US2378541A

US2378541A - Traffic observing apparatus

Info

Publication number: US2378541A
Application number: US462930A
Authority: US
Inventors: Thomas L Dimond
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1942-10-22
Filing date: 1942-10-22
Publication date: 1945-06-19
Anticipated expiration: 1962-06-19

Description

June 19, 1945. T. DIMOND TRAFFIC OBSERVING APPARATUS Filed 001:. 22, 1942 '7 Sheets-Sheet 1 INVEN TOR 7.L.D/MOND fifia z i ATTORNEY June 19, 1945. L, DIMQND 2,378,541

TRAFFI C OBSERVING APPARATUS Filed Oct. 22, 1942 v '7 Sheets-Sheet 2 r INVENTOR T L .DIMOND A TTORNE Y June 19, 1945. I DlMOND 2,378,541

' TRAFFIC OBSERVING APPARATUS Filed Oct' 22, 1942 7 Sheets-Sheet 3 ATTORNEY June 19, 1945. T, DlMOND I 2,378,541

TRAFFIC OBSERVING APPARATUS Filed 001;. 22, 1942 '7 Sheets-Sheet 4 I I BY WrQM ATTORNEY 7 Sheets-Sheet 5 Filed Oct. 22, 1942 not Not III III" lllll lllll but at 2 E.

lNVENTOR T.L.0/M0/v0 6. c9. Gaza A TTORNEY June 19,1945. 1'. 1.. DIMOND I ,5

' TRAFFIC OBSERVING APPARATUS Filed Oct. 22, 1942 7 Sheets-Sheet 6 INVEN TOR 7'. L D/MOND By fiwmea ATTORNEY June 19, 1945. T. L. DIMOND TRAFFIC OBSERVING APPARATUS Filed Oct. 22, 1942 7 Sheets-Sheet 7 ATTORNEY Patented June 1 9, 1945 UNITED-t sTATEs ENT oFF cs TRAFFIC OBSERVING APPARATUS Thomas L. Dimond, Rutherford, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y.,'a corporation of New York Application October 22, 1942,'Seri al No. 462,930

18 Claims.

This invention relates to traffic registers and particularly to traflic registering apparatus in telephone systems.

Objects'of the invention are an increase in'the efficiency and flexibility of traffic registering apparatus and the provision of means'for indicatingat' frequent intervals the number of trunks busy in each of the trunk groups in a telephone ofl'ice having a large number of trunk groups, and particularly in an automatic telephone system.

It is known to provide apparatus for successively testing each or the trunks :in a plurality of trunk-groups and *for registering either the number of, trunks which arebusy or the percentage of the trunkswhich are busy, in each group.

Such arrangements are,- however, inadequate to obtaintr-affic data including thenumber of trunks busy in each of, .a large-number of groups at .frequent intervals, such as is necessary in-an automatic telephone ofilce comprising many The apparatusv shown in the drawings comprises two meters M.-A' and M-B calibrated to indicate the number'of trunks, which are busy in a trunk group under test, the trunks in two groups being tested simultaneously. Traffic flbsei'vers Aand B, one for each meter, record the successive indications for the various trunk groups.

The number of observing meter provided de-' pends upon the. total number of trunk groups, one observer being able to record the indications of the number o trunks bu y .fo about one hun .dred trunk'groups in succession within-a period of about four minutes. A group of busy'register I ortest relays is provided for each t aifi obs rv r,

and groups of crossbar switches are provided'for connecting the. test relays to the test conductors f r up of trunks, ne roup of switches for I each group of relays. The number of test relays groups of line finders,,selectors, connectors, re

peaters, and other'trunk circuits.

This invention is a trunk group usage apparatus 1 arranged to successively test a different plurality of groups of trunks simultaneouslyand give'separateindications of the number of trunks that are busy in each of the simultaneously tested groups, to indicate-the particular plurality of groups being tested, to repeat the test of all trunkgroups at frequentintervalsjto automate ically selectany particular plurality ofv trunk groups which the observer wishes to test or on which it is desired to; start the successive test of different pluralities of trunk groups, to block the further operation if the switching means for connecting thetrunks for testfails to connect all of the groups which, are to be tested simultaneously, and to make repeated tests of a single group. These and other features .of .the,.invention are embodied in the trunk group. usa e circuit shown schematically .on-the" drawingswhich 2 se h l s dtc mm a ii arrangement;

in the group for'one observer depends on the number of trunks in the largest group to be tested simultaneously by the test relays in question; and the number of crossbar switches depends on the total'number 0f trunks and total number of trunk groups in the ofiice. In the arrangement shown, the group of test relays as sociatedwith meter MA consists of ten twostep relays 62l to 630, inclusive, arranged to simultaneously test a maximum of twenty trunks;

