US2471415A - Telephone calling line identification system - Google Patents

Description

May 31, 1949. G. DEAKIN ETAL TELEPHONE CALLING LINE IDENTIFICATION SYSTEM Filed April 30, 1945 3 Sheets-Sheet l l 1949. G. DEAKIN ET AL 2,471,415

TELEPHONE CALLING LINE IDENTIFICATION SYSTEM Filed April 30, 1943 s Sheets- Sheet 2 1 I 29\- Tl/ G. DEAKIN ET AL 15 May 31, 1949.

TELEPHONE CALLING LINE IDENTIFICATION SYSTEM s Sheets-Sheet 5 Filed April 30, 1943 [if-6 Q4 L42,....z4aj

z ,2 Y 2,, r r w INVENTORS AGE Patented May 31, 1949 UNITED STATES PATENT OFFICE TELEPHONE CALLINGLINE IDENTIFICATION SYSTEM Application April 30, 1943, Serial No. 485,262 In France May 22, 1940 Section 1, Public Law 690, August 8, 1946 Patent expires May 22, 1960 25 Claims. 1

The present invention relates to new and useful improvements in central office telecommunication systems and particularly to call-responding circuits which serve to detect a call or to identify the calling line.

One object of the invention is to provide a call-responding circuit adapted to serve a group of lines, such as subscriber, junction or other similar lines, which detects a call or identifies the calling subscriber or junction line, without the need of using an individual relay or switch for each subscriber or junction line.

According to the present invention circuits having switching mechanism of a standard type connect a call-responding discharge tube to a certain number of lines (subscriber lines or junctions, for example) in such a rapid sequence that the contact with each line is only momentary. The discharge tube is so arranged as to operate more or less instantly upon the receipt of a call, and to continue in operation even after the release of the calling line. This will allow other slower equipment time to operate.

One particular object of the invention is to provide an arrangement wherein switching mechanism of standard type is actuated without interruption in order to connect the discharge tube to a certain number of lines in rapid succession and wherein the dis-change tube, upon being operated by a momentary contact, remains in action for a time sufi'icient mechanically to energize a movable switching device, such as a relay, for detecting a call among the lines served by said switching device.

Another object of the invention is to provide call finder circuits wherein a switching mechanism, for example, a line or junction finder, is placed in operation by a calling condition over a subscriber line or group junction, and begins immediately to connect momentarily a test equipment to each of the subscriber lines or group junctions in rapid succession. The test equipment is immediately ready to respond to a calling condition without need of waiting for a warming up period.

Still another object of the invention is to provide responding equipment to detect a call or to identify the calling line which comprises one or more discharge tubes adapted to be operated by very small currents across high resistances associated with the different lines and designed to remain operated even after having been disconnected from said resistances.

Still another object of the invention is toprovide an installation wherein the responding 2 equipment comprises a discharge tube of the cold-cathode type that is constantly ready to operate without need of the heating power of the cathode.

It has already been proposed to connect one or more high resistances to each one of a group of lines of a telecommunication central ofiice and to detect a call condition or to find the line characterized b this condition by means of ionic or electronic discharge devices capable of operating in series with these high resistances.

An installation of this kind is described, for example, in application Serial No. 286,220, filed July 24, 1939 by Deakin, now Patent No. 2,295,032, dated Sept. 8, 1942.

The present improvement consists in that the discharge devices are so arranged as to continue operating after they have been operated once through momentary connection with a calling line, this extended operation serving to actuate a relay or other means requiring longer time.

Thus, in providing a continued operation of the discharge device after a momentary energization, the present invention afi'ords the possibility of operating at very high contact speeds the switching mechanism that connects the discharge device successively to the lines. A switch particularly suitable for this kind of operation at high contact speeds has already been described in application Serial No. 389,352, filed April 19, 1941 by Deakin, now Patent No. 2,339,063, dated Jan. 11, 1944, although any high speed non-numerical finder switch may be employed.

The present invention respresents an improvement in that the potentials applied across the high resistance to the subscriber lines are so chosen that a slight resistance leak between one of said lines and the ground will simulate a call condition rather than put the line out of calling condition.

The present invention further represents an improvement in that the discharge devices are of the cold-cathode type, do not require filament heating current, and are always ready to operate without delay.

Other objects and features of the invention will appear from the following detailed description of the equipment and its operation, which should be read with reference to the attached drawings, in which:

Fig. 1 shows a subscriber line circuit and a call responding circuit, as required in order to understand certain novel principles of the invention;

I Fig. 2 represents another embodiment of the 3 invention comprising a subscriber line circuit, a line finder circuit and a call responding circuit for detecting a call, operating a line finder in response to the latter and stopping the finder when it reaches the calling line;

Fig. 3 shows still another embodiment of the invention comprising a subscriber line circuit, a line finder circuit containing an automatic stop device for a calling line, and a call responding circuit for operating a line finder chosen preferably as a result of a call condition in said line circuit;

Fig. 4 is a schematic diagram showing one of the ways in which a plurality of line finders a certain number of lines may utilize the embodiment of my invention shown in Fig. 3;

Fig. 5 is a modification of Fig. 2; and

Fig. 6 is a modification of Fig. 4.

The same reference numerals are used in the Various figures to designate corresponding elements.

Referring more particularly to Fig. 1, l is a substation equipment connected to a central exchange through a subscriber line 2 having two conductors a and b. At the central exchange, a grounded high resistance 3 is connected to conductor a of line 2, and another high resistance 4 is connected between conductor b of this line and a detector switch 5 constantly rotating at a high contact speed, for instance, 120 to 600 con tacts per second. The wiper of this switch 5 is connected to conductor 6.

