US1543933A

US1543933A - Testing device for telephone-exchange systems

Info

Publication number: US1543933A
Application number: US637417A
Authority: US
Inventors: Eric R Lundius
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1923-05-08
Filing date: 1923-05-08
Publication date: 1925-06-30
Anticipated expiration: 1942-06-30

Description

June 30, 1925.

E. R. LUNDIU TESTING DEVICE FOR TELEPHONE EXCHANGE SYSTEMS Filed May 1925 '7 Sheets-Sheet 1 XQ NNQ RQ RQRQ w@ w W NE fiw 7 .6 m w E. R. LUNDIUS TESTING DEVICE. FOR TELEPHONE EXCHANGE SYSTEMS Filed MayB, 1,925 '7 Sheets-Sheet 2 Mae/#01": fr/b E Land/Z15. by W '7 Sheets-Sheet 3 E. R. LUNDIUS TESTING DEVICE FOR TELEPHONE EXCHANGE SYSTEMS Filed May 8, 1923 June 30, 1925.

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PATEN ERIC LUNDIUS,,OF BROOKLYN, NEW YORK, A$SIGNOB TO WESTERN ELECTRIC CGMPAN'Y, INCORPQEATED, 3F NEW Y BK, l- A QUE-P QEATION OF NEW YORK.

TESTING DEVICE FOR TELEPHONE-EXGHANGE SYSTEMS.

Application filed May a, was. j Serial n 637,417.

exact description.

, This invention relates to telephone e7:- change systems, and more particularly le a testing device for use in such a telephone s stem of the inachine switching typ In theoperation of the telepl'ione exchange system it is importantto maintain a high standard of operating eiiicien'cy in theciraccess to responsive means in cuit paths over which the subscriber has id exchange. In some systems of the machine switching; type non-numerical line switches are used to extend the calling subscribers lines to the selective switches in the exchange. If the line and line switching apparatus are not in proper operating condition to test and seize an idle selector switchthe subscriber will be prevented from making calls.

The "anparatus used in the line switching mechanism of a machine switchin oilice. is ma e up of moving partssubject to loss of an3nstn'ient which may result from normal usage of -t'lie equiy'nnent. This loss of adtinent would result in inip-ro'per functioning of the apparatus or failureto function. There are. also, well known troubles encountered in the maintenance of line conductors (XiIQHCll-RP' fron'i the switching mechanism to ibers station. ures would ordinarily cause the isolation of a subscriber. It is, therefore, inii iori' -ant that eqi-iipinei'it' of this nature be regularly tested to determine. prior to its reported failure, whether it is in suitable condition for rendering efiicicnt service.

it is the object of this invention to provide a device to make tests of the line circuit paths and line switching mechanism of a telephone exchange system.

The disclosure shows the invention applied to a testingdevice arranged for testing lines and line switching apparatus of the type disclosed in Patent No. 1,395,977 issued Nov. 1, 1921. to F. A. .Stearn et al.

.It wi l e i er i, app rent from th fol;

lowing description that the invention has a wide utility and that by slight modification it may be adapted to testing many other types of line switching mechanism and lines.

A feature of the invention resides in the seizure and control of ai final selector switch by the testing circufitto function as a part of the testing circuit by selecting the line or line switch apparatus to be tested. This final selector switch, when not connected to the testing circuit, forms a part of the. ex-

change switching equipment for completing calls in regular service.

A further feature of the invention relates to accurately testing the adjustments of the relays of the line switch circuit on a regulated current flow basis. A step-by-step selector of the type well known in the art is employed to successively associate the apparatus to be tested with the test circuit. Lamps are successively lighted to indicate the particular test being made and the success of preceding tests. p

A further feature of the invention relates to theoperation of the line switch as in regular service to associate a district and sender selector with the testing circuit. The district and sender selector will function in this test, by transmitting dial tone through the selector contacts and contacts of the line switch circuit relays, to a receiver in the testing circuit. This tone is used as a successful test signal.

A further feature of the invention relates tothe ability of the testing circuit to differentiate between a line switch circuit extendingdirectly to a subscribers station and a line switch circuit extending to a private branch exchange, together with the ability to applythe proper test in accordance with this differentiation.

A further feature of this invention will be found in the making of ballistic tests successively on the tip and conductors of the line by the single actuation of a key in combination with a stcp-by-step selector of a well known type. Immediately preceding each of the two successive ballistic tests any latent capacity in the conductors of the line, or electrically responsive apparatus con-' nected to these conductors is discharged to prevent actuation of the responsive apparatus when the ballistic test is applied.

i A further feature of the invention relates to the employment of a potentiometer to discharge latent capacity in a line, or responslve mechanism connected thereto, preceding a' test of one of the line conductors, to prevent actuation of the responsive mechanism.

A further feature of the invention relates to the use of a meter for determining line conditions together with an automatic fea-- ture arranged to stop automatic.progression for alimited time during each line test'to facilitate the rcading of the meter. These and other features'of the invention will be apparent from the following dea diagram showing the order in which the:

drawings should be arranged. I

Fig. 1 shows the control apparatus for causing the final selector, Fig. 6, to select the line to be tested, also the key control lor advancing the final selector, Fig. 6,'in single steps. i

Fig. 2 in combination with Fig. 3 shows the testing device for testing the line switch apparatus.

Fig. 4 showsa circuit for automatic discharge of latent capacit of the line in connection wlth a balllstic test of each side or the line.

Fig; 5 shows the controlling means for making an insulation breakdown test.

Fig. 6 shows a final'selector switch which ias access to the lines and line switch circuits to be tested. This final selector circuit is specially designed with jacks con nected in such a manner that it may be used for test purposes when the patching cord and plugs associated with the testing equipment are inserted in said jacks. The leads of this final selector circuit are connected to the jacks in such a manner that when it is not in use as an adjunct to the testing circuit equipment it may be employed as a part of the machine switching apparatus for service connections.

The left hand part of Fig. 7 shows a line and line switch apparatus to betested. A subscribers station and a private branch exchange are shown optionally connected to the line. When the subscribers station is connected to the line, conductor 783 is connected to are 723 and conductor 7 64: is connected to conductor 715. hen the private branch exchange is connected to the line conductor 783 is replaced byconductor 7 81 and conductor 764 is replaced by 763. A district selector is diagrammatically illustrated in the upper right hand part of this figure. Also a sender selector is diagrammatically illustrated 1n the lower leit-hand part of this figure.

Description of apparatus.

