US2409145A - Control and trigger circuit for telephone systems and the like - Google Patents

Description

Oct. 8, v1946. F A, MQRRls 2,409,145

CONTROL AND TRIGGER CIRCUIT FOR TELEPHONE SYSTEMS AND '.lI-IE LIKE Filed sept. 2e, i944 4 sneetsfsneet 1 7'0 OTHER LINES /A/ SHME TE' N5 GPO/IP IN V EN TOR.

F 19H/VK H. MOR/PAS Hf 7' OHNE Y 946. F, A MORRlS 2,409,145

CONTROL AND. TRIGGER CIRCUIT FOR TELEPHONE SYSTEMS AND THE, LIKE 4 sheets-sheet 2 Filed Sept. 26, 1944 IN VEN TOR.

FFH/VK H MORE/5 F. A MoRRls 2,409,145

CONTROL AND TRIGGER CIRCUIT FOR TELEPHONE SYSTEMS AND THE LIKYE1 Oct. 8, 1946.

Filed Sept. 26, 1944 4 Sheets-Sheet 3 NNN .nu N.

ASN MSN 8, 1946. F. A. MORRIS CONTROL AND TRIGGER CIRCUIT FOR TELEPHONE'SYSTEMS AND THE LIKE Filed Sept. 26, 1944 4 Sheets-Sheet 4 i car-off /Pay l 60 Y T- 6 60 jr' 4 f .sro/P//ve /mfy 54 I UNE c//icz// L//vE F//voE/i 39 60 j /sr L//vk *Lv f 33 60j 2ND L//vx ML 6 H') L1- 163 y. 6 [44 I 124 SUPFR/Mosfo 132 /Nrfmvaprfo JUPERIMPOSED Gf/VERHTOR x 1,23 /Nr-RRUP T50 i. L GFA/ERHTo/ l M5575@ @Roz/No L-/Wyx 9 1,24 Y

12m 200` e) f y '\/\(V\, le@ IN V EN TOR. l 202 20] l ffm/vx H. Mom/5 J30- Q BY l/ v f Y Leef- Patented Get. 8, 1946 CONTROL AND TRIGGER CIRCUIT FOR TELEPHONE SYSTEMS AND THE LIKE Frank A. Morris, Rochester, N. Y., assignor to Stromberg-Carlson Companyyltochester, N. Y., a corporation of New York Application September 26, 1944, Serial No. 555,850

rlhis invention relates to stopping, triggering and testing circuits which are particularly useful in telephone systems and the like.

In such systems and especially in automatic telephone systems, it is important that the automatic switch means employed therein be promptly stopped as soon as a given switching connection has been effected. Also in such systems, it is necessary to test certain equipment, such as lines, trunks or allotters to determine whether or not such equipment should be seized for use. Such testing should be effected in a reliable manner and in an innitesimal period of time. Furthermore, both in automatic telephone systems and in manual systems as well, trigger circuits are essential especially for tripping the ringing current when the called subscriber answers.

The main feature of the invention relates to control circuits generally, wherein electric discharge devices contribute to the reliability and markedly prompt action thereof.

Another feature of the invention relates to novel control circuits incorporating therein electric discharge devices, which circuits determine the availability for use of telephone equipment, govern the action of telephone switching apparatus, and trigger the operations of telephone apparatus.

The various features and advantages of the invention will appear from the detailed description and claims when taken with the drawings in which Figs. 2 and 3. when arranged in the order named, illustrate the novel circuits of this invention incorporated in an automatic telephone system. Fig. l shows two typical telephone lines and duplicate allotter control means. Fig. 2 illustrates an allotter and a portion of aline nder, certain of the brushes oi which are shown at the lower right of this ligure. At the left hand side of Fig. 3 there` are shown the remainder of the finder brushes, while at the center and at the right hand portion of this figure, there is shown the connector switch circuit. Fig. 4 is a schematic circuit arrangement illustrating in somewhat simpler form a low voltage ring circuit for a gas-filled arc discharge device utilized to stop the finder switch in the system of Figs. l, 2 and 3. Fig. 5 is a simplied disclosure of the testing arrangement employed in the mentioned system, two links being shown to indicate the condition prevailing when a busy line is tested. Fig. 6 is a modified form of ringing trip arrangement or trigger circuit which can be substituted for that used in the connector circuit of Fig. 3. Fig. 7 illustrates a trigger circuit of somewhat more 20 Claims. (C1. 179-4752) 2 generalized application than the specic arrangement shown in Fig. 3.

The novel control circuits herein shown, are applicable to many fields of use, but for convenience in disclosure they are shown incorporated in an automatic telephone system. This system is herein illustrated as being of a size employing only nder and connector switches. However, the number of lines served by the system can be increased by the addition of selector switches in the manner well known.

The finder and connector switches herein lndicated, are of the construction disclosed in the patent to Lienaen No. 2,148,824, granted February 28, 1939, although other types of switches having primary and secondary selecting movements may be used instead. The allotter herein indicated may be of the so-called ball-selector type, disclosed in the patent to Blomberg No. 2,127,322, although other types of allotter switches may alternatively be used.