Conductor 6 is normally maintained at a negative potential somewhat lower than -125 volts through a leak resistance 1 connected to the tap of a potentiometer 8 which, in turn, is connected to the terminals of a stabilized 1-25-volt source. The moment wiper 5' passes over the contact con-- nected to resistance 4, the potential of conductor 6 is raised momentarily to a less negative value if the switchhook at station I is closed. Let us assume, for example, that resistances 3 and 4 have a value of 10,0001 each, that line 2 has a loop resistance of 25001.0 and that the value of leak resistance 'l is 25,000w. Therefore, if the tap of potentiometer 8 is adjusted to 1l1- volts and if the resistance of this potentiometer is negligible, the potential of conductor 6 will become at this moment 55 volts.

A gas filled discharge device 20 of the cold-- cathode type has its control anode 2 l connected to conductor 6 through leak resistance 9 which may, for example, be of 500,00010, and its cathode 22 connected to the negative pole of the 125-volt source, the main anode 23 or this tube being con-- nected to ground through a relay 24. Preferably, this tube is of the type sold under the trade mark W. E. 313- and described in an article byIngram appearing on pages 34*2*346 of the Electrical Engineering Transactions, vol. 58, July 1939. The critical breakdown voltage for the control space between electrodes H and 22 is assumed to be around '70 volts.

Consequently, when conductor 0 is brought to a potential of 55 volts, while electrode- 2-2 is maintained at --125 volts, the tube is ionized. The difference in potential between cathode 2'2 and main anode 23 being or 125 volts, the maincircuit between these two electrodes will be closed the moment the control space becomes ionized and will remain ionized even when: wiper leaves the contact connected to resistance 4, so as to restore conductor 6' to its normal potential. The current passing over the main circuit is limited substantially by the resistance of relay 24, which suitably may be of 2500a. The current passing through relay 24 will then .be of approximately 19 m. a. and this relay will' operate. Advantage may be taken of the operation of relay 2a to bring into operation a line finder (not shown) or to start any other desired operation. Suitable means should be provided for causing the deionization of tube 20 after relay 24 has performed its function.

Fig. 2 shows another embodiment of the inven tion wherein a gas filled cold-cathode tube 20, like tube 20 of Hg. 1 is used, not alone to detect a call, but also to identify a calling line. The arrangement shown in Fig. 2 comprises an individual subscribers line equipment i, 2, 3, i, In; a switch 5 common to a whole group of line equipments of this kind; a common detector equipment H a first line finder ILFI, which represents one out of a group of, say, 14 first line finders, and a distributor circuit 12 for connecting six wires from the common detector Ii to the first free first line finder. Distributor [2 may be of any known type normally capable to maintain the common equipment H connected to a tree line finder and to transfer the connection to the next free line finder upon the operation of a relay 50 in the line finder to which the said distributor is connected.

In this figure, elements l-Q and 20-24 are the same as those bearing the corresponding reference numbers in Fig. 1, but conductor 6 is connected to a switch 5 through the left back contact of a relay 25. Relay 24 is grounded via an inner right-hand back contact of the same relay i 25, a connection of the switch of distributor I2,

and the left back contact of a line finder relay 50.

Relays 25, 26 and 21 are supplementary telephone type relays in the common equipment ll; 50 is a similar relay in a line finder ILF I, while 5! is an electromagnetic clutch mechanism for operating the line finder. Ill is a message register associated with the individual subscribers line but installed at the central office.

The circuit shown in Fig. 2 operates as follows: To start a call, the subscriber at station I lifts the receiver, which closes a circuit from ground via resistance 3, line 2 conductor a, line 2, conductor b, resistance 5, wire c, switch 5' (when the latter passes over its corresponding contact), left back contact of relay 2'5, conductor 6, leak resistance 1, upper portion of potentiometer 8*, to the 125 volt battery. In the same way as previously described with reference to Fig. 1, this circuit reduces the negative potential of conductor 6, so that control anode H becomes volts more positive than cathode 22, ionizing the control space of tube 20. Current flows from ground through the outer left-hand back contact of relay Bil, distributor I2, inner right-hand breaking contact of relay 2'5, winding of relay 2 main anode 23' and cathode 22 of tube 28 to the volt battery.

Relay 24 becomes energized and closes a circuit from ground through its front contact, righthand breaking contact of relay 26,- conductor 28, winding of relay 25 to the standard 4 8-volt central battery.

The operation of relay 25 breaks the contact between conductor 6 and switch 5 in its left back contact. The right front contact of relay 25 connects the ground, through the outer left-"hand back contact of relay 50 and the corresponding distributor connection, to the Winding of relay 28 which, however, does not operate onaccount of the short-circuit to ground at the armature of relay 24. Likewise, the operation of relay causes the potential of the standard 48 volt central battery to be applied through its outer right-hand front contact, to conductor 29, and thence across resistance and the corresponding distributor connections to conductor 3|, which is connected to an outgoing circuit (not shown) leading to the second line finders (not shown).

The inner right-hand back contact of relay 25 opens the circuit of relay 24 and the main discharge space of tube 20. This stops the ionization of tube 20 and relay 24 falls back.

