US2438496A - Telephone system employing key type call transmitter - Google Patents

Description

G. DEAKIN March 30, 1948,

TELEPHONE SYSTEM EMPLOYING KEY TYPE CALL TRANSMITTER Filed June 19, 1944 8 Sheets-Sheet 1 G. DEAKIN March 30, 1948.

TELEPHONE sYsTEM EMPLOYTNG KEY TYPE CALL TRANSMITTER Filed June 19, 1944 8 Sheets-Sheet 2 G. DEAKIN March 30, 1948.

TELEPHONE SYSTEM EMPLOYING KEY TYPE CALL TRANSMITTER Filed June 19, 1944 8 Sheets-Sheet 3 March 30, 1948. G, DEAKIN 2,438,496

TELEPHONE SYSTEM EMPLOYING KEY TYPE CALL TRANSMITTER Filed June 19, 1944 8 Sheets-Sheet 4 March 30, 1948. G. DEAKIN 2,438,496

TELEPHONE SYSTEM EMPLOYING KEY TYPE CALL TRANSMITTER Filed June 19, 1944 8 Sheets-Sheet 5 March 30, 1948. G, DEAKlN 2,438,496

TELEPHONE SYSTEM EMPLOYING KEY TYPE CALL TRANSMITTER Filed June 19, 1944 8 Sheets-Sheet 6 N075.' MAI/f5.5 afm/QE March 30, 1948. DEAKlN 2,438,496

TELEPHONE SYSTEM MPLOYING KEY TYPE CAL;J TRANSMITTER Filed June 19, 1944 8 Sheets-Sheet 7 /l i fi 55,9/ X

March 30, 1948. G, DEAK|N 2,438,496

TELEPHONE SYSTEM EMPLOYING KEY TYPE CALL TRANSMITTER Filed June 19, 1944 8 Sheets-Sheet 8 I 2z" fmw /l R/ l n i A WAH/N6 /ff g AR/ i Ila mw I BY Patented Mar. 30, 1948 TELEPHONE SYSTEM EMPLOYING KEY TYPE CALL TRANSMITTER Gerald Deakin, New York, N. Y., assigner' to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application June 19, 1944, Serial No. 540,946

57 claims. 1

This invention relates to new and useful irnprovements .in switching systems of the type useful for controlling telecommunication.

The 'present is a continuation of my application Serial No. 533,465, led May l, 1944, now abandoned.

The object of the .invention is to provide a key-controlled switching system which is so rapid that a single set of ten keys may be used for controlling a plurality of 'successive Vnumerical switching operations, e. g. in automatic telephone systems, and 'yet simple enough to permit installation at lsubscribers stations.

In a telephone system'embodying the various features of the present invention high speed keying (up to 6 per second) into a P. A. B. X or fast central oice equipment is made possible, and slower keying 1 or 2 per second) into'switchboards incapable of receiving at high speeds. Each ten button key set is equipped with means, such as slidingand locking bars which hold a key depressed and prevent any other key from being depressed'until a switching device such as a register is readyto receive another digit, at which time the depressed key is automatically released. ln one form, the register is equipped with three sets of digit storing means, e. g. relays, wherebyithe first three digits may be keyed at the maximum speed, making it particularly suitable yfor high speed three-digit P. A. B. X operation. The number of groups of digit storing relays is not liked. There may be only one group without storage facilities. There may he two groups in which one digit may be stored, pending the selection of the previous digit. Such a register would be useful in high speed two-digit P. A. B. X operation. There may be four or more groups but it isy thought that in most cases the additional expense Would not be warranted. However, when it is necessary to dispose of the calls with extreme rapidity, one group of digitstoring relays should be provided for each digit. The registers couldbe provided for the operators at manual or automatic P. B. X switchboards.

When sending from a P. A. B. X to a slow speed central oliice or from a high speed central oice to a slow speed central office, the speed with which keys are released will depend upon thetime taken to complete selection in the central office. For example, when a three-digit storing register circuit is used for out-trunking from a P. A. B. X to a slow speed central oihce (10 or l2 pulses per second), then the rst three digits may be keyed in rapid succession and stored, respectively, in the three sets of storing relays. As soon as a free out-trunk is selected by the P. A. 'B'. X which ordinarily will be done very rapidly, the rst set of storing relays is freed to receive the fourth digit. From then on the keys will be released as rapidly as the selections (ci. 17e-9e) are completed. Since the register is always capable of storing three digits, the last key button may be depressed before thelast three central oice selections take place. When keying i-nto a central -oce :equipped with registers adapted to receive at a rate of 2l) steps per second, the speed :of keying maybecorrespondingly increased.

The system here 'disclosed is suitable for use with two-wire lines free from appreciable earth potentials having -a maximum loop resistance, including the suhscribers set, of 600 ohms and a minimum leakage to lground of 20,000 ohms. These ngures are not limits and are merely 'given to show that the system is capablefof working in a modern cable plant maintained with reasonable care such as isnecessary regardless of the system used.

While the provision ofv akey-controlled switching system is the important obiectof the invention, some of the features, particularly Athose relating to the register, may be found v.useful Ain other types of control system. 'I'his'willlbe clear from the following description and the appended claims.

In the drawings:

Fig. l is a block diagram of a telephone system embodying the invention;

Fig. 2 is a simplified diagram :illustrating the functioning of the-invention;

Fig. 3 is a substation circuit;

Figs. 4-10 illustrate the key set, Fig. 4 being a section along lines Ll--ll of Fig. 6, Fig. 5 a section along lmes 5-5 of Fig. 6, Fig. `6a section along lines 5 5 of Fig. 8, Fig. 7 an .enlarged view of a detail oi Fig. 6, Fig. 8 a section along lines 8-8 of Fig. 6, Fig. 9 a section along 9-"9 of Fig. 8, and Fig. il) a sectionalong lines 'IG-IO of Fig. 6;

Figs. l1 and 11a are diagrams of the register; and

Fig. l2 illustrates the circuits at various stages of their operation.

SUBSCRIBERS Snr CIRCUIT (F1os. v2 AND 3) The subscrihers set consists of an ordinary telephone set and a ten-button key diagrammatically shown in Fig. 3, allm'ounted in a table or other set, for example, as shown in my cepending design application Serial No. D. 113,244, filed April 13, 1944, now Design Patent No. 340,904, patented April 1'7, 1945. The key set consists of ten buttons, an upper and a lower locking plate. a rectifier reversing plate, a release magnet, and home conta'cts,the Ymechanical construction of which will be described later. First the functioning of the circuit will loe described.

When any key is depressed, home contact 25 opens the receiver circuit and home contact 24 `short-circuits the telephone circuit. The pur- 60 pose of the former is to prevent an objectionable click in the receiver when the line is short-circuited. As soon as any key is depressed, the upper locking bar prevents the depression of a second key until the first key is fully restored.

