, although preferably are of'the well-known rotary type. Similarly, the connector and selector switches ofthebranchexchange may be of any desired form, although pref-- erably are of the well-known Strowger type.

The control of the various displa boards may be effected from any one of the substations of the branch exchangesystern. To this end, a group of paging selectors or connectors is provided. These connectors are accessible to the selectors of the, system; and; in turn, have access. to the display'control relays t9, through the outlet contacts thereof; One such paging: connector [6 is iliustrated in the drawings as being'accessible to the selector it over a trunk 2e. Briefly described, this connector comprises; a two-motion switching mechanism of the welt-known Strowger type, which. mechan sm is equ pp with five banks, of, contacts each including one hundred contact points. The contacts making up this con-- be returned to Iqtary and vertical normal; and two sets of oft-normal springs I16 and I'll which are operated when the wiper carriage structure is moved to any vertical off-normal position. In order to controtthe various magnets of the .Strowger switching mechanism, the line switching,'andthe display control relays l9, the pagii -g; connector [6 is equipped with a plurality of control relays which include a line relay R160, 2; slow to-release hold relay RISE, a slow-to-release transfer relay- RH-t, a busy test relay R130, a slow-to-release transfer relay R920, a slow-tooperateswitching relay R1 HI, and an answer reiay R103 These relays are connected and arranged to operate in the manner more fully explained hereinafter;

As previously indicated, the arrangement of the system is such that when the paging connector to, for example, is directed to a particular setting to set up a, corresponding paging indication for display on the display boards, an answer circuit is partially established. This answer circuit may be utilized establishing a communication connection between the paged doctor andthe person whois paging this doctor; To this end, a group of answering selectors or connectors is provided-L These connectors are also accessible to the selectors of the branch exchange switching equipment and, inturn, have access to a group of answer" trunks. One such answering connector t! is iilnstrated-in the drawings as being accessible to the selector |5- over the trunk 2-? and as having access to the answer trunk 25. The various answer trunks are multipled between the correspondingcontact sets ot'the several answering; and paging connectors. Thus the answer trunk 25 is-illustrated asextending between the corresponding contactsetsof the pagingconnector l6 and the answering connector l1, and as being multipled to the corresponding contact sets of each of the other answering and pagin connectors. I

Bri'eflydescribed, the answering connector l-l comprisesa two-motion switching mechanism of the Weil -known Strowger type, which is equipped with three banks of contacts each including one hundred contact points. The contacts making up this contact field arealso divided: into ten levels of ten each; and each of the three banks has associated therewith one of the three wipers $64 to 36-3, inclusive; Vertical and rotary magnets 364 and 365 are provided for elevating these wipers to a position opposite-a,- desiredcontactl'evel and then rotating thewi-pers' into engagement with aselected contact set of the selected level. The mechanism' further comprises a-release magnet 366-, which when energized permits the wiper carriage structure tobe returned? to rotaryand vertical normal; and two sets of vertical off-normal springs 36! and 368- which are operated when the wiper carriage structure is-moved to any vertical cit-normal position. In order to control the; va-

' ri'ous magnets of the Strowger switching mechanism and the switching of the incoming trunk conductors of the line wipers 36I and 362, a group of control relays isprovided which includes a line relay R300, a slow-to-release hold relay R3I0, a slow-to-release transfer relay R320, a busy test relay R330, a slow-to-release transfer relay R340, and a slow-to-operate line switching relay R350. These relays are connected and arranged to operate in the manner more fully described hereinafter.

As indicated above, provisions are made in the paging facilities whereby the various indications set up through the paging connectors for display by the display boards are displayed in sequence. These facilities include the common equipment or timing apparatus 20. Briefly described, this apparatus comprises a common start relay R200, a sequence start relay R220, a test relay R230, a sequence switch 22, and a set of timing relays 2|. The sequence switch 22 is of the well-known rotary type. More specifically, this switch comprises three sets of contacts 210, TH and 212, each of which includes eleven contact points, wipers 213, 214 and 215 individual to the enumerated contact sets, and means comprising an operatin magnet 216 for driving the wipers over the contacts of their respective associated contact sets. The Operation of this switch is directly controlled by theset of timing relays 2i which comprises only three relays R240, R250 and R200, the last two of which are of the slow-to-operate type.

Current for energizing the indicating lamps and the lamp control relays, as well as the operating magnets and the relaysof the paging and answering connectors, is supplied from a common direct current source, the positive terminal of which is connected to a common bus conductor and to ground. The opposite terminal of this source is connected to a common negative bus conductor which terminates the connections from the various relay, magnet and lamp terminals identified in the drawings by the negative polarity sign. For convenience in describing the circuits involved, the source of current, which may conventionally comprise the exchange battery of the private branch exchange, has not been shown.

In order to facilitate the description of the operation of the system, it may be pointed out that each doctor attached to the staff of the hospital is assigned a predetermined call number, which number, when dialed at any one of the telephone substations of the system, will result in the display of a paging indication individually designating the particular doctor, at all of the display boards. These paging numbers may, if desired, be listed in the branch exchange telephone directory provided at each of the substations located in the hospital. Each doctor attached to the hospital staff is also assigned a predetermined answer number, which number, when dialed at any one of the substations provided in the hospital, will result in the setting up of a connection which extends from the answering substation in use to the calling substation from which the paging indication was posted on the display boards. The call and answer numbers assigned to a particular doctor differ only in the first digit thereof. For example, if the trunks extending to the paging connectors are terminated in the second level of bank contacts of each of the selector'switches, while the trunks extending to the answering connectors are terminated in the'third contact level of each of the selector switches, all call numbers will include a first digit 2 and all answer numbers' will include a first digit 3. The remaining two digits of each of thecall and answer numbers,

r identification number.