After release of relay 24, the circuit of relay 25 is opened and current flows to ground via left back contact of relay 50, corresponding connection of distributor l2, inner right-hand front contact of relay 25, winding of relay 25, conductor 28, winding of relay 25, to the 48-volt central battery. Consequently, relay 25 holds and relay 26 energizes. The operation of relay 26 causes the closing of a circuit from ground, the back contact of relay 24, outer front contact of relay 26, corresponding connection across distributor l2, clutch magnet 5|, to the central battery. Clutch 5! causes the rotation of line finder wipers a, b, c and d.

At this moment tube 20, which has been deionized, is in the same condition as before the call was started, except that conductor 6 remains connected through the inner left-hand front contact of relay 26 and through the corresponding connection of distributor I2, to Wiper c of the line finder instead of to the wiper of detector switch 5. tact associated with calling line 2, the ground potential across resistance 3, loop of line 2 and resistance 4 reduces the negative potential of conductor 6 sufficiently to produce a discharge across the control space of this tube, which, in turn, causes a discharge across the main space, energizing relay 24 as before.

The relay 24 opens the circuit of clutch 5|, thus stopping the line finder wipers on the calling line, and prepares a circuit for relay 5!) from ground, via front contact of relay 24, outer righthand front contact of relay 26, front contact of relay 21, corresponding connection across distributor I2, to the left winding of relay 50.

If, at this moment, the first line finder ILF--l has been found by a secondary line finder, relay 2'! will have already been brought into operation by a ground over wire 0'', right-hand back contact of relay 5!), proper connection of distributor l2 Winding of relay 21, outer right-hand front contact of relay 21, to the central battery.

If relay 2'! is already operated, the circuit prepared for relay will be completed and relay 50 will operate. Otherwise, the equipment will wait until the ground is applied to wire 0''.

The operation of relay 50 breaks, at the outer left-hand back contact, the locking circuit of relays 25 and 26, which release. Likewise, relay 50 breaks, at its right-hand back contact, the circuit of relay 21, releasing the latter, but not without first locking up over its right-hand front contact to ground over wire 0". Furthermore, the relay 50 connects the -125 volt battery via its inner left-hand front contact and wiper c to the 0 wire of the calling line, thus indicating that this line is busy and preventing the initiation of further calls when switch 5 again passes over the associated contact.

The relay 5!] now controls distributor l2 to connect the six wires of the common equipment When wiper c finds the con- 'H to the first free first line finder in any suitable manner. When the connection with this first free line finder is completed, the ground from the outer left-hand back contact of a corresponding relay 5!] is applied to the main anode 23 of tube 20, so as to make this tube ready to respond to another call.

Fig. 3 shows another embodiment of the invention wherein the detector switch 5 not only helps to detect a call, but also serves as a distributor, for determining which line finder must be operated to hunt for the calling line. In this embodiment each line finder is equipped with a discharge device 40, like device 20 provided for the common equipment ll. Each tube 45 serves not only as a control means for identifying the calling line during hunting, but also, in a preceding call phase, to cooperate with switch 5 for determining which line finder must be operated.

The switch 5 to be used in this embodiment should preferably be of the type described in application Ser. No. 389,352, filed April 19, 1941, issued U. S. Patent No. 2,339,063, Jan. 11, 1949, wherein a conductive ball I 4 is displaced and rolls over a series of stationary contacts I5 while it also rests upon a conductive ring.

However, according to the present invention, this conductive ring is made up of a plurality of arc-shaped elements l6, l1, etc., all the arcshaped elements l6 being multipled with one another and connected to conductor 6, while all the arc-shaped elements I! (of which only one is shown) overlap and are connected to conductor 33. It will be understood that switch 5' should be preferably shaped as a complete circle, although only a semi-circle is shown in the drawings for the sake of simplicity.

In the embodiment shown in Fig. 3, each line finder, such as ILFI, comprises two relays 52 and 53 instead of the single relay 5!) of Fig. 2.

The line finder switch itself comprises Wipers a, b, c and d and an electromagnetic clutch 5|, as in Fig. 2, but in addition is provided with off-normal contacts 54 and 55, which are closed as indicated when the line finder switch is in the normal position, and are moved up when the line finder is off-normal, i. e., when it occupies any other position than the one assigned to it as its normal position.

Each line finder, such as ILF-l, further comprises variable resistance 36 and fixed resistances 3'7, 38 and 39, suitably connected to line finder discharge tube 40. The standard equipment II,

F in addition to tube 20 and resistances 5, l, 8 and 9, which are the same as in Fig. 1, comprises two supplementary resistances 34 and 35.

The embodiment shown in Fig. 3 operates as follows: When the switchhook is lifted at substation I, then at the next passage of ball 14 over the corresponding contact I5, the ground potential passes through resistance 3, loop of line 2, resistance 4, line wire 0, proper contact [5 of switch 5', ball [4 and bank I5 of this switch, conductor 6, resistance 1, upper portion of potenti-' ometer 8, to a tap of volts on a stabilized potential source of volts. Exactly as in the embodiment shown in Figs. 1 and 2, this ground potential ionizes the control space of tube 20, which in turn fires the main space between cathode 22 and main anode 23 of this tube. The current flows across this main space and passes from the ground, through resistance 35, main anode 23, cathode 22, resistance 34, to a 125 volt tap of the 180-volt stabilized potential source. Resistsince 35 may have 3i. value of 2230001. It corresponds substantially to relay 2,4 of Figs. 1 and- 2. Resistance 34, however, has a high value, of 1300,0001, for example, and the voltage drop due to the flow of discharge current. through this resistance strongly shifts the potential of cathode 22 and of conductor 33 in the positive sense in such a way that this potential instead of being of ll251volts, may, for instance, be of -'75 volts. Gonsequently, bank l'l of switch 5:, which. normally has a potential of 125 volts, has. its potential raised to 75 volts when ball 14- passes over the contact connected to the wire associated with the calling line.