and the group of test relays associated with meter M-B consists of five two-step relays 92I to 925, inclusivearranged to simultaneously. test a maximum of tenitru'nks. Each of the test relays has two windings, each of these windings being connectedtothe sleeve conductor of a different one of :the trunks in the particular group being tested, and successively to the sleeve conductor of a trunk in each of the groups, the busy indication for which is to be given to the observer with which the test relay in question is associated. If only one ofthe two trunks thus tested by one test"'relay is busy, one winding is energized to close one of the contacts; but if both of the trunks thus tested are busy,both" windings 'are energized'to close both contacts of the relay. The closing of each contact of a test relay connects a resistor in series with the winding of the iobserverfs meter withwhich the relay is associated; so that the number of resistors connected in series with themeter upon test of each group of trunks depends upon the number of busy trunks in thegroup, and the meter is calibrated to indicate this number. In the arrangement-shown in the drawingsJthe'meter is calibrated to give a'maximum reading of thirty so that'not morethan six hold magnet may be connected in a parallel combination and a maximum of thirty trunks may be tested as a group. If the number of switches or trunks in a group exceeds thirty, the group is divided into subgroups which are separately tested and the readings for these subgroups are added to obtain the number of trunks busy in the entire group of switches or trunks.

Each of the

crossbar switches

389, 400, 500, 100 and 866 provided for connecting the test conductors of the trunks to the windings of the register relays is a five-wire one-hundred point switch with ten vertical units and ten select magnets, numbered Si to SII). Each vertical unit consists 'of ten contact groups of five contacts each and a hold magnet. The hold magnets, numbered I-II to HIE, are connected in parallel combinations so that the operation of a select magnet of each switch associated with one observer and one parallel combination of hold magnets effects the connection of all the trunks in a group to the associated test relays. The

switches

300, 400 and 500, associated with observer A, are arranged to connect eighty groups of trunk to the test relays BZI to 638. The first seventy of the'eighty groups consist of twenty trunks each, and the last ten groups consist of only ten trunks each; and there are eight parallel combinations of hold magnets as follows: I-II to H4, inclusive, of switch 30!]; H to H8, inclusive, of switch 360; H9 and HID of switch 300 together with HI and H2 of switch 400; H3 to H5, inclusive, of switch 40!]; H1 to HID, inclusive, of switch 400; III to H4, inclusive, of switch 500; H5 to H8, inclusive, of switch 50c; and H8 and HII! of switch 501 The switches 108 and 80!! associated with observer B are arranged to connect one hundred groups of trunks to the register relay 92I to 925, inclusive, all groups consisting often trunks each; and the parallel combinations of hold magnets are as follows: HI and H2 of switch 100, H3 and H4 of switch 100, H5 and H6 of switch 100, H1 and E3 of switch 100, H9 and HIO of switch 10!),

HI and 1-12 of switch 800, etc. Thusone parallel combination of hold magnets for each observer is operated so as to test as many groups of trunks at one time as there are observers. The total number of hold magnets which may be thus connected in parallel is limited to fifteen hold magnets in the arrangement shown in the drawings so as to prevent excessive current through the contacts of relays I60 and I10. If the total number of trunks to be tested at one time for all observers exceeds seventy-five trunks, not more than fifteen of the-hold magnets for the contacts connected to 2 these trunks are connected to a thermal of the bank of brush 2H4, another fifteen may be connected to the corresponding terminal of the bank of brush 205, and another fifteen may be connected to the corresponding terminal of the bank of brush 206. Thus the group selecting arrangement provides for a maximum of two hundred and twenty-five trunks to be simultaneously tested, the number of observers depending upon the number of test relays associated with the meters I of the various observers.

To control the successive operation of the select magnets and the parallel combinations of hold magnets, two rotary switches are provided. The switch 260 comprising brushes I to 206 and stepping magnet 291 is arranged to successively connect the parallel combinations of hold magnets for operation, one combination for each observer at a time. The switch2l0 comprises brushes 2 to 2I5and stepping magnet 2I1 is arranged to successively connect the select magnets of switches 300 and 100 for operation, the like designated select magnets of switches 45351 and 800 being controlled by the select magnets of switches 3G0 and 1M, and the like designated select magnets of switch 50% being controlled by the select magnets of switch 400. The rotary switches may be advanced under the control of the dial 25I to select any desired plurality of groups, one for each observer, for test, the number of the group which is being tested and for which a busy indication is given on each meter being indicated by the tens and units lamps which are connected to the terminals engaged by

brushes

203 and 2 I2, respectively. If the hold key H5 is operated, the test does not progress to the next group; and if the repeat key I49 is operated, the test of the selected group is repeated at intervals. If the hold key is not operated, the test begins with the group selected by dialing and the test progresses to each succeeding group; and if the timer key 256 is operated, the test of all groups is repeated once every five minutes. The order in which the trunk roups are selected by the rotary switches 2G0 and 2H] for test is as follows: II, I2, I3, I4, I5, I6, I1, I8, I9,.I.!l, 2| to 20, 3I to 39, M to 40, 5| to 5|] 5| to 62, H to 10, 8| to 80, 9| to 90 and 0! to ill). Various other features of this trafiic observing apparatus are set forth in the following detailed description of the operations involved in obtaining desired traffic data.

