US2921116A - Teletypewriter automatic alarm reporting system - Google Patents

Description

Jan. 12, 1960 w. E. MAKARY 2,921,116

TELETYPEWRITER AUTOMATIC ALARM REPORTING SYSTEM Filed AprilV 28, 1958 3 Sheets-Sheet 1 VA rvA /VA KVA fuA rv n R h E m Q n w x r S l km SEH; w ..0`l

y j AT TOR/VY Jan. 12, 1960 w. E. MAKARY TELETYPEWRITER AUTOMATIC ALARM REPORTING SYSTEM 3 Sheets-Sheet 2 Filed April 28, 1958 l/Nl/E/vo? W E. MAKARY BV /ly @M ATTORNEY Jan. 12, 1960 w. E. MAKARY TELETYPEMRITER AUTOMATIC ALARM REPORTING SYSTEM Filed April 28, 195e 3 Sheets-Sheet 5 /NVENTOR W E. MAKARY f z. M4?

ATTO/QN y United States Patent() TELETYPEWRITER AUTOMATIC ALARM REPORTING SYSTEM William E. Makary, Pittsburgh, Pa., assignor to American Telephone and Telegraph Company, a corporation of VNew York y Application April zs, 1958seria1 No. `731,467* 6 claims. (ci. ris- 2) This invention relates to a teletypewriter station alarm reporting system and more particularly to a reporting system wherein a plurality of reporting stations on a multistation line are selectively instructed to report Atrouble conditions to a central control station.

sequentially and transmits teletypewriter code characters back to the control station indicative of the conditions system of this type, the scanning' circuit precludes the reporting of normal conditions and reports trouble conditions only. In such known systems, however, this type of scanning equipment has either required complex (circuitry or operation at scanning rates which are slow relative to the signaling speed at which the system isoperable. A further object of this invention is to provide an `improved teletypewriter station trou-ble alarm scanning circuit which reports trouble conditions only.

Another object is to provide a reporting station scanning circuit which has relatively few components and which passes instantly over switching equipments indicating normal conditions.

In accordance with the preferred embodiment off the present invention,the stations are connected to a common multistation line. Each reporting station is provided with a sending distributor, a sequential selector seleclrelays, in which chain the operation of each relay precludes the operation of relays subsequent in the chain. Assuming none of the prior relays is operated, the'nal leads withV an acknowledgement code character. Each ofthe relays other than the final relay in the chain is operated in turn, when an associated alarm switch'is closed by a trouble condition, assuming no'relay prior thereto is operated.Y 'Ihe operation of any relay'in the chain codes the distributor leads with an alarm code character indicative of the trouble condition. The sequential selector at the reporting station'responds to the station polling Vcharacter transmitted from the central `existing at the reporting station. In a preferred known d line 2 is shown extending from a central control station,

tivelyresponsive to teletypewriter'code*characters imi vpressed on the multistation line and a chain of coding relay in the chain is operated and codes the,l distributor i station by releasing the distributor to send the code chari acter coded on the distributor leads. In addition, the sequential tselector responds to the transmission of each alarm code character by selectively releasing the coding relay individual thereto, permitting the operation of a subsequent relay, and releasing the distributor to send the "ice 2 code character coded on the distributor leads by the subsequent relay. In this manner, the lreporting station sequentially transmits code characters Aindicative of trouble conditions, if any, followed by an acknowledgement character and. then returns to the initial waiting condition which prevailed prior to the reception of the polling character.

The means for fulfilling the objectsand the practical embodiment of the features of this invention will be fully understood from the following description taken in conjunction with the accompanying drawings wherein:

Fig. 1 shows the details of circuits and equipments which form a typical central control station;

Fig. 2 shows the details of circuits and equipments which form a typical reporting station in accordance with this inention; and l Fig. 3 illustrates in block form the layout of the various circuits and equipments of the central control station and the outlying reporting stations and the manner in which theycooperate.