With this brief reference to the switch construction, it is believed that the invention will best be understood by describing the method of establishing a telephone connection from a telephone subscribers line, indicated at A, to a called subscribers line, indicated at B. When the subscriber at substation A removes his receiver from its switch-hook, a circuit is completed for energizing the group line relay 5 which is common to a group of ten lines in the same tens group. This circuit extends from ground, winding of the relay 5, upper back contact and armature of the cut-off relay 6, upper side of the calling line, thence, through the calling substation and over the lower side of the calling line, lower` armature and back contact of the cutoi relay 5, resisto-rs l and 8 in series to the negative side of battery. Condenser S is connected in parallel with the resistor 8 so that the drop across resistor 8 charges the condenser 9, thereby putting an identifying condition on the calling line hunt terminal I0, in the terminal of the group of finder switches serving this line. The operation of the common line relay serves to start an allotted nder to search for the calling line, and also serves to place an identifying ground on the group level ll (Fig. 1) in the line under banks. It will be noted that the upper armature of the line relay 5 is provided with two contact springs I2 and I3 which close in sequence. This insures that the identifying ground will be applied to the group level Contact li in the line finder bank, before the line finder starts to move. The start of the line nder is elected from ground at the upper armature of 3 group relay 5 and front contact I2 thereof, now closed, as well as the front contact I3 subsequently closed, thence, over conductor I4, armature and back contact of the relay I5, conductor I6, back contact and armature of relay I'l, conductor I8, winding of the allotter start relay I9, to negative battery. The operation of the allotter start relay I9 applies ground at its upper armature and front contact for completing a circuit through the armature and back Contact of the relay 2i), armature and back contact of the relay 2|, conductor 22, winding of the relay 23 to the negative side of battery. It should be pointed out that the relay 23 is sluggish not only in attracting its armatures but also in releasing them. The purpose of having the relay 23 sluggish in operating, is to hold open its armature 24 and front contact for a slight interval, to insure that the circuit of the primary stepping magnet of the nder is not completed until the pre-impulse circuit has an opportunity to function. The preimpulse circuit is energized by ground, applied at the inner front contact and armature of the re lay I9, conductor 25, allotter switch contact 23, conductor 2l, current limiting resistor 23, section 29 of the link conductor, lower winding of the combined battery feed and impulse relay 353, to the negative side of battery. Relay 3i) is energized in this circuit and at its upper armature and front contact removes ground from release conductor 83 while completing an obvious circuit for energizing the slow-releasing relay 3| of the connector. Relay 3| thus operates and at its armature 32 and front contact applies master ground for the various circuits or the connector. It will be recalled that the relay 23 is slow to operate and that during the time that it is attracting its armature 2li, the pre-impulse circuit, as described, has an opportunity to be completed. When, however, the armature 2li and front contact of relay 23 is closed, a self-interrupting circuit is completed for the primary magnet t of the finder switch. This circuit extends from the negative side of battery, winding of primary stepping magnet 34, its armature and back contact, through the normally closed olif-normal contacts 35, contacts 36 of the allotter switch, front contact and armature 2Q of relay 23, back contact and armature ofrelay 2 I, back contact and armature of allotter relay 2i), front contact and armature of relay I9, to ground. Under the control of this circuit, the primary stepping magnet advances the tip brush 3l, ring brush 38, sleeve brush 39 (at left of Fig. 3) and hunt brush liu (at right of Fig. 2) in their primary or group selecting movement. Also, the stepping magnet advances the group selecting brushes 4| (at the right of Fig. 2) and 52 (at the left of Fig. 3) in their primary direction. The primary stepping magnet 34 continues to self-interrupt its operating circuit and thereby advances the mentioned nder brushes until the rlnder brush 4I encounters the level contact |I (upper left Fig. 1) of the group of lines in which the calling line is located. As soon as the brush lll encounters the contact |I, this completes a circuit from ground at the armature and contact i2 of relay 5, group contact II, finder brush 4I, allotter brush 43, conductor 44, winding of allotter transfer relay 2 I, to the negative side ci battery. This energizes the relay 2| and at its uppermost armature and front contact it opens the self-interrupting circuit of the stepping magnet 34, thereby stopping the primary movements of the nnder switch. Also, the operation of the relay 2| at its inner armature and back contact, opens the energizing circuit of the relay 23. This relay, it will be recalled, is also sluggish in releasing its armatures. The purpose of this sluggishness is to provide a delay sufficient for the nder switch to come to rest definitely, after its primary hunting movement and before its secondary hunting movement is started. However, after a very brief time, the slow-releasing relay Z3 does release and thereby completes a self-interrupting circuit for the secondary magnet i5 extending from the negative side of battery, winding of this magnet, its armature and back contact, allotter brush l's, back contact and armature of relay 23, front contact and armature of relay 2|, now energized, back contact and armature cf relay 20, front contact and armature of allotter start relay i3 to ground. Under the control of this circuit, the secondary stepping magnet fit advances the nnder brushes 3l, 5, 39 and in their units or secondary hunting direction. This hunting operation continues until the brush lil encounters the hunt terminal I (Fig. l) of the calling line. It Will be recalled that when the subscriber of this line initiated a call, he set up a condition whereby the condenser 9 was charged. Consequently, when the nder brush ri encounters the hunt terminal Iii, a circuit is completed from the negative side of battery, primary winding 48 of a step-up transformer (Fig. 2), front contact and armature 4S of the allotter start relay, conductor El), allotter contact 5I, nder brush t0, hunt terminal I0, through the condenser S, to negative side of battery. This circuit discharges condenser 9 through the primary winding 48 of the transformer. This discharge induces a voltage in the secondary winding 52 of the transformer which voltage is applied ,through the condenser 53 t'o the starter anode 54 of the finder stopping arc discharge device 58. The arc discharge device is gas-lled and preferably of the cold cathode type, sold under the code 1G21. This device comprises the cold cathode 55, the starter anode 54 and the anode proper 55. The mentioned induced voltage, when applied to the starter anode 54, causes the nder stopping device 58 to conduct. As a result of this, the allotter control relay is energized from the positive side of battery through the capacitive network 59 and 6G, winding of the relay 25, across the space between the anode 55 and cathode 55 of the discharge device 58, conductor 7|, lower front contact and armature of relay |9 to ground. The relay 2) is thus energized and at its inner upper armature and back contact, it interrupts the stepping circuit for the secondary stepping magnet 45 so that the brushes of the nder come to rest. The arrangement, just described, for stopping the secondary movement of the iinder switch is shown in simplified form in Fig. 4.

It now becomes necessary to test the calling line to make sure that it has not been seized as a called line by a connector, which condition may have arisen during the time that the finder switch in question was hunting for the calling line. As soon as the allotter control relay 2) operates, it also completes the necessary circuit for testing the busy or idle condition of the calling line, for the purpose just mentioned. The busy test is accomplished by the cold cathode arc discharge device 5I, preferably similar in construction to the device 58, in cooperation with the busy test circuit. When the starter anode causes the gas in the device to ionize the busy test circuit extendsl from the source of high positive voltage of the order of 150 volts, anode B2, cathode 6A, conductor 55, armature and front contact of relay 2li, conductor 56, allotter brush El, conductor 58, upper winding of the connector cut-through relay $3, nder sleeve brush 39, finder sleeve contact Se', which is individual to the calling line, winding ci the cut-off relay 6 to the negative side of battery. Current ows in this circuit and cnergizes the cut-off relay 6 to disconnect the group line relay l? from the control of the calling line and also energizes the cut-through relay B9. lt should be mentioned that the electron discharge device 6| is adjusted by means of a potentiometer P across its -cathode and anode so that it will be conductive when sufficient voltage appears between its cathode Gd and starter anode E53. When the busy test lead, including the conductors S6 and S8 and iinder sleeve brush 39. is extended through the sleeve terminal of the calling line in the multiple bank, the circuit is completed in such a way that the sum of 15G volts plus 48 volts appears across the device Si, if the line is in an idle condition. The potentiometer P is adjusted so that the discharge device (il will become conductive when these voltage conditions are present. When the device becomes conductive, the circuit is then completed and the cut-off relay o and cut-through relay @il become energized in series in the manner above described. When current begins to ow in this circuit, a voltage drop appears across the cut-off relay E s0 that the voltage on the sleeve terminal of the calling line in the multiple bank no longer appears to be 4S volts negative, as schematically indicated in Fig. 5. Thus, any

other busy test lead of another link circuit will f not encounter sufficient voltage on its busy test brush, to ionize the gas in its busy testing device similar to El. rEhe time required for the busy test to be completed and the line to be made permanently buey to any other link, is thus reduced to the ionization time of the discharge device, a matter of microseconds, as compared with operating time or a relay which may be several milliseconds. This shortening of the unguarded interval reduces the possibility of double connections.