in various numerical combinations, serve to dis.- tinguish the difierent doctors. m

With the above brief preliminary explanation in mind, it may be assumed that the substation A is provided for the use of one of the executives of the hospital, and that this executive desires to conferwith the doctor having the call number 265. It may also be assumed that the display control relay R380 is individual to this particular doctor. In order to set up for display the paging indication which designates the doctor'No. 265, the executive removes the receiver provided at the substation A from its supporting hook or cradle and dials the three digits of the doctors When the receiver provided at this substation is removed from its supporting hook or cradle a calling loop circuit is es.- tablished by way of the line I0, which extends to the line switch I2. The line switch I2 nowoperates in a well-known manner to select an idle. one of the selectors to which it has access. If the selector I4 is seized through the outlet contacts of the line switch I2, the calling loop circuit is extended to this selector and dial tone is-returned over the loop to signal the calling executive that the dialing operation may be started. When the first digit 2 is dialed at the calling substation A, the wipers of the selector I4 are elevated to ,a position opposite the second level of bank con: tacts in the associated contact field, and are then automatically rotated to test in succession the trunks terminated in this contact level, until a trunk extending to an idle paging connector is found. Assuming that the paging connector I6 is the first idle connector available, the selector I4, upon positioning its wipers upon the outlet contacts terminating the conductors of the trunk 26, operates to extend the calling loop circuit through the windings of the line relay R I 60. This relay now operates and closes its contacts IBI to complete an obvious circuit for energizing the slow-to-release hold relay RI50, At its contacts I62, the relay RI opens a point in the operating circuit for the release magnet I82 and a point in thecommon portion of the circuits over which impulses are transmitted in succession to the vertical magnet I80 and the rotary magnet I8I.. The hold relay RI50, in operating, closes its contacts I5I to. short-circuit the exchange battery in series with the resistor I63, and thus impress ground potential upon the release conductor 260 of the trunk 26. When this conductor is connected to ground, holding circuits are provided for preventing the release of the selector I4 and the line switch I2, and the paging connector I5 is marked as busy in the bank contacts of the selectors to which it is accessible. In operating, the hold relay RI 50 also closes its contacts I52 to prepare a circuit for en-.

- ergizing the transfer relay RIM and the vertical magnet I in series. At its contacts I53, the re: lay RI50 opens another point in the incomplete operating circuit for the release magnet I82. At its contacts I54, the relay Rl50 prepares operating and locking circuits for the relays RI 00, RI I0 and RI30. Following the operation of the relay RI50, the paging connector I6 is conditioned to respond to the second digit 6 of the call number 265 assigned to the doctor being paged.

When this digitis dialed at the calling substa tion A, the calling loop circuit is opened and closed six times, whereby six impulses are .transmitted to the line relay RI 00. This relay follows the impulses and functions to repeat the same to the transfer relay RI 40, and the vertical magnet I80 over a circuit which initially extends from the winding of RIM] and the winding of the magnet PM: to battery. Each time the relay RI-BU- restores it also opens its contacts "it to interrupt the operating circuit for the hold relay EH55. Due to its slow-to-release characteristic, the hold relay remains operated during impulsing. The transfer relay RIM operates when the abovetraced circuit is initially completed and, due to its slow-to-release characteristic, remains operated until shortly after the second digitisend-ed. In operating, this relay opens its contacts M2 to prevent the impulses of the second digitfrom being repeated to the transfer relay RIZU- and the rotary magnet i8I. At its contacts MI, the relay ft-MU prepares a circuit for Joy-passing the cit-normal contacts I18 in the above-traced pulscircuit. Each time a current pulse is transmitted to the vertical magnet I88 over this circuit it operates to elevate the associated wiper carriagestructure one step, so that at the conclusion of the second digit the wipers III to I! 5, inclusive, are positioned opposite the sixth level of bank contacts in the associated contact field. Incident to the vertical movement of these wipers, the 011 normal contacts H8 are closed and the off-normal contacts I19 are opened. Thus, the second to sixth current pulses are transmitted to the vertical magnet I89 over the above-mentioned bypass circuit which may now be traced as extending from ground by way of the contacts $62, $52, [*18 and Hit, and the winding of the transfer relay RI40i Incident tothe vertical movement of the wiper carriage: structure, the off-norrnal springs I 'I B- are also closed, iurtherto preparethe incomplete operating. circuit for the release magnet I'82'.

At the end of the second digit, and during the inter-digit pause between this digit and the third digit, the line relay R1 60 remains in its-operated position to cause the deenergiz'ation and release of the transfer rel'ayRI m. In releasing, the relay RE-Htll opens its contacts M l tointerrupt the circu t for transmitting current pulses through its winding and the winding of the vertical magnet H in series. At its contacts M2, the retay RI All prepares the above-mentioned circuit for, transmitting current pulses through the series-connected windings of the transfer relay Bil- T and the rotary magnet WI Following the release of the transfer rela-y RIM! the paging connector Iii is conditioned torespondto the five impulses of the third and last digit of the call number assigned to' the doctor No. 265.