Ball I24 continues toroll clockwise on the rim of the switch, leaves bank t6. and starts making contact between bank H and the contacts l associated with the various line finders provided tor the group of lines connected to this switch. If the line finder connected to the first of these contacts l5 is already busy, the conductor runfrom contact. l5 will be opened at back contact of 54 and, consequently, the passage of the ball over said contact l5. will have no effect. Let us assume, however, that line finder ELF-l associated with the first contact i5 is free. Then, when ball l4. establishes a connection between said contact 15 and bank ll, the -75 volt potential now existing on bank ll will be transmittedvia ball l4, contact l5, back. contact '54 in normal position, resistance 38 to. the -l volt terminal of a stabilized potential source. Assuming that resistance 38 has a value of 500,000w, this resistance will cause only a very small variation of potential in bank I? and hence conductor 44 likewise will be brought ver nearly to 75 volts. The control space of tube 40 will be ionized, because the cathode it of this tube is. connected directly to a l80. volt potential source, While anode M is connected via resistance 31 to conductor 44, which is very near to 75 volts. The value of resistance 31 may be 500,000w.

The ionization of the control space between electrodes 4i and 52 causes a discharge through the main space between cathode 42 and main anode 43, the current flowing across. this main space from ground through resistance 35,, relay 52-, outer left-hand back contact of relay 52, anode 43, cathode 4.2. to the 180 volt potential source. Preferably, relay 52 has an inductive winding Working into a non-inductive winding shunted thereto, the resistance of these windings being 1050aand 800w, respectively.

The passage of the current over the above circult produces two. different results. It starts to build up the normal energization of relay 52, thereby causing the latter to operate after a few milli-seconds, as will be explained later on. On the other hand, this passage of current causes instantly a substantial drop of the potential across resistance 35. With the assumed resistance values of resistance 35 and of the none inductive winding of relay 52, the upper end of resistance 35 is brought to a substantially negative potential of 50 to. 60 volts or more. This, in turn causes the de-ionization of tube 2-D, because the potential of anode 23 is no longer positive enough (with respect to cathode 22') to keep the tube ionized. If, for example, the potential drop in resistance 35 amounts to. 60 volts so that the main anode 23 is brought to a potential of -50 volts, then, even if the value of cathode 22 is l25 volts, the difierence in potential between anode 23 and cathode 2;? will now be but 65 volts, which is not enough to maintain the ionization.

Furthermore, it has been found that the deionization. of the tube is substantially hastened by the suddenness with which, the potential of anode 2:3,; is; shifted. negatively. Owing to the distributed capacity of cathode 22, this cathode tendsto. maintain, for a short instant, its previous' potential oi 7.5 volts. Under these conditions, when the potential of anode 23 is brought almost instantly to. the new valueof -60 volts, the difference in potential between anode 23 and cathode 22 is reduced, for a moment, to 10 volts. This; instantaneous reduction of the potential to such a small Valueas 10 volts hastens the deionization, even though shortly afterwards this difference in potential may return to about 65 volts when cathode 22 is nearl restored to its initial potential of 125 volts.

Moreover, even if. the de-ionization of tube 20 is not instantaneous, bank I! will nevertheless be, brought almost instantly to such a potential that it will be incapable of causing the ionization of other tubes, such as tubes 40 of the succeeding line finders.

Experimental tests, have shown that with the circuit of Fig. 3, bank I! is incapable of ionizing other line finders within a very small fraction of a millisecond after tube 40 of the first line finder has discharged. It makes little difference whether this ensues from the complete deionization of tube 20 during this. time or results from. the potentials of the anode and cathode of this. tube 25 being negatively displaced to the extent of rendering bank ll incapable of causing the ionization of other tubes.

It has already been mentioned that the influx of current through resistance 35 likewise causes the energization of relay 52. After an interval of few milliseconds this relay operates and is locked to. the ground, via resistance 35, winding of relay 52, inner left-hand front contact of relay 52, inner right-hand back contact of relay 53, to the standard 48.-volt central battery. After this locking circuit is. closed the outer left-hand back contact of relay 5 2 breaks the above described discharge circuit of tube 40, but the locking current coming from the 48-volt central battery, passing through relay 52 causes a potential drop in resistance 3.5. of about 40 volts, which is sufiicient to prevent tube 20 from responding again to another call.

The outer left-hand front contact of relay 52 connects anode 43 of tube 50, to test relay 53, but this contact is at a great distance from the outer left-hand back contact, so that tube 45 is de-ionized during the passage of the armature between these contacts. To hasten de-ionization, a resistance 39, which may be of 20,00Qw, is inserted' in order to bring anode 43 promptly to the same potential as cathode 52.

The inner right-hand front contact of relay 52 applies ground potential to a conductor 6|], which may serve for any other desired purpose, such as. operating the second group of line finders if two groups are used. The outer right-hand front contact of relay 52 closes a circuit for the ground comingfrom the outer left-hand back contact of relay 53, outer right-hand front contact of relay- 5-2, clutch 5| of the line finder, to the iii-volt central battery. The energization of clutch 5| causes the rotation of line finder wipers a, b, c and d.

When the rotation of the line finders starts, the. off-normal contacts 54 and 55 are displaced in such a way that conductor 44 is now connected over the upper contact of 54, while the outer right-hand contact of relay 52 is shunted by contact 55.