The testing device disclosed in Figs. 1 to 5 inclusive, is enclosed in a portable box mounted on wheels, so that it may be easily moved among the switch frames in a switch ing room of the cities, and is provided with

suitable jacks

320, 321, 322, 323 and 324 shown in Fig. 3, for connection, respectively, to the final selector circuit, insulation breakdown test battery, ballistic test battery and an interrupter.

In actual practice power is transmitted to the testing device through jacks on the testing device which are attached by other circuits to suitable power jacks on the selec tor switch frame. Such power connections include current supply for 48 volt direct current to the relays and step-by-step switches, and alternating current to appa- 'ratns on Figs. 4 and 5. For convenience of illustration, however, these jacks have been omitted and the source of current and ground potential have been shown directly associated to the different pieces of apparatus. I 7

Keys 120 to 129 shown in Fig. 1 are of the well known mechanically locked and electrically released type.

The step-by-step selectors shown in Figs. 2, 4; and 5 may be of any well known type, and are arranged to start at normal for each test.

Fig. 3 illustrates rheostats of the well known type numbered 350 to 357, inclusive. These 'rheostats are used in combination with milliammeter 302 for regulating the current flow in accordancewith the voltage reading of the battery at the time that the tests are being made. This current flow regulation allows very accurate. testing of the non-operate and operate adjustments of the line switch relays 701 and 702.

Meter 450 shown in Fig. 4 is for use both as a voltmeter and as a milliammeter. The milliammeter tap is shown beween resistances 4:33 and dirt, and is used for observation of line conditions when making ballistic and insulation breakdown tests.

The automatic final selector switch shown in Fig. 6, is of the well known power-driven type, in which a plurality of sets of brushes are mounted on a vertical brush shaft arranged to be selectively tripped into engagement with their individual sections of the panel terminal bank. The brush shafts are propelled in a vertical direction by means of constantly'rotating power drums. In general construction and operation, this switch is of the same character as the one shown and described in detail in the patent to E. B. Craft and J. N. Reynolds 1,123,696, issued January 5, 1915. More specifically, the circuits of the final selector shown in Fig. 6 are described in the application of Alben E.

'Lun'dell, Serial No. 487,520, filed January The district and sender selectors, shown diagrammatically in 7 are 01": the same type also specifically described in application, Serial No. 487,520, filed July 25, 1921.

Having now described in a general way the apparatus employed in conducting tests and the manner in which it is to be used, it

is thought that the invention will be better understood from a'consideration of the general manner in which the testing will be conducted.

General description.

Assuming that a :test is to be made of a certain line switch and line, the portable testing circuit will be taken to a point accessible to framejacks such as 382 and 833 associated with a final "selector circuit that 'will have access to the :line to be tested.

.to act as a start key and cause brush selection of the final selector shown in. Fig. 6. 'Atter this has taken place a second one of these keys will be operated for tens selection and as soon as this has been accomplished a third key will be operated for units selection.

Assoon as units selection has taken place and the line to which the testing device is connected has been found in a nonbusy condition, the testing circuit shown in Fig. 2 will automatically determine whether said line isone extending directly to a subscriber, or one extending to a private branch erchange, and in determining this will also automatically associate the proper rheostats and resistances with switch 220 to give proper reglillated current flow for testing the adjustmentso'f the line switch apparatus.

The action of the apparatus functioning to differentiate between the types of line switching circuits as outlined in the preceding paragraph will automatically move switch 22(lfrom its normal position thus starting the test of theline switch apparatus. Each action thereafter will aid in the progress oi the test, excepting in tests where observation requires a longer period of time than an automatic movement of the switch would allow.

A ballistic test of this same line may be made by restoring to normal a key for the line switch test and actuating a key for said ballistic test. Afteroperation of the ballistic test key, the test of both conductors and connected apparatus is automatically carried to completion as follows: first, to discharge the latent capacity of the line and responsive mechanism connected thereto, next, to test one conductor, the condition of which will be shown by the deflection of the voltmeter needle. The conductors of the line are then reversed with relation to the testing apparatus, and any latent capacity in the conductors, and responsive mechanism is discharged. A ballistic test is then made of the other conductor, the condition of which may be noted by the deflection of the voltmeter needle. When this has been accomplished the switch will stop and restore the apparatus to normal, thus completing the ballistic test.

hen the ballistic test is completed and the key for this test is restored to normal, an insulation breakdown test may be made on the same line by the operation of a special key which will cause switch 400 to automatically make one rotation, discharging any latent capacity on the line. Switch 100 in restoring to normal will give impetus to switch 520, causing the potentiometer to be connected to the line in such a manner that an insulation breakdown test will be made on one conductor of the line without actuating the responsive mechanism connected thereto. As switch 520 returns to normal the potentiometer will function for discharging any latent capacity on the line and responsive mechanism connected thereto, preceding the insulation breakdown test of another conductor of the line. This is accomplished when switch 520 restores to normal, actuating relays for the reversal of the line with relation to the testing circuit. The apparatus functioning to reverse the line avill automatically cause a second rotation of switch 520 to perform the insulation breakdown test of the other conductor 01" the line.

In the routine testing oi? the line switch apparatus and lines of a machine switching oifice, the usual practice is to connect the testing circuit to the first line of a group or plurality of lines. \Vhen a test of this line has been completed the .iinal selector is caused to step to the next line above in the same group of lines. In this manner the final selector shown on Fig. (3 is caused to step from line to line until all the lines inv that group have been tested, thus making it unnecessary to restore the final selector after each test. The stepping oi the Final selector from terminal to terminal is accomplished by the operation of a single key which in turn causes the functioning of relays to accomplish the above-mentioned setting of the selector thus saving considerable time in the routine testing of the lines and line switches in an ofiice. I

The ability to test successively the con;

, ductors of a line with automatically progressive apparatus is considered a time sav- 7 into jacks 321' and 333.

the No. 3 key.

mg and accurate device. .This favorable time factor is quite a consideration in the cost of maintenance of the lines in a telephone office. i

The tests outlined in the foregoing general description, i. e., line switch test, ballistic test and insulation breakdown test may all be made upon a single connection to a line or any one of these tests may be made upon a connection to a line.