The cut-thrcugh relay ES its upper airmatures and front contacts, extends the calling line through the lnder brushes 3l and 3B, through both windings in series of the impulse relay 3s, to ground and grounded battery respectively. Also, the operation of the cut-through relay 69 at its armature 'lil and front contact, closes a locking circuit for itself from the master ground, through its lower winding, resistor "il to the negative side of battery. Also, the cut-through relay at armature "i90: and front contact applies master ground through the Finder sleeve brush 39 and to the terminal Sil' of the calling line (Fig. 1) thereby rendering the calling line busy and also locking up the cut-oil relay Master ground is also supplied through the armature l) and front contact of the cut-through relay 63, conductor l2, normally closed fed-normal contact i3 o f the connector, lower winding of the primary motion delay relay ll of the connector, to the negative side of battery. Relay lll is of the slowreleasing type. .es soon as relay 'li is operated, it applies a dial tone over conductor l5, armature and back contact of relay lili?, front Contact and armature of relay ld, conductor l5, condenser 'll and thence over the ring side of the link and the calling line to the calling subscribers substation. This tone, of course, signals the calling subscriber that the dial-controlled apparatus is in condition to receive dialling impulses.

If the finder busy test device 5l indicatesa busy condition on the calling line, brought about by a connector seizing this line during the hunting interval, this device will not become conductive and the connector cut-through relay 69 (Fig. 3) in series with it, will not be energized. The talking connection will thus not be cut through and when the allotter advance relay il operates, as will be described, and the allotter delay relay 23 releases, the pre-impulsing ground will be removed, the connector battery feed and impulsing relay gli and the connector delay relay 3l Will also release and the release signal will be returned to the line finder release magnet 8l (at right of 2). This will release the link seized by the calling party and he will be able to talk through the connection established by the connector which had seized his line during the hunting interval.

Before describing the operation of the connector in seizing the called line in response to the dial impulses, it will be set forth how the allotter is released from this call in the course of the completion of the line nding operation and how the allotter preselects an idle link for a succeeding call. This is brought about when the allotter control relay 2D (Fig. 2) is operated, thereby completing a circuit from ground, upper iront contact and armature of relay I9, inner armature and front contact of relay 20, conductor 22, winding of the slow operating relay 23 to the negative side of battery. This relay is slow to operate for the purpose of giving a suflicient interval of time for the iinder busy test circuit including the device 6| to operate. As soon as the relay 23 does operate, it closes a circuit from ground on the lowermost front contact and armature of relay 2B, lower front contact and armature of relay 23, upper winding of the relay l1, to the negative side of battery. LThe relay l1 is thus energized and at its upper, inner armature and back contact it opens the allotter start circuit which it will be recalled included the winding of the allotter start relay I9, thereby causing this relay to deenergize. Relay Il, at its lower armature and iront contact, closes a locking circuit for itself through its upper winding and through its lower armature and front contact, to ground applied to conductor 18, through the armature and back contact of the allotter busy relay 19. It should be mentioned that this allotter busy relay 19 is normally operated as long as the link is idle but as soon as the link is taken for use, relay I9 deenergizes. The energizing circuit for the allotter busy relay 'I9 which is closed as long as the link associated with this relay is idle, extends from the negative side of battery, upper winding of the relay i9, the allotter brush Se (at right of Fig. 2), armature and back contact of the nder release magnet 8l, armature and back contact 82 of the connector release magnet, to be described, conductor 83, back contacts and armatures of relays 3l and 3i) (Fig. 3) to ground. It will be noted that when the link is taken for use, this energizing circuit for the allotter busy relay 'I9 is interrupted at the armatures and back contacts of both relays 3G and 5 i Vfhen allotter busy relay 19 releases, it places a ground on the conductor l, this ground being applied over conductor Sli, back contact andA armature of the allotter start transfer relay l5, to ground. As soon as'the relay l1 was energized, it interrupted the operating circuit of the allotter start relay I9. This relay deenergizes and at its uppermost armature and front contact interrupts the circuit which has been holding the slow operating relay 23 (Fig. 2) in its operated condition. When the relay 23 releases, it completes a circuit for advancing the allotter to seize an idle link. This operating circuit effects the energization of the relay 85 from the negative side of battery, winding of this relay, back contact and armature of the allotter motor magnet 85, conductor 81, back contact and armature of relay 23, armature 88 and front contact of relay 1, to ground potential that is now present on the conductor 18, as described above. Relay 85 is thus energized and at its front contact and armature, closes in multiple with its energizing circuit, an operating circuit for the motor magnet 86. This circuit extends from the negative side of battery, winding of this magnet, front contact and armature of relay 85 and thence over the conductor 81 and the remainder of the circuit, previously described, to ground potential present on the conductor 18. This operates the magnet 85 to advance the allotter. Also, the armature of the motor magnet 86 interrupts the circuit of the relay 85. Thus, the relay 85 and 86 operate together in a pulse assuring arrangement, sometimes referred to as flip-nop operation. Under the control of this arrangement, the allotter advances until the brush 80 of the allotter encounters the terminal associated with an idle link, which terminal will be characterized by the presence of ground potential thereon. This ground potential is applied over the conductor similar to conductor 83 and thence over back contacts and armtures of relays corresponding to 3| and 30 to ground. When an idle link is located, the mentioned ground potential is applied through the allotter brush 80, lowermost armature and front contact of relay |1, low resistance Winding of the allotter busy relay 19 and the negative side of battery. Also, ground is applied through the upper high resistance winding of this relay to the negative side of battery. The completion of the circuit through the lower winding of this relay, which is of low resistance, insures that the relay will receive a surge of current, causing it to operate promptly. The operation of the relay-19, at its upper armature and back contact removes ground potential from the conductor 18 and thus insures that the relay 85 and the allotter motor magnet 85 cease to operate.