It should be noted that tube 40 is now deionized and has its cathode 42 connected to 180 volts, while its control element 4| is connected, by the 500,000 w leak resistance 31, to conductor 44. When Wiper c finds the contact associated with the calling line, a circuit is closed from the ground, v-ia resistance 3, loop of line 2, resistance 4, wire, wiper c, resistance 35, onnormal contact 54, conductor 44, leak resistance 38 to the 125 volt terminal of the ISO-volt battery. Resistance 36 is adjusted to such a value that, for any loop whatever of 2,500 to or less, the potential of conductor 44 is displaced negatively just sufficiently for ionizing the control space of tube 45. The main space between cathode 42 and main anode 43 is therefore caused to discharge and the current flows from the ground, via relay 53, outer left-hand front contact of relay 52, anode 43, cathode 42, to the 180 Volt potential source. Relay 53 now operates and looks over its outer right-hand front contact to the potential of the 48-volt battery, supplied from a suitable point of the succeeding equipment (not shown).

The outer left-hand back contact of relay 53 breaks the circuit of clutch thus stopping the line finder switch on the calling line. The inner left-hand front contact of relay 53 applies the -125 volt potential through wiper c to a 0 wire of the calling line in order to indicate that th latter is busy and prevent this line from starting another call. Likewise, this potential returns control anode 4| to its normal potential of -125 volts, so that the difference in potential between this control anode and cathode 42 is insufiicient to maintain the ionization.

At its inner right-hand back contact, relay 53 breaks the locking circuit of relay 52 and causes a potential drop in resistance 35, which puts the latter out of operation. Relay 52 is then released and tube starts operating again. The release of relay 52 de-ion-izes tube during the transfer from the outer left-hand front contact to the outer left-hand back contact of this relay.

Line finder ILF-I is now connected to the calling line, with tube 20 and relay 52 returned to normal. Only relay 53 remains energized from .a 48-volt battery applied from the succeeding portion of the connection (not shown). Once the call has ended, this battery connection is momentarily or permanently interrupted by any suitable means to release relay 53. The ground through the outer left-hand back contact of relay 53 and off-normal contact 55 energizes clutch 5| in order to return the line finder to its normal position, whereupon contact 55 opens and the magnet 5| becomes de--energized.

In order to simplify the drawing, switch 5 has been shown semi-circular in Fig. 3, and only two banks i5 and one bank I! are illustrated. How ever, this switch is preferably of circular shape and is provided with several banks ll located between several banks l6. One of the important features of the invention is the use of one and the same switch for detecting a calling line and for starting immediately thereafter the hunting of a free line finder to hunt for the calling line. The system diagrammatically illustrated in Fig. 3 is very flexible and may be arranged to give many different solutions in the distribution of the line finders.

Fig. 4 shows one of the ways in which 6 line finders and 48 lines can be associated with one switch, such as 5', serving both for detecting a call and for distributing the calls to the line finders. As indicated in this figure, the six line finders ILF|, ILF--2, ILF-5 are connected to twelve contacts located in front of six arc-shaped segments while the;48 lines are connected in groups of eight each to contacts located in front of six arc-shaped segments I6. It is assumed that ball I 4 rolls clockwise in the switch of Fig. 4, so that immediately after having tested line groups Ll, L2 L8, this ball will establish the connection to line finder ILF| and then to line finder ILF-B, whereupon it will proceed to test line groups L9, L|0 Ll5, and afterwards it will make contact with line finder ILF-2 and then with line finder ILF|. The

six line finders are arranged so as to occupy dif-' the lines are hunted by the various line finders is indicated in Fig. 4 by the notation in parentheses under the number of each line finder. Thus, line finder ILF-|, upon being operated, starts hunting over line LI and hunts successively over lines Ll, L2, L3, L4, L41, L48, while line finder ILF2 starts hunting on line L9 and hunts successively over lines L9, Llfl, L||, L41, L48 and then continues hunting over lines LI, L2, L1, L8.

By referring to Fig. 4 it will be seen that if a call is made in line group Ll L8, so that discharge tube 20 of the common equipment I will be ionized when ball |4 passes over this group of lines, the first line finder to be chosen, i. e. the first line finder to be tested will be ILF-| and the second line finder to be chosen Will be ILF5. Since line finder ILF| normally is placed just ahead of line Ll, this line finder will find the calling line within a very short time after having hunted at most over eight contacts. Even if line finder ILF-| is busy and it is necessary to operate line finder ILF6, the hunting time will still be relatively short, since there will be but 16 operate the line finders under the same normal conditions and the hunting sequence of each line finder may be the same as that indicated in Fig. 4 (for example, L|, L2 L48 for ILF|; L9, LII] L8 for ILF2, etc.), but ball I4 of switch 5' must be arranged so as to roll counterclockwise, so that, after having passed over line group L8-L|, it will test finder ILF| then line group L48-L4 I, then line finder ILF-B, next line group L4|lL33, then line finder ILF-5, etc.

While the above arrangement may be used exactly as described without multipling the line finders, so that each line finder will appear only once in the bank of switch 5' it may also be used with multipling in order to reduce the distribution time for a finder to be chosen in second place. For example, two contacts may be arranged in front of each bank I! and line finder ILF-I may be connected between LI and L48, but also to the last one tested of two contacts between L9 and L8. ILF-2 likewise would be connected to the first of the two contacts tested, first between L9 and L8 and also to the last one tested of the two contacts between Lll and Ll6. The same applies to the other finders.