When the-third digit is d aled at thecalli ng sub-- station A, the loop circuit extending there through totl'iepaging' connector I6 is opened and closed five times, so that five impulses are transmitted to the'li'ne relay R160. 'I'h-is rel'a'y i-unctions to repeat the impulses tothe transfer relay R120 and the rotary magnet I8! over a circuit which may now be traced as extending from ground by way of the contacts I52, I52, I-Tli, It? and I33, the winding of RI-Z'B, the contacts H and the winding of the magnet I8I to battery. When initially energized over this circuit, the relay RIZII' closes-its contacts I24 to completed path in shunt with the contacts I 33, whereby the impulsing' circuit. is not opened incident to the ope eration of the busy test relay BT39 which may occur as the wipers'IlI to IT5 traverse'thecontacts of the selected level. At its contacts. 5-H, the relay R'I2'Il'opens a point inthe operating circuit for the switching relayRIIli. .At its contacts I22, the relay R120 prepares the operating circuit ground by was or the contacts not, :52 and no,

for the busy test relay RBI]. At its contacts- 23, the relay R I20 opens a point in the locking circuit for thebusy test relay. Due to its slow to-release characteristic, the relay RIZiI remains operated until shortly after the third digit is ended. Each time the magnet WI is energized over the abovetraced circuit, it operates to rotate the wipersill to H5, inclusive, one step, so that at the conclusion of the third digit these wipers are positioned to engage the associated fifth contacts 265 oi the sixth level in the associated contact banks. Thus the control relay R386 individual to the doctor having the identification number 265, is selected.

The operation of the contro1 equipment embodied in the connector I6, which occurs after the third digit is dialed, depends upon whether the control relay R380 has previously been selected through another of the paging connectors from another substation. Thus if the indication individual to the doctor assigned the identification number 265 has already been set up for display on the display boards, the relay R380 will occupy its operated position. With this relay operated, the test contact 2651) individual thereto is connected to ground. Accordingly, when the wipers of the paging connector 16 are positioned to engage the contacts 265 in the manner just explained, a circuit is immediately completed for energizing the busy test relay RI3B This circuit extends from the grounded contact 26522 by way of the wiper I12, the contacts I22 and the winding of RI-3ll to battery. When thus energized, the relay RI3'0 opens its contacts I33 to interrupt the initially completed circuit for transmitting current pulses through the series-connected windings of the transfer relay RIZEI and the rotary magnet I8I. At its contacts I 3I, the relay RI3II opens a point in the operating circuit for theswitching relay RHU. At its contacts I32, the relay RIM prepares a locking circuit for itself. At its contacts I3fi, the relay RI'3I completes a path for transmitting busy tone signaling current over the established loop circuit to the calling" substation A. The path traversed by this current may partially be traced as extending from the ungrounded terminal of the busy tone generator, not shown, by way of the busy tone lead I 35', the contacts I34, the condenser I64, the negative side of the loop extending to the calling substation A, the; receiver'provided at" this substation, the positive' side of the indicated loop circuit and the lower winding of the line relay RIfi'tttothe grounded terminal of the busy tone generator. This current, as reproduced by the receiver provided at the calling substation A, serves to inform the calling executive that the doctor No. 265 is already being paged from another substation.

Shortly following the operation of the busy test relay RIS'O to perform the functions just described, the transfer relay R restores. In re-' leasing, this relay opens its contacts I24 to interrupt the circuit for transmitting current pulses to the nagnetISt. At its contacts I'2"I, the relay RI!!! prepares the operating circuit for the switching relay RI III. At its contacts I23, the relay RI'ZU'compIetes the prepared locking circuit for the busy test relay R, this circuit extending from ground by way of the contacts I54, I32 and I23, and the winding of R130 to battery. After this locking circuit is completed; the relay RiI'ZIl opens its contacts I22 to interrupt the operating circuit for the busy: test relay as traced above: Following the release of the transfer relay RIZII, no further operation of the connector I6 occurs until the connection'is' released at the call- "ing substation. The manner in which the operated switching equipment, comprising the line switch I2, the selector I4 and the connector I6, is released when the call is abandoned at the substation A is explained in detail hereinafter.

In the event the displaycontrol relay R380 occupies its restored position at the time it is selected through the paging connector I6, in the manner explained above, the winding of the busy test relay RI30 is short-circuited over the abovetraced test circuit and remains in its restored position. Accordingly, when the transfer relay RI20 restores shortly following the end of the third digit, a circuit is completed for energizing the switching relay RI I0, this circuit extending from ground by way of the contacts I54 and I3I, the upper winding of RI I0, the contacts I2 I, the test wiper I12 and its engaged contact 265b, the contacts 385 and the resistor 386 to battery. When energized over this circuit the relay RI I first closes its preliminary make contacts I I6 to complete an obvious locking circuit for itself. After this locking circuit is completed, the relay RI I0 opens its contacts II1 further to interrupt the above-traced circuit for transmitting current pulses to the rotary magnet I8I. At its contacts H8 and IIO. the relay RI I0 prepares an answer circuit which extends through the line wipers I14 and I15 to the talking conductors a and 25b of the answer trunk 25. At its contacts II6, the relay RIIO completes an obvious path for impressing ground potential upon the test contact 2651). thereby to mark the display control relay R360 as busy in the bank contacts of the other paging connectors. H the relay RI I 0 disconnects the marking leads 28I and 284 from ground, for a purpose to be described hereinafter. At its contacts II5, the relay RI I0 prepares the operating circuit for the selected display control relay R300.

In operating, the relay RI I0 also functions to initiate the operating of the timing apparatus 20, providing this apparatus is not already operating. Thus when this relay operates, it closes its contacts I I4 to complete a circuit including the start lead I25 for energizing the start relay R200. At

its contacts I I I, the relay RI I0 completes one of the several circuits for energizing the sequence start relay R220, this circuit extending from ground by way of the contacts III and IOI, the lead 281, the resistor 222 and the winding of the relay R220 to battery.