Having now given in general the utilities of the testing circuit it is thought that the invention will be bettter understood from a consideration of the following detailed description. I i r Detailed description of operation. The testing operator before proceeding with the first test ascertains by observation.

that the test selector, Fig. 6, is not busy, i. e., not being used in regular service, then pro coeds by connecting the testing device, Figs. 1, 2, 3, l and 5, into operative relation with the'final selector Fig. 6, by inserting the plugs of patching cord 325 into jacks 320 and 332, also the plugs of patching cord 326 This final selector is thereafter used as a part of the testing device to test lines within its scope of service. Patching cord 325 being inserted in jacks 320 and 332 connects ground to conductor 680 to make the test selector, busy to other selectors in regular service. This busy ground may be traced from the left-hand inner contacts of key 131, sleeve of jack 320, patching cord 325 sleeve of jack 332 and conductor 671 to conductor 680.

Let it be assumed that the testing operator desires to test the line and apparatus connected thereto ofthe subscriber whose station is indicated at K. It will be assumed that this subscribers number is 5322. Since the final selector has immediate access to the line terminals, it is not necessary to consider the first or thousands digit (5). The other numerals must control final brush, final tens and final units selections. To connect the testing mechanism into operative relation with the line above selected for test, the operator first actuates key 123, which is A circuit is thereupon established from ground through the lefthand outer contacts of key 131, left inner contacts of key 130, left contacts of key 123, winding of relay 1 16 to grounded battery, operating relay 14.6. The operation of relay 1&6 establishes a circuit for operating relay 1 15 which may be traced from ground on the outer left hand alternate contact of relay 507. inner right-hand contacts of relay 1 16, winding of relay 145 to grounded battery. Relay 1 16 also establishes a path for the fundamental circuit which may be traced quence switch spring 602,

per left-hand contact of sequence switch lower left-hand contact of selower left-hand contact of sequence switch spring 603, winding of relay 618, upper right-hand contact of sequence switch spring 6042 to grounded battery.

Relays

618 and 1 10 are energize in this circuit. Other active paths closed by the operation of relays 14:6 and 14:5, connect ground to counting relays 100 119 for operating and locking paths for said relays. These paths are obvious and will not be traced.

The operation of relay 1 10 connects ground from its contacts through the norspring 617,

mal contacts of relay 14:7, right-hand-con tact of key 123, normal contacts of relay 113, winding of relay 103 to grounded battery, operating relay 103. The contacts of relay 103 close an obvious locking path for itself, and an operating path for relay 113,

which, however, is not effective until the shunt ground over the operating path of relay 103 is removed. The operation of relay 618 establishes a path for operating relay 621 which 'may be traced from ground on the upper left-hand contact of sequence switch spring 608, left-hand alternate contacts of relay 613, conductor 623, upper lefthand contact of sequence switch spring 607, conductor 622, winding of. relay 621 to grounded battery. The operation of relay 621 establishes a circuit for actu ating sequence switch magnet 600, which may be traced from ground through the right hand alternate contacts of relay 621 and lower left and right contacts of sequence switch spring 609, windingof sequence switch magnet 600 to groundedbattery, moving tion 1 to posit-ion 2. As soon as sequence switch 600 leaves position 1, the initial energizing circuit for relay 618 is opened at the lower left-hand contact of sequence switch spring 603, but relay 618 remains onergized over the fundamental circuit through a locking branch of said fundamental circuit which may be traced from grounded battery through the upper righthand contact of sequence switch spring 604, winding of relay 618, lower right-hand con!- tact of sequence switch spring 610, righthand alternate contact of relay 61S, lower right-hand contact of sequence switch spring 603, lower left-hand contact of sequence switch spring 602,

damental circuit as previously traced. Be-

and thence over the fun dso the sequence switch from posi- I right-hand cont-act fore reaching position 2 a circuit is estab-- lished tor energizing, up drive magnet 626 which maybe traced from groiuided battery through the winding of magnet 6263' upper of a sequence switch spring 611., alternate contacts of relay 618,- upper left hand contact of sequence switch; spring 608; to ground. h lap'net 626'- upon energizing causes the upward n'iove'inent of the brushes oi the switch in the manner well] known: in the art.

During the upward movement of the brushes of the selector switch, ground potential is intermittently connected to the fundamental"circuitat a junction'point be tween the winding of the stepping relay 140; and the winding of line relay 618. This" ground potential is connected to the junctionpoint at upper right hand se quenfce switch spring 602; through brush selection segment- 630, brush" 632, upperleft-hand contact of sequence switch spring 606; to ground. The application of this intermittent ground potential to 'the fundamental circuit has noresu'ltan't effect upon" relay 618, but causes" the intermittent deenergization of steppingrelay 14.0 in synchrohisin with the upwardinovemcnt ofthe brushesotthe selectorQ As previously traced, countingrelay 103 operated upon energization of relay 140, closes the operatingpath for relay 118*whiclroperates upon the" first de'encrgization of step=-' ping relay 140. Upon the second e-nergization of relay 140 a circuit isestablishcdfor operating counting relay 102 extending from ground-through contactsof relay1 h);

left-hand outer normal contacts of relay 147, contacts of key l23 ,-alternate contacts of relay 113 win-ding oi counting relay 102 i to grounded battcry. Counting relay 102-upon energiz-' ingcloses lookingcircuit for itself; extending through the winding of upper "counting relay ng and an operating circuit or relayf112 ei'iective'upon the second deenergizatioirof stepping relay 140. Up

on the third energization of stepping re-v lay 1 10 over the fundamental circuit; a path is extendeditor operating counting' relay 101 in the same manner as described for. count ingirelay'102, and relay 111 in turn oper ates over the obvious path to contacts of re lay 10'1- upon the subsequent deenergization of. relay 140; and-in this same manner the fourth energization' of relay llO establishes path for operating counting relay 100, and the. fourtlr dee'nergization of stepping relay 140 allows the operating path for relay 110 to become effective whereupon re lay=110 energizes opening the fundamental circuit at its normal con'tactswhich opens the holding path for relay 618 causing it'to be deenergized; Relay 618 upondeenergizingi opens the previously traced circuit and 1 normal contact of relay 112;

through the rip-drive magnet 626 to arrest the upward moiement of the brushes. At its left-hand armature and back contact relay 618 closes a circuit extending from grounded battery through the magnet winding of sequence switch 600, upper righthand contact of sequence switch spring 612 contacts of relay 618' to ground on upper left-hand contact of sequence switch spring 608 for driving sequence switch 600 out of position 2 and into position 3. Upon reaching position 3' sequence switch 600 closes a circuit for the trip magnet 635 eXtending from grounded battery through the winding of magnet 685 and thence to ground through the lower right-hand contact of sequence switch spring 606. Trip magnet 6351113011 energizingrotates the trip-ping spindle (not shown) in the manner well known into such a position as will trip the selected set of brushes upon the subsequent upward movement of the switch shaft.

