US2387558A - Teletypewriter testing system - Google Patents

Description

Ot 23, 1945 A. R. BONORDEN A TELETYPEWRITER TESTING SYSTEM y1943 5 sheets-sheet 1 Filed Sept. 11

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A. R, BoNoRDEN TELETYPEWRTER TESTING SYSTEMA Filed sept. 11, 1945 5 ASheets-Sheds 2 LWH .L mm .l uw QNNQQEO I Lush Sm QQYU u QON I Huhu Emy in /NI/E/VTOR 4 By A. fe. lsa/ORDEN ATTORNEY Oct. 23, 1945. A. R. BONORDEN TELETY-PEWRITER TESTING SYSTEM Filed Sept. 1l, 1943 4 5 SheebSShee' 3 E1 Qn\\ L mi @n m. .bfi

/NVENTO'R A R BONORDEN ATTORNEY Oct. 23, 1945.

A. R. BONORDEN TELETYPEWRITER TESTING SYSTEM Filed sept. 11, v1945 5 sheets-sheet 4 /N'VNTOR A. R.. BIONRDE/V www v GFS ARNEY Oct. 23,l 1945. A. R. QNORDEN 2,387,558

TELETYPEWRITR TESTING SYSTEM I Filed sept. 11, "1943 5 sheets-sheet 5 l'I'Hl` /NVENTOR Afa Bon/ORDEN quests that a testing Paiesfed oci. 23, 1945 TELETYPEWRITER TESTING' SYSTEM Allen R.. Bonorden, Plainfield, NJ., assignor to Bell Telephone Laboratories, Incorporated,

New York, N. Y., a corporation of New York Application September 11, 1943, Serial No. 501,972

11 Claims. `(Cl. 178-69) This invention relates to testing arrangements for telegraph circuits employing teletypewriter equipment for transmitting and receiving messages. It is an alternative of the system disclosed in United States Patent 2,347,518, granted to J. S. Soderholm and C. Breen on April 25, 1944.

As is Well known, teletypewriter circuits are now provided having teletypewriter equipment at the subscribers premises and switchboard arrangements at a central oice, so that any' subscrber may be connected for an interchange of messages by a teletypewriter circuit extending from his own equipment through the central ofce to the-teletypewriter equipment of another subscriber.

To test the teletypewriter equipment of circuits of this type the maintenance man goes to a subscribers premises and by means of a start, or power, switch at the subscribers teletypewriter calls the operator at the central oiice and reline. The switching operator passes this information to a trouble operator, who then connects into the line a special testing trunk leading to the test board where a test board attendant will be available to cooperate in making the test. Plugging in the test trunk not only makes the line appear busy at allits multiples at the operators switchboard, but the test trunk is so arranged that the line will appear to be out of order to any operator who tests the line.

Merely plugging in the test trunk does not automatically signal the test board attendant and, indeed, the test trunk is not used immediately for any purpose. On the contrary, the main concern at the subscriber station after the maintenance man has ordered the test trunk, .is for him, ignoring the test trunk for the time being, to proceed to make preliminary and routine tests of the subscribers teletypewriter equipment. These tests include cleaning and adjusting electrical contacts, adjusting relays, oiling mechanical parts and making general mechanical tests to determine whether or not various elements of the printer mechanism are functioning properly.

Having made these preliminary tests, themaintenance man is ready to make those tests which require the use of the test trunk. These tests are oftwo types. One type of test consists of orientation range measurements to determine whether or not the signal pulses received at `the subscriber teletypewriter are of the proper Wave shape, that is, whether or not the teletypewriter is adjusted to receive with equal fidelity test signals having extreme permissible positive and negative,` bias limits. The other type of test involves transmitting messages from the station equipment to a standard test printer, at the test trunk be connected to the board to determine whether the signals are coming through properly, that is, whether thel keyboard mechanism is transmitting signals the distortion and bias of which are within the required limits. 'The test board attendant takes no part in the orientation range measurements, but his services are required in making tests on signals incoming at the test board teletypewriter.

The orientation range measurements take considerable time and where they require the assistance of the test board attendant, it means that during these particular tests the test board attendant is tied up and is not available for other services. It is therefore desirable, as disclosed in the Soderholm et al. patent, supra, toAV have some arrangement by which it will be unnecessary for the test board attendant to take" part in the orientation range measurements, especially as the results of the measurements themselves are actually observed by the maintenance man at theV subscribers station and remedial action taken by him.

As is well known, the individual pulses of the permutation code should theoretically be squaretopped Waves. Actually, of course, this condition does not exist. Even if properly shaped Waves could be sent out by the transmitter, upon their arrival at the printer, they would be considerably distorted by the transmission line and the receiving equipment. It is therefore necessary for the maintenance man to determine to what extent the waves had become changed in shape during transmission. This he does by an orientation range measurement equipment which forms no part of the present invention and is not hereindisclosed. This equipment is so arranged that it measures the amplitude of parts of successively transmitted wave pulses at relatively diferent times with respect to the period during which each individual pulse continues.

The eiect of distortion is to round off the cornners of the square-topped waves s0 that at the beginning of the Waveand at the end thereof the current does not attain its full value. The orientation range measuring device is in eiect shifted back and forth with respect to the time of the wave so that it tests brief time elements of the wave ranging from the beginning of the pulse, through its middle portion to the end of the pulse. If these tests show that the wave is too much distorted, adjustment has to be made either to the teletypewriter, that is, the printer, `or to the line equipment until proper waves are received.

When the maintenance man has completed the preliminary and routine tests of the subscribers teletypewriter equipment, as already mentioned, special signals for use during the orientation range measurements will be automatically applied to the trunk leading from the test board.

I-Ieretofore the special signals used for making the orientation range measurements were of the unbiased type whereas recent practice requires that these `special signals be of the -biased type, namely, marking bias by itself, spacing vbias by itself and switched bias, that is, signals of alternate marking bias and spacing bias. Therefore,

an object of the present invention is to provide a circuit arrangement whereby the maintenance man at a subscribers station may, independently of any assistance by the test board attendant, automatically select any one or all lof t-he three different types of biased signals from a common source at the central oice for transmission of such type or types of biased signals, as desired, back to the calling subscriber station.

A testing set suitable for .furnishing marking bias, spacing bias and switched bias is disclosed in Fig. 2 of H. A. Rhodes, U. S. Patent 2,140,680, issued December 20, 1938. A set of this .character is arranged lto introduce .in test messages known amounts of bias in both the marking and `spacing directions. The amount of bias introduced .can be varied by adjustment and can be .observed in both directions, and the'set after such adjustment may be connected to an external circuit and thus will reproduce in that circuit signals biased to a known extent. The Vknown bias may Abe quickly switched in either direction, without changing the amount of bias, either at .odd times by manual means or at regular intervals by automatic means without the need `of .changing connections. E

According to the present invention means, automatically operated, are provided 'to select, as desired, the different types vof signals biased to any degree. Inasmuch as the procedure at the subscribers station when a maintenance man is making a periodic inspection of the subscribers teletypewriter equipment, requires the continuous use of the biased signals for orientation range measurements over fairly long intervals of time, the present invention serves to reduce the maintenance mans time and to eliminate the assistance of the test board attendant by providing means for automatically Vconnecting the source of signals to the subscribers line under test, together with the control means whereby the maintenance man .can change the type .of the biased signals dur-ing the progress of the test. On the completion of the test the maintenance man can dismiss the source vof biased signals and signal the test board attendant to connect the test board teletypewriter to the subscriber line in order to receive the report of the test. When the -test board attendant receives this signal he connects his test board teletypewriter to `the testing trunk to Vreceive signals sent from .the subscribers station, and as these signals are received at .the test board teletypewriter he determines whether the proper signals are being sent out from the subscribers station. Thearrangement of the trunk is such that the test board attendant and the maintenance .man :are able to communicate with each other about the test signals, the former using the .test board teletypewriter and -the latter employing the teletypewriter lequipment located at the subscribers station.

The invention will now be more fully understood from the following detailed description when read .in connection with the accompanying drawings:

Fig. 1 shows a subscriber station connected to its line terminating equipment 4at lthe `central oice.

Fig. 2 shows an operators cord circuit at the main switchboard in the central office.

Fig. 3 shows the testing trunk terminating in a plug at the main switchboard 4and. in a jack at the attendants test board. Also shown, in diagrammatic form, in Fig. 3 is the attendants teletypewriter adapted for connection to the testing trunk.

Fig. 4 shows two of several line finder switches which lare respectively associated with common sources of biased signals provided at the central station. Each finder switch is of the single movement rotary type and comprises six banks of twenty-two terminals each, the corresponding terminals on the six banks of each switch being associated with .the .termination of a test trunk suchas shown in Fig. 3.

Fig. '5 shows two .of the common sources of biased signals, .one in schematic form and the other in diagrammatic form. Usually one to three common sources .of bias signals are employed at a central station. They are substantially similar to that .shown in Fig. 2 of the Rhodes patent,

supra.