In Fig. 1 and Fig. 2, comprising the detailed circuit disclosure, the detachedcontact method of exposition used vin Patent 2,722,675, granted to J. Michal and R. E. Staehler'onNovember- 1, 1955, has been adopted. In the detached contact method, the relay 'core and its winding, `or windings, are shown physically separated from the contact controlled thereby and is given a letter or letters designation.v Contacts which are closed when the relay is deen'ergized are represented by a single short line perpendicular to the line representing the conductor, and contacts which are 'closed when the relayis energized are represented by two shortcrossed lines diagonally intersecting the conductorline. Each of the contacts is given the same ,letterl designation asY its associated relay core. f

Referring now to Fig. 3, a typical half-duplex party generally indicated by block 1, to'six outlying reporting stations of which only three, namely reporting station A, reportingfstation B and station F are shown in Fig. 3. It is to be understood that any number of outlying stationsmaybe served by party line 2. f t

Party line 2 comprises a loop or channel for transmitting signals from the central station 1 to the outlying stationsV and from the outlying stations to central station, 1. Party line `2 is shown as a metallic transmission loop, but it is to bev understood that it may include any`of the usual' Vtypes of transmission channels suitable for the transmission of telegraph signals in both directions, but not at the same time.

In general, central station 1 is provided with printer 3, sequential selector 4, timer 5 and distributor 6, all associated with party line 2.` Central station 1 is also provided with audible andvisible alarms, indicated by block 7, and coding circuit 8 which functions to code distributor 6 with code characters designed to selectively poll the outlying stations, one at a time and in rotation.

Printer 3, sequential'selector 4 and timer 5 are responsive to all line signals impressed on party line 2. Printer 3 may be a page printer similar to the type disclosed in Patent No. 1,904,164, granted toS. Morton et al. on April 18, 1933. Sequential selector 4 operates selected contacts` in response to predetermined code signals impressed on party line 2. A sequential selector suitable for use in this system is disclosed in Patent No. 2,568,264, granted to W. I. Zenner on September 18, 1951.. The disclosures of these patents are hereby incorporated by reference as though fully set forth herein.

Reporting station A may be considered as typical of the outlying reporting stations and is provided with sequential selector 11 and distributor 12, both associated with line 2. In addition, the outlyingstation is provided with coding circuit 13 and alarm switches 14. Sequential selector 11 is similar to sequential selector 4 at central station 1.

Alarm switches :14 comprise a plurailty of switches associated with individual testing or sensing apparatus of Ithe type, well known in the art, that selectively operate the switches upon the occurrence of a trouble or alarm condition. Upon the operation of one or more of the switches, coding circuit 13 is instructed by alarm switches 14 to sequentially code the distributor 12 with code characters individual to each of the operated switches and coding circuit 13, which normally codes an acknowledgement code character on the distributor leads, removes the acknowledgement signal coding and codes the distributor 12 with the -rst sequential alarm code character.

Assuming now that central station 1 'transmits the polling character individual to station ,A, sequential selector 11 responds by releasing distributor 12 to send the first alarm code character, if any. Upon the trans mission of the alarm code character, sequential selector 11 instructs code circuit `15 to code lthe distributor 12 with the next subsequent character and ,again releases distributor 12. This process is repeated for the transmission of each of the alarm code characters until all the alarm code characters are transmitted whereupon code circuit 13 codes theY distributor 12 with the acknowledgement code character, which is transmittedrupon the -release of distributor 12. Reporting station Athen stops sending.

If outlying station A does not have any alarm conditions to report, only the acknowledgement code character, which is normally coded on the distributor leads by coding circuit 12, will be transmitted when station A is polled.

Printer 3 at central station 1 prints the polling character transmitted by central station 1, the alarm characters, if any, and the subsequent acknowledgement character transmitted by the polled reporting station. When an alarm character is received by central station 1, sequential selector A4 responds by actuating the audible and visible alarms 7 and when the acknowledgement character is received by central station 1, sequential selector 4 responds by instructing coding circuit 8 to code distributor 6 with the code character designed to selectively poll the outlying station next in rotation and releasing distributor 6 to send the polling character.