Assuming that the paging indication under consideration is the onlyindication which has been set up for display by the display boards, the start relay R200 is energized and operates when ground potential is applied to the start lead I25. in the manner described above. In operating, this relay closes its contacts 202 to prepare or complete a circuit for energizing the test relay R230. At its contacts 20I,'the relay R200 prepares a circuit for initiating the operation of the timing relays 2|. Assuming that the wipers of the sequence switch 22 occupy a position which corresponds to another of the paging connectors, the operating ci cuit for the test relay R230 is completed. Thus, under the circumstances assumed, all of the paging connectors, with the exception of the connector I6, are idle. Accordingly, all of the marking leads 282, 283, 285, 286, etc., with the exception of the leads 28I and 284 individual to the connector I6, are marked with ground potential. The leads 28I and 204, on the other hand, are disconnected from ground. Accordingly, if the At its contacts II 2 and H3,

wipers213, 214 and215 occupy positions such that the contacts terminating the marking leads 28I and 284 are engaged by the wipers 213 and 214, respectively, the operating circuit for the test relay R230 is not completed incident to the operation of the switching relay RI I0. On the other hand, if these wipers occupy the positions illustrated in the drawings, a circuit including the grounded marking lead 286, the wiper 214 and the contacts 20 2 is completed for energizing the test relay R230. In operating, the test relay R230 opens its contacts 23I to interrupt the prepared operating circuit for the timing relays 2I. At its contacts 232, the relay R230 opens an incomplete circuit for transmitting current pulses to the magnet 216. At its contacts 233, the relay R230 completes an alternative circuit for energizing this magnet. this circuit-extending by way of the grounded marking lead 283, the wiper 213, the contacts 233 and 211, and the winding of the magnet 216 to battery. When thus energized, the magnet-216 operates to condition the associated ratchet and pawl mechanism to advance the wipers 213, 214 and 215 one step. At its contacts 211, the magnet 216 opens its operating circuit. When the magnet 216 is thus deenergized, the ratchet and pawl mechanism controlled thereby functions to advance the wipers 213, 214 and 215 one step, wherein the contacts terminating the marking leads 282, 285 and 289 are respectively engaged thereby. Since the marking leads 282 and 285 are also connected to ground, the magnet 216 is again energized and deenergized to advance the wipers 213,214 and'215 a second step. It will he understood that the stepping operation of the sequence switch 22 continues until the marking leads 28!, 284 and 288, individual to the paging connector I6, are selected. These leads are marked for selection by the absence of ground potential upon the first two thereof. When the paging connector I6 is thus selected by the se quence switch 22,. the test relay R230 is deenergize'd and restores. In releasing, this relay opens its contacts 233 to interrupt the operating circuit for the magnet 216, and closes its contacts 234 further to prepare the above-mentioned circuit for energizing the selected display control relay R380. At its contacts 232, the relay R230 reprepares the other of the operating circuits for the magnet 216. At its contacts 23I, the relay R230 completes the start circuit for the timing relays 2 I,

When this start circuit is completed, the slowto-operatetiming relay R250 is energized in series with the resistor 253. After a short interval, the relay R250 opens its contacts 25I to interrupt the path normallyshort-circuiting the winding of the relay R240. When this path is opened, the relay R240 is energized in a circuit which includes the contacts 2M and 23I, and the resistor 244. In

operating, the relay R240 closes its contacts 24I to prepare one of the operating circuits for the magnet 216, and opens its contacts 242 to interrupt the path normally short-circuiting the winding of the relay R260. The relay R260 is now energized in a circuit which includes the contacts 20! and 23!, and the resistor 263. In operating, the'relay R260 closes its contacts 26I to complete an obvious path for short-circuiting the winding of the relay R250. The latter relay now restores and closes its contacts 25I' to short-circuit the winding of the relay R240. When the relay R240 restores, it .closes its contacts 242 to short-circuit thewinding of the relay R260. The relay R260 now releases, and opensits contacts 26I to interthe wiper 215, the contacts 234 and one or both sets of contacts 243 and 262. Each time the lead 288 is connected to ground, the operating circuit for the selecteddisplay control relay R380 is completed, this circuit extending by way of the grounded lead 288, the contacts "I I and 105, the wiper I11, and the winding of R380 to battery.

In operating, the relay R380 completes circuits for energizing the lamps which have been preselected to display the indication which identifies the doctor No. 265 as the doctor being paged. In the present case, the three lamps 311, 312 and 313 of the display board 48, and the corresponding lamps of the other display boards, are energized by the'relay R330 over circuits which respectively include the contacts 381, 382 and 383. These three lamps when thus energized at each of the display boards serve to provide an indication that the doctor assigned thepage call number 265 is being paged.

The indicated lamps of the several display boards are intermittently energized under the control of the timing relays 2! until the operated switch train, comprising the line switch I2, the

selector M and thepaging connector I6, is re- 7 leased; an answering connection is set up by way .of the answer trunk 25 to the paging connector or a second indication is set up for display by the indicating lamps of the display boards by another of the paging connectors. In this .last connection, it will be recalled from the preceding explanation that when the switching relay R! 10 operates, it closes a.circuit through the resistor 222 for energizing thesequence start relay R220. The current traversing this circuit is insufiicient to cause the operation of the sequence start .relay. When, however, another paging connection is routed through a second paging connector, not shown, to the, display control relays l9, a parallel circuit including one of the resistors 223, 224, 225, etc, is completed for energizing the sequence start relayR229. Thus if the connector individual to the resistor 223 is utilized in selecting the display control relay R390, for ex ample, a parallelcircuit, including the resistor 223, is completed for energizing the sequence start relay R220 when the switching relay of the second paging connector operates. When the sequence start relay R22!) is energized over two or more of the parallel start circuits individual to the paging connectors, it is sufficiently energized to operate. In operating, this relay closes its contacts 221' further to prepare the alternative operating circuit for the operating magnet 216 of the sequence switch 22. With the two start relays R230 and R220 operated, a current pulse is delivered to the operating magnet 2% of the sequence switch 22 during each cycle of the operation of the timing relays 2|. Thus, each time the timing relay R240 operates, it closes its contacts 251 to complete the abovermentioned alternative operating circuit for the .magnet 275. This circuit extends from ground Assuming that the selector 15 is seized by the line relay R393.