When the key plunger reaches the locking plate at the bottom, contact 38 opens and removes a short-circuit from keys. At aboutl the same time a latch spring is released which causes a weightedr spring momentarily to open contact 31. This is done so that the line circuit may not be opened long enough to cause a release at the central office which could take place if the length of opening depended on the speed of depression or the continuity of depression. When the key is fully depressed, it is locked in position by the lower locking plate and remains so depressed until released by the release magnet RM which, when operated, releases the lower locking bar and thus the plunger returns to normal whereupon another key may be operated.

Buttons 1 and 6 when depressed cut in resistance RI, buttons 2 and 7 cut in R2, 3 and 8 R3, and 4 and 9 Ril. Buttons 5 and 0 do not cut in a resistance. The keys make Contact and cut resistances into the line at the moment when contact 38 removes the short-circuit.

RC is an adjustable resistance which is used to adjust the line loop to a constant resistance of, say, 600 ohms.

When any one of the lower keys 6 to 0 of the iive pairs of keys is depressed, the second locking top plate reverses the connection of the rectifier at 26. This plate is not restored to its normal position until the key plunger is released.

The tip spring of the lower locking bar is associated with the switch-hook in such a way that no key can be locked depressed unless the handset has been removed. Should a subscriber hang up with a key depressed, the key will be releasedl when the handset is replaced and trips the locking plate.

TEN BUTTON KEY SET (F1os. 4-10) Aof frame l2 and at the bottom by a hole in plate I5 which is attached to key frame I2. The keys Vare kept in their normal position by springs It A shoulder on the plunger at I9 limits the upper movement.

There are three sliding plates I6, I'I and I8, each free to slide endwise to the right (Fig. 6). These sliding plates are held in position by lugs projecting through slots in the side of the housing I2`as indicated in Figs. 5 and 10.

Y The key plunger I8 normally pierces the sliding plates I6 and I'I as shown in Fig. 10. The hole 28 in plate I6 is such that whenever any key is depressed the slanting surface 2l of the plunger forces plateV I8 to the right. Pin 22 molded in the depressed plunger I8, however, passes through hole 20 in the plate before the hole is moved suiiiciently to prevent the depression of the key. A

second key may not be depressed when one key is already depressed.

Locking bar I'I is similarly arranged, except that the holes 23 for keys l to 5 are longer. The slanting surface 2| of the plunger does not engage 4 this plate when any button 1 to 5 is depressed. However, when any key 6 to 0 is depressed, sliding plate II is moved to the right along with sliding plate I6.

When any button is depressed, sliding bar I6 moves to the right, opens contact 25 (Fig. 9) and closes contact 24 (Fig. 6). These are the contacts identified in the circuit of Fig.' 3. When any button 6 to 0 is depressed, sliding bar I 'l moves to the right and operates contacts 26 (see Figs. 4, 6 and 10).

The upper part 0f the plunger is provided with a lug 21. When any key except keys 5 and 0 is depressed, the depressed lug forces two adjacent springs together to close contact 28. Such contact is not provided for keys 5 and 0. It will be seen from Fig. 10 that the same contact is closed when any other pair of keys, such as l and 6 are depressed. v

Just as the depressed key nears the end of it stroke, sliding surface 29 at the bottom of the key plunger engages the edge of hole 38 in sliding plate I8 and forces the plate to the right. When the plunger is fully depressed, pin 3l attached to plate I 8 engages a, catch on spring 32, whereby when pressure is released from the key, plate i8 does not return to its normal position and the tip 33 of the plunger catches under the edge of hole 38 in plate I8 and the key remains depressed (see Fig. 7)

`When the plunger forces plate i8 to the right, spring 38 attached to plate I8 forces spring 35 also to the right. Just before plate i8 reaches the end of its movement, lug 38 attached to frame I2 engages the slanting tip of spring 34 forcing it downward to release spring 35 which now returns under considerable tension of its own to engage weighted spring 36, forcing this spring away from the center spring 3l, thereby opening contact 36-31 long enough to allow the requisite opening of the line circuit. This snap opening of the line circuit is provided so that the line circuit may not be opened too long when a key is depressed slowly. Plate I8 also opens contact 38 (Figs. 8 and 9).

To release a depressed key, electro-magnet RM is energized. Armature 68 is attracted and depresses spring 32, thereby freeing pin 3l, after which plate I8 returns to its normal position under the tension of spring 4I, the free end 0i which rests against lug 42 of frame i2. The inclined back of the catch on spring 34 permits this spring to assume the position shown in Fig. 6.

When the key is restored, plates I5 and Il return to their normal positions, the former under the tension of springs 24 and 25 and the latter under the tension of spring 26.

Part 43 is connected to the switch-hook of the subscribers set in such a way that it forces 32 out of reach of pin 3| when the switch-hook is in its normal position, whereby a key will not be locked down when the handset is on the switchhook. Parts 43 and 32 are shown with handset removed.

Radio type resistances RI to R5 are connected to and supported at one end by lugs 45 of the one spring making contact 28. The other end is strapped to wire wL The plug-in adjustable resista-nce RC is conveniently located at the bottom of the set. The socket for RC, not shown, is attached to the base of I2.

Reotiiier 45 is also attached to the base Yframe I2.

FUNDAMENTAL SIoN-ALING CIRCUIT (FIG. 2)

The fundamental signaling circuit is substantially :a Wheatstone bridge circuit and when the potentials of the opposite corners of the square bear a predetermined relationship to one-another, e. g. are the same, the Vresponsive device in the registering circuit operates. The potentials involved and how they are obtained are shown on Fig. 2. Any source ofdirect current may be used, e. g. the normal exchange battery of 48 volts. The potential of this battery may vary from 40 tori@ volts without disturbing operation; thus no voltage regulation of the battery -s necessary.

At the central oice four potentials PI to Pf; are obtained by Vmeans of .a potentiometer placed across `the lexchange battery. These potentials are applied in rotation to the grid of triode VI, of the register by counting or other step-by-step operated means such as counting relays CRI- 3. The corresponding potentials applied :to the grid of V2 are obtained from the same battery 'by 'in- Serti-ng vat the keys into the metallic line loop the proper resista-noos RI--i as indicated in the table on Fig. 2. lt will be seen that a, pair oi keys, such as l and 6, '2 and 7, etc., introduce the same ren sistance. `Keys .5 and 0 are not equipped with contacts since these two digits are 'recorded without the use of potentials. The manner in which odd and even Ykey Vbuttons of each pair are tected will be explained in connection with the register circuit. I-t -will suffice to say here that the sig-nal circuit is always as shown in Fig. 2 when an operating potential is applied Ito the grid of V2. At this time the lconnection of the rectier S in series with the release magnet RM is always such as to prevent vthe ow of current from the b wire to the a wire and thus RM does not interfere with signaling.