Timer 5 times the duration between the transmission of the polling character and the reception of the reply from the polled outlying station. If the outlying station fails to respond within a predetermined time, timer 5 actuates the audible and visible alarms, instructs coding circuit 8 to code distributor `6 with the next polling character and releases distributor 6 to send the polling character. ,y

Referring now to Fig. l, showingy the detailed -circuitry of the central control station, negative line battery is Vapplied to the loop of the half-duplex transmission line by way of the winding of relay L, the stop contact of the distributor, generally indicated at 21, and

the winding of polarized line relay LR. Thus, relay LRv follows the line signaling and relay L is maintained 'operated during the marking or closed condition of the line.

A path is completed from ground to battery by way of the armature and marking or break contact of relay LR and the winding of the select magnet of printer 22 whereby printer 22 prints all line signals. In addition, a .path is vcompleted from ground to battery by way of the armature and marking contact of relay LR and the winding .of the select magnet of the sequential selector,

vgenerally indicated at 23, and sequential selector 23 follows all line signals.

'Sequential selector 23 is sirnilarto the type described in the above-mentioned 'Zermer patent. As shown in Fig. "l, sequential selector 23 is provided with eight 4 normally open contacts 31 through 38. Contacts 31 through 36 momentarily close when code characters P, Q, U, S, X, and W, respectively, are applied to the line and contacts 37 and 38 momentarily close when code characters H and Carriage Return are applied to the line. As subsequently described, characters P, Q, U, S, X, and W constitute the alarm code characters of the outlying stations and character H, the acknowledgement character of the outlying stations.

With the line in the idle marking condition, relay L is maintained operated completing an obvious operating path for slow-to-release relay BK via the make contacts of relay L. Relay BK operated opens the A.C. circuit of open line lamp 25 via A.C. source 40 and break contacts of relay BK and opens the A C. circuit of buzzer 26 via A.C. source 40, break contacts of relay BK and the contacts of buzzer disable key 27, maintaining lamp 25 and buzzer 26 deenergized. Relay BK being slow `release, will not release during normal line signaling.

Relay L operated also removes the negative cathode voltage applied to thevcontrol anode of gas tube T-Z by way of the break contacts of relay L and resistor R-2. In addition, relayL operated removes the ground applied to the lower plate of condenser C -1, as shown in Fig. 1, whereby a negative pulse is applied to the junction of resistors R-l and R-2 by way of resistor R-3 and condenser C-l. The resulting negative charge on the upper plate of condenser C-'l is slowly discharged to ground by way` ofrresistor R-l. After approximately three minutes of idle line condition, condenser C-l suiciently discharges to ground to raise the voltage of the control anode of tube T-2 to the point where tube T-2 res, vdrawing plate current from ground by way of the winding of relay TA, the break contacts of relay B, and the make contacts of relay L, operated, operating relay TA.

Relay TA operated completes a path from ground by way of lthe winding of relay A, the make contacts of normally-operated slow-to-release relay S and the make contacts of relay TA to battery operating relay A which locks by way of its own make contacts and the make contacts of relay S. v

Relay A operated completes an obvious operating path for slow-to-release relay B which ylocks by way of its own make contacts and the break contacts of relay TM.

Relay B operated opens the previously described plate circuit for tubeA T-Z, extinguishing the tube and releasing relay TA. The release of relay TA opens the operating pathfor relay A.

In addition, relay B operated removes the negative `cathode battery applied to the control anode of gas tube T-1 by way ofthe break contacts of relay B and resistor YR-S; Condenser C-Z starts vto discharge towards ground `by way ofresistor -R-4 and after approximately twoseconds the voltage on the upper plate of condenser VC-2 is suiciently raised to re tube T-1 which draws plate current from groundby way of the winding of relay TM and the make contacts of relay B operated.

