US2559468A - Code transmitting apparatus in track circuit signaling systems - Google Patents

Description

Q 4 .m f m 8 1 5 m m M, a i 5ml m m ww m I 5, s SA QM 2 u m 5o.... 2 .MW a. Imi@ M A SCHEG CODE TRANSMITTING APPARATUS IN TRACK CIRCUIT SIGNALING SYSTEM July 3, 1951 July 3, 1951 Filed Aug. 51, 1944 M. A. scHEG 2,559,468

CODE TRANSMITTING APPARATUS IN TRACK CIRCUIT SIGNALING SYSTEM 2 Sheets-Sheet 2 :inventor (Ittorneg Patented July 3, 1951 CODE TRANSMITTING APPARATUS IN TRACK CIRCUIT SIGNALING SYSTEMS Marcian A. Scheg, Rochester, N. Y., assignor to General Railway Signal Company, Rochester,

Application August 31, 1944, Serial No. 552,108

4 Claims.

The present invention relates to block signalling systems for railroads using coded track circuits, and more particularly pertains to the improvement of the code transmitting apparatus employed in such signalling systems.

Each block of a signalling system employing coded track circuits usually comprises a single track circuit extending throughout the length of such block with suitable code transmitting apparatus at one end of the track circuit and suitable code responsive means at the other end. The code transmitting apparatus usually applies code pulses at different distinctive rates to provide the different codes in accordance with traic conditions, although Various different types of codes may be employed. Since coded track circuits are thus usually relatively long, as above mentioned, a substantial current iioW occurs during the application of each code pulse especially when the ballast along the trackway drops in resistance to its lowest value under adverse conditions. Also, when a train enters a block and shunts the track rails at the code receiving end of the track circuit, the code transmitting apparatus continues operation at the leaving end of the block and in so doing must supply a relatively large current during the application of each code pulse.

In View of this fact that the code transmitting apparatus of a coded track circuit must under :y

certain conditions supply code pulses of relatively high current values at very low potentials, it is apparent that a problem is presented in providing contacts on the' code transmitting apparatus which will adequately handle such relatively high currents and yet be of sufficiently low Contact resistance as to not materially affect the applied potential.

The present invention proposes to obviate these difficulties by applying direct current code pulses to the track rails of a track circuit through a rectier supplied from an alternating current source with suitable means for controlling the application of the alternating current potential to the rectier in a manner so as to minimize the value of current to be broken by the coding contacts, Since the energy is to be provided from an. alternating current source, it is proposed that the coding contacts control the energy at potentials higher than that supplied to the track r rails but with correspondingly reduced current Values, and in this way make it possible to employ relatively high resistance non-arcing contact material, such as tungsten, or the like.

In many coded track circuits it is not only desirable to transmit driven code pulses in one direction over the track rails, but it is also de'- sirable to transmit so-called inverse code pulses between the successive driven code pulses in an opposite direction over the track circuit. In order to accomplish this, it will be evident that the direct current carrying circuits connecting to the track rails must be commutated in order to include and exclude the code transmitting and code receiving apparatus at each end of the track circuit. Thus, another object of the present invention is to so control the application of energy through the code transmitting apparatus as to minimize the current to be carried bythe commutating contacts.

Generally speaking, and Without attempting to define the exact nature and scope of the present invention, it is proposed in one form of the invention to provide the energy for a coded track circuit by connecting the alternating current source through a full-wave rectifier with a resonated impedance included in series' with the alternating current source and the rectler, which resonated impedance may be shunted and unshunted by suitable code transmitting contacts so as to control the supply of current to the track rails. In order that such coding contacts may be of the high resistance arc: resistance type, it is proposed that the resonated impedance be of the auto-reactor type so as to raise the voltage to be governed by the coding contact considerably above that supplied to the rectier.

It `is also proposed that the commutating contact, which is included in the direct current: side of the rectifier so as to connect the rectifier and a code receiving relay alternately across the track rails, be suitably adjusted with respect to the coding contacts, so that the control of the current by the resonated auto-reactor is effected subsequent to the closure of the commutating contacts and prior to their opening.