by way of the contacts 2!, 23l, 241., 232 and 231, and the winding of the magnet 216 to battery, and is obviously brokenat the contacts 241 each time the timing relay R240 restores. When thus energized and deenergized, the magnet 215, in conjunction with its associated ratchet and pawl mechanism, functions to advance the wipers 2%, 214 and 215 one step. Incident to this movement of the sequence switch wipers thesearching operation of the sequence .switch is again initiated for the purpose of finding the next paging connector through which an .indicationhas been set up for display. In thecase under consideration, onlythe two connectors individual to the. resistors 222. and 223 are operated. Accorclingly,a11 of the marking leads extending to the contact sets 21.0' and 211, with the exception of the leads 28], 282, 284 and- 285, are connected to ground. Hence, the wipers 213, 214

and 225 are rapidly driven to .a position wherein the contacts terminating the leads 282, 285 and .net .215. With the wipers 213, 214.and 215 engaging the contacts terminating the conductors .32; 285 and 239 respectively, the timing relays 2| cooperate to transmit a measured ground pulse through the operated paging connector individual to the lead 289, to the display control This relay, in operating, closes its contacts 391 and 392 to energize the two lamps 31! and 312 and the'corresponding indicator lamps of the otherdisplay boards. Thus an indication is displayed which identifies the doctor who has been called from a second substation of the system. After this indication is exhibited "for a p-redetermined'time interval,the timing relay R245 interrupts the completed operating circuit for the magnet 215, whereby the wipers 213, 214 and 2l5'are again advanced to engage the contacts terminating the leads 281, 284 and "288. With the wipers of the sequence'switch 22 in this position, another ground pulse is transmitted over the display lead 288' to cause the reoperation of the display control relay R380. From the above explanation, it will be apparent that when two or more indications have been set up for display by the indicator lamps of the displayboards, the timing apparatus 20 functions to control'the selected display control relays .19 so that the 'indic'ationsare posted in succession and without overlap between the different indications.

The doctor assigned the call number '265, upon observing the posting of hiscall indication upon oneof the-display boards,'may answer the call by dialing his answer number 365 at any one of the substations of the system. Assuming that the substation B is utilized for this purpose, the answering doctor, upon removing the receiver provided at this substation from its supporting hook or cradle, completes a loop circuit which extends by way of the line H to the line switch i3. This line switch now operates to seize an idle one of the selectors to which it has access.

switch 13, the calling loop circuit is extended thereto and dial tone is returned to the substation B in a manner well understood in the art. When the first digit 3. is dialed at this substation, the wipers of the selector I are elevated to a position opposite the level of bank contacts at which the trunks extending to the answering connectors are terminated. At the end of the digit, and during the inter-digit pause between the first and second digits, the wipers of the selector I5 are automatically rotated until the trunk extending to an idle answering connector is found. Assuming that the answering connector I! is the first idle connector available, the selector I5, upon positioning its wipers on the contacts terminating the conductors of the trunk 27, extends the calling loop circuit to the line relay R300. When energized in this loop circuit, the relay R360 closes its contacts 302 to complete an obvious circuit for energizing the slowto-release hold relay R3I0. At its contacts the relay R360 opens a point in the circuit for energizing the release magnet 366, and a point in the common portion of the circuits over which impulses are transmitted to the vertical magnet 364 and the rotary magnet 365.

I'he hold relay R3I0, upon operating, connects the release conductor 210 of the trunk 2'! to ground over a path including the contacts 3! I, thereby to mark the connector I! as busy and to provide locking circuits which prevent the release of the selector I5 and the line switch I3. At its contacts 3I2, the relay R3I0 opens another point in the operating circuit for the release magnet 366. At its contacts 3L3, the relay R3l0 prepares the above-mentioned circuits for transmitting impulses to the vertical and rotary'magnets 364 and 365. Following the operation of the hold relay R3), the answering connector I! is conditioned to respond to the impulses of the second digit 6 of the answer number assigned to the calling doctor.

When this digit is dialed at the substation B, the loop circuit extending from this substation to the connector I! is opened and closed six times, whereby six impulses are transmitted to the line relay R300. This relay, in follOWing the impulses, repeats the same to the series-connected windings of the transfer relay R326 and the vertical magnet 364 over a circuit which initially includes the contacts 36!, 3I3 and 363. Each time the relay R300 restores, it also opens its contacts 362 to interrupt the operating circuit for the hold relay R3 0. The latter relay, due to its slow-to-release characteristic, remains operated during impulsing.

When initially energized at the beginning of the second digit, the transfer relay R320 opens its contacts 32! to prevent the impulses from being transmitted to the transfer relay R340 and the rotary magnet 365. At its contacts 322, the relay R320 prepares a pulse by-pass path around the off-normal contacts 369. Each time the vertical magnet 364 is energized in the pulsing circuit traced above, it operates to elevate the wipers 36! to 363, inclusive, one step so that at the end of the second digit these wipers are positioned opposite the sixth level of bank contacts in the associated contact field. Incident to the first vertical step of the wiper carriage structure, the off-normal contacts 310 are moved into engage- "ment and the oil-normal contacts 369 are disengaged. Thus the second and succeeding impulses of the second digit are transmitted to the transfer relay R320 and the vertical magnet 364 over a circuit which includes the contacts 36!, (H3, 310 and 322. Incident to the vertical movement of the wiper carriage structure the oil-normal springs 361 are also moved into engagement to prepare the operating circuit for' the release magnet 366.