Upon the operation of relay 110, as previously traced. acircuit is. established for operatingrelay 142 which'may be traced from grounded battery through ,winding of rela .142, normal contacts of relay 1 11, alternate contacts'of relay 110, contacts 150 of key 131 to ground. The operation of" relay 142 closesa circuit for operating the key release magnet 182 extendihgfrom ground through contact of relay 142, normal contacts of l'Q- lay 14:1,, winding of key release magnet 132 to grounded battery causing the contacts of key 123 to be opened which in turn opens the energizing path-for relay 14:6 which releases. The release of relay 146 in turn opens the energizing path for relay 145 which releases removing the locking circuit for the counting relays extending through the contacts of relays 145 and 146 to ground thusreleasing the counting relays which up to this time had remained locked. Upon the release of counting relay 110 ground is removed from the energizing path of relay 14-2 it, however, remains looked over a path which may he traced from grounded battery through winding of relay 14-2., left-hand contactof relay 142, winding of relay 141, con tacts 150 of key 131 to ground operating relay 1491, the utility of which will be de scribed after unitselectio'ns'have been complet-ed.

Brush selection h'ax' ing been completed. the testing operatorwill actuate key 122 (the #2'key) to cause unit selection to take place. Relays 14:6 and 145 will be operated from the actuation of key 122 over the same paths as were traced upon the actuation of key 123, with the exception that the left hand contact of key 122 is used instead of key 123. The circuit paths resultant from the operation"'otrelays 146 and 1&5 are the same as previously described. Since the fundamental circuit is again closed by. the

all

release of relay 110, and operation of relay 1&6, and since sequence switch 600 is in po sition 3 relay 618 and stepping relay 1 are again energized over a circuit extending from grounded battery through upper righthand contact of sequence switch spring 60 1, winding of relay 618, lower left-hand contact of sequence switch spring 603, lower left-hand contact of sequence switch spring (302 upper left-hand contact of sequence switch springGl'Z, ,tip of jack 332, patching cord 325 and jack 320, conductor 370, outer right-hand contact of relay 2141, outer righthand contact of relay 146, right normal contact of relay 1417, resistance 150, stepping rei lay 1&0, normal contact of relay 110 contacts 150 of key 131'to ground, operating relays 1 10 and 618.

Relay 618 when operated closes a circuit for driving sequence switch 600 out of position 3 and into position 1, said circuit eX- tendin over a path including grounded battery r g e winding of sequence switch 600, lower r ht-handcontacts of secuence switch spring 612, lett-hand'contacts of relay 618 to ground at upper left-hand contact of se quence switch spring 608. Relay 618 in operating also'closes the locking circuit previously traced for holding itself energized over the fundamental circuit after sequence switch 600 leaves position 3. With sequence switch 600 in position 4 and relay 618 energized the circuit previously traced through the up-drive magnet 626 is again closed and the brushes of the switch are again driven upwardly. During the initial upward movement of the brushes, the 4th set of brushes is tripped by tripping spindle in a manner well known and during the subsequent upward movement of the switch shaft the tripped set of brushes travel in engagement with the terminals of the bank with which they are associated. During the upward movement tent ground is connected to the junction point at lower left-hand sequence switch spring002 over the circuitpreviously traced with the exception that the intermittent ground is derived from a circuit which'inay be traced from this contact through'upper right-hand sequence switch spring 6053, conductor G36, tens selecting segment 63?, brush 638 to ground at upper left-hand contact of sequence switch spring 606.

The energization oi the stepping relay 110 with'sequence switch 00 in positions and closes a circuit through the winding of counting relay 102 which may be traced from grounded battery through w1nding 0t 7 relay 102, normal contact of relay 112, righthand contacts of key 122,,outer left-hand normal contact of relay 1 17, contacts of relay 1 10 to ground. Counting relay 102 cuergizes in this circuit and locks in the manner previouslydescribedthrough the windof the switch shaft an intermit ing oi counting relay 112 which circuit isefi'ective for energizing relay 112 upon the first deenergization of stepping relay 140.

As brush 638 progresses in its upward movement connecting ground intermittently to the energizing circuit for relay 140, the

counting relays 101, 111, 100, and 110 are successively energized in the well known manner of operating counting relays as previously described. When counting relay 110 is energized on the third deenergization of stepping relay 1 10, or at the time the tripped set of brushes have beenpositioned on the first set of terminals of the group selected the fundamental circuit is opened and relayl618 is deenergized, arresting the upward movementof the brushes and establishing a circuit for driving sequence switch 600 out of position at and into position 5. This circuit may be traced troinrgrounded battery through sequence switch magnet winding 600, upper right-hand contact of sequence switch spring 612, normal contacts of relay 618 to ground on upper left-hand contact of sequence switch spring 608.

The energization of counting relay 110 establishes a circuit for operating relay 14 1' over a pathextending from grounded'battery through the wlnding oi relay 144,

- normal contact of relay 1 13, inner alternate contact of relay 1 11, alternate contact of relay 110, contacts 150 of key 131'to ground. 1

through key release magnet 182, right-hand alternate contacts of relay 1 11, left-hand normal contact of relay 1 13, to ground on right middle contactsof relay 144. Relay 200 operated from the aforesaid path established by relay 16% connected grounded battery through the rightrhand winding of relay 211 to ground over the path for operating relay 200. The functions of relay 211 will be described after unit selection. The actuation of key release magnet 132 causes the release of key 122 which in turn opens the locking circuit for the counting relays by releasing relays 145 and 116. The re lease of counting relay 110 removes the shunt ground from the operating path for relay 1413 which operates. This operation may be traced as follows: Grounded bat.-

tery through winding of relay 1 1 1, righthand inner contact of relay 144:, winding of relay 1&3, contacts 150 of key131 to ground. The utility of relay 14-3 will be described after unit selection.