Another arrangement of the line finders with respect to the lines is shown in Fig. 6, wherein 4 banks I1 are used, each having eight distribution contacts associated with it, and wherein the eight line finders are so multipled that each appears in each one of the four distribution contact groups. In this arrangement, the ball would roll counterclockwise and the finders would hunt over the lines in ascending numerical order from four difierent normal positions. For example, Ll, L2 L68 for ILFI and ILF-5; Ll3, Ll4 Ll2 for ILF--2 and ILF-6; L25, L26 L24 for ILF'3 and ILF1, and, finally, L36, L31 L35 for ILF4 and ILF8. In that case, the order in which the eight line finders would appear in the group of eight contacts located between LI and L48 could be as follows, (counting counter-clockwise, i. e., in the direction of rotation of ball l4) ILF--l, ILF5, ILF4, ILF8, ILF-3, ILF4, ILF2, ILF6. The corresponding order in which the eight line finders will appear in the group of eight contacts located between LIB and LIZ is as follows (counter-clockwise) ILF--6, ILF-2, ILF--5, ILF-l, ILF-B, ILF-4, ILF!, ILF3. Similarly, the order of appearance of the line finders of the other contact groups should likewise be such that, after having passed over any one line group, ball l4 would test first those line finders whose hunting time is a minimum for the said line group and then test those line finders having the next shortest hunting time. Although 4 banks I! have been mentioned, a larger or a smaller number may be used. Preferably, for this type of arrangement, it would be well to provide for the various line finders as many normal positions as there are difierent banks l1. Hence, if only 3 banks I! have been provided in the switch, the line finder off-normal contacts should be arranged preferably so as to stop the finders only in three different normal positions.

Between the arrangement just mentioned, in which the line finders appear in front of each bank I1, and the arrangement previously described (but not shown), in which each bank I! is associated only with a single distribution contact, so that each line finder will appear only once, there are numerous possible intermediate solutions. For example, each line finder may be multipled two or three times, without thereby multipling it so completely that it will appear in front of each bank 11. Also, if desired, the principle on which the several line finders are operated simultaneously may be combined with the principle of operating a single line finder chosen in advance. For example, the above described selective distribution principle may be used for determining that a certain pair of line finders (for instance, ILF-3, ILF7) be the nearest ahead of the calling line group (for example, L25, L26 L36) and then the principle of simultaneous operation may be applied by operating the two line finders thus brought nearest if both of them are then free. With such an arrangement the number of distribution contacts to be provided around the circumference of the switch may be reduced somewhat.

In certain cases it is desired to use certain line finders always as overload line finders, and select them only when all the others are busy. If, for instance, it is desired to use finders ILF5 and ILF6 as overload finders, it will be advisable to provide only four banks I1, each having six distribution contacts associated with it, three of the banks being located between lines L48 and L4 l between lines LI 2 and U3, between L24 and L25 and between L36 and L31, respectively.

Each of the six line finders could then be multipled so as to appear four times, but being arranged in variable sequences in front of four segments ll. Assuming that the normal positions of the first four line finders are L48, Ll2, L24 and L36, respectively, and assuming that the ball. rolls counter-clockwise while the line finders hunt over the lines in numerical order startin from the various above-mentioned, normal positions, the six line finders could then be connected to the six distribution contacts located between lines Li and L48 in the following order (counting counter-clockwise) ILFI, ILF-4, ILF-3, ILF2, ILF5, ILF-6. In like manner, the six line finders may be connected to the six distribution contacts located between lines M3 and H2 in the following sequence (counting counterclockwise) ILF-2, ILF-l, ILF-4, ILF-3,

For the group of six distribution contacts located between lines L3! and L36 the correspondin order of appearance of the finders would be ILF-4, ILF--3, ILF2, ILF-l, ILF5, ILF--6. With such an arrangement the first line finder to be chosen for a line group would always be one of the first four that can find the line faster. The second to be chosen would be that one of the first four that is nearest ahead of the line and so on, but in all cases line finders ILF-5 and ILF-6 will be the last to be chosen and will be able to operate only if the other four are busy.

Numerous other arrangements of line finder contacts with respect to line contacts lnay be used depending upon the results desired. It is obvious, however, that the embodiment of a combined call detector and line finder distributor switch is a problem capable of many solutions involving all manner of combinations based upon staggered line finder normal positions, division of finders into regular and overload finders, and/or any other system.

While the form of the discharge device preferably used in the above described embodiments is a gas filled cold-cathode tube, normally maintained in non-ionized condition, it will be understood that automatic blocking discharge devices of other types may be employed. Thus, for instance, a screen grid high vacuum thermionic tube may be used with one of the known automatic blocking connections which serve to keep the tube in an abnormal conductive or blocking condition after the tube has been brought to this condition by momentary application of a calling potential to its grid. A device of this type is shown in Fig. 5. A gas filled hot-cathode tube, a Thyratron for example, may also be used, since this tube is also of the automatic blocking type and will remain ionized momentarily after having been brought to this condition by a momentary signal on its grid. It will be understood, however, that it is preferable to use a gas filled cold-cathode tube according to my invention and to operate it so that normally it will be de-ionized, but biased in such a way as to be capable of maintaining the ionization as described above.

Also, it will be noted that, according to one of the features of the present invention, the ground potential is applied to the far side of each finder, i. e., to the conductor of the line loop that is not connected to the fast-rotating detector switch.