Shortly following the end of the second digit the transfer relay R320 restores. In releasing, this relay opens its contacts 322 to interrupt the by-pass pulsing circuit which extends through its winding to the vertical magnet 364. At its contacts 32!,the relay R320 further prepares the circuit for transmitting impulses to the transfer relay R340 and the rotary magnet 365.

When the third digit 5 of the answer number assigned to the doctor using the substation B is dialed at this substation, the loop circuit extending to the connector I! is opened and closed five times, whereby five impulses are transmitted to the line relay R300.' This relay, in following the impulses, repeats the same to the transfer relay R340 and the rotary magnet 365 over a circuit which may now be traced as extending from ground by way of the contacts 30!, 3I3, 370, 32! and 33!, the Winding of R340, the contacts 352 and the winding of the rotary magnet 365 to battery. When initially energized over this circuit the transfer relay R340 closes its contacts 34! to shunt the break contacts 33! of the busy test relay R330. At its contacts 344, the

characteristic, the relay R340 remains operated until shortly after the third digit is ended. Each time the rotary magnet 365 is energized in the above-traced pulsing circuit, it functions to ro tate the wipers 36! to 363, inclusive, one step so that at the conclusion of the third digit these wipers are positioned to engage the contacts of the fifth contact set in the sixth level of contacts in the associated contact field. More specifically, these wipers are operated to engage the contacts 3650, 365d and 365s at which the conductors of the answer trunk 25 are terminated.

The operations whichfollow the selection of the answer trunk 25 in the manner just described, depend upon the idle or busy condition of this trunk. Thus, if a connection is routed to this trunk from another substation of the system, prior to the operation of the answering connector I! to select the trunk, the private conductor 250 is marked with ground potential over a path which includes the wiper I13 and the contacts I54 and I66. In such case, the busy test relay R330 is energized immediately the wipers of the answering connector I! are positioned to engage the contacts 365, the circuit fonenergizing this relay extending by way of the grounded test conductor 250, the contact 3650, the wiper 363, the contacts 342, and the winding of R330 to battery. In operating, the relay R330 opens its contacts 33! to interrupt the initially traced operating circuit for the relay R340 and the rotary magnet 365. At its contacts 333, the relay R330 opens a point in the operating circuit for the switching relay R350. At its contacts 332, the relay R330 prepares a locking circuit for itself. This locking circuit, which includes the contacts 3 and 343, is completed at the contacts 343 when the transfer relay R340 restores shortly after the dialing of the third and final digit. In releasing, the relay R340 also opens its contacts 34! to prevent current pulses from being transmitted through its winding to the rotary magnet 365. At its contacts 342, the relay R340 opens the operatingjxcircuit for the busy test relay R330. At its contacts 344, the relay R340 prepares the operating circuit for the switching relay R350. Atits contacts .334, the busy test relay R330, in operating, also completes a circuit for transmitting busy tone signaling current over the trunk '211to the calling substation B. This circuit may partially be traced as extending from the ungrounded terminal of the busy tone generator, not shown, by way of the condenser 135, the 'con tacts 334., the negative side of the .loop extending to the-substation B, the receiver provided at this substation; the positive side of the loop, and the lower winding :02 the line relay R300 to the grounded terminal of the busy tone generator. The current traversing this circuit is reproduced by :the receiverprovided at the substation B to -inform the answering doctor that the paging indication displayed by the indicator lamps has already" been answered. In this regard, it will be noted that the answer trunk 25 is provided for the individual use of the doctor assigned the page call number 265. Accordingly, the busy condition ofthis trunk as described above will not ordinarily be encountered, unless the doctor has previously instructed his secretary or one of his-assistants to answer his paging indications asthey are posted on the display boards,

In the case under consideration, the answer trunk 25 will normally be idle at the time it is selected through one of the answering connectors. With the answer trunk 25 idle, the test conductor 25c thereof'is marked with negative battery potential through the winding of the answer relay RI00, so that the-busy test relay R330 is shortcircuited when the wipers 36L 362 and 363 are positioned to engage the contacts 3656, 36511 and 365e, respectively. Accordingly, the busy test relay does not operate. When the transfer relay R-IvHl restores shortly after the end of the third digit, the prepared operating circuit for the switching relay R350 is completed, this circuit extending from ground by way of the contacts 3M and 333, the lower winding of R350, the contacts 344, the Wiper 363 and its engaged contact plete an obvious locking circuit for itself. Thereafter the relay R350 opens its contacts 352 to interrupt the circuit for transmitting current pulses to the rotary magnet 305. At its contacts '3-5I, the relay R350 opens another point in the operating circuit for the release magnet 366. its contacts 354, the relay R350 completes a more direct circuit for energizing the answer relay RI and for impressing ground potential upon the test conductor 250 of the answer trunk 25. This circuit extends from ground by way of the contacts 354, the wiper 363, the contact 3650, the test conductor c, the contact 2650, the wiper I13 and the winding of Rl00 .to battery. At its contacts 355 and 356, the relay R350 connects the talking conductors of the trunk 2'! to the line wipers 362 and thereby to complete a communication circuit which includes the talking conductors 25a and 25b of the answer trunk 25 and extends between the substations A and B. After. this communication circuit is completed the answering doctor and the calling eXecutive,