It will be recalled that at the point where the dial tone had been applied to the calling line to indicate that the connector was in readiness to receive dial impulses, the description was interrupted to explain how the allotter operated to assign an idle link for use. It will be understood, however, that in normal operation these operations take place simultaneously. On receiving the dial tone, the calling subscriber operates his d'al sender to transmit impulses corresponding to the tens digit of the wanted number. In response to each of these tens digit, the impulse relay 30 releases its armature to complete a circuit for operating the primary stepping magnet 89 of the connector. This circuit extends from the negative side of battery, winding of this magnet, conductor 90, through the very W resistance winding (3 ohms) of the relay 14, its upper front contact and armature, front contact and armature of relay 3|, back Contact and armature of the impulse relay v3|) to ground. In response to each of the tens impulses, the stepping magnet advances the tip, ring and sleeve brushes 9|, 92 and 93 and connector hunt brush 94 and also the group brush 95 of the connector. As soon as the connector switch takes its rst step oi normal, it opens its o normal contact 13 (top center Fig. 3). This interrupts the initial operating circuit of the relay 14, insuring that this relay will not reoperate until the connector switch has been fully restored to normal. However the relay 14 is maintained operated through its upper Winding during the reception of the remainder of the tens impulses. At the conclusion of the tens series of impulses, the relay 14 will deenergize because its locking circuit is interrupted at the back contact and armature of the impulse relay 30. As soon as the connector switch moved off normal in its primary direction, it closed a circuit through its normally open primary oi normal contacts 91 and through its normally closed secondary oi'f normal contacts 98, high resistance, lower winding of the slow releasing secondary delay relay 99, to the negative side of battery. This relay is thus energized preparatory to receiving the units series of impulses. Thus, when the impulse relay 30 responds to the units series of impulses, the secondary motor magnet |00 will be operated in a circuit extending from the negative side of battery, conductor 0|, low resistance winding of relay 99, its front contact and armature, back contact and armature of relay 14, now released, front contact and armature of relay 3| back contact and armature of the impulse relay 30 to ground. Thus, in response to each unit impulse, the mentioned circuit will be completed to operate the secondary motor magnet which advances the brushes of the connector switch in their secondary direction. As soon as the secondary delay magnet 99 operated, it closed a circuit from ground through its armature |0| and front contact, lower winding of the slow releasing connector busy delay relay |02 to the negative side of battery. The operation of the relay |02 disconnects the dial tone and closes a break point in the test circuit. Consequently, when the secondary delay magnet 99 releases at the conclusion of the series of units impulses, thereby closing a second break point in the tes circuit, and when the connector brush 93 is resting on the test terminal of the called line, the testing of that line can be effected. If the called line is idle, the starter anode |05 of arc discharge device |03 will become conducting in the same manner as the arc discharge device 6|, as described above. When discharge device |83 becomes conducting, a circuit from the positive source of battery, anode |04, cathode |06 of the device, lower winding of the busy test relay |01, lower armature and front contact of relay |02, armature |08 and back contact of relay 99, conductor |09, connector brush 93, sleeve terminal ||0 (Fig. 1), winding of cut-off .relay of the called line to the negative source of battery. The relay |01 is operated in this circuit and at its upper front contact and armature locks itself operated to master ground. The relay |31 at its uppermost armature and front contact applies ground over conductor H2, back contact and armature |08, conductor |09, connector brush S3, sleeve terminal ||0, thereby locking up the cutoff relay This application of ground to the sleeve terminal ||0 of the called line makes this line permanently busy to any other link. Relay |01, when it operates, prevents the application of busy tone at its armature ||3 and back contact. At the armatures ||4 and ||5 and iront contacts of relay |01, the link is extended through the tip and ring brushes 9| and 92 of the connector to the terminals of the called line, in readid iiess for applying the ringing current to this line.

If the connector arc discharge device |03 indicates a busy condition of the called line, this discharge device will not become conductive and the connector busy test relay lill in series therewith will not become energized. When the connector b d y relay |92 then releases, busy tone will be extended through the armature i i3 and back contact or the connector busy test relay lill, armature and back contact of the connector busy delay relay H82, conductor 26, armature and back contact of the connector primary motion delay relay M, conductor l, and through condenser l? to the ring side of the link and or" the calling line.

Ringing current is now applied 'to the called subscribers line from the ringing generator, through the ringing delay device H8, which ai'- fords suicient time for the ringing trip heater type gas tetrode iig to become available for D- eration. The ringing circuit extends from the device llt, over conductor |29, upper armature and back contact or" the ringing trip relay li, conductor i222, armature i iii and iront contact, through the tip brush 9| of the connector and thence over the calling subscribers line and station B, thence through the ring brush Q2 of the connector, front contact and armature H5, conduc-tor its, armature and back contact of trip relay |25, resistor ld to ground. Interrupted superimposed ringing current is applied over the circuit just described to signal the called subscriber at'B. During the time that the ringing current is being applied, a ringing tone is transmitted back to the calling subscriber, this tone being applied over conductors |22 and 25, armature and front contact or" relay itl, back contact and armature of relay |522, conductor |26, back contact and armature or" relay lil, conductor le, condenser ll' and to the ring side of the calling end of the link to the calling subscribers substation.

When the called party answers by removing his receiver from its switch-hook, a direct current circuit is extended through the called substation B. This sets into operation the ringing trip circuit which may be described as follows: An electron discharge device lle has been maintained in its non-conducting condition by means of the negative bias supplied over potentiometer 28 through resistor |29 to the control grid of this device. The alternating current voltage which exists across resistance |25 during the ringing period does not affect the bias of this tube since the cathode ilgb and grid liga are maintained at the same potential being coupled on an alternating current basis by condenser |39. Thus, alternating voltage will not fire the tube. However, when direct current continuity is established in the ringine circuit, as a result of the subscriber answering as just described, a constant drop occurs across resistance |2li which is negative as it is applied to the cathode oi the ringing trip device H9. This in effect reduces the bias on the ringing trip device and the device becomes conductive. The conducting circuit then extends from the grounded side of resistance 52e through ringing trip device H9, conductor itl, armature and front contact of relay l, conductor 232, armature and back contact of relay S33, lower winding of ring trip relay |2I, to a positive source of voltage of the order of 150 volts. When the ringing trip relay operates, it locks up to master ground at its uppermost armature and iront contact. At its inner armatures switchhook, the impulse relay Se deenergizes.

At its armature and iront Contact, it interrupts the circuit of the slow-releasing relay 3| which on releasing disconnects master ground from the various circuits. This relay at its upper inner armature. and back contact, applies a release ground to release conductors |54 and 83 which energize the connector release magnet |35 and nnder release magnet 5|. These magnets, on operating, release the connector and the finder switches respectively, allowing them to return to their normal idle positions.