Assume that the test of all trunk groups in the office is desired but that automatic repeating of the test is not desired. normal, the brushes of switch 200 are in engagement with terminals 0 of the associated banks and the brushes of switch 2I0 are in engagement with terminals 22 of the associated banks. The operation of dial key 250 closes a circuit from ground through brush 2 I 5 and the engaged terminal 22 of switch 2 ID, conductor I14, brush 203 and the engaged terminal 0 of switch 200, conductor I15, contact of key 250, conductor I16, and through the winding of start relay I10 to battery. Relay I10 operates and it locks under the sole control of key 250. The operation of relay I19 closes the circuit for lighting the pilot lamp I19 to indicate that the chief observer may dial the number of the first groups to be tested, disconnects ground from conductors I13, 213 and 214, connects ground to conductor I39 to energize the filament of gas-filled tube IIB, connects ground to conductors I14, I15, I11 and I18, and connects battery to conductors HI and I12, The connection of ground to conductor I11 effects the operation of the impulse relay 245' in series with the lower, impulse contact of dial 25L The chief operator now dials the digits I I designating the first trunk group to be tested by the test relays of each observer. When the first digit 1 is dialed, a circuit is closed from grounded conductor I11, through the upper, off-normal contact of the dial 25I, conductor I84, inner right back contact of relay I80, and conductor I for operatively energizing the winding of the dialoff-normal relay 240. Theoperation of relay .240 closes a circuit, including conductor I 18, for operating relay 220, and relay 220 locksdirectly to conductor I18. As the 'dial 25I returns to normal, the impulse contact opens the circuit for energizing the winding of relay 245 as many-times as there are units in the digit dialed.- Thus the dial ing of the digit 1 causes relay 245 to release and reoperate once. The release of relay 245 closes a circuit for operating stepping magnet 201 of When the apparatus is switch-200; and the re'operation of relay 245 causes the release of stepping magnet 201, thereby advancing the brushes 20I to'206 one step. With brush-i 203 in engagement with terminal I, the tenslamp I is lighted since brush 203 is connected through conductor I14 to ground at a front con- :tact of relay I10. When the dial reachesvnormal atthe endof 'the first digit, relay 240 releases, thereby closing a circuit, including a front contact of relay-220, for operating relay 225. Relay 225locks directly to grounded conductor I18.

When the chief observer dials the units digit 1 of the. number of the first trunk groupto be tested, the closing of the off-normal contacts of the dialcauses the reoperation of relay 240. The

operation of relay 240 closes a circuit, including a front contact of relay 225, for operating relay 230, and relay 230 looks directly to conductor I18. When relay 245 releases in-response to the impulse created by the dialing of the units digit 1,

a circuit is closed from ground at the left front contact ofrelay 240, through the back contact of relay 245 and left front contact of relay 225 for operating stepping magnet 2 I1 of switch 2I0. When relay 245 reoperates at the end of the impulse, the steppin' magnet 2 I1 releases, thereby advancing the brushes of 'switch 2I0 intoengagement with terminal I of their respective banks' of terminals. When the dial reaches normal, relay 240 releases, closing a circuit, through conductor I89 and a front contact of relay 230, for operating relay I80. Relay I80 locks to conductor I18; connects ground to conductor I03 thereby lighting the units lamp I in a circuit which includes brush 2 I 2 and terminal I, conductor I91, and a back contact of relay I95; closes a circuit through brush 2I5 and terminal I and conductor I82 for operating the audible signal device I85 to indicate that test of the first group is about to begin; connects ground through conductor IBI to'terminal 22 of bank 2II; connects ground to terminal of bank 20I; disconnects the off-normal contact of the dial from the winding of relay 240; and closes a circuit from ground at the back contact of timer key 256, through conductor I94, a back contact of relay I95, a front contact of relay I10, a front contact of relay I80, conductor I31, aback contact of relay I35, a back contact of relay I30, through the winding of relay I50'.to battery. Relay I50 operates thereby connecting ground, through conductor I5I, to brush 2I3 of switch 2I0 to effect theoperation of the select magnets SI of crossbar switches 300, 400, 500, 100 and 800. With the SI select magnets all operated, a check circuit is closed from ground at the front contact of select magnet SI of switch 800, through conductor 61I,. the-front contact of select magnet SI of switch 500, conductor I64 and the winding of relay I00 to battery. Relay I60 operates, connecting ground, throughconductors ISI," I62 and I63, to

brushes

204, 205 and 206 of switch 200 to effect the operation of the parallel combinations of hold magnets connectedto the terminals engaged by these brushes. Thus with the brushes of switch 2 I0 in position 1, hold magnets HI to H4, inclusive, Of'sWitCh 300 are actu ated to connect the sleeve conductors of the trunks in group GII of observer A, through conductors GM to 620, inclusive, to the windings of test relays 62I to 630, inclusive; and hold magnets HI and H2 ofswitch;100 are actuated to connect the sleeve conductors of the trunks in group GI I' of observer B, through conductors 90I to 9I0, inclusive, tofthe. windings of the test relays 92I to 925. "The test relay windings thus connected to the sleeve conductors of busy trunks are operatively energized, both sets of contacts of each test relay being actuated if both windings are energized and only one set of contacts being actuated .conductor I46,and the winding of relay I40.