The value of the resistors RI to R4 -is given in the table. Resistor RC is always adjusted so that the loop resistance of the metallic line from the cinco to the key, but excluding the key resistor, 600 ohms. VRIC may be a small plug-in radio type resistor.

When key y1 or key 6 is depressed, the total Vloop resistance is 3300 ohms. When the line has .an infinite insulation resistance to ground, the resulting potential on the grid of V2 is 30 volts.

When the b wire has a leak to Vground of 20,000

The

ohms, the potential is reduced to 28 Volts. average is 29 volts and the potentiometer at the central oiiice is adjusted to give PI this average potential of 29 volts.

The resistances R2, R3 and R4 are selected to OPERATION oF REGISTER CIRCUIT (F1os 1, 11, AND 11a) Subscriber removes handset When the subscriber removes the handset and closes the line circuit, the line relay operates,.after which an R-link seizes a B-link and ythen aregister. After this the yregister .causes the line finder of the B-link to seize the vcalling line,

whereupon relays RAR and RBR of the register .Y

circuit .(Fig. 1l) v,tall away and pull vup respectively, all as-.described inapplication Serial No. 521,160, filed .February 5, .1.944. I-t is .at this stage that the pants-of .the .register circuitshown in Fig. 11 come into -eiect When RAR makes its back contacts, it connects .in Vsaid application a stepping relay to the calling Aline. This stepping relay receives thefdigit pulses .and passes them on to digit switches through an irl-control distributing switch. fdigit switches store the vdigit record. In the present case, when RAR makes its back contacts, it connect-s to .the calling line a tube circuit, including -four counting relays CRI to CRIl. These counting relays transfer the record of lthe digit keyed 'to digit storing relays XRI, .the counterpart of the digit switches above .referred to .and the distribution of these .digit storing relays -i-s made `by counting relays C-R5 to CRS and transfer relays TR! to TRS, the counterpart of ythe -in-control switch. En both cases .the result is the same. .PN potentials accor-.ding Ito the digit keyed are placed on the terminals yof the C bank of the yout-control switch PO and ground -on the B terminals, either directly or through vtranslator switches. The operation .of 'the selectors in 'completing the connection in D'. A. B. X vor central office, as the case may h .nd :the generation of dial pulses for outt'-un .ing remain as described in said application. To control the release Iof the key, an extra bank is .added to `the PO switch and an extra Contact the GSRI relay :so that `whenever GSRI operates, it places 'battery on .a terminal in bank :c at the Asame instant it energizes PO.

When (Fig. ll) makes its front contact, it l'encrgiszes .AR over 1a back contact of BR. AR connects AARfI to ythe b wire and a circuit is established from battery, winding ARI, front back CR, back RAR, b wire through telephone set, a wire, backRAR, back CR, back ER, front AR, resistor RI, back BR to ground. ARI oper- Lates and Lenergizes BR, ground, front ARI, back :BR and winding BR to battery. BR disconnects itself from .ARI and locks .up over front RI R. at :the sometime BR disconnects winding of AR from a front contact oRBR rand in place thereof Vconnects iit to a vdiront .contact 0I ARI without openingthe .circuit of AP.. .ARI now locks up AR. BR removes ground 'from the a wire but the line `circuit remains :closed to ground over a front contact of ARI. BR closes the primary circuit .of the dialing tone transformer TT. The secondvary winding .of this transformer is bridged across the .calling line through condenser C. The subscriber hears .the dialing tone. is energized, circuit from :ground :back back GVR, front BR, rfront AR, winding FR, to battery. IThe cirfcuit remains in 'this condition until a key is depressed.

Key lgroup selection When lany key is depressed, the line circuit is momentarily opened by the 'key set (B, Fig. 12). 'This momentary ope-ning of the line circuit releases ARI (Fig. 11). ARI breaks its front contacts and opens its own holding circuit and at the same time releases AR. AR falls away and makes :its back contacts, .among other things connecting from battery to the a" wire via back contacts .or DR, ER and JCR. The b wire is grounded over a :back contact of AR and a back contact of LCR.

Should .la key 1 to :5 'have been depressed, the .connection of .the rectifier S in the subscribers set circuit will be as shown at C in Fig. 12. Current Will not iiow through release magnet RM and the current which flows through the low resistance winding of NR (Fig. 11) and the key resistor RI to R4 (Fig 2), as the case may be, will not be suicient to energize NR. However, should a key 6 to 0 have been depressed, the connection of the rectifier is reversed (E, Fig. 12). Suiiicient current now flows through the low resistance winding of NR, the rectifier, and the release magnet to operate NR which breaks its back contact quickly and introduces an additional vresistance RN of some 2,000 ohms under which condition RM does not operate. NR has tWo windings, a low resistance winding 'and a high resistance Winding. Normally the latter is short-circuited. The former winding enables the relay to be adjusted to operate over the maximum loop of 800 ohms (the maximum permissible line resistance of 600 ohms plus the resistance of the rectiiier and release magnet) but not to operate over the minimum keyed resistance Rli which, as will be seen from Fig. 2, is 1600 ohms. When NR closes its front contact, it energizes CR (Fig. 11) which reverses the line connections so that current ceases to ow through RM. By means of this reversal of the rectier connections, it is possible to reduce the number of diierent subsequent key selecting pulses from to 5 and thus cut in half the nurnber of potentials necessary for the operation of the tube circuit. Keys l to 5 develop the same potentials as keys 6 t0 0 respectively (see Fig. 2).

When AR breaks its front contact, it opens the circuit of slow releasing relay FR, the purpose of which is to allow time for NR to operate CR, if CR is to be operated at all. After the elapse of a short interval of time, FR closes its back contact and energizes DR, circuit from ground, back GVR, front BR, back AR, back FR, winding DR to battery.

Key 1 depressed When key 1 is depressed, ARI falls away and releases AR. AR connects relay NR to the a wire, ground to the b wire and releases FR. When FR makes its back contact, DR becomes energized and disconnects NR, and in place thereof connects the grid of V2 in multiple with resistor RN to the a wire. Resistor RN is connected to battery over a front contact of RBR. The keying circuit is diagrammatically shown at D in Fig, 12. DR operates DTR Which operates and locks up and disconnects the dialing tone transformer. The resistance RI, which key 1 introduces into the line circuit, is such as to produce a potential PI on the grid of V2, the average value of which potential is arbitrarily assumed to be 29 volts. Since the grid of VI is normally connected to the saine potential over the back contact of CRI, gas valve GV fires instantly and energizes `GVR which opens its back contact and consequently the circuit of CRI before the latter has had time to opcrate and energize CR2. Similarly, if digit 3 were keyed, GV would re when CR2 isA operated and connects P3 to the grid of VI over the back contact of CR3.