In systems or this type it is frequently desirable that a called subscriber be provided with two or more lines so that in the event that the iirst one oi these lines is busy, a second or third will be available so that the subscriber can always be reached. This arrangement is commonly known as consecutive number hunting, since in originating a call, the calling subscriber will dial the number assigned to the called subscriber and in the event that that line is busy, the connector will hunt over the remaining lines of a group assigned to the given subscriber until a line is found that is idle. To achieve this end, a vpermanern; ground is placed on the connector hunt multiple i-l oi all numbers in the consecutive group except the last. When the connector switch rests on the iirst number of the consecutive group, ground is red from the multiple bank contact 35 through connector hunt brush S4, conductor 35, back contact and armature of relay 9d, conductor iSi, baci; Contact and armature oi relay itil, to conductor |38. This ground is extended to the busy delay relay m2 so that the test may be made over the regular busy test circuit. In the event that the rst line in the consecutive group is busy, the electron discharge device iiiwill not become conductive and thus relay le? will not be energized. rhe ground potential is applied from conductors |36 and |39 through the back contact and armature of the connector secondary motor magnet ll through the winding oi the connector pulse assuring relay li to negative battery. The operation of this relay lilo completes a circuit through its front contact and armature, extending ground to the secondary motor magnet ,thus advancing the switch to the second line in the group. The connector sleeve brush sli then rests on the second line in the consecutive group and the busy test is again applied in the same manner as described previously. il" the second line in the group is also busy, the relays illl and Eile will operate together in the pulse` assuring arrangement to advance the connector switch in its secondary motion until either an idle line is found and out through by the conventional busy test operation or if all the lines in the group are busy, ground no longer appears on connector hunt brush 94 and relay H32 will be deenergized to allow busy tone to be applied to the calling subscribers line. Relay |37 operates to interrupt the operating circuit of magnet ltdwhen an idle line is found.

Frequently in systems of this type, the connector is provided with a series of trunks leading to a distant exchange. In such a system, when a calling subscriber of the local exchange wishes to reach a distant exchange he will dial a single digit. In response to this single digit, the connector will operate to effect its group selection after which this connector will operate to hunt for an idle trunk in the group selected. This is accomplished in this system by extending a lead from one of the group multiples into all connectors in this office. In the connector circuit under discussion, this is lead number |4| (Fig. 3). Upon the completion of the series of tens impulse, ground is extended from master ground in the connector through normally opened primary off normal contacts 91, and the normally closed secondary off normal contacts S3 through back contact and armature of relay 14, conductor |42 'to the connector brush 95. If the number dialed brings the connector brush 95 into contact with lead |4|, the group is thus identified as a trunk group and the hunting circuit is energized. This circuit extends from negative battery through the winding of relay |40, armature and back contact of magnet |00, lead |39, armature and back contact of relay |01, lead |31, armature and front contact of relay 99, which is in its operated condition, conductor |4|, connector brush 95, conductor |42, armature and back contact of relay 14, through the off normal contacts 91 and 98 to master ground. This sets into operation the pulse assuring arrangement of relay |40 and magnet |00 which act to advance the brushes in their secondary motion. As soon as the trunk group is reached, a circuit is completed for energizing relay |43. This circuit extends from negative battery through winding of relay |43, make before break contact of this relay, conductor |14, lead |4|, connector brush 95, lead |42, armature and hack Contact of relay 14, the off normal contacts 91 and 98, to

master ground. The operation of relay |43 acts to remove battery and ground respectively from relay |33 and to interconnect the windings of this relay so that it becomes merely an impedance across the called trunk. This interconnecting path extends from lead |44 to relay |33,

through lead |45, armature and front contact of relay 30, lead |46, armature and front contact of relay |43, lead |41 to relay |33. The operation of relay |43 also extends ground through its armature and upper front contact, through lead v|48 to energize the upper winding of relay |2|,

thus immediately tripping the ringing current and thereby preventing ringing current from going out on the trunk. The switch now hunts in the secondary motion direction. As soon as the switch moves off normal in its secondary direction, contact 98 opens, thus interrupting the circuit of relay 99. When this relay falls back, ground is continued from multiple bank terminals opposite the connector hunt brush 94 and pulsing is completed in the same manner as in consecutive number hunting, the busy test being applied at each step. When an idle trunk is found, the busy test device |03 becomes conductive and the talking connections are cut through to the trunk in the conventional manner.

Several safety features have been employed in the design of this system to protect the mechanism and circuits from extensive tie-ups due to Yfailure of parts or dirty contacts in relays which hinder'the closing through of circuits. One of these features involves the use of the gas filled 12 cold cathode arc discharged device 53 which lsl also used to stop the line finder in its secondary hunt motion. It will be recalled that as soon as the master start ground is applied to the circuit by means of the group line relay 5, the allotter stop relay I9 (Fig. 2) is energized. The operation of this relay closes through a circuit extending from a positive source of voltage through variable resistance |10, front contact and armature |1| of relay I9, conductor |12, to condenser |13, thence over conductor 1|, front contact and armature of relay |9, to ground. Resistance |10 is adjusted so as to permit condenser |13 to charge slowly and so that the rise in potential appearing across this condenser will not be sufficient to re arc discharge device 58, this voltage being applied to starter anode 54 through protective resistance |16 until sufficient time has elapsed for the normal operation of the allotter and the line finder. If this time is exceeded, the ring of the device 58 will cause the operation of relay 20 as if the device had been red through current flowing in winding 48 in a normal manner and the allotter will thus release. If, however, the allotter successfully completes its operation, the charge of condenser |13 will be removed upon the release of relay I0, over the path which can be traced from condenser |13 through conductor |12, back contact and armature of relay |9, through resistor |18 and back to condenser |13.

In the event that the line finder goes to the overflow position due to failure of the allotter transfer relay 2| or some failure in the secondary motion circuit, the arrival at the overfiow position of the switch will close the overflow contact |50 (Fig. 2) in the switch itself which will return a ground through allotter brush 5| to the hunting lead 50 of the line finder. This pulse of ground will be transmitted through the armature 49 and front contact of relay I9 and through the primary winding 48 of the transformer. The voltage induced in the secondary winding 52 of the transformer initiates conductivity in the electron discharge device 58 which will again simulate the completion of the line finding operation. The allotter and line finder will be released as previously described and a new link will be seized.