Relay I40 operates, locks under the control of relay I60, connects resistor MI in series with the winding of meter M-A so that a zero reading will be given if no trunks are busy in the group associated with observer A, and connects resistor I42 in series with meter MB so that a zero reading will be given if no trunks are busy in the group associated with observer B. If'there are busy trunks in the group connected to test relays 62I to 630, the winding of meter M--A,is further energized in series with the actuated contacts of thetest'relays and the associated ones of resistors 63I to 650, so that meter M-A indicates the number of trunks busy in the trunk group being tested; and if there are busy trunks in the group connected to test relays 92I to 925, the winding of meter M-B- is further energized in series with the actuated contacts of the test relays and the associated ones of resistors 93I to 935 and MI to 945; so that meter M--B indicates the number of trunks busy in the group being tested." As shown in therdrawings, three trunks in the group GII associated with observer A are busy; ground being connected to conductor .602 to energize the lower winding of relay 62I and ground being connected to conductors 6I9 and 620 toenergize both windings of relay 630. 640 and 650 are connected in parallel with resistor I4I to energize meter MA to give a reading of three trunks busy. x 1

The aforementioned operation of relay I40 closes a circuit for starting the charging of condenser I21, which circuit is traced from battery through potentiometer I2| and its movable contact, resistor I23, upper back contact of relay I35,

condenser I21, a front contact of relay I40, resistor I48, resistor II1, resistor H8, and conductor I39, to ground at a front contact of relay I10. The grid of tube IIO assumes thesame potential as the plate of condenser I21 to which it is connected through resistor I09; and when condenser I21 starts charging, the grid is sufficiently negative with respect to the cathode to block the tube. After condenser I21 has charged to a certain percentage of the oflice battery voltage, the potential of the grid approaches that of the filament and the tube energizes, the current in theanodecathode circuit being effective to operate relay 4. The operation of relay II4 closes a circuit,

including the contact'of key I I5 and a back contact of relay I30, for operating relay I35, Relay I35 locks to conductor I39; transfers condenser J I21 from potentiometer I2! to potentiometer I22; causes the release of relay I; and closes a cirrelay I95, to battery. Relay 235 is thereby operativelyenergized, connecting ground to brush 2 I I and closing a, circuit for operating steppin mag- Thus resistors 64I,

net 2I1. The release of relay I50 causes the release of the select magnets SI and release of the hold magnets of switches 300 and 100 which were operated to test the first two groups of trunks, one for each observer. When these hold magnets and select magnets have released, relays I60 and I40 release, the test relays which were operated release, and the meters MA and MB restore to normal. The release of relay I40 causes the release of relay 235, and the release of relay 235 causes the release of stepping magnet 2 I 1 thereby advancing each of the brushes of switch 2I0 to terminal 2.

When brush 2I2 advances from terminal I to terminal 2, units lamp I is extinguished and lamp 2 is lighted. The release of relay I40 opens the anode-cathode circuit of tube I I0, thereby causing the release of relay II4; efiects the discharge of condenser I21 through resistor I26; and closes a circuit from ground at a front contact of relay I10, through conductor I39, lowermost back contact of relay I40, and inner lower front contact of relay I 35, for operating relay I30. Relay I30 is slow in operating so that condenser I21 discharges and relay I I4 releases before relay I30 operates. The operation of relay I30 again closes the anode-cathode circuit through the winding of relay I I4; and closes a circuit for charging condenser I21, from battery through potentiometer I22 and its movable contact, resistor I24, a front contact of relay I35, condenser I21, a back contact of relay I40, a front contact of relay I30, resistor I25, resistor II1, resistor H8, and conductor I39 to ground at a front contact of relay I10. When the potential of the plate of condenser I21 which is connected to resistor I09 approaches that of the filament of tube I I0, the tube breaks down and relay I I4 reoperates. The operation of relay II4 causes the release of. relay I35 by closing a short circuit, across the winding of relay I35, through the lower front contact of relay I30. The release of relay I35 opens the anode-cathode circuit releasing relay II4, transfers condenser I21 from potentiometer I22 to potentiometer I2I, and opens the circuit for enerdenser I21 discharges through resistor I26. With both of relays I30 and I35 normal, relay I50 reoperates, thereby reconnecting ground, through conductor I5I, to brush 2I3 to effect the operation of select magnets S2 of the crossbar switches to which the trunk groups are connected. With all S2 select magnets operated, a check circuit is closed from ground at the front contact of select magnet S2 of switch 800, through conductor 612, front contact of select magnet S2 of switch 500, and conductor I64 for operating relay I60. Relay I60 again connects ground to