Returning now to relay A operated, an obvious energizing path for step magnet 41 of the step-on release selector, generally indicated at l42, isv completed Via the make contacts of relay A energizing step magnet 41. The energization of step magnet 41 opens interrupter contacts 43,- thus opening the operating path for normally-operated {slow-to-release relay S.

When relay S releases, the previously described operating and locking paths for relay A are opened releasing relay A. The release of relay A opens the operating path `for relay B and opens the energizing path for step magnet 41 which releases and steps the wrpers of step-on release selector 42.

Step-on release 'selector 42 is provided with six arcs designated A through F and associated wipers. The Ywiper of :arc A .is vconnected to ground and the wipers of arcs B through F are connected to contacts 1 through 5, respectively, of distributor 21. In the specific embodiment shown in Fig. 1, position l of arcs B and C are connected to line battery by way of resistor R-6 so that with the wipers on position 1, contacts 1 and 2 of the distributor 21 are connected to line battery, coding the distributor for the'character A. vIn a similar manner, distributor 21 is coded for the characters B, C, D, E, and F when the wipers are on positions 2, 3, 4, 5, and 6, respectively. In addition, with the 4Wipers in position 7, distributor 21 is coded for the character Carriage Return and with the wipers on position 10, distributor 21 is coded for the character Letters.

Characters A through F constitute the selection codes for the remote calling stations. It is apparent that the arcs ofsrelector 42 may be coded in any suitable manlner to poll outlying calling stations in any desired rotation.. Assuming that upon the release of step magnet 41 the wipers of selector V42 step to position 1, distributor 21 is coded for character A, the selection code of the rst outlying station A. S

.l Returning now to the` operation of relay TM, an obvious energizing path via the make contacts ofrelay TM is completed for clutch magnet 45 of distributor 21. Distributor 21 is released and impresses character Aon the line and printer 22, following the line signals, prints character A. Relay TM operated also opens the previously described locking path-for slow release relay B and when relay B releases it opens the previously described plate circuit of tube T-1 extinguishing tube T-1 and releasing relay TM. v

Relay L is periodically being released during the transmission of `the character-A, maintaining the negative cathode voltage'on the upper plate of condenser C-l whereby condenser C-1 cannot discharge to tire tube T-Z. f

The outlying reporting station, 'shown in Fig. 2, is typical of the six remote stations A through F with the several exceptions noted hereafter. In the normal idle condition the loop of the half-duplex transmission line terminating in the outlying station is maintained closed by way of lead 101, the stop contacts of the distributor, generally indicated at 121, and the winding of polarized line relay RR and a path is completed from ground to battery by way of the armature and the marking or break contact of relay RR and the winding of the select magnet of the sequential selector generally indicated at 123 whereby sequential selector'123 follows all vline signals.

Sequential selector 123 is similar to central station selector 23, previously described, with the exception that certain selective contacts are maintained closed by latching bars in a manner disclosed in detail in the above mentioned` Zenner patent. Sequential selector 123 is provided with normally open contacts 131 through 137 which are momentarily' closed when characters P,Q, U, S, X, W, .and A, respectively, are applied to the line and normally open contacts 111 through 117 which are closed When characters P, Q, U, S, X, W, and A,1respectively, are applied to the line and maintained closed by means of latching bars, not shown; When the character H is impressed upon the line all the latching bars are released, releasing the contacts which are latched. Contacts 111 through 116 prepare individual operating paths for relays SP, SQ, SU, SS, SX, and SW, respectively. Y

It is noted that contacts 117 andl 137 selectively respond to the selection character A for remote station A. Each of the other remote stations are selected by their respective selection code by providing sequential selector contacts similar to contacts 117 and 137 but responsive.

to the impression of the selectionrcode character individual to the respective station.'

. The remote station is provided With alarm switches AC1, ACZ, AC3, AC4, ACS, and AC6 which have normally 'open contacts in the operating paths of relays DP, DQ, DU, DS, DX, and DW, respectively. Switches AC1 through ACG are associatedwith individual testing or sensing apparatus, not shown, and close their normally openv contacts in response to the occurrence of an alarm or trouble condition in any well known'manner.