Digit 1 stored When GVR makes its front contact, it energizes 'IRI and CRB over back contacts of CRS. As soon as TRI makes its front contacts, XR! operates over a circuit from ground, back CRI and front rIRI. XRI, according to the followingtable, places the required potential PNI on terminal I of bank C via the back contacts of XRZ, XRS, and XR4.

TABLE Relays energized Digit keyed XR CB1/4 1 N one 2 l 3 2 4 3 1+3 4 1-I-2 None 2|3 l 8 3+4 2 9 -l- 3 0 l-l-Z-I-B 4 F is a lter to prevent improper operation of the triodes by the dialing tone or the like.

Key released GVR energizes GSR. A low resistance circuit is established from ground, front GSR, back Y ER, back CR, back RAR, a wire, release magnet of subscribers set (G, Fig. 12), rectifier S, b wire, back RAR, back CR, front GSR, Winding ARI to battery. The current through this low resistance circuit is now in such a direction and of such a strength as to energize release magnet RM of the subscribers set. RM releases the depressed key. ARI remains energized and locks up AR. GSR removes battery from NR so that NR is not energized when GSR grounds the a` wire. GSR removes ground from the b wire. This is `done so that ARI will not buzz on a premature release. When GSR releases, it removes the shunt from resistor RI and this resistance is introduced into a holding circuit of ARI. The line circuit is now restored to the waiting position (A, Fig. l2) and it remains in this condition until another key is depressed.

Register prepares `for storing second digit GSR opens the circuit of the high tension battery. GV is `de-ionized and releases GVR. When GVR breaks its front contact, CRS locks up over its front contact in series with CRE. CRE transfers the front contact of GVR to the back of CR'i which is connected to the Winding of TR2.

In parallel with the foregoing, TRI releases when GVR breaks its front Contact. 5ml, however, remains energized and locked up over its front contact and the winding of Xl-IRI XHRI places ground on terminal I, bank B of the outcontrol switch PO.

First selection takes piace When XHRI places ground on bank B, the AR relay of the selector under control operates and the selector searches for a trunk having potential PNI on the t Wire.' When a free trunk is found, GSRI (Fig. 11a) is energized and energizes PO, at the same time placing battery through'R- on the brush a3, terminal I, therebi7 shunting out XRI which releases. When YRi breaks its front contacts, Xl-IRI releases and frees the rst group of XR relays for another digit, but as previously indicated, the next digit when it does arrive will come in on the second group since TR2 is now connected to the front Contact of GVR.

Digit 5 keyed We will assume that digit 5 is keyed after digit 1 and, as will be seen from the potential diagram (Fig. 2), this key inserts no operating potential resistance in the line circuit. Thus counting relay CRI will operate, circuit from lineair-'9c ground, back ER and GVR, front BR, back AR, backFR, front DR, winding CRI to battery. CRI connects CR2 to this grounded circuit and CR-2 operates. GRZ' connects CR3- and CR3V connects R41 The tube circuit does notA operate, but when CR- closes its front Contact, the ground is extended over front CRS andl back CRIy to energize TR2'. XRI and XR3- (see-table above) operate and lock up. CRdl-also-operates GSR, re-energizing ARI which locks upto the line and releases the key. When A-R operates, FR is energized andl DR and the counting relays are released, whereupon TR2 releases. Another rela-y energized by CRI! is CRS which locks upA over its iront contact in series with CR'F. GR'II' transfers the front contact of GVR from 'lL-R2l to TRS. When TR?. is released, XHRZ operates and places .a ground on terminal 2 in bank B of PO and the second selection mayl nowV be made in the usual way for digit 5.

Digit 6 keyed When key 6 is depressed, the same potential is pla-ced on the grid of V2v as when key 1 was'd'epressed, but because of the reversal of the rectifier, as previously explained, NR operates momentarily and' locks up CR, thus reversing the line connection at the central oce as shown at F in Fig. 12. When TR3 operates, relays XRI and XR2 are energized in accordance with the above' table.

When XHRBl operates, counting relays CRE to CRS are released and ground is placed on terminal 3 of bank B of PO.

Digi-t 0 keyed- We will assume that the fourth digit keyed is the digit 0. In this case NR locks up CR but no potential is placed on the line, the same as when the opposite digit 5 was keyed. Therefore, counting relay CRfI operates with the result that relays XRI, XRZ., and XR3 of the rst group. are again energized' as per the table, assuming.. of course, that the llrst selection has been completed.

Key set blocked Assume now that the second selection is still incomplete, in which event XHRI, XHRZ, and Eil-IRS will be energized and close over their front contacts a series circuit for relay ER to RIR front. ER opens the line circuit, energizes GSR and removes grou-nd from the armature of GVR, thus releasing DR. The circuit remains in this condition untilthe second selection is complete, after which the above traced hold-ing circuit is opened at a front contact of XHRZ, whereupon ER falls away and GSR closes the line circuit. ARI locks up to the line, since GSR is slow releasing, and releases the key set.

The fth digit may now be keyed. The call will corne in on the second group of XR relays, after which the holding circuit will be again closed unless the third selection has been completed. In this manner a key is held depressed until there is a free group of XR relays to receive and store pulses.

The bank of the cut-control switch PO has in this particular case 12 terminals which are multi plied in four sets of three to accommodate the three groups of XR digit storing relays. In other words, PO may accommodate 12 digits, using each group of XR relays four times.

It will be readily seen that the number of groups of digit storing XR relays may be decreased or increased. If there were only one group of relays, the out-control switch PO would not be necessarysince'the three wires running to banks X,.B and C could be permanently attached toI their respective brushv circuits; Ii there were six groups of XR relays, the multipling of the PO switch ban-ks would be changed to two groups of sixnstead of four groups ofthree. If one group ofk storing relays; were provided for each of a seven-digit num-ber, there would be no multipling in the banks of the PO switch. The ease with which arrangements may be made for storing various numbers. of digits adds important flexibility to the circuit.

Out-trunk calls from a P. A. B. X

LocalY calls within a P. A. B. X equipped or key sending ma-y be completed rapidly but when a cally is out-trunked, the PN potentials selected. bythe .digit storing relays are placed on a bank of an out-trunk pulse controlling switch, suc-hv as PT in the register circuit described in said copending application. The speed and character of the outtrunk pulses may be adjusted to the character and speed or the pulse receiving equip,- ment in the. central silice. As soon asr the outtrunk pulse; control switch PT has completedK a selection, GSR'I- operates as describedin said application, releases the digit storing relays and. consequently determines the speed with which` the keys are released.