F or units selection the testing operator will actuate key 122, (the N0. 2 key) which will reoperate relays 146 and 1&5 in the manner described for brush selection. Relays 200 and 211 released upon the deen ergization of relay 14.5. They will, however, again be operated at this time over the previously traced paths. The remaining contacts of

relays

145 and 1 16 establish the same paths as described upon the operation for tens selection, the same key being actuated. Since sequence switch 600 is in position 5, and since the fundamental circuit has again been established by the release of counting relay 110, and the operation of relay 146, as previously traced, relay 618 and stepping relay 140 will again be operated over the path previously described. Relay 618 in attracting its left-hand armature establishes a path for moving sequence switch 600 out of position 5 and into position 6 which may be traced from grounded battery through the sequence switch magnet winding 600, lower right-hand sequence switch spring 612, contacts of relay 618, to ground on upperlett-hand sequence switch contact 608. Relay 618 is again held over its locking path as previously traced. When sequence switch 600 reaches position 6 a circuit is closed for the slow speed updrive magnet 639, over a path which may be traced troni grounded battery through winding of slow speed up-drive magnet 639, lower left hand contact spring 607, left-hand alternate contacts of relay 618, to ground on upper left-hand sequence switch spring 618. The brushes will again be driven in their HPWEILlIDOVGHIBIIiI. The fundamental circuit being closed in

positions

5 and 6 of sequence switch 600, causing the operation of relay 1 10, a path is established for the operation of counting'relay 102 which may be traced from ground on contacts of relay 1 10, left-hand normal con tacts of relay 1 1?, right-hand springs of key 122, normal contact of relay 112, winding of relay 102, to grounded battery. The operation of relay 102 establishes a locking path for itself and prepares an operating path for relay 112 in the well'known manner of operating counting relays.

The brush 632 is propelled upward by intermittently connecting ground to the coin 1nutator segment 680, conductor 629, upper right-hand contact of sequence switch spring 602, lower right-hand contact of sequence switch spring 603, contacts of relay 6.18, lower right-hand contact of sequence switch spring 610, and thence over the fundamental circuit as previously traced throughupper right-hand contact o'fsequence switch spring contact of of sequence switch .ment of the selector brushes by opening the energizing path for Lip-drive magnet Since the path for moving sequence switch 600 out of position 6 is open at jack 332, the sequence switch 600 will remain in position 6 untilpatching cord 325 is removed from jack 332. The operation, of relay 110 establishes a path for the operation of relays 205 and 501 which ina be traced from ground through contacts 150 of key 131, contacts of counting relay 110, alternate contacts oi" relay 1411, alternate contacts 01" relay 1 1-3 and thence over a divided path, one path leading to the contacts and windings of relay 205 to grounded battery operating re lay 205, the other path extending through the winding of relay 501 to grounded battery operating relay 501. Relay 205 locks over a path extending through its right-hand outer contacts, right hand contacts of key 130, left-hand contacts or" key 131 to ground. The operation of relay 205 removes the energizing path from relay 200 which releases in turn removing battery from the holding circuit of relay 211.

The operation of the finalselector shown in 6 is otherwise the same as that disclosed and described in the previously men tioned application, Serial No. 187,520.

Assuming that line isa regular sub-- scribers station, (not extenderlto a private branch exchange), and again assuming that this subscribers line is in a noirbusy con-drtio-n, there will connected to conductor 280 lay 211 will'be released.

A busy subscrihers line characterized by the presenceof battery on terminal 643. This battery is connected toterininal 043 from sequence switch spring 601 of a selector switch the same as thats-liown in Fig. 6, or from the source connected to are 723 of line switch 705. Upon connection of the test final selector to the line terminals this battery may be traced from terminal 643 through brush 642, sleeve of jack 833, sleeve of patching cord 326, sleeve of jack 32], conductor 280, contacts and winding of relay 211, contacts of relays 1 15 and 14A- to ground.

Relay 211 upon releasing establishes a circuit from grounded battery through right inner contacts of relay 205, winding of relay 206, winding of relay 207, terminal No. 1 ofswitch 222, brush 261, left inner contacts of key 241, left and right contacts of relay 301, right-hand contacts of key 241, lefthand normal contacts of relay 211, conductor and therefore renot be a battery potential ntion ol cor-.nt-

280, sleeve of jack 321, patching cord 326,.

sleeve of jack 333, brush 6&2, terminal 6&3, line switch brush, 710 and its normal contact, lower and upper winding of relay 702, to ground, operating

relays

207 and 702. Marginal relay 206 does not, however, op-

erate in this circuit because the resistance of lighting of lamp 23% indicated to the test man that line 5322 chosen for test is not busy and therefore the test may proceed.

Assuming that the line switch apparatus is to be tested, key 2415 is actuated by the testing operator; The actuation of key 2&5 establishes a circuit for the operation of relay 212 which may be traced from grounded battery through windings oi relay 212, left-hand outer contact of key 245, terminal 1 of are 223, brush 262, to ground.

The operation of relay 207 establishes a path for operating relay 215i which may be traced from grounded battery through. win ding of relay 214, right-hand contact of relay 207, rightshand contact of key 130, lefthand contact of key 131 to ground.

The combined operations of relays 212 and 207 establish a. path for actuating switch magnet 220 from grounded battery through winding of switch magnet 220, contacts of magnet 220, brush 263, terminal 1 of are 22 1, left-hand alternate contacts of relay 207, right-hand alternate contacts of relay 212 to ground, causing it to advance the brushes controlled by it into engagement with their secondcontacts. \Vhen the switch moves from terminall to terminal 2, the operating path for relay 702 is opened, causing the release of this relay. A path is, however, established for the non-operate test of the cut-oil relay 702 as follows:

A path is first established for the operation of relay .201 from grounded battery through winding of relay 201, terminal 20f switch 223, brush 262 to ground. The operation of relay 201 establishes a path for .connecting the non-operate current value to cutoff relay 7 02, which may be traced from grounded battery, through resistance 362,

rheostat left-hand normal contacts of relay 20a, winding of relay 202, right-hand inner contacts of relay 201, terminal 2 of are 222, brush 261, lett-hand inner contacts of key 241, contacts of relay 301', right-hand contacts of key 241, left-hand'normal contacts of relay 211, conductor 280, sleeve of jack 321, patching cord 326, and jack 333,

ack 321,

brush 642, terminal 6 13, conductor 722, brush 710, terminal 1 of are 723,

conductors

785, 715 and 764;, lower and upper winding 7 cates that the non-operate test of cut-oft relay 702 is being made. 1V hen the switch controlled by magnet 220 moves from terininal 1 to termlnal 2 the operating path for relay 207 was opened, causing its release. Therefore,'the operation of relay 208 will establish a path for actuating the switch magnet 220 from grounded battery through magnet 220, contacts of magnet 220, brush 263, terminal 2 of are 224, right-hand con tacts of key 3 10, right-hand alternate contacts of relay 20S, right-hand outer con" tatcts of relay 201, outer left-hand normal contacts of relay 207, right-hand alternate contacts of relay 212 to ground, thus actuating switch 1nagnet'220 andcausing it to step from terminal 2 to terminal 3 under the control of its self-interrupting contacts.