Fig. 6 shows the relative arrangement -of Figs. 1 to 5.

APPARATUS .Subscribers apparatus and line equipment Referring to Fig. 1 'the subscribers teletypewriter IUI is shown connected to a line circuit consisting of tip conductor |02 and ring conductor H33. The subscribers teletypewriter includes a sender .104, conventionally represented, .aline relay I U5 connected in the line circuit, vand a printer magnet 106 whichbyknown means, not'here illustrated, .operates the receiving printer to type received messages. The subscribers station also includes a ringer, or bell, llll Afor ringing the subscriberstation, .and a power switch |118 for starting the printer motor `lili) and throwing the subscribers vline circuit into .operative condition. As is well known, the switching arrangement for starting up the teletypewriter .motor and other- Wise putting the subscribers circuit into operating condition may be automatically controlled from the central oiiice, `'but as these facilities form no part of the ,present invention they are .not herein illustrated. It will vbe understood, however, that they may be used with the-present invention, if desired.

The .subscribers station line circuit extends to the central o'ice wher-.e .it terminates in a jack 'l I0 and multiples thereof, such .as jack -I I l, through which connections may 'be established to other line operator positions at the main switchboard Whereat all` the subscriber lines terminate` Other multiple jacks may .be provided, .such as a jack, which enables .a practice .cord vcircuit to Abe connected to the line; a jack which enables a busy cord .circuit to be connected to the line; and a jack which enables an out-of-order cord circuit to be plugged into .the .line for purposes which are described in the Soderholm et al. Patent No. 2,347,518, supra. At the trouble operators position in the .main switchboard appears test jack H2 which is ralso `a multiple of the .subscribers line circuit. By means of test jack H2 the testing trunk shown in Fig. 3 may for testing purposes be Yplugged into the subscribers line as will be hereinafter described. Adapted for connection to jacks H0 and Il is an operators switching cord circuit shown in Fig. 2 whereby a subscribers operator makes connection from the subsoriberfs line AH12-|03 to vany other of the .other subscribers lines by plugging opposite ends of the cord circuit into the jacks terminating the respective two `lines between which a connection is desired.

The subscriber line |02-I03 has also asso.

ciated therewith at the central oilice sleeve relay II3 and a controlling relay II4, both of the differential type. Relay I|4 controls relays ||5 and IIS, the former of which under proper conditions Operators cord circuit The operator, or switching, cord circuit shown in Fig. 2 is provided with an answeringplug 202 and a. calling plug 203 which are used in establishing connections. It also includes a telegraph repeater comprising repeating relays 204 and 205 of the polarized type, with associated apparatus whereby telegraph code impulses may be relayed in either direction through the cord circuit. In the sleeve of the cord circuit associated with the answering plug is a polarized sleeve relay 206 and an additional sleeve relay 201. 'I'he former operates two relays 208 and 209, the former of which controls the circuit of the supervisory lamp 2|6, while the latter renders repeating relays 204 and 205 operative. Relay 201 controls the busy cir# cuit connected to thetip of the answering plug 202. The busy circuit includes polar relays 2|0 and 2|| which respectively operate a busy lamp 20| and buzzer 2| 2, thus enabling the operator to distinguish between a line which is merely busy and one which is out of order as is described in detail in the Soderholm et al. patent, supra.

The calling end of ciated therewith a sleeve relay 2I3 controlling relay 2|4 which in turn controls the busy circuit and the calling supervisory lamp 2|5. The busy circuit is connected to the tip of the calling plug 203 and includes polarized relays 2| 'I and 2|8. The last-mentioned relays, like the corresponding relays associated with the answering end ofthe cord circuit, respectively controlv the busy lamp 2 I 9 and buzzer 220.

In order that the operator may communicate with the calling subscriber, an operator teletypewriter 22| including a sender 222 and a printer relay 223, `is provided. The printer magnet 223 functions to operate the receiving printer (not shown) in a manner well known in the art.

Testing trunk In order'that a maintenance man may make orientationrange measurements and signal tests, a plurality of testing trunks, such as that shown in Fig, 3, are provided, each terminating at one end in a plug', such as plug 30|, at the troubleoperators position in the main'switchboard and at the other end in a jack, such as jack 302, at. the test board. This testing trunk cord circuit has in its sleeve conductor of its answering plug30| sleeve relay 3-A. Relay 3-A, upon operating, operates relay 3-BB which, when operated, (1) controls guard lamp 303 and (2) closesthe tip and the ring conductors of plug30I in circuits respectively extending through the winding of relay `3-CC and the winding of stepping magnet 304. Relay 3CC, when operated, transfers the" ring `conductor to the windingV of the lamp relay the cord circuit hasasso- 3`L which, in turn, controls the lighting of answering lamp 305, lamp 305 serving to call the test board attendant for the purpose of connecting the test board teletypewriter to the testing trunk jack 302. Stepping magnet 304, upon cperating, controls the operation of minor switch 306 which when operated to its No. 1 terminal, prepares the connection of source 308 of interrupted ground to terminal No. 1 in bank No. 6 of each of finder switches A, B, etc., finder switches A and B only being shown in Fig. 4. Off-normal switch 309 of minor switch 306 operates as the minor switch moves its brush 301 off its normal position. Oli-normal switch 309, upon operating, closes at its upper normally open contacts a circuit for operating start relay 4-ST of a start circuit 40|. Each of the testing trunks that are provided in the system is connected in multiple to the iinder switches A, B, etc., each trunk being connected in multiple through finder switches A, B, etc. A set of electromagnetic devices, such as relays 4-CT, 4--SI-I and 4HT, and stepping magnet d-STP is provided for each nder switch. The joint operation of minor switch 306 and subsequent seizure of the test trunk by any one of the finder switches prepares the signal biasing set associated with the operated iinder switch for producing biased signals.

Signal biasing set As hereinbefore stated, asignal biasing set is provided for each of the under switches A, B, etc. Signal biasing sets A and B only are shown, the former being shown in schematic form and the latter in diagrammatic form. The start circuit 40|, which is common to all test trunks and to all finder switches A, B, etc., serves to start all idle Ender switches hunting for any calling testing trunk.

Signal biasing set A which is `shown in schematic form will be briefly described herein. Biasing set A is conditioned for operation by the joint operation of a minor switch, such as minor switch 306 and nder switch A whereby an operating circuit for relay 5-RV is closed. Relay 5-RV operates to close the operating circuit for relay 5-A. Relay 5--A operates and thereby operates relays 5--B and 5-C. Relays S-RV and 5-A may also be operated by operating start key 5-K3 when manual starting of the set is desired. Various sources of signals are adapted to be respectively connected to biasing set A, through key 5-KI A source of current reversals may be connected in the input circuit by 0perating key 5-KI to its left-hand position whereby receive relay E-RE'C is capable ofoperating continuously between marking and spacing contacts inV response to the signals transmitted through interrupter 503. Another source, sch as source 504, may be connected to the input circuit by operating key 5 -KI to its righthand position for impressing neutral signals, that is, open and closed circuit conditions upon the operating, or lower, winding of receive relay 5-REC, as by means of a (iO-speed transmitter which automatically impresses test sentence signals upon theoperating winding of relay 5-REC.

A bias measuring circuit is associated with the output circuit and comprises relay 5-MEAS and bias measuring indicator li-BI. For purposes of furnishing biased signals to a maintenance` man at a subscribers station to make orientation range measurements, switch 5-K4 will normally be in the position shown and relay 5-MEAS is therefore held on its marking contact by current flowing :in tits operating, lor upper, lwinding Ywhich nowextends from lthelarmature ofre'lay i5-BIAS, retardation coil i508, .contacts No. l2 of switch 5K4, :through ithe upper winding of 4.relay B-QMEAS, contact No. i4 of :switch B-Kll to the output circuit which may .be traceable over .conductor 410, armature No. `5 :and .contact of .relay 4-CT-A, conductor 409 t@ the ibrush sin bank No.5 ci finder switch .'A. Norm-allyVshouldthere be rio-current in the operating, :or upper, winding of relay 5--.MEAS, the current in :the lower or biasing winding would operate the relay itc -its spacing position. 4The meter, or bias indicator 5-BI has a double scale with zero in the center and Adivisions ior indicating Vmarking 'bias 'in per cent Von the vright side fof the .Scale and :spacing bias on the left side oi the scale. `The meter vis operated to the rig-ht when relay -ME-AS is on its marking contact and to the left when the relay is on 'itsspacin'g contact. yCondenser 552 serves .to kdampen the moveinent'of the meter needle.

Provisions are made for v'changing ithe 'bias .in-

- troducing set at intervals to A:produce Lsignals alterna'tely with marking lbias .and with :spacing bias.