Release, regular mid premature The method of release` when a-call is completed is. the same asv described in said copending application. However, should the subscriber hang up. before the completion of selection, the partially completed selection is released when ARI falls away upon the opening of the line circuit. ARI releases AR.` The release of AR energizes DR, in the usual way and the counting relays CRI- 4 are energized. When CRA operates, GSR is energized but asV the line circuit is opened, ARI is not re-energized and therefore does not re-en ergi-ze AR. In due course RIR, the circuit of which is now opened by AR, breaks its front contacts and releases the connection.

three sets of storing -relays is calculated as follows:

Time in Milli-Seconds, Digits Keyed l or 6 5 0r (l Depression of key- 50 50 ARI breaks front contact 2 AR makes back contact 6 FR makes back coutact 20 DR operates 6 CRl-4 operates 3 GVR opens back con 2 2 TR operates l0 l0 XR operates. l0 lo Release of key 50 50 Keys per second 6.5 5. 3 Average maximum Approx. 6

Remark: The above assumes 50 milliseconds for depressing a key 5S.

Theoretically at least, the three keys may be successively depressed in a total of one-half a seclo NOOQM ond which is faster than the selectors can complete the call. During hours of normal traic it should be possible to complete a call to number 555 in a keying P. A. B. X in an average of 1.5 seconds after the depression of the first key, provided 'that all three keys are depressed rapidly one after the other. In actual practice it is not likely that an average familiar number will be depressed at a rate faster than three keys per second sro that the delay of the ringing tone after depressing the last key will not be noticeable in a P. A. B. X local operation.

Subscriber-to-subscfibe trunk calls 'from a P. A. B. X

Under normal traic conditions a subscriber will pick up a free trunk almost instantly after the trunk key is depressed and if the P. A. B. X is equipped with three sets of digit storing relays, the next three digits may be rapidly depressed. In large a-reas, such as New York, these digits would be the office prefix digits. The speed with which the keys will be released to permit the completion of the keying of the four-digit oiiice number will depend upon the speed with which the central office is able to absorb the digit pulses.

When keying into a straight Strowger exchange without digit storing facilities, time must always be'left for the vertical stepping of the switch and for the horizontal hunting for a free trunk and, since a straight Strowger system has no means of signaling to the sending equipment whether the haul is long or short, time must always be allowed for the long haul. Thus keying into such a Strowger exchange cannot be done more rapidly than about 1 digit per 1.25 seconds. This means `that since three digits may be stored, the last key may be depressed 4 or 5 seconds before the ringing or busy tone is heard. This delay may be noticeable but it may not be objectionable. In actual practice, subscribers will probably learn to key at a slower rate so as more or Vless to anticipate the slower speed of the switch.A

When keying into a system provided with a register in which provision may be made for more rapid reception, keying may be done at approximately .75 secondV per digit, thus reducing the average time of the ringing or busy tone after the last key is depressed to approximately three seconds, this also upon the assumption that the next digit is keyed as soon as the key for' the previous digit is freed.

Key set applied to central ojce operationV When keying is applied to central cnice operation, it will probably not be necessary te provide for more than three sets of digit storing relays since in the Universal System, by virtue of the disposition of trunks which multi-potential selection makes possible, all selections may be very rapidly made, with the exception of the 4tens selection which must of necessity be spread out over the entire bank. The average for all selections, except the tens selection, during hours of normal traiilc should be less than .5 second and that of the average tens selectons may be depressed very rapidly. This will take care of the oce prex. With translation'the tion 1 second, thus making the total selection third key would be freed in about 1.5 seconds after its depression, the time taken to translate the oihce prex. The keys would then become free at an average rate yof .5 second and the waiting time after the depression of the last key would be about two seconds. This wait is not objectionable and if the time of keying is spread out the delay will not be noticeable.

The fact that digits may be stored tends in itself to increase the speed of selection. In the customary dial system, -for instance, the pulses for the next digit may not even be prepared for sending in until after the dial comes to rest. The subscriber must locate the finger hole and this in itself is often a source of delay, next he must pull it to the finger stop, and only after he has removed his finger from the nger hole does the sending of pulses to the central oce commence. With a key set and storing relays, the subscriber can easily select the proper keys one after the other since the designations of the keys are not concealed during keying. The designations visible through the holes of a stationary dial are concealed during dialing.

When it is desired to provide P. B. X attendants and toll or other operators with means to key rapidly the entire number, additional groups of storing relays may be added to the registers used by these operators. In this way the numbers may be disposed of as fast as they can be keyed, but the delay after the keying of the last digit may be 5 or 6 seconds. Such delay, however, is generally of little importance to a P. B. X attendant or toll operator who usually has something else to do while awaiting answer by the called party.

Figs. 3a and 3b illustrate a modication of the control circuit in which the triode V2 is eliminated. The line loop is connected with the cathode of the single triode Vl to whose grid the various potentials may be applied as previously explained. The a and b wires are crossed as compared to Fig. 3. Otherwise, the two embodiments are identical. Y

What is claimed is:

1. In a telecommunication system, a plurality of lines, each having a multi-digit number, means including a plurality of stages of numerical selector switches for establishing a connection between a calling and a called line, a central exchange register for variably operating the selectors in accordance with the different digits of the called number, a plurality of keys associated Iwith each line, an electric discharge tube in the register, means for connecting the keys of the calling line with said tube, means responsive to the operation of the connected keys for applying various potentials to said tube, and means oontrolled by the tube for variably operating the register.

. In a telecommunication system, a pluralityv 13 a predetermined order,- and means for preventing the actuation of the keys if all the digit switches are busy.

3. rlhe system according to claim 1 and means for preventing the operation of the keys until the control of a selector by the register is completed.

4. In a telecommunication system, a signalcontrolling device, a signal responsive device, a circuit interconnecting said devices, a source of electrical potential, means including av plurality of resistances for establishing a plurality of potential changes in said circuit in accordance with the operation of the controlling device, and means in the responsive device for detecting said potential changes..

5,. The system according to claim 4, and means in the responsivev device for recording said ptential changes.

6. The system according to claim 4, and means for switching one resistance or another into the circuit depending on the operation of the controlling device.

7. In a telecommunication system, a signalcontrolling device, a signal responsive device, a circuit including a two-wire line interconnecting said devices, a source of electric potential, means including a plurality of resistances at the controlling device for establishing a plurality or predetermined potential changes at the responsive device by changing the resistance of said circuit in a predeterminedmanner, and means in the responsive device for detecting and recording the potential change.

8. In a telecommunication system, a signalcontrolling device, a signal responsive device, a circuit including a two-Wire line interconnecting said devices, a source of electric potential, means including a plurality of keys and a lesser number of resistances at the controlling device for establishing a plurality of predetermined potential changes at the responsive device by changing the resistance of said circuit in a predetermined manner, and means in the responsive device for detecting and recording the key which has been actuated.