It will be apparent from the following,

thatvif relay 702 operates in the above test, the circuit path for operating relay 701 is opened. The progress of this test is then blocked with a signal lighted to indicate the trouble.

An operate test of line relay 701 is made with switch 220 in position In making this test the non-operate test is continued on cut-off relay 702 for a check on the nonoperate test and for the purpose of testing pressure on the contacts through which the conductors for operating line relay 701 are carried. 2 The path for continuing the nonoperate test of the cut-off relay 702 is the same as previously traced with the creep tion that terininal'3 of arc used instead of terminal 2. The path established for making the operate test of line relay 701 may be traced from grounded battery through right-hand winding of line relay 701, lower alternate contacts of cut-off rclay 702, conductor 703, terminal 657 ,brush 653, ring of jack 333, patching cord 326, and left-hand contacts of relay 214, left-hand inner contacts of key 2 15, contacts of relay 300, brush 204, terminal 3 of are 225, left-hand winding of induction coil 366, resistance 359, rheostat 351, terminal 3 of are 226, brush 265, inner right-haud contacts of key 245, right-hand inner contacts of relay 214, tip of jack 326, jack 333, brush 652, terminal 659, conductor 706, lower normal contacts of cutoff relay 702, right-hand alternate contacts of line relay 701, conductor 707, brush 708 and the No. 1 terminal of are 754, to ground. The line switch now rotates under the control of itsself-interrupted contacts until, a

1 non-grounded terminal on are 754 is encountered. The non-grounded condition of the terminal on are "754 indicates that the corresponding trunk leading to a district selector is idle. l/Vhen switch 705 stops in its forward movement it is connected to'a district selector diagrammatically shown;

This district being idle and thus in position 1, grounded battery will be connected to the terminal of are 754 thus connecting this grounded battery to brush 708, conductor 707 ,left-hand contacts of line relay 701, left winding of line relay 701,

conductors

786, 715 and 764, lower and upper windings of cut-oil relay 702 to ground, operating relay 702. The operation of relay 702 establishes a path forthe operation. of relay 742 which may be traced from grounded battery through winding of relay 742, conductor 719, sequence switch spring 757, conductor 718, brush 709, terminal of are 755, conductor 720, lower middle contacts of cut-oft relay 702, conductor 7 80, upper winding of relay 702 to ground. The function of relay 742 is to actuate the apparatus in the district se lector to cause it. to hunt and find an idle sender, shown diagrammatically in lower right hand portion of Fig. 7, as described in the previously mentioned application, Serial No. 487,520, filed July25, 1921. The

detailed operation of this portion of the circuit will therefore not be described in this application. When an idle sender has been found dial tone isinduced through the winding of relay 746 and is thus carried over lead 753, sender selector brush 743, upper lefthand contacts of sequence switch spring 760, conductor 717, brush 713 of are 700, upper alternate contacts of cut-off relay 702, terminal 659, conductor 704, brush 752, tip of jack 333, patching cord 326, and jack. 321.

inner right-hand contacts of relay 214, in-

ner right-hand spring of key 245, condenser 371, rheostat 351' and resistance 359, lefthand winding of induction coil 366, are 225, brush 264, contacts of relay 300, left inner contacts of key 245, left-hand contacts of relay; 214, ring conductor of jack 321 patching cord 326, jack 333, brush 653, terminal 657, conductor 703, lower inner alternate con} tacts of relay'702, brush 711 are 756,-. conductor 716, lower left-hand contacts of se 321, patching cord quence switch 761, sender selector brush winding of relay 747 t battery. This induced dial tone through the left-hand wind ing of induction coil 366 is again induced on to the right-hand winding of induction coil 366 in turn being transmitted to receiver 338 over the obvious path-closed by plug 337 being inserted in jack 335 and plug 336 being inserted in jack 334. This tone being transmitted to the test operator indicates the following:

A. That the cut-off relay 7 02 did not operate with the proper non-operate current impressed upon its winding. i

B. .That the line relay 701 operatedwith a current impressed upon its winding of such value that its operating adjustment is tested.

C. That the line switch functioned properly to g establish connection to a district selector,

D. That the cut-off relay 702 then operated properly. 7

E. That the district selector put into operation a sender selector to seize an idle sender.

F. That the seized sender transmitted dialing tone back to the testing apparatuslVith the line switch shown in the left hand portion of Fig. 7, in its operated po-.

sition, grounded battery is connected through a resistance to are 723, brush 710, over conductor 722, terminal 643, brush 642, sleeve of jack 333, patching cord 326 and jack 321, thence over contacts of relay 211, right-hand contact of key 241, contacts of relay 301, left-hand contacts of key 241, brush 261, terminals of are 222, right-hand contacts of relay 201, winding of relay 202, left-hand normal contacts of relay 204, rheostat 354, resistance 362 to grounded battery, thus causing relay 202 to release which in turn causes the release of relay 208, closing the path for actuating switch magnet 220. This may be traced from winding of magnet 220, contacts of magnet 220, brush 263, terminal 3 of are 224, lefthand contacts of key 341, right-hand normal contacts of relay 208, right-hand outside contacts of relay 201, left-hand contacts of re lay 207, right-hand alternate contacts of relay 212 to ground. The actuation of switch magnet 220 causes the switch to advance to position 4 under the control of the selfinterrupting contacts of magnet 220.

In position 4 of the progression switch a test is made to ascertain whet-her resistance 727 is of the proper value to indicate a busy line switch of the type used for con nection to a subscribers station. shorts or crosses are also indicated in this test. Lamp 232 is: lighted to indicate to the Leaks,

testing operator that the progression switch be traced from grounded battery through s s ance lamp 232. ef -hand. inner ama c a ts of 1 y-2 Jar 23, 1 5 2 2 is ro nd. T e toi s e n la sto mpre e 1 1 indu tion Qi 266. to n .dicate that the line switch 7 has remained n the p op p sit on or h test, T

mak the O m c es stan e test of r sista ce 2 he Operator wi rst ctu te k y 2 :1] and 340, "Relay 301 operated over an ob ices. pa h to ground key 3 Ani at -r 302 is actuated in series with resistance 727 which path may be traced as follows: roun d b t y, h ough resi tan .2 are 723, brush 710, conductor 722, terminal .13 b sh, 4 le e etii k p ns cord 326 and jack 321 over condnctor'280 hr ugh norma con a s oi re ay. H,. r g thand outside contacts of key 241, right hand wands. of r ay 3 amme eii 3. 59 hand contacts of" relay 301, left-hanchonter contacts of key 241 to ground, The d ec tion of the needle of ammeter 302will indicate to the test man whether resistance 727' is of the proper value.