The input "circuit of the signal biasing set A comprises the repeating `relays v-ii--REC v.and E-BIAS. Relay Ei-REC has its .opera'ting, or lower, winding included in the input circuit for operating its armature to marking. The biasing, or upper, winding of relay E-REC is permanently energized during operation of the `signal biasing set A to operate the armature of relay 4rii--REC to its spacing position when the operating winding connected to the marking and spacing contacts respectively of relay 5-REC for operation of the armature of relay 5-BIAS to marking and spacing respectively. The armature .and contacts .of relay -BIAS are included in the output circuit oi 'the signal biasing set A.

Signals are impressed upon the input relay 5-REC for testing purposes and are, in lturn,l

repeated to operate relay S-BIAS for production -of impulses in the output xside of the sign-al biasing set. For the purpose of biasing the youtput signals, relay 5BIAS is provided with two lower biasing windings Nos. 3 and l acting in opposite ydirections to aid or oppose Vone or the other of the operating windings to varying eX- tents in accordance with the current strength in the biasing windings. Thus, during operation of signal biasing set A biasing winding No. l is connected through a retardation coil 5793 to potentiometer 514 which, in turn, is connected to source 528 of positive potential .over 'the armature in operated condition of relay 5-VIB. Similarly, biasing winding No. 3 .of relay ii-BLAS lis connected through retardation coil i515 to pdten'tiorneter 516 which in turn is lconnected over the armature in retracted position fof relay 5`VIB to source 528 of positive potential.

It will rst be assumed that the circuit `is in the condition as shown in the drawings, however, With potentiometers 514 and 5|6 adjusted to ground. Under these conditions, the operating, or lower, winding of `relay E-REC is energized to hold the armature toits marking position over a circuit which may be traced from source l529 of negative potential, left-hand armature .and contact of relay 5-B, conductor 523, over tip contacts of jack 501, conductor 524, contact No. 1 rof key 5-K4, through the operating, or lower, winding of relay S-REC, vcontacts Nos. 1 and '5 is currentless. .R'elay 5-BIAS has two upper operating windings Nos. '1 and .2

assures of vkey zii-Kl., over tip contacts for :jack i502 .and auxiliary, or upper, :contacts of ijack 15M to sa groundedpositive source 525, With relay .fi-REC in marking position, the current flows in wind ingNo. 1 of Yrelay .5-BIAS tohold thearma'ture o relays 5-BIAS in its marking position. 'Under the assumed lconditions :windings fNos. Ail kand 4 will be currentless fand winding No. 3 will 'be ine'fective. 'The :output circuit Lfrom relay B--BIAS when subsequently closed, may be traced 4'as v-follofwsz `From na grounded positive source 53D, contact and cuter `right armature of relayE-B, over the frontfcontact and inner righthand armature of yrelay '5i-RV, marking Lcontact and armature .of relay 54E-IAS, 'retardation coil 508, contact No. 2 of key 5-Kl upper winding of relay 5MEAS, contact No. 4 of key 5-K4, conductor` 4l!! to the armature-No. 5 of relay 4-CT-A. Thus immediately after the closing of the 'sta-rt circuit condition, 'the output circuit is vin marking position.

If now the input circuit to the operating, or lower, -`winding of relay li-REC be opened asin the case of a spacing signal, relay 5-"REC `will operate 'to spacing. Winding No. 1 of rielay 5-BIAS will'now become deenergized and winding No.12 will 'be energized and'will operate relay E-BIAS to spacing, thereby 'opening 'the output circuit `at the marking :contact `and `closing it to grounded negative source '531, over the 'front contacts and inner right-hand armature of relay 5-13, over the front contact and inner left-hand armature of relay '5-RV, and the spacing contact vand armature oi relay 5--BIAS- The output circuit is now iin spacing condition. When the input circuit again is .closed relays S-REC and 1i-BIAS return to their respective marking positions, thereby .placing the output .circuit in marking condition.

Condensers 5H and 513 and .high resistances 5|.9 andf52 are included in the .operating circuit for .windings Nos. 1 and .2 of relay .fi-BIAS for the purpose of .shaping Athe .operating current.

- These Condensers are comparatively lar-ge, and

besides .acting as spark protection, serve in cornbination with the high resistances lto round .the

`front .of the operating impulses and to adda fairly long tail to the rear of :the impulses thereby permitting a bias of relay E-BIAS -to the extent of -60 per cent in Aeither direction. Thus when .relay -E-REC leaves its marking contact, condenser 518 will Adischarge slowly through winding No. 1 of relay 5-`BIAS. AIn ythe meantime relay vE-fR-EC reaches .its lspacing Ycor-itact and current begins to .build Aup in winding No. 2 oi' relay E-BIAS. The result of these two currents will be a gradual `reversal of the operating flux in relay 5-B1AS for operating this relay'to spacing. When relay :.S-REC returns 'to marking, these conditions are reversed. Thus with .no current in windings Nos. .3 :and 4, relay 5BIAS will follow relay 45---RiZlC after 'a -deiinite short interval in both directions of yoperation.

It can readily be vseen that foy adjusting resistanc'es v5'1'4 and 516 .and properly operating relay -VIB a biasing current may be established in either winding No. 3 or winding No. 4 which will affect the operating flux in relay E-BIAS to bias lthe operation Aof the relay #either to marking or to spacing. winding No. 3 is connected .to aid 'the spacing winding No. 1 and thus will produce a .spacing bias, whereas winding No. 4 aids the marking winding No. 2 and will proing kick-off of relay 5-BIAS. Thus, in ree peating` signals to the signal biasing set, both the `marking andfspacing impulses impressed .upon the set will be repeated as current im# pulses which are subject to shaping' and are `combined with biasing effects to be repeated as biased signals in the output circuit. i

Relay 5-VIB is connected over contacts Nos. 2 and 3 oi' key 5-K2 to a source 308 of impulses for continually operating and releasing `the relay. In this manner the grounded positive source 528 is connected alternately to potentiometers 5|4 and 5 6, thereby alternately energizing the biasing windings Nos. 3 and 4 of relay 5BIAS. The rate of these alternations may conveniently be one or two cycles per second. By operation of key 5-K2 to its righthand position so as to open contact No. 2 and close contact No.1, relay 5-VIB will be continuously operated and relay E-BIAS will be continuously biased to marking'. By operation .of key 5-'K2 to its left-hand position, relay `5-VIB will be continuously deenergized and relay 5-BIAS will be continuously biased to spacing.

A bias measuring circuit comprises relay E-MEAS and bias indicator 5BI. The operating. or upper, winding of relay 5--MEAS is included in the output circuit as already traced and serves to hold the relay to marking. The

biasing, or lower, winding is energized through the normal contacts of key 5-K6 to operate the relay to its spacing position winding is currentless. The current in the meter 5-BI may be adjusted by means of potentiometer 52| and the current in the biasing winding when the operating by means of potentiometer 522.

For the purpose of impressing impulses upon vthe operating winding of relay 5-REC, key 5K| may be operated to the left thereby including a source 503 of interruptions to effect current rei.;

versals of substantially equal intervals in the input circuit. The'input circuit may now be traced as follows: from grounded negative source 529 adapted for connection to conductor 523, overtip contacts of jack 50|, conductor 524, ofA key 5-K4, through `the operating, or lower, winding of relay 5 REC, contact No. 6 of key 5-K|, through source 503 of` interruptions, contact No. 4 of key 5-Kl, tip contacts of jack 502, auxiliary, or upper, contacts of jack 50|, conductor 526, to grounded this circuit the receiving relay 5-REC is operated in unison with source 503 of interruptions. With resistances 5M and 5| 5 adjusted to ground, the `bias relay E-BIAS will repeat the reversals in the output circuit which, as already traced above, in-

fcludes the operating winding of relay 5-MEAS.

Any bias that may be present in the impulses from the source 503 of reversals, or interruptions, may thus be noted'on the bias indicator 5-BI and should be taken into account in subsequently adjusting the signal biasing set for a desired output bias. v For the purpose of checking relay S-BIAS, an additional test may be made by switching key 5-K4 to the left, thereby disconnecting the operating, or upper, winding of relay 5`MEAS from the output circuit `which includes conductor 4|!) and connecting it into the input circuit. The in-V put circuit may now betraced as follows: from contact No. 1 'I positive battery 525. In`

A(El) the: grounded negative source 529 adapted for connection to conductor 523, over .tip conductor of jack 50|, conductor 524, contact No. 3 of key 5-K4, through the. upper winding of relay 5-MEAS, contactNo. 5 of key 5-K4, through the operating, or lower, winding of relay 5-REC, contact No. 6 of key 5K|, interrupter 503, contact No. 4 of key 5-K|, tip contacts of jack502, auxiliary, or upper, contacts of jack 50|, conductor 526 to grounded positive battery 525. With the circuit in this condition, the bias of the source of reversals at interrupter 503 maybe dejtermined independent of the operation of relay 5-BIAS. .iFrom any disagreement between the two readings, it may be determined whether. relay 5-BIAS requires adjustment.