9. In a telecommunication system, a signalcontrolling device comprising ten keys and four diierent resistances, a signal responsive device, a circuit including a two-wire line interconnecting said devices, a source of electric potential, means including said keys and resistances at the controlling device for establishing predetermined potential changes at the responsive device, and means in the responsive device for detecting and recording which key has been operated.

l0. In a telecommunication system, a controller comprising a plurality of resistances and a rectifier, a responsive device, a connection between the controller and the device, a source or potential, means responsive to the operation of the controller for connecting to the device said source over one of said resistances and the rectifier poled in a predetermined manner, switching means in the responsive device operable in accordance with the potential applied thereto, and switching means in the responsive device operable in accordance with the poling of the rectiiler.

11. In a telecommunication system, a controller comprising a plurality of keys, a lesser number of dierent resistances and a rectifier, a responsive device, a connection between said device and controller, a source of potential, means responsive to the actuation of certain keys for switching certain resistances in said connection, means reeponsive to the actuation of any' one oi a group of said keys for switching the rectier in one direction in the connection and for switching the rectiiier in the opposite direction when one of the other keys is actuated, switching means in the responsive device operable inv accordance with the potential applied thereto, and switching means in the responsive device operable in accordance with the Doling of the rectier.

12. In a telecommunication system, a controller comprising ve pairs of keys, four difierent resistances and a rectier, a responsive device, a connection between said device and controller, a source of potential, means responsive to the actuation or any key of four pairs for selectively switching said resistances in said connection, means responsive to the actuation of one key of any pair for switching the rectier in one direction in the connection and for switching the rectiiier in the opposite direction when the other key of any pair is actuated, switching means in the responsive device operable in accordance with the potential applied thereto, and switching in the responsive device operable in accordance with the poling of the rectier.

18. In. a telecommunication system, a signalcontrolling device comprising a plurality of keys, a lesser number of diierent resistances and a rectiiier, a signal responsive device, a circuit including a two-wire line interconnecting said devices, a source oi electric potential, means at the controlling device for connecting a resistance across the wires when either one of a pair of keys is actuated and for inserting the rectier in the circuit in one direction o-r the other depending on which key of the pair is actuated, and means in the responsive device for detecting and recording the potential change and the direction oi current in the circuit.

14. In a telecommunication system, a signalcontrolling device comprising iive pairs of keys, four different resistances, one for each ofv four of said pairs of keys, and a rectifier, a signal responsive device, a circuit including a two-wire line interconnecting said devices, a source of electrical potential for said circuit, contacts for selectively bridging said resistances across the wires when a key of said four pairs is actuated, contacts for connecting said rectier in the circuit in one direction when one and the opposite direction when the other key of said ve pairs is actuated, means in the responsive device responsive to the potential changes, andA means responsive to the current direction changes in the circuit, and a switching device having ten positions corresponding to the ten keys variably operated by said means in the responsive device.

l5. In a switching system, a controller comprising a plurality of keys operable in accordance with successive digits, means for locking the conn troller in the actuated position whenever a key is operated to prevent the operation of any other key, means including a magnet for unlocking the controller, a responsive device, a source of potential, means for establishing a connection between the controller and the device for repeatedly operating the latter in accordance with successive digits, and means for actuating the magnet upon each operation of the device.

I6. The switching system according to claim l5, and in which diierent resistances are switched into the connection depending on the key actuated, and means in the device variably operable under the control of said resistances.

17. In a switching system, a controller operable l in accordance with successive digits, means for locking the controller in the actuated position, means including a magnet for unlocking the controller, a rectifier forming part of the controller, a source of potential, a responsive device, means for establishing a connection between the controllei` and the device for repeatedly operating the latter in accordance with successive digits, means for connecting the rectiiier in the connection, in one direction upon certain and in opposite direction upon certain other operations oi the controller, means in the responsive device variably operable depending upon the connection of the rectier, and means for actuating the magnet controlled by said device.

18. The switching system according to claim 15, and in which means are provided for connecting the rectier and controller in series in the connection, in one direction upon certain and the opposite direction upon certain other operations of the controller, and means in the responsive device for reversing the direction of current ow in said connection.

19. In a switching system, a controller operable vvin accordance with successive digits, means for locking the controller in the actuated position, means including a magnet for unlocking the controller, a responsive device, a source of potential, means for establishing the connection between controller and the device for repeatedly operating the latter in accordance with successive digits, means in the controller for switching said magnet into said connection, means at the responsive device for establishing a circuit from said source over said connection and magnet, and means at the device for varying the resistance of said circuit to control the operation of said magnet.

20. The switching system according to claim 19, and in which means are provided at the device for varying the direction of current flow in the circuit to contro-l the operation of the magnet.

21. In a switching system, a controller operable in accordance with successive digits, means for locking the controller in the actuated position, means including a magnet for unlocking the controller, a plurality of digit responsive devices, means for successively associating said controller with idle responsive devices, and means for actuating the magnet upon the completion of the actuation of a responsive device but only if the next device is idle.

22. In a switching system, a controller operable in accordance with successive digits, means for locking the controller in the actuated position, means including a magnet for unlocking the controller, a plurality of digit-storing devices, means variably responsive to the actuation of the controller, means for associating the variably responsive means with successive idle storing devices to actuate them, means for performinga plurality of successive stages of switching operations under the control of the storing devices, means for successively associating actuated storing devices with successive stages to control the switching operations, and means for actuating the magnet upon the completion of the actuation of a storing device but only if the next device is idle.

23. In a switching system, a controller having ten keys operable in accordance with successive digits, means for locking an actuated key and preventing the actuation of the other keys, means including a magnet for unlocking the keys, a plurality of digit-storing devices, means variably responsive to the actuation of the keys, means for associating the variably responsive means with i6 successive idle storing devices to actuate them, means for performing a plurality of successive stages of switching operations under the control of the storing devices, means for successively associating actuated storing devices with successive stages to control the switching operations, and means for actuating the magnet upon the completion of the actuation of a storing device but only if the next device is idle.

24. In a switching system, a controller having ten keys operable in accordance with successive digits, means for locking an actuated key and preventing the actuation of the other keys, means including a magnet for unlocking the keys, a plurality of groups of digit-storing relays, means variably responsive to the actuation of the keys, means for associating the variably responsive means with successive groups of idle storing relays to actuate them, means for performing a pluraliti7 of successive stages of switching operations under the control of the storing relays, means for successively associating actuated group of storing relays with successive stages to control the switching operations, and means for actuating the magnet upon the completion of the actuation of a group of relays but only if the next group is idle.

25. In a telecommunication system, a plurality of signal-controlling devices, a signal responsive device, a plurality of circuits, means for connecting a controlling device over one of the circuits with said responsive device, a source of potential common to all the circuits, means including a plurality of normally inactive keys at each con.. trolling device for establishing a plurality of predetermined potential changes in the connected circuit, electromagnetic means for locking the keys in their actuated position, means at the responsive device responsive to the potential of the connected circuit, and means controlled by the last-mentioned means for operating the electromagnetic means of the controlling device over the connected circuit.