In another form of the present invention, it is proposed that the secondary windings of two like transformers be connected in series across the terminals of a rectier but with their potenials in opposition to each other. Under such a condition, there is no current flow through the rectier to the track rails. The codingk contacts are arranged to control one of the transformers so as to deenergize it and remove its opposing potential, and thus allow a potential to be applied from the directly connected transformer to the rectiiier to cause a current flow in the track rails. In this way, the coding contacts by controlling such opposing transformer merely have to carry current of a sufficient value to supply the transformer losses; While the load current is directly supplied by the other directly connected transformer. It is also proposed that this form of the invention be adapted to the commutation of the low Voltage direct current portion of the connections to the track circuits so as to provide for the transmission and reception of vinverse codes as Well as the driven codes.

Other objects, purposes and characteristic features ol the present invention will be in part obvious from the accompanying drawings, and in part pointed out as the description progresses.

In describing the invention in detail, reference will be made to the accompanying drawings, in which those parts having similar features and functions are designated by like letter reference characters which are generally made distinctive by reason of distinctive preceding numerals representative of their location or association with other devices having reference characters with like numerals, and in which:

' Fig. 1 illustrates in a diagrammatic manner one .form' of av coded track circuit system embodying the present invention and employing a resonated reactor for controlling the coded track circuit energy;

Fig. 1A illustrates a modified form of inverse `code receiving track relay for use in Fig. 1;

Fig. 1B illustrates a modified form of resonated Vreactor for use in Fig. l; and

Fig. 2 illustrates another form of coded track circuit system embodying the present invention in which opposing alternating current potentials are provided to intermittently limit the current now in the track circuit to produce the code pulses.

For the purpose of simplifying the illustration and facilitating the explanation, the various parts and circuits constituting the embodiment of the :invention have been shown diagrammatically and vcertain. conventional illustrations have been employed, the drawings having been made more with `the purpose of making it easy to understand the principles and mode of operation than with the idea of illustrating the specic construction and arrangement of parts that would be employed in practice. Thus, the various relays and their contacts are illustrated in a conventional manner, and symbols are used to indicate the connection of terminals to batteries or other suitable sources of electric current instead of showing all of the Wire connections to these terminals.

` The symbols and are employed to indicate the positive and negative terminals respectively of suitable batteries or other sources of direct current; and the circuits with which these symbols are employed are assumed to always have current flowing in the same direction, `although it is to be understood that in some cases alternating current might be substituted for the direct current, and in such cases the and are to be considered as indicating the relative instantaneous polarities of the alternating current. In some of the circuits, alternating current is employed, and the opposite terminals of a suitable source or sources for such alternating current circuits have been indicated by the symbols (BX) and (CX).

With reference to Fig. l of the accompanying drawings, a stretch oi track has been divided into track sections by suitable insulated joints of which the track section 2T has been shown completely and the track sections iT and 3T in part only. Color light type signals and are shown at the entrance ends of the track sections 2T and 3T respectively, assuming a normal direction of trahie from left to right. These signals can of course be of any suitable type desired.

At the exit end of each track section (such as section ZT), a suitable code transmitting appara-n tus is located to transmit driven codes of diierent distinctive rates in accordance with traic conditions in advance as governed by the code reeiving means for the entrance end of the next adjoining track section. This apparatus also has associated therewith suitable inverse or oi code receiving means which detects the presence of an approaching train and can be used ifor approach lighting signals, highway crossing protection, approach locking and the like.

At the entrance end of each track section (such as section 2T) a suitable code receiving apparatus is located for receiving the diiierent driven codes and decoding them so as to properly control the associated signal. Also, associated with this code receiving apparatus is suitable inverse or oi code transmitting apparatus, for transmitting inverse code pulses during the ofi periods between successive driven code pulses.

As typical of all such track sections above brieiiy described, reference may be made to the track section 2T ci Fig. l, in which a code transmitter relay 3GP of the neutral type is energized and deenergized in accordance with different code rates as selected by the home signal relay 3H associated with the signal 3. More specifically, when iront contact 5 of relay 3H is closed, a coding contact |800 energizes the relay 3GP at the clear code rate of 180 times er minute, but if the back contact 5 of relay 3H is closed the relay 3GP is energized at the caution code rate of 75 times per minute. v It is to be understood that the relay 3H is rie-energized whenever a train is in the track section 3T, but is picked up when ever a caution or clear code rate is being received at the signal 3 location. Also, the usual clear and caution code rates of '75 and 180 pulses per minute have been selected for the coders C and I50C for the purposes of this disclosure, but it should be understood that other suitable code rates might be selected.