Relays DP through DW and final relay DH are in a chain sequence wherein Vthe break contacts of each relay arein the commony portion ofthe operating path of the relays subsequent in the chain sequence. Thus operation of relay DP precludes the operation of all the other relays by opening their common operating path by way of the break contacts'of relay DP. Furthermore, if relays DP through DW are released, the operating path .of relay DH is normally completed from ground by Way of the break contact of relay DP, the break contacts of relay DQ, the break contactsof relay DU, the breakcontacts of relay, DS, the break contacts of relay DX, the break contacts of relay DW, and the winding of relay DH to battery.

Assuming now that the contacts of switches AC1 and ACS are closed due to thel occurrence of their associated alarm conditions at the station, an operating path is 'closed from ground by way of the contacts of switch AC1 operated, the break contacts of relay ASP and the Winding of relay DP to battery operating relay DP. Relay DP operated opens the previously described operating paths for subsequent relays DQ through DH and completes paths from loop lead 101 to distributor contacts 2, 3, and 5 of distributor 121 by way of the three make, contacts of relay DP and distributor leads DL-2, DL-3,vand DL-S, thus coding distributor 121 for the character P which is the designated alarm character to indicate the alarm condition associated'with switch AC1. y

When station selection character A is received by the outlying station, Ysequential selector contacts 117 close and latch and sequential selector contacts 137 momentarily close completing a path from ground by way of contacts 137 and the winding of relay ST to battery operating relay ST which locks by way of its own Vmake contacts and the break contacts of relay ST1.

Relay ST operated completes an obvious operating path for relay ST1 which in turn completes an obvious energizing pathfor clutch magnet 145 of distributor 121 releasing distributor 121 and thus sending the character P in accordance with the coding of distributor leads DL'-1 through DL-S. v

Relay ST1 operatedv also opens the locking path of relay ST. Relay ST released releases relay ST1 and relay ST1 released opens the energizing path forclutch magnet 145. Y

The transmission of the character P to the line is followed by sequentiahselector 123 which momentarily closes contact 131 and closes latching contacts 111 com- 117, contacts 111 and the winding of relay SP to battery operating relay SP.

Relay SP operated opens the previously described operating path of relay DP by way of the break contacts ofl relay SP releasing relay DP. Relay SP operated also completes a path via the make contacts of relay SP shunting the break contacts of relay DP whereby a path is completed from ground by way of the make contacts of relay SP, the break contacts of relays DQ, DU, and DS, the closed contacts of switch ACS, which under the assumed condition was previously operated, the break contacts of Vrelay SX and the winding of relay DX to battery where- Relay DX operated opens the common portion of the operating paths of relay DW and relay DH by way of the break contacts lof relay DX and codes distributor leads DL-'1, through DL-S withtlie character X by way of the make contacts of relay DX. The character X, in this case, constitutes the code character designating the alarm condition associated with switch ACS.

Returning nowto the momentary closure of sequential selector contact 131 in response to the impression of the character Pon theline, a path is completed from ground by way of the latched contacts 117, momentarily closed contacts 131 and the winding ofrelay ST to batteryoperating relay ST. In the same manner as previously described, relay ST locks and operates relay 'ST1' which in turn energizes nclutch magnet `145 to release distributor 121 which mipresses the character X on the lline in accordance with the coding of distributor Vleads DL-l through The operation of relay ST1 also releases relay ST, which in yturn releases relay ST1 and relay ST1 released opens the energizing pathfor Vclutch magnet 145. t When the character X is transmitted to line, sequential selector contacts 135 momentarily close and sequential selector contacts 115 close and latch completing a path from ground by way of latched contacts 117, contacts 115 and the winding of relay SX to battery. Relay SX operated opens the previously described operating path for relay DX, releasing DX and completes a path via ythe make contacts of relay SX shunting the break contacts of relay DX whereupon the previously described operatingfpath vfor relay DH is completed. Relay DX re- ,leased further recloses the common operating path for relays DW and DH, and removes the coding of the character X from distributor leads DL-lthrough DL-S. Relay DH operated codes distributor 121 with the character H bycompleting paths from loop lead 101 to contacts 3 and 5 of the distributor 121 by way of the make contacts of relay DH and leads DL-3 and DL-5 whereby distributor 121 is coded for the character H which designates the acknowledgement signal of the remote reporting station.