Again operating key 5-K4 to normal, that is, into the position shown, relay S-MEAS will be included in the output circuit which includes conductor 4|0, and resistances 5|4 and 5|6 may each be adjusted to eiect the desired bias with the key 5-K2 operated to the right, or marking, or to thev left, or spacing as desired. The amount of bias produced in the output circuit is read on bias indicator S-BI and at this time any bias previously observed in the source of reversals produced by interrupter 503, may be taken intoaccount. Thus if a bias of 35 per cent be desired in both directions and it has been found that the reversals produced by source 503 has a 2 per cent marking bias, it will be necessary to adjust the mark potentiometer 5|4to give a reading of 37 per cent marking on the bias indicator 5-BI and` to adjust the space potentiometer SI5 to give a reading on the bias indicator 5 BI of 33 per cent spacing. f i

It should be understood that the source 503 used with the'signal biasing set though customarily termed a source of reversals, is in thenature of a circuit interrupter serially included in the operating circuit for relay 5-REC to produce current and no-current impulses of substantially equal length and in continuous succession.

When key 5-KI is operated to its right-hand position, the source of reversals 503 will be disconnected Yfrom the input circuit'and the source 504 of standard test sentence signals'sentout by a transmitter, will be substituted therefor. The input circuit may now be traced as follows: from the grounded'negative source 529 adapted for connection to conductor 523, over tip contacts of jack 50| conductor 524, normal contact No. 4 of key 5--K4, through the operating, or lower, winding of relay S-REC, contact No. 2, through source 504, over contacts Nos. 3 and 5 of key S-Kl, over tip contacts of jack 502, and auxiliary, or upper, contacts of jack 50|, .conductor 526, to grounded positive battery 525. Standard telegraph signals are thus impressed upon relay 5-REC and will be repeated in the output circuit with a 35 per cent bias to marking or to spacing, depending upon whether relay 5-V1B is in an operated or unoperated condition.

The output circuit which includes conductor 410 may be associated with any external circuit which it is desirable to observe under various biasing conditions by connecting such external 4circuit by means 'of plugs to any of the jacks neutral," LPG,or polar as shown and described in the Rhodes patent, supra. In the present application current reversal impulses, marking impulses and spacing impulses each having a predetermined amount of biasmay be selected by the maintenance man at the subscribers station over conductor 4|0 `which isthe part of the outputl circuiti extending tofth'e testingr trunks` shown lilg. 3' andv thef method oi operation which will' bei hereinafter described. witlf. show lhow the maintenance man. may automaticallyA select the three difierenttypes oil'hiased signals.

METHOD F Oriuuirioiir Call from suscrierstlation 101. to axlmther subscriber station .(not'shown). whose. Zine. also terminutes. in the same central. oice It. the subscriber at station v|11 I?` wishes to make a: call* to another subscriber, he. will' operate power switchI |081 to'r lits alternate. position?. Switch |118, upon being: operated.; closes at. its left-hand conrtacti a. circuit for connecting; alternating' current source Ile to rectifier Z211' and also tofpri'nter motor' |09... Theleft-handi, or direct current, side of rectiiier |i20- furnishes current for operating printer magn'etl |06 and; tor biasing the upper winding of linerel'ay H151.` At itsri'ght-l'fiandl side, switch |08. closes the: subscribers loop extending from grounded positive f8-volt battery |2l|-, makebefore-break' contactr No. 3 of relay M3?, through the .lower winding of relay H543. ring conductor |203; right-hand. operated contact of power switch |t0r8, through the lower winding of relay' |05, normally closed contact of breakf. key |232; transmitting contacts |114, tip conductor |02, upper armature: and back Contact oi relay H31, malte-before`h break contacts No. 2v ot relay I I6' toA ground. Re lay ||4 operates. and closes at its armature and contact a circuit containing two obvious operating paths for relays` lil/5: and M6; respectively. Relay H52 operates and. connectsatfits armature and contact a ground connection. through the tip conductor of the multiple jacks ||0, and |12. Relay operates. and closes. (1)` at itsA upper amature, the tip conductor of: the vsubscriloers loop to grounded negative '48voltbattery' |24 and disconnects ati its makebeforebreak contacts No. Zthe ground connection; (.2) at its inner lower armature andA contact connects grounded negative: 24e-volt battery to a circuit extending through the lower winding and' the 'upperwinding, series.. of relay |.|.3A` tol ground;l and (3) at its outer lower armature and. contacticlos'esf an operating: circuit for calling lamps ||f`|z and |`|8 respectively'associatedf with jacks HG' and lrl'l` at the operatozrrs` switchboard. Relay Im Visv held oper-'atedunder'the` influence of its lower winding and' thecircuit of the: vsubscriber.s loop: is now in readiness to receive the. answer plug. 202 of the operated cord. circuit; Relay tl3 is of: the differential. typev and therefore' does. not operate at this time inasmuch as its' two energized windings b oppose each other.

Switching .operator answers.

Assuming that the operator at. whose position a calling lamp such as lamps tl't andi H81, becornes lighted, answers the call, lthe operator will insert plug 202 of the switching 'cord' into the jack associated with the lighted lamp `at the: answering operatorsposition. Over. the sleeve conductor of. plug 'M12v andv .the particular jack, say jack I Hl,A the following circuit is now established: Grounded negative 2li-volt battery 224,. through 20G-Ohm resistance: 221,. throughv they winding of relay- 201, through the: lower winding of relay 296,y sleeve conductors of plug 20.2: and jack |10, through the upper winding of relay H3, to ground. Another circuit is established.. from grounded. negative 2li-volt battery 225K,V through the l'Tf-ohrnv winding; oi relay 226., through the ,SIb-ohm resistance 221i, through the 3 5-ohm upper winding. of relay 2116, over thes1eevef-comductors. oi` ,plug 202 and: iacl U50, the 20G-ohm upper' winding oi relay' IIi3 toi'groim.

The upper winding of relay' H5 now' receives current. from; the grounded negative` 24.vol1i`bat 'tery over threey sep'araife.- paths-one; over the-"im- `ner lower armature and contactof relay' ||6ffand the lower winding., of relay H3 to point 12.51,. a, second throughy thel winding. of relay 20.15 andthe lower winding of relay 20S to point; litigano.; a third through the winding of. relay-226 A:afridlthe upper wfinidingy of. relay 2lliA to lpoint |25; rThe first or these paths includes a resistance of' 15390 ohms, through the lower winding of relay M13. The second.- path through. the-winding of. relay lMl-I includes a resistance' ot 712 ohms made upf of the 20G-ohm resistance; 2213,. the: 432-ohm' re'- sistance of the winding of relay 2.01 andthe: 80 ohm. resistance. of the: lower winding. of relay 206. The third: path has aresistance of 52 ohms between groundednegative.- battery 225i and point |25 this resistance. being made up' of. the lil-ohm resistancel of the winding of relay y221i, the 3f1'.5' ohm resistance 22'8I and the {t5-ohm resistance ofthe upper winding of relay 285. li'heresistanoe of this third path. is-'so low compared. the other two` that'the current lowthroughthe. upper winding of relay |3 is greatly increased andis much greater than they current through-.the lower winding, thus-"causing relay 1|. lftobe operated. Relay H3,y upon operating/extends the sub.- scribers loopl which now `may be. traced: from grounded negative 4,8.-volt battery |24, through the upper winding ot relay H4, tron-t Contact Aand upper armature-,of relay H3, tipv conductor |2012, through the. subscriber' station, ring, conductor |113 through thev lower winding ot-relay I |4-,;roni; contact No. 4 and.I lower armature rot relay |.|.3, ring conductors vof jack. .|.|.0 and plug. 202:,l normally closed contact of ringing, key `23| normally closed. contacts of. teletypewriter key 232, through the upper winding oi repeater relay 2.04 arm-a.,- ture-and spacing contact of, repeater relay 205,360 grounded negative battery 229.. Relay H4 being of theli'ferential. type and. having. both windings energized at this time now releases. Relays H5 and IIB also releasesl at this; time.,

We now have the relays2|l-`| and. Zilliv in the. cord circuit energized. and the sleeve relay H3 of. the line operated. Relay 2.01, upon operating, opens the busy circuit to the tip conductor ci plug 262.. This circuit, however, does not come into play at the present time.. Relay 20.6, upon operating. ac tu'ates relay 208 and also completes. a path through the left-hand winding of relay 2`|l`9` which operates. Relay 208, upon operating.opens atits f backcontact and armature the busy circuit at another point, and at its front contact and armature closes the circuit for operating supervisory lampwZl B, which circuit extends over .the tip conductorV of plug 2021 Supervisory lamp 2.|.6, howf ever, clue to the release ofrelay H5', is. prevented from lighting.