Each of the code transmitter relays, such as relay BCP, is provided with at least two contacts, one of which is conveniently termed an advanced contact while the other oi which is termed a retarded contact. Each advanced contact a is so connected to its operating armature as to close its front contacts prior to the closure of the front contact of its associated retarded contact b; while the opening of the advanced front contact a is effected subsequent to the opening of the retarded contact b. Although this relative advance and retardation of contacts a and b may be of any suitable amount for accomplishing the purposes of the present invention, it has been found in one typical embodi-1 ment that the advanced contact a may be closed approximately ten thousandths oi an inch earlier than the retarded contact h, which inference in inches of course refers to the air gap adjustment. This relative closing of the contacts has been inu dicated on the drawing by a suitable legend.

Also, associated with the leaving` end of track section 2T is an inverse code receiving track relay SATR. This relay is or the magnetic stick type as indicated in the drawings, and thus its contacts are operated to opposite positions upon the energization of such relay in opposite direc tions, and such contacts remain in their last actuated positions until the relay is energized in the opposite direction. This relay is shown as having three windings for purposes which will be described hereinafter.

The opposite terminals (BX) and (CX) of a suitable alternating source supplies energy to the primary winding of a transformer STF, and the secondary of this transformer supplies energy at a suitable voltage to the input terminals of the rectiier 3R. The current ow in this circuit must pass through the winding 6 of an autoreactor unit 33T which has a second winding '1. Connected across the outer terminals of the autoreactor BRT is a suitable condenser 9 which is preferably of such a value as to resonate the inductive reactance of the auto-reactor BRT, although it should beV understood that the inventions may be practice-:l although exact resonace is not accomplished. The resonant condition is oi course for the same frequency of alternating current as supplied to the transformer STF. The outer terminals of the auto-reactor BRT are shunted and unshunted by Contact 3 of the code transmitting relay 3GP, as will presently be described.

The primary winding of the transformer STF may be connected to the usual commercial supply of 60 cycle alternating current at 110 volts for example, while its secondary winding may be of such a ratio as to produce 6 volts, for example. This voltage supplied to the input of the rectifier through the winding 6 of the auto-reactor SRT will supply a relatively small. current through front contact l0 of the transmitter relay BCP to the track circuit when this advanced Contact l0 initially closes and connects the output of the rectiiier 3R through the resistor Il to the lower track rail and the other terminal of the rectiiier 3R through the lowest winding of the inverse track relay BATR to the upper rail of the track section 2T. This is because the resonant impedance of the auto-reactor SRT is very high and limits the current to a low value such as '75 milliamperes for example. But as soon as the retarded contact 8 closes its front points, the outer terminals oi the auto-reactor SRT are shunted so that the impedance of the autoreactor 3R is reduced to substantially the resistance drop through its winding 6, and the current thus supplied to the track rails of the track section 2T is in accordance with that required under the particular adjustment of the limiting resistor l! and the conditions of the track section including the track relay 2TH. This is because the closure of iront contact 8 shunts the condenser 9 and destroys the resonant condition, and also shunts the eiective secondary of the auto-reactor RBT which reduces its inductive reactance to substantially Zero. The winding 6 of the auto-reactor 3RT is of relatively large wire so that its resistance is low compared to winding 1, Thus, the eiiect of the auto-reactor SRT on the input to the rectier 3R is relatively slight under its shunted condition. The current which iiows in the lower winding of the inverse code receiving track relay SATR passes through the relay in such a direc'- tion as to cause its contacts to be moved to their lower or dropped away positions, as indicated by the arrow within the lower winding.

Since the Winding l of the auto-reactor 3RT has a greater number or" turns than the winding E, the potential across the outer terminals of the auto-reactor 3RT, before the outer terminals are 6. shunted, is considerably higher than. the' potential given by the secondary winding of the transformer aTF, and this higher potential may be made of any desired value by properly selecting the ratio of the two reactor windings. However, this potential should be suiciently high. that the retarded contact 3 may be constructed of suitable relatively high resistance arc resisting material, such as tungsten, for example, so that it may readily produce a shunt across the outer terminals of the reactor and yet provide a sturdy and reliable contact for breaking any current flow upon the opening of the contact 8.