26. In a telecommunication system, a plurality of signal-controlling devices, a signal responsive device, a plurality of two-wire circuits, means for connecting a controlling device over one of the circuits with said responsive device, a source of D. C. potential common to all the circuits, means including a plurality of normally inactive. keys at each controlling device for establishing a plurality of predetermined potential changes in the connected circuit, electromagnetic means for locking the keys in their actuated position, means at the responsive device responsive to the potential of the connected circuit, and means controlled by the last-mentioned means for operating the electromagnetic means of the controlling device over the connected circuit.

27. In a telecommunication system, a plurality of signal-controlling devices, a signal responsive device, a plurality of two-wire circuits, means for connecting a controlling device over one of the circuits with said responsive device, a source of D. C. potential common to all the circuits, means including a plurality of normally inactive keys at each controlling device for establishing a plurality of predetermined potential changes in the connected circuit, a rectifier, contacts controlled by certain keys for connecting the rectifier in the circuit in one direction, contacts controlled by theY other keys for connecting the rectifier in the circuit in the opposite direction, an electromagnet at each controlling device, means for locking the keys in their actuated position controlled by the associated magnet, means at the responsive device responsive to the potential' and the for connecting a controlling device over one of-Y the circuits with an idle responsive device, a source of potential for saidL circuits, means inm cluding a plurality' of normallyl inactive keys at each controlling device orestablishinga plurality of predetermined potential changes in the connected` circuit, electromagnetic mea-ns for locking the keys in their actuatedl position, means at the responsive device responsive to the potential of the connected circuit, and means for operating the electromagnetic means or the controlling devlceover the connectedA circuit while the responsive device is operated.

29; Inl a switching system; a normally inactive controller variably operable in accordance with a plurality of successive digits, a source of current, means for establishing a circuit including said controller withthe source bridged across the circuit, av multi-electrode tube having cathode, grid and plate electrodes, means responsive to every actuation of the vcontroller rst momentarily to open said bridge and then to connect the grid oi thev tube with the circuit, means for applying potentials to said gridl depending` on the` opera-- tionoi'- the controller, a relay, means for operating saidrelay controlled by the tube, and' a switching device'variab'ly operable under the controlofsaicl relay.

30. The system according to claim 29, and in which said controller comprises resistances and keys arranged selectively to switch the rfesistanccs in the circuit, and'means to connect the grid with the circuit irrespective of the speed at which a key is operated;

3l. Ina switching system, a normally inactive controller Variably: operablein. accordance with a plurality ot successive digitsaD; C. source,.rneans for establishing a. circuit including. said controller with the;sourcebridged across thev circuitJ a of multi-electrode tubeshaving cathode,gridl and plate. electrodes, means responsive to every actuation oftli'econtrol'lei: iirst momentarily to openvr saidbridgef and then. tol connect the grid or. one tube with thev circuit, means. for applying various: potentials to said grid,l depending on the operation of the 'controller a: relay, a circuit for operating said relay when thesamepotentials are appliedtofthegrids. of the two'tllbes,l step-by-step means-V controlledwby said relay for applying said various potentials tothe grid' or thesecond tube, means actuated by the controller el? Starting the operation of thestep-by-stepnfieans, and switchingr devices variably operable under the control of said relay and step-by-step means.

32. The system according to claim 3l, and in which the controller comprises a plurality of different resistances and: keys arranged selectively to swgitch the resistancesA in the circuit, andmeans to connectV the gridr of the. nrst tube with the circuit irrespective of the speer-i at which thev key isoperated;

33; The'switching system: according to claim 29, andv means for re-establishing said bridge upon the operation of the switching device.

34. The switching systernacccrding to claim 29, a' plurality of switching devices, means. for associating the relay with one switching device after is' the other for variably controlling its operation, and means for re-establishing the bridge upon the operation of a switching device.

35. The switching system accordingto claim 29, means for associating the relay with one switching device after the other` for variably controlling its operation, and means for re-establishing the bridge upon the operation of each. switching device.

36. The switching system according to claim 29, means for locking thecontroller in its actuated position, and meansfor unlocking the controller and re-establishingth'e bridge upon the operation oi the switching device.

37. The switching system according to claim 29, means for locking the controller in its actuated position, and means for rst unlocking the controller and then ire-establishing the bridge upon the operation of the switching` device.

38. The switching system according` to claim 29, and in which saidy controller comprises keys, means for locking. the actuatedA key and preventing the operation of the otherkeys, a magnety for controlling the locking means, and means operative upon the operation of the switching device for first operating the magnet and then re-estab lishing said bridge.

39. The switching system according to claim 29, and in which said controller comprises keys, means for locking the actuatedkey and preventing the operation of the other keys, a magnetv for controlling the lockingl means, a plurality of switching devices, means for associating the relay with one switching device after the other for variably controlling its operation, and means operative upon the operation of each switching 'device for rst operatingl the magnet and then re-establishing the bridge.

40. In a switching system, a controller variably operable in accordance with a plurality oisuccessive digits, a source of potentials, a multielectrode discharge device, means for establishing a connection between said controller and said device, a relay, means for operating' saidA relay when potentials applied to two electrodes of said device bea-r a predetermined relationship tor oneanother, means including said connection for applying various potentials to one electrode in accordance with the operation of the controller, means actuated by the controller for applying various potentials to the secondelectrode, and switching means variably operable under the control of said relay and the last-mentioned means.

4l. The system according to claim 40, and means for operating the relay when the same potentials are applied to the two electrodes.

42. In a switching system, a controller operable in accordance with a plurality of successive digits, a source of potentials, a responsive device, means for applying various potentials to the responsive device in accordance with the operation of the controller, step-by-step means for applying various potentials to the responsive device, means for operating the step-by-step means when the controller is actuated, a relay operated when the potentials applied to the responsive device bear a predetermined relation to one-another, and switching devices variably operable under the control of said relay and stepby-stepmeans.

43. The switching system according to claim 42, and means for operating the relay when the two potentials applied to the responsive device are the same.

means for establishing a connection between saidv controller and said triodes, a relay, means for operating said relay when the potentials applied to the grids of the two triodes bear a predetermined relationship to one-another, means for applying various potentials to the grid of the first triode in accordance with the operation of the controller, step-by-step means controlled by said relay for applying various potentials to the grid of the second triode, means actuated by the controller for starting the operation of the step-by-step means, and a plurality of digit storage devices variably operable under the control of said relay and step-by-step means.