This system is particularly adapted for use in remote and unattended branch exchanges. Therefore, adequate protective devices must be incorporated therein so that extensive tie-up of service will not occur. Since the relays in the first allotter are common to all the links in the systems, it is necessary to provide a secondary allotter which will function in the event of failure of the first. In order that this secondary allotter will not stand idle during functioning of the first allotter, the system is arranged so that each will serve one-half of the lines and one-half of the links in the system. A transfer circuit is incorporated which will allow the lines served by the first allotter to start the secondary allotter in the event of the failure of the first. If all the links served by the first allotter are busy, a ground is extended through normally open off-normal ycontacts |5| (upper left in Fig. 2) in series of all .negative side of battery. When this relay is energized, any master start ground which comes from the group line relays, such as 5, which are ordi- Anarily served by the first allotter will be transferred to the master start lead |52 (Fig. 1) of the second allotter. Thus, the second allotter will respond to signals from all the lines in the system. When any link served by iirst allotter again becomes idle, allotter start transier relay i will be deenergized and will again allow signal ling from the group line relays ordinarily 'served by the rst allotter to be transmitted into this allotter. if allotter start relay l5 is energized and a signal from any group line relay, such as 5 ordinarily served by the first allotter, is tran-smitted into the second allotter, the operation of the allotter start relay ES in the second allotter, will complete its cycle of operation. This is eifected by a circuit extending from ground through the lowermost armature and front contacts of an allotter start relay similar to relay i9 (at left of Fig. 2), conductor l d8, armature and front contact of the number one allotter start transfer relay i5, the lower winding of this relay. to the negative side of the battery. This maintains allotter start transfer relay |5 in number one allotter in its operated position until the com pletion of the line finding operation and thus pre'- vents this relay from being deenergized in case a link. ordinarily served by this allotter becomes idle during that hunting period of the iinder started by the number two allotter.

As soon as a group line relay similar to relay 5 is energized, a circuit is closed which energizes the allotter failure relay |55. The operation of this relay opens a contact which removes ground from the allotter failure circuit. This allows condenser |55 to start charging through resistors |55 and iig. The charging circuit extends from a positive source of voltage, of the order of 150 volts, through the upper winding of the allotter start transfer relay i5, through resistors |79 and |56 to condenser |55, and ground. In the event of mechanical failure of certain relays in the allotter circuit or mechanical failure of the allotter motor magnet 85 (Fig. 2), the allotter would not move to seize a new link and any subsequent calls would not be completed. The condenser |55 then charges through this circuit until the voltage on the starting anode |59 or" the electron discharge device itil (Fig. 1) becomes high enough to initiate conduction between the electrodes |52 and |63. When the electron discharge device becomes conductive, it energizes the allotter start transfer relay l5 through a circuit which extends from a positive source of voltage through the Lipper winding of this relay |5, key i6@ through the anode |62 and cathode it oi the electron discharge device it to ground. This acts to transfer the master start ground which cornes from the group line relays ordinarily served the rst allotter to the master start lead |52 of the first allotter. The allotter start transfer relay l5 remains operated until the circuit through the electron discharge device |55 is broken at the manually operated key |54 by a repair man who is also signalled by the operation oi this device. The completion of the line finding operation is indicated to the allotter failure circuit by the operation of the allotter control relay 2?; and by the allotter advance relay il' which close a circuit from ground in series with the armatures and front contacts of these relays over the lead ilt through resistors |51 and |55 to condenser |55. Condenser |55 is thus discharged through this path and prevents electron discharge device |559 from operating, The time interval allowed the line finder and allotter to complete their operations is determined by the magnitude of resistor H9; The completion of v that disclosed in Fig. 3, is shown in Fig. 6.

denser |55 through the armature and back contact of allotter failure relay |513.

A modiied form of ringing trip arrangement or trigger circuit which can be substituted for this arrangement, the voltage on the starter anode |8| of the gas-filled arc discharge device |35 is adjusted by means of the potentiometer P, to be within a few volts of the iiring potential of the device. superimposed, interrupted ringing current is applied vto the called line through resistor |2 and condenser |86. During the ringing and silent periods the voltage drop across condenser it is negligible and thus the potential between the cathode |82 andstarter anode its of the discharge device remains constant. When, however, the hook-switch at the called substation is closed and direct current ows in the line, a drop appears across resistor |24 and condenser |86, such that the cathode |82 of the discharge device becomes more negative. This brings the device to firing potential and it becomes conductive. The ring trip relay l2 lo. operates in series with the discharge device and acts to disconnect the ringing current and to apply talking battery to the line in the manner similar to that shown in Fig. 3.

A further modified form oi trigger circuit is shown in Fig. 7 which differs from the trigger or ringing trip circuit of Fig. 3 in the specific manner in which the tripping Voltage is applied to the cathode H of the gas discharge device or Thyratron H9. In the arrangement of Fig. 7, the resistor 2% and the condenser I 31| constitutes a voltage divider. With no direct current flowing through resistor |24, the grid ||Sa of the discharge device HS is biased by means of a potentiometer |23 so that the discharge device does not conduct. Alternating current may also be passed through the resistor i213 and the discharge device still will not conduct, if the time constant of the resistor 2S@ and the condenser |3 is greater than the period of the alternating current. When direct current iiows through the resistor i at the time when the called partly answers by removing his receiver from its switchhook, a drop appears across resistor iil as a result of which the condenser |39 is charged so that a negative voltage appears on the cathode M927 of the discharge tube. The vacuum or gas rectifier 253|, as the case may be, in the cathode circuit ci the discharge device I I9, prevents the discharge of the condenser. Thev mentioned negative voltage present at the cathode ||9b efectively reduces the bias on the discharge device ||9 causing it to conduct. The rectifier tube ti now passes the plate current of the discharge device HQ, in a circuit from ground, through rectifier 2B cathode l IBb, anode ||9c of the arc discharge device H9, lower winding of relay |2|a through armature |3341 of relay |33, to the positive source of high voltage. Ringing trip relay i2! becomes energized to disconnect the ringing current and to cut through the connection from the calling line to the called line.

Resistor |24 may be made quite low so that any circuit associated with this trigger circuit will not be appreciably affected thereby. Rev

15 sistor 200 can be made quite high so thatV the trigger circuit is of such impedance as to have a negligible effect on any associated circuit.

If the present arrangement is used only to detect the presence of direct current and no alternating current discrimination is desired, condenser l3ll can be omitted. Resistor 282 is inserted to dampen any relaxation oscillation.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

What I claim is:

l. The method of initiating electrical conduction through an arc discharge device having an anode, a cathode and a starter electrode, said cathode and said anode being connected in series with a source of unidirectional electrical energy, which method comprises accumulating an electrostatic charge from a relative low voltage source, discharging said charge, utilizing said discharge to develop a voltage of a higher order, applying said higher voltage to the starter electrode to cause a discharge in said device.

2. The method of initiating electrical conduction through an arc discharge device having an anode, a cathode and a starter electrode, said cathode and said anode being connected in series with a source of unidirectional electrical energy which method comprises accumulating an electrostatic charge from a relative low voltage source, discharging said charge, inductively utilizing said discharge to develop a voltage of a higher order, applying said higher voltage to the starter electrode to cause a discharge in said device.