brushes

204, 205 and 206 to effect the reoperation of hold magnets HI to H4 of switch 300 and hold magnets HI and H2 of switch-100. The twenty sleeve conductors of a trunk group GI2 on switch 300 are thereby connected to test relays Bill to 630; and the ten sleeve conductors of a trunk group GI2 on switch 100 are connected to test relays 92! to 925. With all of these hold magnets operated, the check circuit for operating relay I40 is again closed and meters M-A and MB indicate the number of trunks busy in the groups tested. Relays H4, I and I and tube IIO are again effective to measure short intervals of time, the tube H0 and relay I35 controlling the length of the interval during which the meter circuits are closed and the tube H0 and relay I30 controlling the length of the interval during which the meter circuits are open before the test of the next group can begin. When relay I35 operates, relay I50 releases, relay 235 and stepping magnet 2I1 operate, the select and hold magnets which were operated release, relay I40 releases, the meters return to normal, relay 235 releases, and stepping magnet 2I1 releases, thereby advancing the brushes of switch 2I0 to terminal 3, all in the manner above described for advancing these brushes to terminal 2. When relay I30 operates, relay I35 releases; and when relay I30 releases, relay I50 reoperates to start another test.

It may be noted at this time that the measurement of the meter-closed and meter-open intervals by tube H0 and relays I30 and I35 is independent of the oflice voltage, because the potential of the filament and the potential of the grid at the'end of a desired interval of time during which condenser I21 is charging are both proportional to the ofiice battery voltage; By an adjustment of potentiometers I2I and I22, the measured intervals may be varied until the desired requency of successive meter indications is obtained. The resistor H3 limits the anode-cathode current to prevent damage to the tube; and resistor I I2 prevents the anode from attaining a potential while the anode-cathode circuit through relay I I3 is open which might cause immediate op-eration of the tube upon reclosure of this circuit.

The above-described cycle of operations is repeated to test additional groups, switch 2I0 being advanced one step after each test; so that the select magnets S3, S4, S5, S6, S1, S8, S0 and SH) of all crossbar switches are successively operated simultaneously with hold magnets HI to H4 of switch 300 and hold magnets HI and H2 of switch 100, thereby successively connecting the sleeve conductors of groups GI3 to GIO to the test relays.

When the brushes of switch 2I0 are advanced to terminal I0 to operate select magnets SIO for test 01 groups Git, relay 249 is operated. The operation of relay 249 closes a circuit for energizing steppingmagnet 201 and closes a circuit for lighting the units lamp 0. After the test of groups G! 0 has been completed, the brushes of switch 2 I 0 are advanced to terminals II to again operate select magnets SI. Relay 249 releases when the brushes of switch 2E0 advance to terminal II, causing the release of stepping magnet 20'! and thereby advancing the brushes of switch 200 to terminal 2 to select the second group of parallel combinations of hold magnets. The operation of select magnets SI and the operation of hold magnets H5 to H3, inclusive, of switch 300 and hold magnets H3 and H4 of switch connect the test conductors of trunk groups G2I to the two sets of test relays. At the end of the test, the brushes of switch 2I0 are advanced to terminals I2 and select magnets S2 are operated in combination with the same parallel combinations of hold magnets to connect trunk groups G22 for test. Thus groups G2I to G20 are tested successively, switch 2 I0 being advanced one step after test of each group. Relay 249 is again operated when the brushes of switch 2I0 reach position 20 and remains operated while switch 2| 0 is being advanced to position I and the operation of relay 24S again closes the circuit for operating stepping magnet 201. When the brushes of switch 2I0 are advanced to terminals 2 I' after the test of groups G20 is completed; relay 23.5'is operated in a circuit switch 2I0 from position 22 to position I is ef fected in like manner, except that the circuit for operating relay 235 is traced through terminal 22 of the bank associated with brush 2H and through conductor IBI, to ground at a front contact of relay I80. When the brushes of switch 2| Iladvance to position I, relay 249 releases .causingthe release of stepping magnet 20'! to ad-- vance the brushes of switch 200 to position 3, in which position the third group of parallel corn binations of hold magnets is connected for operation. Thus switch 200 is advanced'one step each time switch 2I0 is advanced to position II or to position I to; connect another group of parallel combinations of hold magnets for operation. Each time the brushes of switch 2H] are advanced to position I or position I! to start another ten readings, the audible signal device I05 is operated to aid the observers in making a correct record of the meter readings with respect to the trunk group numbers on the recording form. During each test by the test relays of each observer, the number of the trunk groups being tested is indicated by the tens and'units lamps, the corresponding tens and units lamps being lighted successively in circuits which include brushes 203 and 2I2, respectively. When the brushes of switch 200 are advanced to position II, relay I95 operates preventing the further operation of relay I50 and the further advance of

switches

2,00 and H0. While relay I95 is operated the 0 tens and 0 units lamps are energized, terminals I0 and II of the bank of brush 203 being strappedtogether.