47. In a switching system, a controller comprising a set of keys operable in accordance with a plurality of successive digits, a potential source, a pair of triodes, means forV establishing a connection between said controller and said triodes, different. resistances selectively switched into the connection depending on the key operated, a relay, means for operating said relay when the same potentials are applied to the grids of the two triodes, means including said resistances for applying various potentials to the grid of the iirst triode in accordance with the operation of the keys, step-by-step means controlled by said relay for applying said various potentials to the grid of the second triode, means actuated by the controller for starting the operation of the step-` by-step means, and a plurality of digit storage devices variably operable under the control of said relay and step-by-step means.

48. In a switching system, a normally inactive controller variably operable in accordance with a plurality of successive digits, a D. C. potential source, a pair of triodes, a relay, means for operating said relay when the same potentials are applied to the grids of the two triodes, means for applying various potentials to the grid of the rst triode in accordance with the operation of the controller, means including a set of counting relays controlled by said relay for applying said various potentials to the grid Aof the second triode, means actuated by the controller for starting the operation of the counting relays, and a plurality of digit storage devices variably operable under the control of said relay and counting relays.

49. In a switching system, a normally inactive controller comprising a set ofA ten keys operable in accordance with a plurality of successive digits, a D. C. potential source, a pair of triodes, a twowire circuit connecting the controller with the triodes, a relay, a gas lvalve for operating said relay when the same potentials are applied to the grids of the twotriodes, a plurality of different resistances selectively switched into the circuit by the keys for applying various potentials to the grid of the first triode in accordance with the operatic-n of the keys, means including a set of counting relays controlled by said relay for applying said various potentials to the grid of the second triode, means actuated by the actuated key for starting the operation of the counting relays, and a plurality of digit storage devices variably operable under the control of said relay and counting relays.

50. The switching system according to claim 49, and in which four resistances may be selectively switched in circuit by the keys, and four counting relays having contacts for applying ve different potentials.

51. In a telecommunication system, a plurality of signal-controlling devices, a signal responsive device, a plurality of two-wire circuits, means for connecting a controlling device over one of said circuits with said responsive device, a source of potential common to all the circuits, means including resistances at each controlling device for establishing a plurality of predetermined potential changes in the associated circuit, and means in the responsive device for detecting the potential change.

52. In a telecommunication system, a plurality of signal-controlling devices, a signal responsive device, a plurality of two-wire circuits, means for connecting a controlling device over one of said circuits with said responsive device, a source oi D. C. potential common to all the circuits, means including a plurality of resistances at each controlling device for establishing a plurality of predetermined potential changes at the responsive device by changing the resistance of the connected circuit to a predetermined extent, and means in the responsive device for detecting and recording the potential change in the connected circuit.

53. In a telecommunication system, a plurality of signal-controlling devices, a signal responsive device, a plurality of two-wire circuits, means for connecting a controlling device over one of said circuits with said responsive device, a source of D. C. potential common to all the circuits, means including a plurality of keys and a lesser number of resistances at each controlling device for establishing predetermined potential changes in the connected circuit, means in the controlling device for altering the direction of current flow in the connected circuit, and means in the responsive device for detecting the potential and direction of the current in the connected circuit.

54. In a telecommunication system, a plurality of signal controlling devices, a signal responsive device, a plurality of two-wire circuits, means for connecting a controlling device over one of the circuits with said responsive device, a source of D. C. potential common to all the circuits, a plurality of dierent resistances at each controlling device, variably operable contacts in the controlling devices for varying in a predetermined manner the potentials in the connected circuit. and means in the responsive device responsive to said potentials and to a predetermined range of variations thereof for indicating which contact was actuated.

55. In a telecommunication system, a plurality of signal-controlling devices, a signal responsive device, a plurality of two-wire circuits, means for connecting a controlling device over one of the circuits with said responsive device, a source of D. C. potential common to all the circuits, a compensating resistance for each circuit, four dierent control resistances at each controlling device, five pairs of keys for establishing five predetermined potentials in the connected circuit, and means at the responsive device responsive to the iive potentials in the circuit and to avpredetermined range of variations thereof.

56. In a telecommunication system, a plurality of signal-controlling devices, a signal responsive device, a plurality of two-wire circuits, means for connecting a controlling device over one of the circuits with said responsive device, a source of D. C. potential common to all the circuits, a compensating resistance for each circuit, four diierent control resistances at each controlling device, iive pairs of keys for establishing ve predetermined potentials in the connected circuit, means at the responsive device responsive to the ve potentials in the circuit and to a predetermined range of variations thereof, means in the control device for causing current to ilow in the connected circuit in one direction when one key of a pair is operated, and in the opposite direction when the other key of the pair is operated, and means in the responsive device for detecting the direction of current flow in the connected circuit.

57. In a telecommunication system, a controlling device comprising rive pairs of keys, a diierent resistance for each of four pairs, each key having a normal and an actuated position, means.

for locking a key in the actuated position and preventing the actuation of the other keys, a magnet for unlocking the keys, a rectifier in said controlling device, a responsive device, a two-wire line circuit interconnecting said devices, a telephone transmitter and receiver associated with the controlling device, a normally closed rst contact connecting the receiver with the circuit opened upon the actuation of any key, a normally open second contact closed upon the actuation of any key for short-circuiting the transmitter, a third contact normally short-circuiting said resistances, rectifier and magnet, said third contact being opened upon the actuation of any key to a point near its locking position, a weighted fourth contact operated thereupon for momentarily opening the line circuit, normally open ilith contacts, one for each pair of keys, the fth contacts being in parallel and normally short-circuited by said third contact and connecting the associated resistance in the circuit when either key of the pair is actuated and opens the third 22 contact, an adjustable resistance connected between the third and iifth contacts, a sixth contact normally connecting one pole of the rectiiier to the fourth contact and the other pole to the winding of the magnet, means operated upon the actuation of one key of any pair for actuating the sixth contact to reverse the connection of the rectifier, means in the responsive device for connecting said source in the circuit including the transmitter, the receiver, and the third and fourth contacts, means in the responsive device operated by current flowing over a, relatively low resistance path including the magnet, but the latter energizing only when the sixth contact is actuated by a key and reverses the connection of the rectifier, means in the responsive device for reversing the direction of current flow in the circuit, said responsive device comprising an electric discharge device having a plurality of electrodes, a source of direct current, means in the responsive device for applying to one electrode a potential determined by said resistances, counting means in the responsive device for applying to another electrode various potentials in succession, a relay operated when the potentials applied to the two electrodes bear a predetermined relationship to one-another, a low resistance path for the line circuit closed by said relay to allow energize.- tion of the magnet, and a variably operable storing device controlled by said relay and counting means.

GERALD DEAKIN.

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

UNITED STATES PATENTS Number Name Date 944,537 Bullard Dec. 28, 1909 1,708,949 Matthies Apr. 16, 1929 1,761,115 Gardner June 3, 1930 2,060,184 Dimond Nov. 10, 1936 2,041,083 Myers May 19, 1936 1,982,290 Gardner Nov. 27, 1934

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