3. In a low voltage arrangement for initiating electrical conduction through an arc discharge device responsive only to voltage of a higher value, said arc discharge device comprising a cathode, an anode and a starter electrode enclosed in a gaseous atmosphere, a load unit and a source of unidirectionl current connected in series with said anode and said cathode, said source having its positive and negative terminals respectively connected to said anode and said cathode, a step-up transformer having a primary winding and a secondary winding, said secondary winding being connected in circuit with said starter electrode, and means for causing varying current or relatively low voltage to flow through said primary winding.

4. In a low voltage arrangement for initiating electrical conduction through an arc discharge device responsive only to voltage of a higher value, said arc discharge device comprising a cathode. an anode and a starter electrode enclosed in a gaseous atmosphere, a load unit and a source of unidirectional current connected in series with said anode and said cathode, said source having its positive and negative terminals respectively connected to said anode and said cathode, a stepup transformer having a primary winding and a secondary winding, said secondary winding being connected in circuit with said starter electrode, a condenser, means including a relativelylow voltage source of electrical energy for charging said condenser, and means for discharging said condenser through said primary winding.

5. In a telephone system, a line having a terminal, means for associating an electrostatic charge with said terminal when said line is to be selected, a movable switch for selecting such line, means for moving said switch to engage said terminaLan arc discharge device having an anode, a cathode and a starter electrode enclosed in a gaseous atmosphere, a unidirectional source of electrical energy, a circuit including said source as well as said cathode, said anode and the gaseous atmosphere, whereby current ows in said circuit when an arc discharge is initiated in said device, means for discharging said electrostatic charge responsive to the engagement of said switch with said terminal, and means responsive to said discharge for applying a starting potential to said starter electrode to eiect arc discharge in said device, and means for stopping said switch operated in response to current owing in said circuit.

6. In a telephone system, a line having a terminal, means for associating an electrostatic charge with said terminal when said line is to be selected, a movable switch for selecting such line, means for moving said switch to engage said terminal, an arc discharge device having an anode, a cathode and a starter anode enclosed in a gaseous atmosphere, a unidirectional source of electrical energy, a circuit including said source as well as said cathode, said anode and the gaseous atmosphere, when an arc discharge is initiated in said device, means for discharging said electrostatic charge responsive to the engagement of said switch with said terminal, and means including a step-up transformer responsive to said discharge for applying a starting voltage to said starter anode to effect arc discharge in said device, and means for stopping said switch operated in response to the arc discharge in said device.

7. In a, telephone system, a telephone line comprising tip, ring and huntconductors, contacts in which said conductors respectively terminate, a switch having tip, ring and hunting brushes movable into engagement respectively with said tip, ring and hunt contacts, operating means for moving said switch brushes into engagement with said contacts, a condenser and a resistor connected in multiple, a circuit closed responsive to the initiation of a call on said line, said circuit including a battery as well as said tip and ring conductors in series with the multiple-connected resistor and condenser whereby said condenser becomes charged, said hunt contact being connected to one terminal of said condenser, an arc discharge device including a cathode, an anode and a starter anode enclosed in a gaseous atmosphere, a stopping relay, a discharge circuit including a source of unidirectional electrical energy in series with said relay and also in series with said cathode and said anode as well as the space therebetween, a step-up transformer having a primary winding and a secondary winding, a circuit including said secondary winding and said starter anode, a circuit including said primary winding, said hunting brush and said hunt terminal and also said condenser whereby said condenser discharges through said primary winding, and means including said relay for stopping said operating means.

8. In a telephone system, a telephone line comprising tip, ring and an associated hunt conductor, contacts in which said conductors respectively terminate, a switch having tip, ring and hunting brushes movable into engagement respectively with said tip, ringand hunt contacts, operating means for moving said switch brushes into engagement with said contacts, overflow contacts closed as a result of a predetermined movement of said switch, a condenser and a resistor connected in multiple, a circuit closed responsive Ato the initiation of a call on said line, said circuit including battery as well as said tip and ring conductors in series with the multiple-connected resistor and condenser whereby said condenser becomes charged, said hunt contact being connected to one terminal of said condenser, an arc discharge device including a cathode, an anode 'and a starter anode enclosed in a gaseous atmosfspace therebetween, a step-up transformer havinga primary winding and a secondary winding,

a circuit including said secondary Vwinding and .said starter anode,ha circuit including said primary windingsaid hunting brush and said hunt terminal and `also said condenser whereby said condenser discharges through said primary winding, means responsive to the closure of said overiiow contacts for transmitting current through said primary winding whereby the discharge circuit isclosed through said device, and means including said relay for stopping said operating means.

9. In a telephone system, a group of telephone lines, each having a pair of talking conductors, a group relay common to said group of lines, said relay having one terminal of its winding connected to one pole of battery and having its other terminal connectable in series with the talking conductors of any one of said lines on theinitiation of a call thereon, a hunt conductor for each line terminating in a hunt contact and'normally connected to one of said talking conductors of its line, a condenser and a resistor each having a pair of terminals, the first terminal of each pair being connected in common tov said hunt conductor and the second terminal of each pair being connected in common to the other pole of battery, whereby said conductor becomes charged, a cut-off relay individual to each line and eliective on operation to disconnect said group relay and to disconnect the hunt conductor from said talking conductor, va switch for seizing a line characterized by a charged condenser, said switch having brushes including a hunt brush movable into successive engagement with the hunt contacts of said lines, means for moving said switch brushes, means responsive to the engagement of the hunt brush with the hunt contact connected to said charged condenser for causing said switchv to seize said line, and means responsive to the seizure of said lineior operat-` ing the cut-o relay thereof. Y l

10. In a telephone system, a, line, means for characterizing said line as idle by a negative voltage of a given value and for characterizing said line as busy by a negative voltage of a lesser value, a test circuit, an arc discharge device included in saidcircuit, said arc discharge device comprising a cathode, an anode and a starter anode enclosed in a gaseous atmosphere, a source of relative high positive voltage connected to said anode, means for connecting said cathode to said line, a voltage divider having its iXed terminals connected respectively to said anode and to said cathode and having its movable element connected to said starter anode, said movable element being adjusted so that the starter anode has a starting voltage of such value applied thereto that it renders said device conducting when said cathode is connected to the line when characterized as idle but the starter anode has a volt- 18 ageof such low vvalue applied thereto that it fails to render said device conducting when the cathode is connected with the line characterized as busy, and means controlled vby the conducting condition of said device for indicating the idle condition of said line.