In the arrangement proposed in patent application Serial No. 286,220, filed July 24, 1939, issued U. S. Patent No. 2,295,032, Sept. 8, 1942, the battery potential is applied to the far side of each line loop and the call detector devices are biased so as to respond only to a battery potential but not to a ground potential. In such a system, consequently, the presence of a low leak resistance to ground on a line could put this line out of calling condition, but would not simulate a call condition. According to a feature of the present invention, these connections are reversed so that the far side of each line loop is grounded and the detector device is connected so as to respond to a ground potential. Therefore, with such a system, a resistance leak to the ground on any line will simulate a call condition and will cause the seizure of a line finder, thus making it easier to discover defective lines. Furthermore, such an arrangement ensures that a subscriber on a defectiv line will not be prevented from calling.

It will be understood, however, that the arrangement may be reversed if desired, so as to apply the battery potential to the far side of the subscriber loop and to have the detector equipment arranged to operate in response to this battery potential.

What is claimed is:

1. In a telecommunication system, a plurality of lines, a discharge device, a switching mechanism, means for operating said mechanism for successively connecting said lines to the discharge device, means operative upon the connection of the device with the calling line for actuating said discharge device, means controlled by the device for stopping said mechanism, and means independent of said switching device for maintaining said discharge device operated.

2. In a telecommunication system, a plurality of lines, a discharge device, a switching mechanism for successively connecting said lines to the discharge device, said switching device having two sets of cooperative contacts, to the first of which said lines and to the second said discharge device are connected, means for moving said sets of contacts with respect to one-another, means operative when the second set of contacts and the contacts of the first set with which a calling line is connected come into engagement with oneanother for actuating said discharge device, means controlled by the device for stopping the relative movement of the contacts, and means for maintaining said discharge device operated after the separation of said contact sets.

3. In a telecommunication system, a plurality of lines, a discharge device, a switching mechanism for successively connectin said lines to the discharge device, said switching mechanism having a brush to which said discharge device is connected and a set of terminals to which said lines are connected, means for moving said brush to Wipe over said set of terminals, means operative when the brush engages the terminals of a calling line for actuatingsaid discharge device,

and means for maintaining said discharge deviceoperated after the brush leaves the terminals of the callin line.

4. The system according to claim 1, in which said discharge device has a gas filling, means for biasing said discharge device to such, a potential that it retains its ionization once the said ionization has been started, and means for starting the ionization of the discharge device upon its connection with a calling line.

5. The system according to claim 1, and in which said discharge device is a gas filled coldcathode tube which is normally non-ionized but biased to such a potential that it remains ionized once the ionization has started, and means for starting the ionization upon the connection of the discharge device with a calling line.

6. In a telecommunication system, a plurality of lines, a first discharge device, a switching mechanism for successively connecting said lines to the discharge device, means operative upon the connection with calling line for actuating said discharge device, means independent of said switching mechanism for maintaining said discharge device operated, a trunk line, a switch for connecting the calling line with said trunk, an operating circuit for said switch, and a second discharge device controlled by the first discharge device and controlling in turn said circuit.

7. In a telecommunication system, a plurality of lines, a discharge device, a switching mechanism for successively connecting said lines to the discharge device, means operative upon the connection with a calling line for actuating said discharge device, means independent of said switching device for maintaining said discharge device operated, a trunk line, a line finder having a brush in which said trunk line and terminals in which said lines terminate, a magnet for moving said brush over said terminals in succession, a circuit for said magnet, means for closing said circuit upon the actuation of said discharge device, and means controlled by said device for opening said circuit when the brush engages the terminals of the calling line.

8. In a telecommunication system, a plurality of lines divided into groups, a discharge device, switching mechanism for successively connecting a group of lines to the discharge device, said switching mechanism having a row of terminals in which a group of lines terminate and a brush to which the discharge device is connected, means for operating said brush continuously to wipe over said terminals in succession, means opera-.

tive upon the engagement of the terminals of a calling line by the brush for actuating said discharge device, means for maintaining said discharge device operated after the brush leaves the terminals of the calling line, a trunk line, a switch for connecting a calling line with the trunk line, and a circuit for operating said switch controlled by said discharge device.

9. In a telecommunication system, a plurality of lines divided into groups, a discharge device, switching mechanism for successively connecting a group of lines to the discharge device, said switching mechanism having a row of terminals in which a group of lines terminate and a brush to which the discharge device is connected, means for operating said brush continuously to wipe over said terminals in succession, means operative upon the engagement of the terminals of a calling line by the brush for actuating said discharge device, means for maintaining said discharge device operated after the brush leaves the terminals of th'ecalling line, a trunk line, a line *finder 'for connecting a calling line with the trunk line, said line finder having 'a brush in which said trunk line terminates and terminals in which a group-of :sai'd lines terminates, a circuit for operating the brush of said switch to wipe over the cooperating terminals, and means controlled by said discharge device for closing and opening said circuit.

10. In a telecommunication system, a plurality of lines divided into groups, a discharge device,

a-switc'hing mechanism for successively connecting a=group of lines to the discharge device, said switching device having a row of terminals to Which the groups of lines are connected in a predetermined orderand a-contact, aconnection between said contact and the discharge device, means for operating said contact continuously to wipe "over said terminals in succession, means operative upon the engagement of a terminal of a calling line by the contact for actuating said discharge device, means for maintaining said discharge device operated after the contact leaves the terminals of the calling line, a plurality-of trunk =lines, a plurality of switches for connecting various groups of lines with an idle trunk line,'a circuit for operating each switch, including the contact *o'f-said switching device and contacts controlled by said discharge device, and terminals in saidswitching devices intermediate the terminals'of groups of lines also included in said circuit.