Returning now to the momentary operation of sequential selector contacts 135 in response to the impression of the character X on the line, a path is completed from ground via the latched sequential selector contacts 117, contacts 135, and the winding of relay ST to battery.

In the manner previously described, relay ST operated operates relay ST1 which completes the energizing path for clutch magnet 145 whereupon distributor 121 is released andthe character H is impressed on the line. Relay ST1 operated also opens the locking path of relay ST and relay ST released releases relay ST1 which in turn opens the energizing path for clutch magnet 145.

When the character H s impressed on the line, latchying contacts 111, 115 and 117, which were previously operated, areunlatched and released, releasing relays SP and SX and returning the remote reporting station to its initial condition. v

If switches AC1 and ACS have remained operated,

'relay DP reoperates but the station will await the reception of its selection character A before resuming transmission. If none of switches AC1 through ACS are operated, relay DH operates and the remote reporting station will send only the acknowledgement character H upon the reception of the selection character A, indicating no alarm conditions.

The number of alarm conditions and associated'alarm switches need' not be limited to the'si'x disclosedin the present embodiment. Any number of alarm switches may be employed so long as a chain relay similar to relays DP through DW is provided for each switch and a momentarily operated contact anda latching contact are provided for'e'ach'alam code'characteralong with an asso- "ciatd frelayisi'njiila'r"to` relays SP through SW. The cen- "Eral control station'should beprovidedwith 'a sequential 8 selector contact, similar to contacts 31 through 36, for each alarm code character, as will become apparent presently.

Returning now to the central control station shown in Fig. l, the receipt of'the alarm code character P is foliowed by polarized relay LR and printed by printer 22 in the manner previously described. In addition, sequential selector 23, which is also responsive to the line signals, momentarily closes contacts 31 in response to code character P. The momentary closure of sequential selector contacts 31 completes a path from ground by way of the wiper and position 1 of arc A of selector 42, lead 51, the back contact of skip key 61, lead 67, contacts 31 and the winding of relay AL to battery operating relay AL, which locks by way of its own make contacts and the back contacts of an alarm release key 71.

Relay AL operated completes the A C. circuit for buzzer 26 via the buzzer disable key 27 and the make contacts .of relay AL and completes the A.C. circuit for an alarm lamp 72 by way of make contacts AL. Thus, upon the reception of alarm character P by the central station, printer 22 prints the character P after the reporting station polling character A and buzzer 26 and alarm lamp 72 are energized.

Relay AL can be released by the momentary operation of alarm release key 71 with the consequent de-energization of buzzer 26 and alarm lamp 72. In addition, buzzer 26 may be maintained de-energized by the operation of the buzzer disable locking key 27.

When the alarm code character Xyis received by the central station it is printed by printer 22 in the same manner as previously described and sequential selector 23 momentarily closes contacts 35 completing the previously -described operating path for relay AL with the exception that the path is completed by way of contacts 35 instead of contacts 31. Relay AL operated energizes buzzer 26 andalarm lamp 72 in the same manner as`described previously.

When acknowledgement code character H is received at the central station, the character H is printed by printer 22 and sequential selector 23 momentarily closes contacts 37 completing a path from battery Vby Way of contacts 37, make contacts of normally operated relay S and the winding of relay A to ground operatingrelay A. As previously described, relay A operated locks by way of make contacts S and its own make contacts, energizes step magnet 41 and operates relay B. The energization of step magnet 41 opens interrupter contacts 43 releasing relay S, which in turn Vreleases relay A and relay A released opens the-energizing path of step magnet 41 whereupon the wipers of selector 42 step to position 2. Tube T-l tires two seconds after relay B operates, operating relay TM; which, in turn, completes the energizing path for clutch magnet 45 releasing distributor 21 and thereby impressing the polling character for station B on the line in accordance with the strappings of position 2 of selector 42.