Cord circuit repeater operation Relay 269i which isoperatedE under' the influence of its` lett-hand winding connects ground1 to the lower winding of repeater relays 204-and 205 in `the cord circuit. Current now .ilows from grounded negative iS-volt' battery 2129 overtlie spacing, or rightehand, contact and' armature of relay 201, through the lower winding of relay 205, to ground at the: right-hand armature- 'and contactof relay 209i. This current is in vsuch' adirec'- tienes to shiftthe armature of relay 2'05 toits marking, or right-hand position. CurrentA from the grounded positive Liii-volt battery 230 now flows over the marking, or right-hand, Contact and armature of-relay 205, through the lower winding of relay 204, to ground at the left-hand armature and contact of relay 209. This current is in such a direction as to hold the amature of relay 204 upon its spacing, or right-hand, contact until `a circuit is completedthrough theupper winding of relay,204` as will be hereinafter described. Y

As hereinbefore stated, sleeve relay ||3 operated and thereby opened at its outer lower arma-` ture and contact the operating circuit for relay I |6 thereby causing relay I I6 to release and calli ing lamps H1 and 8 to be extinguished. Relay H6, upon releasing, opens at its inner lower armature and contact the path extending through the lower and upper windings in series of relay |93, but relay |3 remains energized and `operated through its upper winding. Relay ||3, in

its operated position, completes the subscribers` loop as hereirrbefore described. A

It will be noted that the grounded positive 48- volt battery 230 is in series aiding with respect to the grounded negative 48-volt battery |24. A circuitpreviously traced also extends from the grounded positive Llil-Volt battery 230, over the marking, or right-hand, contact of relay 205, through -the lower winding of relay 204 and over the left-hand armature and front contact of relay 203 toA ground. Only halfas much current flows in the lower winding as flows through the upper windingof relay 204 due to the fact that the two batteries are in series aidingin the circuit eX-.

tending through the upper winding. Since the two windings of relay 204 oppose each other when the currents flow as above described, the upper winding prevails and shifts the armature of the relay to its marking, or left-hand, Contact where I it remains as long as the circuit conditions above described exist.

'Ihe shift oi the armature of relay 204 reverses the direction of current flow through the lower winding of relay 205 because grounded positive litl-Volt battery 233 is now connected over the marking, or left-hand, contact and armature of relay 204 through the lower winding of relay 205. The current through the lower winding of relay 205 is now in such a direction as to tend to shift n the armature of relay 205 to its spacing, or lefthand, contact. This action is prevented by current flowing through the upper winding of relay 205 `iromgrounded positive 48-v0lt battery 233, overgthe marking, or left-hand, contact and armature of'relay 204, through the upper winding of relay 205, outer left-hand armature and contact `of relay 2|3, to grounded negative 48-volt battery 235. This current being slightly greater than that'lowing through the lower winding, and the upper winding being oppositely poled, the armature of relay 205 remains on its marking, or right-hand, contact.

It will be noted that even if the armature of relay 205 should be shifted to its spacing, or lefthand, contact, under conditions which will be described hereinafter, the armature of relay 204 willnot shift. When the armature of relay 205 is on its spacing, or left-hand, contact the grounded negative Ll8-volt battery 229 now connected to the upper winding 204 over the spacing, orleft-hand, contact and armature of relay 205 opposes the potential of the grounded negative battery |24 applied to the upper winding of relay 204, through the winding of relay ||4 of the line circuit. `Current therefore ceasesto now through the upper winding of relay 204. However, the direction of current through the lower winding of relay 204 is reversed by the sluiting of the armature of relay 205 to its spacing contact and is now in such a direction as to hold the armature or" relay 204 on its marking, or left-hand, contact.

Operator communicates with the maintenance man at the calling subscribers station The operator is now able to communicate withv the maintenance man at the calling subscribers station and to use the sender` contacts 222 of teletypewriter 22S by operating teletypewriter key 332 to ask the maintenance man what connection is desired. The operation `oi" the sender contacts for extending the code combination will cause an open circuit condition of the circuit through the upper winding of relay 204 for each spacing impulse. During each spacing impulse the armaturelof relay 204 will therefore be shifted to its spacing contact. This produces a no-current condition in the upper winding of relay 205, but it also reverses the current through the lower winding of relay 205 and causes said lower winding to hold the armature of said relay upon its marking contact. No current impulses through the upper winding of relay 205 are without effect, however, because plug 203 is not connected to an outgoing line and hence the signals are in eiTect not repeated. As soon as the armature ofrelay 204 is shifted back to marking, the current through the lower winding of relay 205 is again reversed, but the current through its upper winding prevails and holds its armature on its marking contact as hereinbefore described.

Each time the line circuit is opened 'as above described, the circuit through the two opposing windingsof relay ||4 is opened but this is without eirect. The two windings oppose each other during the marking condition and receiverno current during the spacing condition so thatl the relay is not actuated under either condition.

. Line relay |05 at the subscriber station, however,

responds to the marking and spacing signals to operate the subscribers printer magnet |06 which causes printed characters to be recorded at teletypewriter |0|.

The maintenance man now uses his sender contacts |04 to send to the central operators printer 22| a request that the testing trunk at the trouble operators position be connected `to the calling subscriber line. When his request is acknowledged he disconnects. Theoperator re'N ceiving the request will convey the request by any available means, such as a call Wire, telee phone, or other means, to the operator at the trouble position who will, in turn, insert the plug ofy a test trunk, such as plug 30| of the test trunk shown in Fig. 3, in the test jack H2 which is a multiple of the line jacks I0 and Etend'ing connection to the testing trunlc The operator at the trouble operators position upon inserting plug 30| into jack H2 automatically starts the testing trunk functioning. The maintenance man at the calling subscribers station in the meantime restores power switch |08 to its normal position and proceeds to make preliminary tests of the subscribers printer while the test trunk is being set up. These preliminary tests as hereinbefore stated, include oiling parts, cleaning and adjusting contacts, adjustingre lays, and making general mechanical test of the printing mechanism. i

When the' trouble operator inserts. plugr 30| into. test-jack H21, a sleeve circuit is completed from` groundedl negativezM-velt battery, .through the windingY of relay 3-A, .sleeve conductors of plug: 30|z and jack'. ||2,1 through the upper windingfofirelay |..|3.to groimd. Relay ||3 operates aty this time 'mseries with relay 3-A.

Relay 3-A, uponv operating, operates relay 3`BB which, in-turn, causes red guard lamp 303 to light, and closes the tip and the ring conductors of plug 30| oyer'two paths respectively, the tip extending throughthe winding ofv relay 3C to grounded negative .Z4-volt battery, and the ring extending through the winding of stepping: magnet 304i to grounded positive 48volt battery; Because the station power switch |08 is in its- 'oposition at this time the ringconductor Willjbel opened but the tip conductor will bei grou-ndedatthe armature and Contact oi relayV H thereby`r causingv relay 3--CC` to operate and. transfer the ring conductor to the. winding off relay SY-L. Relays' H5 and` Hl happen, at this time; to be in operatedconditionbecause re:- lay |f| 4 is operated by current in itsfupperl winding." only,v the current Ilowing in a path. extending from ground at` the normally closedr contact of power. switch |08, through. the lower winding: of relayA |505, normally closed' contact of bre-ak key |13-, transmitting contacts |504, tip' conductor |02., upper armatureand: front contact of relay H3, through the.V upper winding of relay H4, to groundednegative. battery I Z4...

Should) theL maintenance man operate. the power switch |08-` as. he.l normally would do to initiate a call', the removal'. oi the ground cone nection from the. tipf conductor at: thenormally closed contacts of power switch.` |08, followed by the immediate closure ofv the loop, would cause relay 3-L to operate and the slow-release relay 3=CC to. release. Should. relay 3`L operate it would. lock throughits own; contactV to the ring conductor andxprepare a path for `lighting) of the answer lamp 305 when relay 3.-'-CC subsequently releases.v The lighted answer lamp 3135 would call the testv board attendant; to the circuit as at present.