It will be mentioned at this point that the advanced contact Iii is preferably constructed of a suitable low resistance material such as silver' so that the relatively low potentials applied to the track circuit will not be materially changed by the inclusion of the contact, and so that such potentials will be reliably maintained at the same values for successive impulse periods.

At the end of each pulse period the relay 3GP is dropped away thus opening the retarded contact 8 prior to the opening of advanced contact iii. The opening of contact i3y of course unshunts the auto-reactor SRT and its inductive reactance is inserted into the input circuit of the rectifier 3R. prior to the opening of contact Hl. This reduces the current in the track circuit energy applying circuit to a very low value, so that the opening of contact I0 breaks a relatively small current such as '.75 milliarnperes as compared to a track circuit pulse current which may under some conditions be as high as l0 to l5 amperes. Any arc which is made at the contact B has a very small current value in view of the reactor Winding ratio and the relatively high resistance of winding l. Also, any arc that might be produced at this contact is substantially absorbed by the confenser S. In other words, the condenser 9 serves two purposes, namely, that of resonating the auto-reactor ERT, and also suppressing any arc across the contact 8.

While the back contact l0 of the transmitter relay 3GP is closed, the intermediate winding of the inverse code receiving track relay SATR is connected across the track rails of section 2T for receiving an inverse code pulse, if there is one, and actuating its contacts to an upper position as indicated by the arrow included within its winding. The operation of the driven code receiving and inverse code transmitting apparatus at the other end of the track section 2T will be described hereinafter, but for the present it is 1 sufiicient to understand that an inverse code pulse may be received at the leaving end of the track section 2T and this will flow in such a drection that the contacts of this relay ATR are picked up. This differential connection of the windings of relay ATR will be readily apparent from the drawing of the circuits. current flow in the inverse track relay SATB, during an inverse code pulse can be suitably adiusted by the limiting resistor I4. Upon the cessation of the inverse code pulse, and when the next driven code pulse is applied by the transmitter relay SCP in a picked up position, the current flow `through the lower winding of the relay SATR is in such a direction to cause its contacts to be actuated to their lower positions.

lt will thus be seen that this relay SATB, is alternately operated to its opposite positions, being caused to have its contacts moved to their upper positions by inverse code pulses and having its contacts moved to lower positions in response to driven code pulses. Upon the cessation of inverse code pulses, the contacts of the relay are of course maintained in their lower positions to which they are actuated by the first driven code pulse following the last received inverse code pulse.

Associated with this inverse code receiving track relay BATR, is a suitable decoding relay SAH which has an associated decoding transformer I2 of the usual mid-tapped type controlled by contacts on the relay SATB, in the usual way. Thus, whenever the relay SATB, receives inverse code pulses, the relay .'iAH is picked up, but when the relay SATR ceases to receive inverse code pulses this relay SAE-I is dropped away to close its back contact i3 and thus approach light the signal 3.

It will be appreciated that each inverse code pulse will be of relatively short duration, and since the relay SATR is restored to its dropped away position due to the application of the driven code pulse, it will be readily apparent that the relay BATH would ordinarily be in a picked up position for a relatively short time compared to the duration of an "oi period or an on period of the driven code. But in order that the contacts of the relay 3ATR. may be in their picked up positions for such a time as to make the picked up condition of substantially the same duration as the dropped away condition during the reception of inverse code pulses, it is proposed to make the relay SATB. slow to be restored to its lower position, although quick to be operated to its upper position in response to a relatively short inverse code pulse. with the magnetic stick type relay BATR, its upper winding is provided with a shunt circuit through a front contact I5. The slow action produced by the shunting of this upper winding, is eiective only upon the energization or the relay by energy during a driven code pulse iiowing through a local circuit of the relay to delay its operation to its lower position. The amount oi retardation may be regulated by the number oi turns and resistance of such turns as shorted through this contact I5, but it is preferable that this be arranged so as to cause the relay SATR to be picked up for substantially the same time that it is dropped away. This gives a better decoding operation of the relay SAI-l.