The next test of the line s'witchapparatns is a non-operated test of the line relay701. This is accomplished by releasing keys 340 and 241 and operating key 243 which establishes a-path for operating relay 207 which may be traced from gronnded battery through right-hand inner contacts of relay 205 winding of relay206, winding of relay 207,'resis,tance 253, contactsoi key 243, terminal 4 01 are 223, brush 262 to. gro nnd.

Resistance 253 is snffici'ently high to prevent the operation of relay 206.

The operation of relay 207 extingnishes lamp 232 and in attracting its outer left-hand armature connects ground from the contacts'of relay 212 through outer left-hand contacts of relay 207, terminal 4 of are 224, brush 2.63, contacts of switch magnet 220, winding of switch magnet 220 to grounded battery actuating the switch magnotnnder the control of its self-interrupted contacts: and causing it to rotate to terminal. No. Key-243 is thereupon. released, and as willhe noted, the operating'circuit for relay 20? was opened at" are 223, when brush. 262stepped' from terininal 6 to terminal 7.

Upon leaving terminal No. 4 the line circuit is opened at are 226 causing the release of the district selector in the well-known manner; The release of the district selector opens the holding circuit of cut-off relay 702. The release of line relay 702 establishes a path for-switch magnet 705 toroQ-l tate the line switch to. normal un er the control its; self-interrupted contacts.

This path may be traced from grounded bat terj through switch magnet 7 05, contacts of switch magnet 705, conductor .7 06, lower normal contactsof relay 702, right-hand normal contacts of line relay 1, brush 712 to ground on arc 724. The switch, 705 is arrested in its rotary mOVQment upon leaving the grounded portionof are 724.

The release of the line switch apparatns With line switch 705 in its normal posi tion, a circuit is established for operating relay 202 which maybe traced from ground;

ed battery through resistance 362, rheostat;

354, inner leift-hand normal contacts. of re: lay 204, winding of relay 202, right/hand inside contacts of relay 20.1, terminal 7 of a1 c 222,-brus h 261v, left-hand inner contacts of key 241, contacts of relay 301, right:

hand contacts of key 241, normalcontacts oi relay 21], conductor 280, sleeve of jack 321 patching cord 326, jack 3:33, brnsh642, terinitial 643, conductor 722, brush 710, 0011-

ductors

785, 715, and 764, lower and upper windings oi relay 702; to ground. Belay 702 is not operated in this circuit. The operation of relay 202 establishes an obvious path I for operating relay 208, which by attracting its right-hand armature, establishes a path for rotatlng switch 220. intoposition 8.

This path may be traced from battery through switch magnet 220, contacts of switch magnet 220, brush 263, terminal 7 of switch 224, right-hand contacts of: key 340,

alternate contacts of relay 208, outer right- 7 hand contacts of relay .201, outer normal contacts of relay 207 right hand contacts of relay 212 to ground.

In position 8 lamp. 233 is lighted to show.

the testing operator that switch 220 has 3.1 1 Y rived in position 8. The. path for lighting la1np233 may be traced from grounded bat.

tery'throughresistance 25 0, lamp 233, left hand contacts of; relay 208, terminal 8 of are 223, brush262 to. ground. The arrival ot' switch 220 in position 8 indicates to the testing operator that theline switch apparatus shown nFig. 7 has restored to nor-.

inal. The non-operate test of line relay 701 is; now made. This is accomplished by. a

bridge across the tip and ring conductors oi. the line, includlng a rheostat previously accurately adjusted. The circuit of relay 701 may be traced as follows: grounded battery through right-hand winding of line relay 701,, lower inner normal contacts of cut-o0? relay 702, conductor 703,terminal- 657, brush 653, ring of 130k 3 33, patching cord 226 and jack 321, left-hand contacts of relay. 214,

left-hand inner contacts of key 245, con-j tacts' of relay 3.00, brush 264, terminal 8of 1 arc 225, leit-handwinding of induction coil i 366, resistance 358, rheostat 350, terminal 8 of are 226, brush 265, right-hand inner contacts: of key 245, right-hand inner con? tacts of'relay 214, tip of jack321, patching cord 326 and jack 333, brush 652, terminal of .coil 366 to the receiver 338 over the path described for the operate test oil the line relay. 5

The "non-operate test of the line relay 701 having been successful, an operate test may now be made of the cut-oflt" relay 702. This is accomplished by operating key No. 244

to advance switch 220 from position 8 to position 9. The-path for this advancement may be traced asiollows: rounded battery through winding of switch magnet 220, contacts of key 244,-terminal 8 of arc 223,

brush 262 to ground. The arrival of switch 220 in position 9 is indicated by the lighting of lamp 237 over an obvious path from ground on brush 262 and terminal 9 of are 223. i

The operating path for the test of the cut-0d relay 702 may be traced from ground through the upper and lower windings of cut-oft relay 702,

conductors

764, 715 and 785, terminal 10f arc723, brush 710, conductor 722, terminal 643, brush 642, sleeve of jack 333, patching cord 326 and jack 321, left-hand normal contacts of relay 211, right-hand contacts of key241, contacts of relay 301, left-hand contacts of key 241, brush-261, terminal 9 of arc'222, normal contacts of key 242, normal right-hand con-- tactsof relay 204, rheostat 357, resistance 365. to grounded battery. During this test the meter 450 is connected to the tip and ring of the line switch circuit to indicate by a; deflection of the needle, a ground or battery, potential on these conductors. This ground and battery potential would be con nected to; the tip and ring leadsif cut-oil relay 702 failed to operate when the current valuetor its operate test is carried through its windings as above described. The path for deflecting the needle of the meter may be traced from ground through normal contacts of relay 702, conductor 704, terminal 650, brush 652, tip of jack 333, patching cord 326, jack 321, right-hand inner contacts of'relay 214, right-hand inner con tacts of key 245, brush 265, terminal 9 of switch 226, resistance 254 to a junction point, which is also connected to the ring conductor, traced from grounded battery through right-hand winding of line relay 701, lower normal contacts of cut-oii relay 702, conductor 703, terminal 657, brush 653, ring of'jack 333, patching cord 326, jack 321, left-hand contacts ofrelay'214, left inner contacts-of key 245,'contacts of relay circuit to normal the test man 300, brush 264, terminal 9 of are 225, resistance 255, to the junction pointtraced "from the tip conductor. From this unction point a path may be traced through contacts of key 530, winding of meter 450, 7

resistance 432, right-hand outer normal con; tacts of relay 506, jack 323, plug 328, to a volt battery poled in the opposite direction to the battery connected to the winding of line relay 701. It must be assumed for this test that plug 328ehasbeen inserted in jack 323 by the testing operator.