However', in this casesthe. maintenance man does not want to call in the attendant at'once but' desires to-obtainf the source of signals.. He therefore operates and holds the break key |23 of the subscriberst teletypewriter operated where-v by the groundv connection isi disconnected. from thetipl conductor of the-testing trunh, then op crates power switch lt-to its on position, and one' second later releases break key |123; The operation. ofbreakkey |23 removed groundv from tipconductor |02 to cause relay |14 to release and, inVA turn', the release of relaysY |15, H6. and #MCCl Hence relayI 3-CC will have released before the subscribers loop ist closed andA after the power switch |08 is operated to its on position will have included in the loop circuit the stepping magnet 300l of: the minor switch 305. Stepping magnet. 304` operates thereby causing the brush 301 of minor switclfrlr to step-tothe Contact No; l` thereby connecting source 308` of interrupted ground operating at sixty impulses per minute, to the term-inalfNo l of bank No.. 6 of each of the lnder switches- Al and B. The offn'ormal springy assembly 3000i minor switch-303 will also operate, removing busy ground at its normally closed contaetffrom. terminal No. 1 of bank No.. 1 (which is the hunting bank) of each of the finder switches' and will connect onits lower normally open contact a ground connection to. a circuit extending` over` conductor 3.10,.. outer lowerA armatureand. back contact of relay 3-L', contact and;l outer lower armature orV relay 3 '-BB,. through` the winding ofi signal relay :iv-SIG, holding conductor 35| to terminal No. 1 ofi. bank'. No. 21 of each of" the... nder switches. Also ofi-normal spring assembly 309 closes at-:its upper; normally open ContactK a circuit extending from. ground'vv at. the outer lower armature and baclc contact of release relay 3;RLS, upper,

normally open Contact of assembly 309.; lower armature andbackcontact of relay 3-SIG, conductor 328,. through; the winding of startl relay 4-ST, to grounded negative 2li-volt battery, and start relay 4*ST operates.v Start relay 4-ST together with. overflow relay i-OFL and overfow magnet. i-OFL-MGT of a register comprisea. common start: circuit which is common toall thetesting trunksrespectivelyterminating, in.' multiples, att the finder 'switches A and B.

Start relay lf-ST., upon operating, `closes at each of. itsrrigIrt--hand armatures, Nos. 2; 3; 4 and 5, etc., a circuit extending to. groundk at the normally closed" contact; of a local tesi'l key in. its resp'ectivelnderi switch` of switches A, B, etc'., the circuit'. for-operating iinder switch A being traceable from ground at: the. normally closed contact ot local testlseybe--Kv conductorV 4 I4, overfNo. 4 armature and contact of relay 4-ST, conductor 403, backV contactl and armature-l No; 2 of relay 4--Cl-A, through the winding of' slow-release relay 4.-SHf-A, to grounded, negative 24i-volt battery and: relay-4-SH-A operates A` similar circuitV is closed; for' operating relay 4-SH-B at findery switch B' and al similar circuit is closed for each of. the other finder switches'y provided; The; local testkeys are provided for respectively adjusting: the. signal biasing sets and.` during the adjusting operation of any one set, the finder switch associated with such set will not attempt to accept calls.

Relay 4-Sll-A, upon operating, closes at its right-hand armature and contact a circuit extending fromy grounded battery,. through. the winding of relay'l-HT-A right-hand armature and cont-actv of relay 4--SHe-A, armature. and contactA of stepping magnetI 4-STP-A, to` a common pointy 404-, backcontactand armature No.r 1 of relay 4-GTA, conductor 405, to the bridging brushof bank. No. l. In general; the brushes ofA each finder switch are resting on the terminals last served and-a ground will be found connectedV on the Y terminal` ifv the associated testing` trunk. isnot. calling for a. signal biasing set novground will. be found on terminals of such trunkcalling for a set. Where the banks ot a finder switchy are provided with twenty-two terminals, only theunequi-pped terminals ot bank No.. 1,. tha-t'isg those terminals to which no. test trunks are. connected, will be grounded. Hence, a finder switch when started tooperate, may only engage a grounded terminal when the start relay 4-ST and a relay of those designated 4-SH releasel as the` nder switchv islstepping; onto a grounded. terminal.. Usually banksNos. 2.110 6 have onlyA twenty-one terminalsl and bank No, l has twenty-two.- terminals in which case the twenty-second` terminal. is grounded. This is doneibecause when one brush. arm of a finder switch is passing.. over to associated.v terminals,

the other brush arms. of theswitch arev passing over. their respective twenty-second termin-als re.- sulting in a. double frictional load, By omitting tive twenty-second terminals-.the load' is increased by one. terminal only, namely, the twenty-secass'auts ond on -bank No. 1. Also relay 4-SH.A, upon operating, closes at its left-hand armature and contact an operating circuit for relay 4--.CTVA, the circuit being traceablefrom ground, over the left-hand armature and contact` of relay 4-SH-A, through the winding of relay 4-CT-A, to the common point `404 in the path hereinbefore traced. Relay 4-CT-A istherefore 'short-circuited during the time that the brush arm in bank No. 1 of finder switch A is connected to ground on its twenty-second terminal or terminal last served. The ground connection in bank No. 1 of lnder switch A is effective to close the operating circuit for relay 4-IITA which operates. Relay 4-HT-A, upon operating, closes at its armature and contact an obvious operating circuit for stepping magnet 4- STPA wh-i'ch operates to open the operating circuit of relay -4--HT.-A. 'Relay 4`HT-A releases and in turn causes stepping magnet 4--STP-A Ato release. The release of magnet d-STP-A causes to step the brushes of iinder switch A to their respective next terminals. This sequence of events is repeated .until the brushV in bank No. Al f finder switch A moves into engagement with a terminal not grounded since the terminal associated with the testing trunk on which the maintenance man is awaiting the source of `signalhas an operated offnormal `switch assembly such as that designated 309, Whereat the normally closed grounded contact is open. `When brush No. 1 of finder switch A becomes non-grounded, the shunt around re.- lay 4-.CT-A is removed, permitting it to .operate, immediately connecting ground at the lefthand armature and contact of relay A-SH- A tothe terminal, say in this case terminal No, 1 of bank No. 1 thus preventing other finder switches `from stopping on this terminal. `Relay 4-HT-A is marginal and therefore does not reoperate in series with relay 4--CT.-A and stepping magnet A-,STP-A remains released.

When relay 4--CT-A operates, the operating path of relay 4-.SH-A which is of theslow-torelease type, is transferred from the start con- '.ductor 403 to the .brush in bank No. 2 of nder switch A and over the holding `conductor 3H., through the winding .of relay 3-,S.IG, outer lower armature and contact of relay :a2-BB, back con.-

tact and outer lower armature of relay 3.A-`L, to Aground at the lower vnormally open contact 1of `off-normal switch assembly 309 in operated position. Signal relay .3-SIG in the circuitcompris.- ing holding .conductor 3|| thereupon operates, and relay 4-SH-A is held .operated over the holding .conductor 3| Relay `3--.SIGr, upon operating, opens the operating circuit for common `start relay 4-ST which thereupon releases .unless other testing `trunks are awaiting connection to signal sources. Relay .3L-SIG, upon operating, .closes a circuit extending from ground at the outer lower .armature and back contact of relay 3RLS, operated, upper normally .open `contact of oli-normal switch .assembly .3.0.9, lower armature and front contact of relay -FSIG, conductor 3| 3, to contact No.1 engaged by the brush arm in bank No. 4 of lnder switch A, conductor 4.0.6, contact and armature No. .4 of relay 4CT-.A, conductor 40.1, through the winding battery ,and relay .S-RV operates to provide .the proper polarity termination of ,the .signals available at the biased signal source lrequired by the station circuit. .Other test trunks, aecessible to operators `cord circuits, would not connect ground conductor 401, inasmuch as they are respectively connected to diierent terminals in bank No, 4 of the lnder switch A.

Relay 3-SIG, upon operating, opens at its upper armature and back contact the operating circuit for stepping magnet 304 of minor switch 306 and stepping magnet 304 releases, leaving the brush arm 30] of minor switch 306 in engagement with lcontact No. 1 and placing the further operation of the minor switch under control thereafter of relay 3..-CC. Also relay 3-SIG, upon operating, extends the ring .conductor of plug 30| over conductors 3| 4 and 408 to terminal No. 1 engaged by the brush arm in bank No. `5 of finder switch A and then over conductor 40.9, contacts and No. 5 armature of relay 4.-CT-*A, conductor 4|.0, normally closed contacts No. .4 of key 5.-K4, through the upper winding of relay 5-MEAS, normally `closed contact No. 2 of key 5--K4, retardation coil 508, to the armature .of relay `E-BIAS at which point the signals lfrom the biased signalsource are applied.