It is apparent that if the acknowledgement code character was not proceeded by alarm code characters, the central stationwould transmit the polling character for reporting station B without the prior energization of the Visible and audible alarms.

The central station now proceeds to raise the alarms in response to the reception of alarm code characters and step the selector in response to the acknowledgement codecharacters from stations B through F in the same manner as the reception of the alarm and acknowledge- Vment characters from station A and after the reception of the acknowledgement code character from station F Vselector 42 steps to position 7, which is coded with the character Carriage Return.

In response to the impression to the character Carriage Return on the line, Sequential selector 23 momentarily closes contacts 38'eompleting a path from battery by way of contacts 38, make contactsfofrelay'S andthe winding of relay Alto ground. The operationfof relay A steps the vwipers of sequential selector 42 to position 8` completing a path'from ground'b'y way Jof the wiper and posi.- tin 8 'of arcA, lead 57,"make lcontactsofrelay SY operated and the winding` ofstep magnet 41 to battery. The energization of step magnet 41 opens interruptor contacts 43, releasing relay S which, in turn, opens the energizing path for step magnet 41,' stepping the wipers to position 9. An energizing path is now completed from ground by way o f the'wiper and position 9 of arc A, lead 57, contacts of relay VS and the winding of step-magnetlrll, `energizing step magnet 41 which opens interrupter" contacts 43 releasing relay S, which, in turn, opens the energization path of step magnet 41, stepping the wipers to position l() where distributor 21 is coded with the character Letters.

Returning now to relay A operated, relay B is operated as previously described and tube T-l tires operating relay TM, which, in turn, energizes clutch magnet 45, releasing distributor 21 to impress the character Letters on the line.

Since the reporting stations do not respond to the character Letters, the line remains thereafter in the idle marking condition maintaining relay L operated as previously described. Tube T-2 tires after relay L has been maintained operated for about three minutes operating relay TA, which, in turn, operates relay A. Relay A operated eiects the stepping of the wipers of selector 42 to position 11 and releases distributor 21 whereby the reporting stations are again polled in the same manner as previously described.

In the event that station A does not respond to the polling character within three minutes, tube T-2 tires operating relay TA. Relay TA operated completes a path from ground by way of the wiper and position 1 or 11 of arc A, lead 51, the back contact of skip key 61, lead 67, the make contacts of relay TA and the winding of relay AL to battery raising the audible and visible alarms. In addition, relay T operated completes the previously described operating path for relay A, whereby the wipers of selector 42 are stepped and the polling character for the next reporting station is transmitted to line.

Skip keys 61 through 66 are provided to omit the polling of stations A through F respectively. Assuming that it is desired to omit the polling of station B, locking key 62 is operated and when the wiper of arc A steps to position 2 or l2, a path is completed from ground by way of the wiper and position 2 or 12 of arc A, lead 52, front contacts of skip key 62, lead 57, make contacts of relay S and the winding of step magnet 41 to battery whereby selector 42 self-steps to position 3 or 13. Any other station can be omitted in the polling cycle in a similar manner by operating the skip key associated with the reporting station.

In the event of a prolonged openrcondition, relay L releases, releasing slowtorelease relay BK, as previously described, thereby raising the audible and visible alarms. In addition, tube T-2 cannot fire with relay L releases, whereby the station circuitry is maintained disabled until corrective action is taken.

The specific embodiment of this invention shown and described herein is by way of illustration only and should not be considered as limited thereto, but capable of modification Without departing from the spirit of the invention and within the scope of the appended claims.