:aesacas 'manner explained above, the indication individual to the answering doctor is eliminated from the different indications which are sequentially posted on the display boards under the control of the timing apparatus 20. Thus when the ans- Wer relay RI-00 is energized over the above-traced circuit it operates and locks to ground over a path including the contacts I06 and 'I-54. At its contacts 1'05, the relay RI 0'0 interrupts the abovetraced circuit over which ground pulses are transmitted to the display control relay R380 under the control of the timing relays 2|. After this circuit is opened the indication individual to the answering doctor No. 265 obviously cannot be posted on the display boards. At its contacts I04, the relay R opens the path, individual to the paging connector 46, over which ground potential is impressed upon the start lead I25. At its contacts I02 and I03, the relay R-I00 connects the two marking leads 2 8I and 284 to individual to the paging connector I6, over which the sequence start relay R220 is energized. In this regard, it will be understood that if only one other paging connector is operated at the time the answer relay R100 operates, the sequence start relay R220 is insuiiiciently energized to retain its operated position after the circuit extending through the resistor 222 is opened at the contacts 'IOI. Accordingly, this relay will restore and open its contacts 22I to prevent further operation of the sequence switch 22. It will also be understood from the foregoing explanation that if the paging connector I6 is the only operated one of the paging connectors, the operation of the timing apparatus 20 is arrested incident to the operation of the answer relay RI-Ull. In such case the relay RIDE, in operatingto open its contacts I04, interrupts the last available operating circuit for the start relay R200. The relay R200 accordingly restores and opens its contacts 20I to interrupt the start circuit extending to the timing relays 2|. At its contacts 202, the relay R200 interrupts the circuit for energizing the test relay R230. Following the release of the relays R200 and R230, the timing apparatus 20 is fully restored to normal.

The release of the connection established between the substations A and B through the paging connector I6 and the answering connector I1 is effected from both of these substations. Thus when the calling 100p circuit is interrupted at the substation A, the line relay RI60 is deenergized and restores. In releasing, this relay opens its contacts Ir6l to deenergize the hold relay R150. The latter relay restores, after an interval, and opens its contacts I5I to disconnect the release conductor 230 of the trunk 26 from ground and thus open the locking circuits for the operated relays of the selector I4 and the line switch I2. When the last-mentioned relays are deenergized the selector I4 and the line switch I2 are released in a manner well understood in the-art- In restoring, the hold relay RI50 also opens its contacts I54 to interrupt the locking circuits for the relays RIM and RI I6. At its contacts I53, the

. relay RI56 completes a circuit including the contacts I62 and the off-normal springs I16 for energizing the release magnet I82. This magnet, in operating, attracts its associated holding pawl, whereby the wiper carriage structure of the connector I6 is restored to rotary and vertical normal, in the usual manner. Incident to the release of the Strowger switching mechanism, the offnormal contacts I18 are disengaged, the off-normal contacts I19 are moved into engagement, and the ofi-normal contacts [16 are disengaged .to deenergize the release magnet I62. Following the release of the magnet I82, the connector; is fully restored to normal. The manner in which the paging connector I6 is released, when a connection is set up therethrough to an operated or busy one of the display control relays, is substantially the same as described above. In the latter case, however, the two relays RIDE! and RI III are not operated. On the other hand, the busy test relay Rl36, which is operated, is deenergized and restores incident to the release of the hold relay RI56. In the event no answering connection is established through the paging connector I6 in the manner explained above, the answer relay RIDE! is not operated at the time the call is abandoned at the calling substation A. In this case the release of the connection is effected inthe exact manner described above. The display of the indication set up through theconnector I6 continues, however, until theswitching relay RI I restores. In releasing, the relay RI I6 exercises the same control over the timing apparatus 26, as is accomplished through operation of the answer relay RIM in the manner explained above.

When the above described connection set up between the substations B and A is cleared out at thesubstation B, the calling loop circuit extending from this substation to the answering connector I1 is interrupted to cause the deenergization and release of the line relay R300. Upon restoring, this relay closes its contacts 3M further to prepare the operating circuit for the release magnet 366, and opens its contacts 302 to deenergize the holdv relay R3I6. The latter relay restores after an interval and opens its contacts 3I4 to cause the deenergization and release of the switching relay R356. At its contacts 3I2, the relay R3I6 further prepares the operating circuit for the release magnet 366. At its contacts 3| I, the relay R3I0 disconnects the release conductor 210 of the trunk 21 from ground, whereby the selector I and the lin switch I3 are caused to release, in the usual manner. The relay R356, upon restoring, closes its contacts 35I to complete the prepared operating circuit for the release magnet 366, this circuit extending by way of the contacts 31, 3I2 and 35I, the off-normal springs 361 and the winding of the magnet 366 to battery. At its contacts 354, the relay R356 disconnects the private wiper 3 63 from ground'to open one of the paths over which ground potential is impressed upon the test conductor 25c of the answer trunk 25. When the release magnet 366 is energized, it attracts its associated holding pawl to permit the wipers EM, 362 and 363 to be returned to rotary and vertical normal, in the usual manner. Incident to the release of these Wipers, the off-normal springs 361 are disengaged to. deenergize the release magnet 366, the offnormal contacts 310 are disengaged, and the offnormal contacts 369 are moved back into engagemerit. .Following the release of the magnet 366 the answering connector I1 is fully restored to normal. "In the eventcthe answering connection, as routed from the substation B through the line switch I3, the selector I5 and the answering connector'Ilto the answer trunk 25, is not extended to the substation A due to the busy condition of the trunk, the three enumerated switching units may be. released from the substation B in substantiall the exact manner described above. In this case,,however, the switching relay R356 is not operated. on the other hand, the busy test relay R330, which is operated, is deenergized and restores in response to the release of the hold relay R3I6.