When relay .5.RV operated it closed at its contact and outer rightehand armature a circuit traceable over conductor 533, through the winding of relay .5-A to grounded negative 24.v.odt battery and relay .5--A operates. Relay 5--A upon operating closes at its right-hand armature and contact obvious operating circuits for relays 5?.-13 and -C. and relays 5-B and 5.-. C operate. Also when relay 4-CTA operated it closed at its contact and No.6 armature -a circuit'traceable from source 308 of interrupted ground, Ycontact No. `l in engagement with brush `30"| of `minor switch ,306, conductors .310 and 4|3, vterminal No. 1 engaged by the brush arm of bank N0. 6 of lnder switch A, .conductor 4|4, vcontact and armature N o. 6 lof relay -4--CTA, conductor 4| 5, normally closed contacts Nos. 43 and 2 of key 5-K2, conductor .52.6, inner left-hand armature and contact of operated relay B-A, through the winding of vibrating relay 5-VIB to grounded ,negative `2li-volt battery, and relay `li--VIB Vbrates at .the .the rate of impulses `per minute in .accordance with the source .308 of interrupted ground. As hereinbefore described, relay 5-BIAS operates in response to current alternately impressed on windings Nos. 3 and 4 by the vibration ofthe armature of relay v5--VILB and the armature of relay 5-BIAS serves in this ease as a source of switched biased Vsignals .to be Vfurnished to the maintenance man over conductor 4I0 as hereinbefore described. The teletypewriter at the subscribers .station will now receive `the switched .biased signals, followed Aby the test sentences, all mar-k and space signals of whichare biased. The maintenance man will utilize the biased impulses for testing the subscribers teletypewriter .on in- .coming signals. l

In the event the ,station teletypewriter records errors on switched biasedsignals the maintenance ,at the .subscribers kstation will require the source of signals having .steady mark bias, and later steady `space bias. `Tochange .the type of signals from .switched .to markbias the maintenance man will turn powerswitch |08 to its 01T position therebyclosing the circuit traceable from ground, normally-closed contacts of power switch m8, through the lower winding of line relay |05, normally closed contacts of break key |23, through the v sender contacts |04, .tip conductor 102, upper armature `and front vcontact of relay 3 through the upper winding of differential relay U4 .to Ygrounded negative L8-volt battery |24, Relay IIA operates to close an obvious op- Vopen contacts of power lower winding of line relay |05, normally closed 1 O rating' circuit for relayf|,|5. Relay ||5 operates and connects ground on its armature and contact to the tip conductor of jack ||2 and of plug 30| in a circuit traceable over the outer upper armature and contact of" relay v3 BB, outer upper armature and back contact of relay 3-DD, through the winding of relay 3-CC, to grounded negative battery and relay 3-CC operates. Relay. 3-CC, upon operating, closes at its outer lower armature and contact a circuit extending from ground, over the make-before-break contact of relay 3--SIG, through the winding of stepping magnet 304 to grounded positive Ll-volt battery. Stepping magnet 304 operates to advance brush 301 of minor switch 306 to its No. 2 position thus removing source 308 of interrupted ground from the circuit traceable over conductors 3|5, 4|3, contact No. 1in engagement with .the brush arm of bank No. 6 of yinder switch A, conductor 4|4, contact'and No. 6 armature of relay 4-CTA, conductor 4|5, normally closed contacts of key 5-K2, inner left armature and contact of relay 5-A, through the winding of vibrating` relay 5-VIB, to grounded negative 2li-volt battery, and relay E-VIB ceases to vibrate and remains in its released position. Winding No. 3 of relay 5-BIAS is energized whereas winding No. li of relay 5-BIAS is deenergized, the energizing circuit for winding No. 3 being traceable from ground through the No. 3 winding, retardation coil 5|5, resistance 5|6, back contact and armature of relay 5-VIB, conductor 521, contact and outer left-hand armature of relay 5-C, to grounded positive 24-vo1t battery 528. Relay E-BIAS under the inuence of winding No. 3 is operated to its marking, or right-hand, position so that the bias signals outgoing over the outgoing circuit are now biased marking, the outgoing circuit including retardation coil 500, normally closed contact No. 2 of key 5-'K4, through the upper winding of relay 5-MEAS, normally closed contact No. 4 of key 5-K4, conductor 4|0, armature No. 5 and contact of relay 4-CT-A, brush in engagement Awith contact No. 1 in bank No. 5 of nder switch A, conductors 408 and 3|4, frontcontact'and upper armature of relay 3-SIG to the back contact associated with the operated upper armature of relay 3-CC. The maintenance man now operates and holds operated,

break key |23, causing relay 3--CC to release. One second later he operates power switch |08 to its on position and Vthen releases the break key. Relay 3-CC upon releasing, closes the subscriber loop at the back contact and upper armature of relay 3-CC, the loop now extending over the make-before-break contact of relay 3L, back contact and inner upper armature of relay 3-DD, iront contact and inner upper armature of relay 3-BB, ring conductor of plug 30| and of test jack ||2, inner lower armature and front contact of relay ||3, through the lower winding of differential relay ||4, right-hand normally switch |08, through the contacts of key |23 (which is released one second after thepowerswitch is operated), sender contacts. |04, tip conductor |02, upper armature and front contact of relay ||3, through the upper .winding of differential relay H4, to grounded negative 48-volt battery |24. The release oi slow- .to-release relay 3-CC occurs before the release of break key |23 and therefore lamp relay 3-L is prevented from operating and the station teletypewriter will therefore receive thetest signals.

When the maintenance man at the subscriber circuits.

ascissa station having made the necessary adjustment required in accordance with the steady mark bias signals received over the output circuit lfrom the signal biasing set, he repeats the procedure hereinbefore described to advance th brush 301v o f minor switch 306 to position No. 3. A ground connection at position No. 3 of minor switchf306 completes the operating circuit for vibrating relay E-j- VIBand relay 5-VIB operates to close an energizing 'circuit for winding No. 4 of' relay 5I-B1As and deenergizing the winding. N053 of relay 5,-B1As. Relays-BIAS now operates to its spacing, vor left-hand, position and thereby completes the outgoing circuit for transmitting steady space bias signals to the subscribers loop. This procedure may be repeated alternately obtaining steady mark bias and steady space bias signals so that the maintenance man may make the necessary repetition in checking the teletypewriter.- Afterwards he may senda recall signal to dismiss the set and call in thel test board attendant. In. the event the maintenance man desires to obtain the attention of thetest board attendant he will operate the power switch |03 to its oi positionand reoperate it after `two seconds, this being the standard procedure for sending a recall signal. When the power switch is turned to its oli position, ground from' the subscriber line overthe tip conductor operates relay 3-CC and when the power switch is again operated to its "on position the subscribers loop will be reclosed before relay 3- -CC releases, thus causing the operation of relay 3- -fL which operates, loks to the subscribers loop yand opens the holding path of relays 3-SIG and 3,-SIG and relay 4-SH-A of the seizednder switch A'release, the latter relay upon releasing, releasing its associated relay 4f-CT-A to open the connection to signal biasing set A associated with seized finder switch A. The brush arms of seized iinder switch A remain in their respective operated positions so that signal biasing set A vmay be available for use with other testing trunk erates relay 3-RLS in a circuit4 traceable from ground, lower normally open contact of off-normal switch assembly 309, outer lower armature and front contact of relay 3-TL, through the winding of relay B-RLS to grounded-negative battery, and relay 3-RLS operates. Relay 3--RLS, upon operating, (1) locks up in ,a circuit traceable over its inner lower armature ,and front contact; (2) closes at its upper armature .and

front contact, the operating circuit for release magnet 3 1. Release magnet 3 1, upon operating, causesbrush 301 of minor switch 306 to return to its normal position. When the. minor switch 306 is .infits normal position, the `olf-normal spring assembly 309 releases thereby releasing relay 3-RLS which in turn releases magnet 3|1. When relay 3-CC subsequently releases answer lamp 305 becomes lighted, indicating to the test board attendant that he is wanted. When the attendant inserts plug 3|8 into jack 302 andoperates power switch 3|0, relay 3-DDbecomes 0D- erated and the attendants teletypewriter becomes conditioned for operation. Relay 3-DD, upon oper.ating(1) closes at its make-before-break contact, an obvious operating .circuit for relay 3,-CC which again becomes operated andtherebyreleases relay `?,L, (2) transfers the extension of the subscribers loop circuit tothe ringconductor of jack 302 and plug 3| 8 and thenceinto the attendants teletypewriter and (3) opens the a-sH-A. Relay RelayA 3-L upon operating also op deafness locking circui'tfor lamp :relay :3-L :which releases to extinguish .answer lamp;30i5.

Relay 3-1CC,1upon ;opera`ting, at lthis :time prevents ,a -*false seizure by .a dinder :switch circuit in the `eyent ,the test :boardattendant disconnects iirst. In such a case the release Aof relayzS-DD will permit .relay 3-L `gto reoperate before relay 3-CC releases, :thus .preventing connection of the extension of Lthe subscriber-s doop cir-.cuit to the operating circuit of stepping magnet i304 aof the `minor switch. If the maintenance :man has already disconnected, )relay B-eCC `will be held operated by vthe rtip conductor :ground at :thesubscribers station. The momentary operation or this disconnect `key B-'DISC .will 4provide a yisual disconnect signal to the operator at the :trouble position in the operator switchboard Iso that the trouble operator will thereupon `,disconnect the testing trunk from the subscribers fline. l

:In asimilar manner, the ,test `board .attendant by his biased signal cord may ,also -be :terminated on the yterminals -of `the :banks of :all the `lnder switches Aso that when he :desires -a source -cf l.signals, he maycause any idle `signal hiasingset to lle-,associated -withfhis cordV by'means .of `the `nder switch circuit. lThe-biased signal cordicircuitprovides 'appearances zin `the form oi tenninati-ng plugsat the attendants test 4.board [for use in as sociatinga signal biasing setsuch as one 1of sets A and -B with .any subscriber line 1er intertoll trunkior checking operators 'teletypewriters and regenerative repeaters at `the switchboard. ,In the euer-1t all sources of signals are busy, the, .overow relay 4--O\FL releases :and the neX-t `subsequent operation of start relay A--SZI will cause magnet 4-OFllr-MGEI of theregister tooperate, indicating the number of fsuch foccurrences..