Since one observer may have more groups to test than another, and a correct readingis given only when relay I40 is operated bythe closing of the check circuit, an omitted readingrelay 650 is provided and is. connected through a resistor such as either of resistors 659 and 600 to take the place of a parallel combination of hold magnets which would be operated for each of a group of ten readings. In the arrangement shown, observer B observes 100 groups and observer A observes only 80 groups, and the low resistance relay 650 is operated through resistor I G55when groups G9I to G90 are being tested for observer B and is operated through resistor 659 when groups G0! to G00 are being tested for observer B. In either case the operation of relay 650 completes the check circuit for operating relay I40.

If the dial key 250 is released either'before or after all groups have been tested, relay I10 releases, thereby causing the release of all operated relays and crossbar switch magnets. The release of relay I70 also closes a circuit, including brush 20!, and the associated terminals, including terminal II, for repeatedly energizing relay I913 to effect the repeated operation and release of stepping magnet 20'! and thereby advance the brushes of switch 200 to normal. The release of relay I10 also closes a circuit, including brush 2H and the associatedte'rminals, for repeatedly energizing relay 235 to effect the repeated operation and release of stepping magnet v2II and thereby advance the brushes of switch 2I0 to normal.

If the hold key I I5 is operated before a number is dialed or any time after test has started, the meters M-A and M-B give a continuous indication of the number of trunks which are busy in the particular groups then being tested. If the hold key is restored to normal, relay I35 may operate and test of the succeeding groups proceeds. If the hold key is restored to effect advance to the next group and then reoperated, a 7

continuous indication of the next groups tested is given by the meters.

If the repeat key I is operated before a number is dialed or any time after test has started, the switches 200 and 2I0 do not advance; and test of the same groups, one for each observer, is repeated under the control of timing relays I35 and I35. If the hold key H5 is also operated, the operation of the timing relays is stopped and the meters M-A and M-B give a continuous reading.

In case the repeated test of all groups of trunks is desired, the timer key 253 is actuated prior to operation of the dial key 250, and ground is thereby disconnected from conductor I94 to place the operation of relay I under the control of relays 28A and 210. The operation of key 255 connects ground to conductor I86 and closes a circuit for operating the timer motor 250 to effect the closure of interrupter contacts 259 for'two seconds, at intervals of fifteen seconds; After two digits have been dialed by the chief observer and switches 200 and 2 I 0 have selected the groups of select and hold magnets which are associated with the first groups of trunks which it is desired to test, the operation of relay I80 connects ground at the front contact of timer key 256,

through conductor I80, a front contact of relay 4S0, conductor I81, brush 283 of timer switch 280 and the normally engaged terminal 22, to the winding of relay 260. If the interrupter contact 259 is closed when relay I80 operates, the winding of relay 260 is shortcircui-ted by this contact. If the interrupter contact 259 is open when relay 9 30 operates, or as soon thereafter as this contact is open, relay 260 operates. Relay 260 locks under control of key 256, and transfers the interrupter contact to the winding of relay 206. When contact 259 is next closed, relay 286 operates, closing a circuit for operating stepping magnet 284 and closing a circuit for operating the audible signal-device 287, so that the observer will be prepared to. take readings. When contact 259 next opens, relay 285 releases, causing the release of stepping magnet 284 to advance brushes 28I, 282 and 283 to terminal I of their respective banks. With brush 282 in engagement with terminal l, a circuit is closed for operating relay 204. Relay 284' looks under control of relay 260, connects the winding of-relay 210 to terminal 22 of bank 285, connects ground at key 256 to conductor I01, and connects'ground to conductor IEldto effect the operation of relay I50; whereupon testing and reading of the meters start as hereinbefore described. While the tests are proceeding, each closure and opening of interrupter contact 259 causes the successive operation and release of relay 280 and stepping magnet 284; whereby the brushes of switch 280 are advanced one step every fifteen seconds. When the brushes I of the switch 280 reach position 10,.relay 285 is operated in a circuit through terminals 10 and brush 28L theoperation of relay 285 causing the tion of stepping magnet 284 causes the release of relay 285; and the release of relay 285 causes the release of stepping magnet 284, thereby advancing the brushes to position II. Relay 285 immediately reoperates, thereby causing the advance of the brushes to position I2 in the same manner as that in which the brushes were advanced from position I to position II, without I waiting for the closure of interrupter contact 259. The brushes are advanced from position I2 to position 2| under control of interrupter contact 259 and relay 236. When position 2| is reached, the operation of relay 286 also efiects the operation of the audible signal device 281 to warn the observers that an interval of four and threequarter minutes has elapsed since the test started. When the brushes are advanced to terminal 22 by the release of relay 286, relay 210 operates connecting ground to conductors I13, 213 and 214 and lighting the warning lamp 212. The connection of ground to conductor 213 causes the repeated operation and release of relay I90 and stepping magnet 201 to effect the advance of the brushes of switch 200 to terminal II, if not already advanced to this terminal; the connection of ground to conductor 214 eifects theoperation of relay I90 and stepping magnet 201 to advance the brushes to terminal I2; the repeated operation of relay I90 through brush 20I and terminals I2 to 2I, inclusive, effects the advance of the brushes of switch 200 to normal; and the connection of ground to conductor I13 causes the repeated operation of relay 235 to efi'ect the advance of the brushes of switch 2I0 to normal. The operation of relay 210 also disconnects ground from conductor I94 to prevent further testing, holds relay I10 to render the operation of the dial inefiective to step switches 200 and 2H], and disconnects ground from conductor 21I to prevent the operation of relay 249 from interfering with the advance of switch 200 to normal. If relay 210 is operated without the observer having operated the dial to select the first groups for testing, the operation of relay 210 also causes the operation of relay I80 thereby to effect the operation of relays I90 and 235 and advance switches 200 and 2 I 0 to position I in which groups GII are selected for test. operates after brush 282 engages terminal 22, the audible signal device 281 is again operated, indicating that a cycle of readings is about to start. When relay 288 next releases, the brushes of switch 280 are advanced to position I, causing the release of relay 210. 210 closes the circuit for operating relay I 50 and a cycle of tests begins. After key 256 is restored to normal, testing ends when a cycle of tests is completed.