What `is claimed is:

1 In a telegraph system, a two-way communication line, a plurality of leads, a chain of coding relays for individually ceding said leads, switch means individual to each of said coding relays for operating said individual coding relay, a normally operated nal relay for coding said leads, means responsive to said operated coding relay 10 for precluding the'operation of saidnalrelay and each subsequent oneof said coding relays in said chain, a normally 'disabled code transmitter for transmitting a sequence of signals to said line in accordance withthe coding of said leads, means responsive to the reception of a signal from vsaid line for enabling said code transmitter, and Vselectively operated means responsive to the transmission' to said line of saidV sequence of signals individual to said operated coding relay forselectively releasing said operated coding'relay and for enabling said code trans, mitter and selective means Iresponsive to the transmission to said line of said sequence of `signals individual to said final relay for releasing said -selectively operated means. v A

2. In a telegraph system, a communication line, a plurrality of leads, a chain of coding relays for individually coding said leads, switch means individual to each of said coding relays for operating said individual coding relay, means responsive to said operated coding relay for precluding Ithe operation of each subsequent one of said coding relays in said chain, a code transmitter for transmitting signals to said line in accordance with the coding of said leads and selectively operated means responsive to the transmission to said line of said signals individual to said operated coding relay for selectively releasing said operated coding relay.

3. In a telegraph system, a two-way communication line, a plurality of leads, a chain of coding relays for individually coding said leads, switch means individual to each of said coding relays for operating said individual coding relay, means responsive to said operated coding relay for precluding the operation of each subsequent one of said coding relays in said chain, a normally disabled code transmitter for transmitting a sequence of signals to said line in accordance with the coding of said leads, means responsive to the reception of a signal from said line for enabling said code transmitter and selectively op-.

erated means responsive to the transmission to said line of said sequence of signals individual to said operated coding relay for selectively releasing said operated coding relay and enabling said code transmitter.

4. In a telegraph system, a communication line, a plurality of leads, a chain of coding relays for individually coding said leads, switch means individual to each of said coding relays for operating said individual coding relay, a normally-operated final relay for coding said leads, means responsive .to said operated coding relay forprecluding the operation of said final relay and each subsequent one of said coding relays in said chain, a code transmiter for transmitting signals to said line in accordance with the coding of said leads, selectively operated 'means responsive to the transmission to said line `of said signals individual to said operated coding relay for selectively releasing said operated coding relay and disabling said precluding means and selective means responsive to the transmission to' said line of said signals individual to said nal relay for releasing said selectively operated means.

5. In a telegraph system, a communication line, a distributor for impressing code characters on said line, a plurality of distributor input leads, a chain of coding relays for individually coding said leads in accordance with a predetermined code character, operating means associated with each of said coding relays for operating said associated coding relay, a normally-operated final relay for coding said leads in accordance with a nal' code character, means responsive to the operation vof said coding relay for precluding the operation of sa'id final relay and each subsequent one of said coding relays in said chain, selectively operated means responsive to the impression of said predetermined code character on said line for selectively releasing said operated codingl relay and selective means responsive to the impression of said final code character on said linefor releasing said selectively operated means.

6. In a telegraph system, a communication line, a

1 1 start-stop distributor for impressi-ng code characters 011 said line, start means for momentarily releasing said Adistributor, a ,plurality of `distributorinput.'leads,achain of coding relays for individually Acoding saidleads in accordance with a predetermined code character, loperating means associated with each of said coding relays for operating said associated coding relay, alnormally-operated nal relay `for coding said leads in accordance with afinal code character, means responsive to the operation offsaid coding relay for precluding the operation of said nal relay and each subsequent one of said coding relays in said chain, selectively operated means responsive to the impression of said predetermined code character -onlsaid line for selectively releasing said operated coding relay and disabling said Yprecluding means, selective means responsive to `the impression of said` predetermined code character on said line for enabling said .start means and selective means responsive to the vimpression of said final code character on said line for releasing said selectively operated means.

References Cited in the le of this patent UNITED STATES PATENTS

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