What is claimed :is:

1.. A .teletypewriter .signal testing tor testing rsignal trnsmission comprising animal-ity (Ji-transmission channels each having operable means. .a vswitchboard whereat said transmission channels terminate. a test board, a circuit .interconnecting said switchboard -and said test board. a source 'of .different vtypes of signals .biasedpto .any desired degree, means under the control of said operable means .associated withtone of said .transmission channels for remotely selecting .any one of said types `of signals from said. source, .and `other `means associated with .saidsource or `automatically `trarrsrnitting the dilerent types 1ci said biasing signals .from saidsource to said `one transmissionchannel when an operable connection is established between said one channelancl said .terconnecting '.circuit.

2. .A teletypewriter signal testing system for .testing signal transmission comprising .a ,plural-ity 4,of transmission circuits each having operable ,-means, .a switchboard whereat said transmission circuitsterminate, .a test board, a .circuit connecting said switchboard and `said test board, a

.source Vof different type 'of signals .biased to any .desired degree, means under the` control of any .one of said .operable means for automatically selecting .any .one of the diierent types of signals `from said source, other means-for `autlnnatically transmitting the diierent types .of signalsfrom said source to ,any .one of Ysaid transmission circuits when said interconnecting circuitis connected to said one transmission circuit in r e sponse to the operation of said one operable means associated with said one transmission circuit, an indicating means at said test board responsive to the release of said operable means from its operated position and reoperation of said operable :means V'after a :prolonged `interval for calling the Vattendantatsaid :test boa-rd'lin on .the

testing telegraph transmission comprising ia, plu` rality of telegraph transmission circuits leach having ta xtelegraph printer and a power switch,

a switchboard .whereat said 'transmission Icircuits terminate, `a. test board, la circuit interconnecting said vswitchboard and said test board, 1a source :of dinerent types-of code signals biased to any .desired degree, means operable in -coni'unction with said power switch in its operating condition for automatically -selecting any one :of the different types of biased signals -from'said sources-or :testing the printer in said `one transmission circuit w-hen said interconnecting circuit is connected to said .one transmission circuit in an Aestablished connection.

4. In a vtelegraph system, a plurality -of outlying stations, telegraph sending and receiving equipment-,at each of said stations, a main entice,l a plurality `oi" channels respectively connecting said stations `to said main ollice, a testing nunk i adapted for yconnection at said main office `:to lanyl one -of said channels, a source consisting of a single circuit vhaving `apair of adiustable network paths, located Yat said main oilice and capable of vproducing different types of signals biased. to any desired degree and `means at each of said outlying stations forautomatically selecting over an established connection betweenone of said channels and said testing trunk, anyone of said types of biased signals v'for Ltesting the sending and receiving equipment at the calling outlying station. 1

V5. In a telegraph system, Ya plurality of outlying stations, telegraph sending and receiving equipment at each of said stationsy a main cnice. an operators` Vswitchboard and a test board at said main office, a plurality Aof channels respec tively connecting said stations .to said switchboard, a testing trunk adapted for connection at said switchboard to any one 4of said channels, a

plurality of switches connected in multiple to said testing trunk, a 'plurality of sources located at said test board and capable of producing different types of signals 'biased to 4any desired degree, each of said sources ybeing connected to `one of ,said switches, and means4 at `each of said outlying stations for automatically selecting over an established connection between one of said ,channels and said testing trunk any one of said types of biased signals from any one of said sources for testing thesending and receiving equipment at a calling outlying station.

6. In a telegraph system, a `plurality of subscribers stations, telegraph printing, sending and receiving equipment at .each of said stations. .a central ofce, an operators switchboard and a test board at said central oflice., telegraph printing sending and receiving equipment at said switchboard and` said test boardJ a `plurality of lines respectively connecting said stations to said switchboard, a plurality of `testing trunks each adapted for connection to any one of said lines at said switchboard and to said sending and receiving equipment at said test board,` a. plurality of `selecting switches each connected in multiple `to. said testing trunks, a signal` biasing `set connected to each of said selecting switches a source of biased signals in each of said signal biasing sets, and means in each of said subscribers stations for automatically selecting over an switchboard and a test board at said main sta-` tion, a sending and receiving device at each of said outlying stations and at each position of said switchboard and said test board, a plurality of line circuits respectively connecting said out-I lying stations to said switchboard, a testing position forming a part of said switchboard and having means for respectively terminating each of said line circuits, a testing trunk having means at one end for conductively engaging any one of said line terminating means at said testing position and means at theother end accessible to the sending and receiving means at said test board, bias signaling means included in said testing trunk comprising a plurality of sources of test signals having predetermined values of bias distortion, each source having means for producing signals with different types of bias distortion, and means under control of any of said outlying stations and operativefafter said testing trunk is conductively engaged to the line circuit of the selecting outlying station for selecting independently of any attendant at-said test 4board and said switchboard, any of said sources of test signals for connection to the line circuit of said s electing outlying station. v

8. A telegraph system comprising a central ofce, a plurality ofl subscribers stations, a plurality of subscriber lines respectively connecting said stations to said central oice, telegraph printing, receiving and sending equipment Vat each of said subscribers stations, means in said central office to switch any one of said lines in communication with any other of said lines, a testing trunk to associate anyone of saidlines with a test board position, means whereby said trunk may be associated` with a given line without calling the test board attendant, a source of biased signals at the central oiiice, calling means and breaking means at each of said subscriber'stations, means at said central oflice responsive to the prolonged operation f said breaking means and the operation of said calling means followed by the release of said-breaking means for automatically selecting said source of biased signals for connection to said given line, said responsive means comprising stepping means for alternatively connecting the different types of biased signals from said source, to said given line in response to the repetition of successive operation and release of said calling and said breaking means.

9. In a teletypewriter system, a central ofilce, subscriber stations, a pluralityY of subscribers lines having telegraph printing and sending equipment -associated therewith at each subscribers station, means at the central oice to switch any one of said lines in communication with any other of said lines, a test board position at said central cnice, a teletypewriter adapted for connection to said testboard position a testing trunk to associate any of said lines with a test board position, means wherebysaid trunk may be associated with a given line without calling .the test. board attendant, a source located at said centraloiiice and capable of producing different types of signals4 biased vto any desired degree, means under control of the equipment at the subscriber station for automatically selecting any one type'of biased signals from said source and connecting said source to said calling subscribers line for transmission of the desired type of` biased signal to test the equipment at said subscribers station, means under the control of a subscriber station to indicate to the test board attendant that said trunk is in use, and other means under the control of a subscriber station to indicate to the test board attendant that monitor signals are to be sent from the subscribers station `to said teletypewriter at said test board position.

1.0. In a teletypewriter system, a central ofiice, subscriber stations, a plurality of subscribers lines having ytelegraph printing andfsending equipment associated therewith at each scub-y scribers station, means at the central oiiice to switch any one of said lines `in communication with the other-,of saidlines, a test board position at said central oice,ka'testing trunk to associate any one of said lines'with the test board position, means whereby said trunk may be associated with a given line without calling the i'festv board attendant, asource `located at said central oice and capable of producing diierent types of signals biased to any'desired degree, means under the control of a subscriber station to indicate to the test board attendant that the trunk vis in use, means whereby any one of said types of biased signals from 'said source may be transmitted over said trunk and a given one of said lines in established connection to a vsubscribers vstai-,ion under the control of the equipment lat saidfsubscribers station, means where-by the subscribers station may notify the test board attendant over said trunk to monitor signals sent from the subscribers station, and means to signal an operator at the central ofce to disconnect the trunk from the given line.

11. In a teletypewriter system, a` central oiiice. subscriber stations, a plurality of subscribers lines having telegraph printing and sending equipment associated therewith at each subscribers station, means at the central office to switch any one of said lines into communication with any other of said lines, a test board position at said central oflice, a testing trunk to associate any of said lines with a test board position` means whereby said trunk may be associated with the given line without calling the test board attendant, sources located at said central ofce for respectively producing signal impulses having different types of bias distortion, means in each of said sending and receiving equipments for automatically associating selectively each of said sources with said one line for testing equipment at the calling subscribers station, means under the control of a subscriber station to indicate to the test board attendantthat the trunk is in use. means whereby the subscribers station may notify the test board attendant over said trunk to monitor signals sent from the subscribers station, and means under control of said selecting means for indicating the number of times said selecting means is unable to iind an idle source of biased signals.

ALLEN R. BONORDEN.

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