The potentiometer I01 which is connected in series with the central oflice battery ma be adjusted according to the ofiice voltage before starting tests, so that the readings will be correct. To make the required adjustment, the observer operates the dial key 250 and the calibrating key 253, thereby operating relays I05 and I10. Relay I05 connects battery, through resistor I04, to meter M--A and connects resistor I05 to the potentiometer I01 to simulate an average load of meters. The potentiometer is adjusted so that the meter gives a full scale deflection. If there are more than five observers, there will be another relay similar to relay I05 connected to conductor 254 and the potentiometer I08 which is provided for those observers will be adjusted so that the meter of one of those observers gives The release of relay.

When relay 286 refull scale deflection. 'When key 253 is released, relay I05 releases and testing may proceed.

In order to adjust potentiometers I2I and I22 to obtain the desired frequency of readings, the dial key 250 and repeat key I49 are operated and the observer dials the number of an unused trunk group in which all sleeve conductors have been connected to ground. The switches 20!] and 2l0 will not be advanced and repeated tests of the unused group will be made. Potenticmeter I22 should then be adjusted until the meter associated with the artificially busied group definitely remains normal for a short period after each reading. The potentiometer I2I should then be adjusted until ten readings are made in about twenty-six seconds. With these potentiometer settings, one-hundred readings should be completed in about four minutes and fifteen seconds.

Although indicating meters are shown for giving the traffic readingsto be recorded by 0b servers, it is obvious that recording meters might be used. Individual test relays might be provided, one for each trunk of the largest group to be tested, in place of double wound two-step relays. Instead of a single indicating meter being provided for giving an indication of the number of busy trunks in a tested group, a plurality of indicating means, such as lamps, may be associated with each observer, the lamps being connected to the contacts of the test relays in such a manner as to display the number of busy trunks in the tested trunk group. These and other modifications may be made in the trafiic observing apparatus, shown in the drawings, within the scope of the invention hereinafter claimed.

What is claimed is:

l. A traflic observing apparatus for testing groups of trunks and for indicating the number of busy trunks in each group, said apparatus comprising means for selecting each group in succession, test relays for individually testing each trunk in the selected group, means for simultaneously connecting all of the trunks in the selected group to said test relays, and a meter controlled by said test relays calibrated to indicate the number of busy trunks in the tested group.

2. An observing apparatus for determining the extent of use of groups of like units each of which has an individual conductor to which a busy marking potential is connected while the unit is in use, said apparatus comprising means for selecting each group in succession, test relays for individually testing each unit in a selected group, means for simultaneousl connecting all of the units in a selected group to said test relays, an electrical meter, and means connecting said meter to the contacts of said test relays, whereby the meter is energized to give an indication of the number of busy units in the tested group.

3. A trafiic observing apparatus for testing groups of trunks and for indicating the number of busy trunks in each group, said apparatus comprising a plurality of meters, one for each of a plurality of observers, a set of test relays for each observer, means for selecting groups of trunks for test, a group for each set of test relays, means for simultaneously connecting the trunks in the selected groups to the sets of test relays, and means including the contacts of each set of test relays for energizing the associated meter to give an indication of the number of busy trunks in the associated one of the simultaneous ly tested groups.