11. In a telecommunication system, a plurality of lines divided into groups, a discharge device, a switching mechanism for successively connecting a group of lines to the discharge device, said switching mechanism having a row of terminals to which the groups of lines are connected in a predetermined order and a contact, a connection between said contact and the discharge device, means for operating said contact continuously to wipe'over said terminals in succession, means operative upon the engagement of the terminals of a calling line by the contact for actuating said discharge device, means for maintaining said discharge device operated after the contact leaves the terminals of the calling line, a plurality of line finders, each having a brush, terminals to which said lines are connected in different order, two special terminals for said switching device between the terminals-of adjacent groups, a magnet for each line finder to operate the brush to wipe over the line terminals in succession, a circuit for each magnet, each circuit including a different special terminal of the switching device, and all the circuits including a contact controlled by the switching device.

12. In a telecommunication system, a plurality of lines divided into groups, a discharge device, a switching mechanism for successively connecting a group of lines to the discharge device, said switching mechanism having a row of terminals in some of which said groups of lines terminate and a contact to which the discharge device is connected, means for operating said contact continuously to wipe over said terminals in succession, means operative upon the engagement of the terminals of a calling line by the contact for actuating said discharge device, a plurality of line finders for extending connections from calling lines, a circuit for selecting said line finders for operation in a predetermined order, said circuit including the contact and terminals of said switching mechanism.

13. In a telecommunication system, a plurality 16 of lines divided into groups, a dischargedevice, a switching mechanism for successively connecting a group of lines to the discharge device, said switching mechanism having a row of terminals in some of which said groups of lines terminate and a contact to which the discharge device is connected, means for operating said contactcontinuously to wipe over said terminals in succession, means operative upon the engagement o'f the terminals of a calling line by the contact for actuating said discharge device, a plurality of line finders for extending connections from calling lines, a circuit for selecting said line finders for operation in a predetermined order, said circuit including the contact and terminals of said switching mechanism and said discharge device.

14. In a, telecommunication system, a plurality of lines divided into groups, a discharge device, a switchin mechanism for successively connecting a group of lines to the discharge device, said switching device having a row of terminals in which said groups of lines terminate and a contact to which the discharge device is connected, means for operating said contact continuously to wipe over said terminals in succession, means operative upon the engagement of the terminals of a calling line by the brush for actuating said discharge device, a plurality "of line finders for extending connections from calling lines, a circuit for selecting a, line finder for operation including terminals of said mechanisms, a discharge device associated with each line finder, and means jointly controlled by the first-mentioned discharge device and the discharge device associated with the selected line finder for stopping the latter on the calling line.

15. In a, switching system, a plurality of lines, a plurality of switches each having a'bank of multipled terminal sets in which said lines terminate, and a set of wipers arranged to wipe over said terminals, magnets for controlling the movement of the switch wipers, sources of potentials of various characteristics, connections for placing characteristic potentials on terminals of lines depending on their condition, a multi-electrode electric discharge device, a first circuit for applying a potential to one electrode, a second circuit for applying to a second electrode the potentials existing on the terminals engaged by said wipers, said device being adjusted to operate when the potentials applied over the two circuits bear a predetermined relationship to one-another, and means actuated upon the operation of the device for controlling said magnets to stop the wipers.

16. The system according to claim 15, and in which coincident with the-operation of the device the potential is altered on the terminal with which the second electrode of the device is connected.

1'7. The system according to claim 15, and in which the device is provided in common for a plurality of switches.

18. The system according to claim 15, and in which a device is provided for each switch.

19. The system according to claim 15, and in which the device is a gas-filled discharge tube having a cold cathode in the first circuit, a control anode in the second circuit, and a main anode connected with a relay constituting the last-mentioned means.

20. The system accordin to claim 15, and in which the device is a gas-filled tube having a cathode in the first circuit, a control grid in the second circuit, and an anode connected with a relay constituting the last-mentioned means.

21. The system according to claim 15, and

' 17 means independent of the second circuit for maintaining said device actuated.

22. The system according to claim 15, and means controlled by the device for controlling through the magnet of a switch the starting and the stopping of th switch wipers.

23. In a telecommunication system, a plurality of lines, a plurality of non-numerical finder switches each having a bank of multipled terminal sets in which said lines terminate, a set of wipers for each switch cooperating said terminal sets, said sets of wipers and terminals including one for testing, a magnet for each switch and a circuit therefor controllin the movement of the switch wipers, a source of DC. potentials, means for placing characteristic potentials on the test terminal of a line depending on its calling, idle or busy condition, means including a multi-electrode electric discharge device for causing one of the switches to hunt for the calling line, a first circuit for applying a potential to one electrode, a second circuit for applying to a second electrode the potentials existin on the test terminals over the test wiper of a switch, said device being adjusted to operate when the potentials applied over the two circuits bear a predetermined relationship to one-another, means coincident with 18 r the operation of the device for altering the pctential on the test terminal, and means actuated upon the operationnof the device for controlling said magnet circuit to stop said wipers.

24. The system according to claim 23, and in which the discharge device is common to said finder switches.

25. The system according to claim 23, in which a multi-electrode discharge device is associated with each finder switch, and means operated by each device for controlling the closing and the opening of the magnet circuit of the associated finder.

GERALD DEAKIN. WILLIAM HATTON. 'LUCIEN A. B. (BABES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,242,776 Clark May 20, 1941 2,295,032 Deakin Sept. 8, 1942

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