A holding test is now made by the operating key 242, which reduces the current through the windings of cut-off relay 702 by placing additional resistance in series with said winding. The path from cut-otf relay 702 to key 242 is the same as previously traced for operating the relay and from this point is extended over the of key 242 through the normal contacts oi relay 203, rheostat 352, resistance 360 and resistance 364 to grounded battery. Since switch 220 has not changed position the meter 450 remains connected to the tip and ring of the line switch and therefore will cut-0H relay 702 release while being connected to the holding current value.

It will be noted that relay 213 is bridged across the tip and ring leads, previously traced. From the line switch connection, it will also be noted that under certain condition of test the sleeve lead connected to the line switch is not retained in a busy condition to other selectors of the oftice.

inside spring SPO show a deflection of the needle should the" Therefore, should a connection be made by a second final selector to the line switch under'test, during one of these unguarded periods, the attempt to ring the subscriber will operate relay 213 which path may be traced from ringing current applied from an incoming selector of the type shown in the previously mentioned application, Serial No. 487,520, over the ring conductor of a final selector similar to the one shown in Fig. 6, brush 653, ring of jack 333, patching cord 326, jack 321, left-hand contacts of relay 214, left-hand inner contacts of key 245, condenser 266, windingof relay 213, right-hand contacts of key 245, right-hand inner contacts of relay 214, tip of jack 321, patching cord'326, and" jack 333, brush 652 to ground over tip conductor of final and incoming selectors. Relay 213 looks to the locking ground of relay 212 and connects this same ground to lamp 236 and resistance 256 to grounded battery, lighting lamp 236 as an indication to the testing operator that serving directly a subscriber. To restore the releases key 245 andoperates key 131, releasing all apa ing directly a subscribers line.

relay 208 over an obvious path which need not be traced. The actuation of relay 208 establishes a circuit for moving switch 220 .No. 2 of arc 224, contacts of key 340, contacts of relay 208, 'right-hand outer cont-acts of relay 201, outer left-hand contacts of relay 207, contactsof relay 212 to ground.

In position 3 of switch 220, the test of line relay 701 is made in the same manner as described for the test of the line switch serv- This test,

however, in this case, is made in connection with the non-operate test of cutoff relay702,

as described above, regulated for a non-operate test when the line switch is connected to a private branch exchange. The operate test of line relay 701 being successful, line switch 705is rotated to find an idle district and sender which in turn induce tone into receiver 338, as previously described. The rotation of line switch 705 also connects battery in place of ground to the circuit of relay 202, causing it to be deenergized. The release of relay 202 will in turn release relay 208, the latter relay establishing a circuit for moving switch 220 into position 4. This circuit may be traced from grounded battery through switch magnet 220, contact of magnet 220, brush 263, terminal 3 of arc 224, contacts of key 341, right-hand normal contacts of relay 208, right-hand outer. contacts of relay 201, outer left-hand contacts of relay 207, righthand contacts of relay 212 to ground. v I

In position 4 of switch 220, lamp 232 is lighted to show the progress of the test and the successful operation and dismissal of the preceding test. This path may be traced from grounded battery through resistance 250, lamp 232, inner left-hand contacts of relay 207, terminal 4 of arc 223, brush 262 to ground. In position 4, the ohmic resistance of line switch resistances 726 and 727 is measured by the operation of key 241 and key 340. The operation of key 340 establishes an obvious circuit for operating, relay 301 which connects ammeter 302 in the sleeve circuit. The deflection ofthe ammeter needle will indicate to, the testing oper ator the ohmic resistance value of resistances 726 and 727. This circuit may be traced from grounded battery through resistances 727 and 726, conductor 781, arc 723, brush a 710, conductor 722, terminal 643, brush 642,

sleeve of jack 333, patching cord 326, jack 321, left-hand normal contacts of relay 211, right-hand contacts of key 241, right-hand contacts of relay 301, ammeter 302, lefthand contacts of relay 301, outer left-hand contacts of key 241 to ground. Keys 241 and 340 are then released.

It will be remembered that the progression switch upon leaving position 4 opens the line conductors causing the release of the district selector. The release of the district selector opens the circuit of cut-off relay 702 thus establishinga path to restore the line switch to normal.

The next progressive test is the non-operate test of line relay 701. This is made in the same manner as described for the test of the line relay in a line switch extending directly to a subscribers station, after which the progression switch is moved into position 1 In position 9 of switch 220, the operating test of cut-ofi relay 702 is made with rheostat 356 adjusted in such a manner as to give proper current flow for testing the operating adjustment of relay 702 through its upper winding only. This operating path may be traced from ground through the upper winding of cut-ofl' relay 702, conductors 780. 763, 715 and 785, brush 710, conductor 722, terminal 643, brush 642, sleeve of jack 333, patching cord 326 and jack 321, left-hand normal contacts of relay 211, right-hand contacts of key 241, contacts of relay 301, left-hand contacts of key 241, brush 261, terminal 9 of switch 222, contacts of key 242, right-hand alternate contacts of relay 204, rheostat 356, resistance 364 to grounded battery. In this operate test of the cut-off relay, the voltmeter 450 is connected to the tip and ring of the line in the same manner as was done for the operate test of a cut-off relay of a line switch associated with a direct line. 1 Therefore, this voltmeter will show a deflection should the cut-off relay 702 fail to operate from the current applied to its upper winding.

The operate test of the cut-oft relay being the last test of the line switch apparatus extending to a private branch exchange, the testing operator will restore switch 220 to normal by releasing key 245.

All paths established through the contacts of

relays

300 and 301 may be carried through milliammeter 302 by the operation of keys 341 and 340 which establish obvious operating paths on said relay. This accomplishes accurate regulation of adjustment current flow values.

BaZZistz'c test of Zinc.