4. A traflic observing apparatus for determinobservers indicating meter, a set of test relays, and a group of switches for connecting the groups of trunks to the test relays one group at a time, saidswitches being of the crossbar type, each having a plurality of select magnets and a plurality of hold magnets, the hold magnets being connected in a plurality of parallel combinations whereby the operation of a group of like numbered select magnets of said switches and a particular combination of hold magnets is effective to simultaneously connect said test relays to all of the trunks in one group, means for successively operating each group of like numbered select magnets with each different combination of hold magnets, thereby to successively connect the trunks of each group to said test relays, and means including the test relays for energizing the meter to indicate the number of busy trunks in each group tested.

15. A traffic observing apparatus for a plurality of groups of trunks, each group of trunks being individually allotted for observation by a particular one Of a plurality of observers, said apparatus comprising a meter, a set of test relays and a group of'swltches for each observer, each group of switches adapted to connect the groups of trunks allotted to the associated observer to the associated test relays, said switches being of the crossbar type, each having a plurality of select magnets and a plurality of hold magnets, the hold magnets of the switches associated with each observer being connected in a plurality of parallel combinations whereby the operation of the like numbered select magnets and a particular parallel combination of hold magnets of the switches asso ciated with each observer is effective to simultaneously connect the associated test relays to all of the trunks in one of the associated groups of trunks, switching means common to all observers for effecting the successive energization of each group of like numbered select magnets of the switches associated with each observer with each particular parallel combination of hold magnets to effect the connection of each set of test relays to each of the trunk groups allotted to the associated observer, and means including the test relays for each observer for effecting the energization of the associated meter to indicate the number of busy trunks in the group being tested.

16. A trafific observing apparatus for a plurality of groups of trunks, said apparatus comprising an observers indicating meter, a set of test relays, and a group of switches for connecting the groups of trunks to the test relays one group at a time, said switches being of the crossbar type, each hav ing a plurality of select magnets and a plurality of hold magnets, the hold magnets being connected in a plurality of parallel combinations whereby the operation of a group of like numbered select magnets of said switches and a particular combination of hold magnets is effective to simultaneously connect said test relays to all of the trunks in one group, means for successively operating each group of like numbered select magnets with each different combination of hold mag nets, thereby to successively connect the trunks of each group to said test relays, means for preventing the testing of the next group in case any of the like numbered select magnets or any of the hold magnets in a particular parallel combination of hold magnets, the operation of which select and hold magnets is required for the testing of a selected group, fail to operate, and means including the test relays for energizing the meter to indicate the number of busy trunks in each group tested.

17. A traffic observing apparatus for a plurality of groups oii trunks, each group of trunks being individually allotted for observation by a particular one of a plurality of observers, said apparatus comprising a meter, a set of test relays and a group of switches for each observer, each group of switches adapted to connect the groups of trunks allotted to the associated observer to the associated test relays, said switches being of the crossbar type each having a plurality of select magnets and a plurality of hold magnets, the hold magnets being connected in a plurality of parallel combinations whereby the operation of the like numbered select magnets of all switches and a particular parallel combination of hold magnets of the switches of each group is effective to connect the associated test relays to one of the associated groups of trunks, switching means common to all observers for effecting the successive energization of each group of like numbered select magnets of the switches associated with each observer with each parallel combination of hold magnets to effect the connection of each set of test relays to each of the trunk groups allotted to the associated observer, means for preventing the testing of the next group of trunks for each observer in case any of the like numbered select magnets or any of the hold magnets of the particular parallel combinations of hold magnets for each observer, the operation of which select and hold magnets is required for the testing of a selected group for each observer, fail to operate, and means including the test relays for each observer for effecting the energization of the associated meter to indicate the number of busy trunks in the group being tested.

, 18. A traffic observing apparatus arranged so that each of a plurality of observers observes the trafiic carried by each group of a different plurality of groups of trunks, said apparatus comprising a meter, a set of test relays and a group of switches for each observer, said switches bein of the crossbar type each having a plurality of select magnets and a plurality of. hold magnets, the hold magnets being connected in a plurality of parallel combinations, whereby the operation of the like numbered select magnets of all switches and a particular parallel combination of hold magnets of the switches associated with each observer is effective to connect each set of test relays to one of the groups of trunks of the plurality associated with each, observer, switching means common to all observers for operating in succession each group of like numbered select magnets of said switches in combination with each parallel combination of hold magnets whereby all groups of trunks associated with each observer are successively connected to the associated set of test relays, means operated only in case all of the select magnets and all of the hold magnets, the

operation of which is required to connect a group of trunks to the associated test relays of each observer, are operated for effecting the advance from one group of trunks to the next, the last-mentioned means including an omitted reading relay in case one observer has a smaller number of trunk groups to observe than the other observers, and means including the test relays for each observer for effecting the energization of the associated meter to indicate the number of busy trunks in the tested group.

THOMAS L. DIMOND.