11. Ina telephone system, a line having Va terminal, means forv associating an electrostatic charge with said terminal when said line is to be selected, a movable switch for selecting such line,

lmeans for moving said switch to engage said terminal, an arc discharge device having an anode,.a cathode and a starter anode enclosed in a Igaseous atmosphere, a unidirectional source of electrical energy,l a circuit including said source i' as jwellfas said 'cathodajsaidfanode and the gaseous atmosphere, whereby current' ows in saidcircuit vwhen an arc discharge is initiated in said device, means, for discharging said electrostatic charge responsive to the engagement of said switch with said terminal, means responsive to Vsaid discharge for applying a starting' potential to said starter anode .to operate said arc discharge devicemeans including acondenser having a delayed charging rate for applying a starting potential to said starter anode after a predetermined'interval to effect arc discharge in said device, and means for rendering said condenser ineffective as aresultofthe normal operation of said arc discharge device in response-to the discharge of said electrostatic charge, and means for stopping said switch operated in re sponse to current flowing in said circuit.

12. In a ringing trio arrangement, a conductor having a source of alternating current superimposed on. direct vcurrentconnect'ed thereto, said conductor` during a rst period being connected ina circuit continuous-only to alternating current and being connected'during a second period ina second circuit continuous to direct current, a dischargedevice having a cathode, an anode and a control electrode, an anode circuit including said anode, Vsaidcatl'ioda-a ringing trip.re. lay and also,afsource of current, meansfor biasf ing' said control electrode-tc a degree. that said device does not conduct`.during saidrst period, and means responsivefto-the flow of direct, cure. rent through said conductor duringlthe second period .for rendering said cathode `negative` with.

respect ltofit'scondition during said frst 'period' whereby .the bias. on ls'aidgde'vice is effectively re...

duced s'th'at thedevice becomes conducting'an'd. thetrio rt-:la-y.- operates. l.' '1`..

13.' In @ringingtriparfaugement, a. conductor.. having a source 'of alternating current superim-v posed o`n 'direct current' connected thereto, .said conductor duringT aiirst vperiod being connected in a circuit continuousonly to alternating current and being connected during a second period in a second'circuit continuousto direct current, a resistor connected 'in' series with said conductor, a discharge device having a cathode, an anode and a control electrode, an anode circuit including said anode, said cathode, a ringing trip relay and also a relatively high voltage source of current, a second resistor and a condenser connected in series and placed across the terminals of said first resistor, one terminal of the condenser being connected to the positive side of said direct current source, and a rectifier tube having a cathode and an anode, the anode of said rectifier being connected to the cathode of said device and the cathode of the rectier being connected to the positive side of said direct current source.

14. In a ringing trip arrangement, a wanted telephone line, a conductor, a source of ringing current, a ringing trip relay for controlling the connection of said source of ringing currentlto said conductor, means for connecting said conductor to said wanted telephone line in the course of extending a telephone call to said line whereby said line is signalled, an electron discharge device having at least a cathode, and an anode, .an anode circuit including said anode, said ringing trip relay and a source of current, means responsive to the answering of the signal on the wanted line for causing said discharge 4device to pass sucient current to operate .said relay whereby the source of ringing current is disconnected from said wanted line.

15. In a ringing trip arrangement, .a wanted telephone line, a conductor, a source of ringing current, a ringing trip relay for controlling the connection of said source of ringing current to said conductor, means for connecting said conductor to said wanted telephone line in the course of. extending a telephone call to said line whereby said line is signalled, an electron discharge device Vhaving a cathode, a control electrode and an Y anode, an anode circuit including said cathode, said anode, said ringing trip relay and a source of current, means for applying a bias to said control electrode whereby said device vdoes not pass current, means responsive to the answering of the signal on the wanted line for overcoming said bias whereby said discharge device passes suicient current to operate said relay thereby disconnecting the ringing current from said wanted line.

16. In an arrangement for vdiscriminating between the ow of alternating current and direct current in a given circuit, a discharge device including a cathode together `with an anode constituting an electric discharge path, said device also including a control electrode, meansv normally biasing said control electrode to a value whereby said device does not discharge, a network comprising a capacitor and a resistor together having a period or time constant ,of a given value, asource of alternating current of shorter period than that of said network and a source of direct current to be discriminated, a second .resistor connected in saidcircuit through .which either said alternating current or said direct cur-f rent can be caused to now, means for applying to said network the ydrop across said second resistor due to direct current flow.. therethrough whereby said capacitor is charged, means for connecting the negative terminal of said capacitor to said cathode, a cathode circuit connected to said cathode, a rectier connected in said cathode circuit ,to prevent unwanted discharge of said capacitor, a relay connected in said discharge path to be `operated by the electric discharge therethrough, and means responsive to the operation of said relay for stopping the flow 20 of alternating current through said second resistor.

17, In an arrangement for initiating electrical conduction through a discharge path, a discharge device including a cathode together with an anode constituting said discharge path, said device also including a control electrode, means normally biasing said control electrode to a value whereby said device does not discharge, a network comprising a capacitor and a resistor together having a period or time constant of a given value, a source of alternating current of shorter period than that of said network, a source of direct current, a second resistor through which either said alternating current or said direct current can be caused to ow, ,means for applying to said network the drop across said second resistor due to direct current flow therethrough whereby said capacitor is charged, vmeans for connecting the negative terminal of said capacitor to said cathode, a cathode circuit connected to said cathode, anda rectier .connected in said cathode circuit to prevent unwanted discharge of said capacitor.

18. In an arrangement for initiating electrical conduction through a discharge path, a discharge device including a cathode together with an anode constituting said discharge path, said device also including a control electrode, means normally biasing said control electrode to a value whereby said device does not conduct, a cathode circuit connected to said cathode, and means for applying a negative potentia1 to said cathode whereby the bias applied to said device is effectively reduced and it becomes conducting.

19. In an arrangement for initiating electrical conduction through a discharge path, a discharge device including a cathode together with an anode constituting said discharge path, said device also including a control electrode, means normally biasing said control electrode to a value whereby said device does not conduct, a cathode circuit connected to said cathode, a rectier connected in said cathode circuit, and means for applying a negative potential to said cathode whereby the bias applied to said device is eiectively reduced and it becomes conducting.

20. In an arrangement for initiating electrical conduction through a discharge path, a discharge device including a cathode together with an anode constituting said discharge path, said device also including a control electrode, means normally biasing said control electrode to a value whereby said device does not conduct, a cathode circuit connected to said cathode, an anode circuit connected to said anode, a rectier connected in said cathode circuit and connected to said anode circuit, and means for applying a negative potential to said cathode whereby the Abias applied to said device is effectively reduced and it becomes conducting.

FRANK A. MORRIS.

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