It may occur that the paging indication as posted on the various display boards through the paging connector I6, in the manner explained above, will not be answered by the person paged, or one of his subordinates, before the calling end of, the connection is cleared out at the calling substation; In such case if an answering connection is routed through the line switch II, the selector I5 and the connector II, to the answer trunk'25, neither the busy test relay R336 nor the switching'relay R350 is operated incident to the release of the transfer relay R346. Accordingly, the. doctor answering the page call at the substation E fails ,toreceive busy tone or to obtain aconnection with the calling party. The absence of the busy tone signal and the dead character of the connection indicates to the doctor that the call'has been abandoned befor it was answered. Accordingly he may restore the receiver provided at the substation B to its supporting hook or cradle to initiate the release of the operated switch train, in the exact manner described above. While there has been described what is at present considered to be .the preferred embodiment of the invention, it will .be understood that various modifications may be made therein, and it is contemplated to cover in the appended claims all such modifications as 'fall within the true spirit and scope of the invention.

What is claimed is: 1.;1n a paging system, a display board including a'plurality; of indicatorsfor displaying indicationspf persons being paged, a plurality of remote control stations each including an impulse transmitting means, a plurality of impulse responsivedevices for setting up a plurality of indicationsi'o'r display by said indicators, means including a cyclically operating'sequence switch interconnecting said indicators and said impulse responsive devices for successively and repeatedly displaying a plurality of indications set up for display by said impulse responsive devices, means responsive to the setting up of an indication on one of said devices for causing said first means to display an indication, means responsive to the setting up of two or more indications on said impulse responsive devices for causing the said cyclic operation of said sequence switch, and means for arresting the said cyclic operation of said sequence switch when only one indication remains set up on said impulse responsive devices to repeatedly display said indication as long as only one display remains to be displayed.

2. In a paging system, a display board including a plurality of indicators for displaying indications of persons being paged, a plurality of remote control stations each including an impulse transmitting device, a plurality of selectively controllable devices for setting up in accordance with impulses received from any of said transmitting devices indications for display by said indicators, means interconnecting said selectively controllable devices and said indicators for-repeatedly displaying an indication set up until the calling control station releases the indication set up, means responsive to the setting up of a plurality of indications on said selectively controllable devices for causing said indicators to successively and repeatedly display said plurality of indications, and means for arresting the operation of said latter means when only one indication remains set up on said selectively controllable devices to repeatedly display said indication as long as only one display remains to be displayed.

3. In a paging system, a display board including indicators for displaying indications of persons being paged, a plurality of remote control stations each including a signal transmitting device, a plurality of selectively controllable devices for setting up in accordance with signals from any of said transmitting device indications for display by said indicators, means interconnectin said devices and said indicators for repeatedly displaying an indication set up until the calling control station releases the control device of the set-up displayed, means responsive to the setting up of a plurality of indications on said selectively controllable devices for causing said indicators to successively and repeatedly display said plurality of indications, and means for arresting the operation of said latter means when only one indication remains set up on said selectively controllable devices to repeatedly display said indication as long as only one display remains to be displayed.

4., In a paging sy tem, a display board, including indicators for displaying indications of persons being paged, a plurality of remote control stations each including a digit impulse transmit, ing device, a plurality of digit impulse responsive switches for setting up a plurality of indications for display by said indicators, a cyclically operat ing sequence switch interconnecting said indicators and said impulse responsive switches for successively and repeatedly displaying a plurality of indications set up for display by said impulse responsive switches, means responsive to the setting up of two or more indications on said impulse responsive switches for causing the said cyclic operation of said cyclically operating sequence switch, and means for arresting the said, cyclic operation of said sequence switch when only one indication is set up on one of said impulse responsive switches to repeatedly display said indication as long as only one display remains to be displayed 5. In a paging system, a display board including theindicators for displaying indications of persons to be paged, a plurality of control stations each including a signal transmitting device, a plurality of selectively controllable set-up apparatus for settin up indications for display by said indicators under the control of the signal transmitting device at any one of said plurality of stations, sequence switch means for operatively connecting in sequence the plurality of set-up apparatus to the indicators of the display boardand thereby causing the indicators to display in sequence the indications set up in the plurality of set-up apparatus, operating means for said switch means to cause said switch means to perform its sequential switching, and means operative by each set-up apparatus only if an indication is set up therein for arresting the operation of said sequence switchin cooperation with said one set-up apparatus for a predetermined time and thereafter permit said sequence switch to continue its sequential operation.

6. a paging system, a display board including indicators for displaying indications of persons to be paged, a plurality of control stations each including a signal transmitting device, a plurality of selectively controllable set-up apparatus for setting up indications for display by said indicators under control of the signal transmitting device at any one of said plurality of stations, a normally inoperative sequence switch, means: for starting said sequence switch inoperation responsive to the set up of an indication in y one Of Said p pparatus to operatively connect the indicators of said display board with the said operated set-up apparatus, means for operatively connecting said sequence switch in sequence to a plurality f set-up apparatus and thereby causing the indicators to display in sequence the indications set up in the plurality of set-up apparatus, operating means for said sequence switch to cause said sequence switch to perform its sequential switching, and means operative by each set-up apparatus only if an indication is set up therein for arresting the operation of said sequence switch in cooperation with said one set-up apparatus for a predetermined time and thereafter permit said sequence switch to continue its sequential operation.

CLARENCE E, LOMAX.

Images