At the entering end of the track section 2T, and associated with the signal 2, is a track relay 2TR, which is preferably of the polarized type, that is, its contacts are biased to one position by gravity or suitable resilient means, and are operated to picked up or actuated positions in response to only a particular polarity. This track relay ZTR is connected through a limiting resistor 2D and the advanced back contact 2l of the repeater track relay ZTPA to the track rails of the track section 2T. Each driven code pulse causes the contacts of the relay 2TH to be picked up, while the deenergization of the track section 2T between two successive driven code pulses results in the releasing of the contacts of this relay 2TR. The successive operation of the track relay ZTR in response to driven code pulses causes suitable decoding apparatus to be controlled through contact 22 so as to pick up the distant relay 2D in response to the clear code of the 18) code rate as well as the home relay 2H, out to pick up only the relay 2H in response to the caution code of the '75 code rate. Whenever no code is received both of these relays 2H and 2D are deenergized This decoding apparatus may be of To accomplish this result any suitable type such as shown for example in the Patent No. 2,342,489 granted N. D. Preston February 22, 1944, or such as shown in Fig. 2 of the accompanying drawings, but only the dotted rectangle has been indicated for the sake of simplicity in the disclosure of this Fig. 1.

It will of course be understood, that suitable driven code transmitting and inverse code receiving apparatus is associated with the leavin-g end of track section IT, but this has been merely indicated by a suitable dotted rectangle in which the relay ZCP is shown and from which the inverse decoding relay 2AH is indicated as controlled. This apparatus is of course the same as that shown at the leaving end of track section 2T. Normally inverse code pulses are being received so that the relay 2AI-I is picked up, but assuming that a train is approaching on the track section IT, this relay QAH would be dropped away closing its back contact 23. Assuming that a clear code is being received by the track relay 2TR and the associated decoding apparatus, circuits would be closed from (-1-) through back contact 23, front contact 24 of relay 2H, front contact 25 of relay 2D, the green lamp G of signal 2, to thus causing signal 2 to give a clear indication. Ii, however, a caution code were being received by the decoding apparatus, the distant relay 2D would be dropped away while the relay 2H would be picked up so that the yellow or caution lamp Y of signal 2 would be energized through back contact 25. On the other hand, ir" a train were standing in the track section 2T, so that no code is being received by the coding apparatus at signal 2, both the relays ID and 2H are dropped away and the red lamp R of signal Z is energized through back contact 24 of relay 2H, thus causing this signal 2 to indicate danger or stop.

Upon each deenergization of the track relay ZTR during the reception of a driven code7 a circuit is closed through back contact 25 for energizing the repeater relay ZTPB by an obvious circuit. During its pick up period, which may be suitably adjusted by well-known means and design of such a relay, a circuit is closed for the inverse code transmitting relay ZTPA. from (-1-), through back contact 26 of relay ZTR, back contact 2l of relay 2TPB, winding of relay ZTPA, to As soon as the relay ZTPB picks up and opens back contact 2l, the relay ZTPA is deenergized. The relative pick up and drop away times of these relays is so selected and organized that the relay ETPA is picked up for a short period during each deenergization of the track section 2T between successive driven code pulses.

The closure of the advanced contact 2 I oi relay ZTPA connects the output terminals of the rectiiier unit ZRA through a limiting resistor 3'! to the track rails of section 2T. Since the transformer ZTFA is supplied with alternating current from a suitable source indicated by (BX) and (CX) its secondary Winding applies a voltage through thc winding 3| of the auto-reactor ZRTA to the input of the rectifier unit ZRA. Thus, the output of the rectier ZRA supplies a potential to the track rails, but the current flow in this circuit is relatively small since the impedance of the resonated auto-reactor ZRTA is relatively However, as soon as the retarded contact 255 of relay ZTPA closes, the outer terminals o1 the auto-reactor 2RTA are shunted, which reduces the reactancc to substantially zero, so that substantially the full voltage of the secondary winding of the transformer ZTFA is applied to the input oi the rectiiier unit ZRA. Thus, an inverse code pulse is applied to the track section 2T of a value as determined by resistor 3l and the conditions of the track circuit, which inverse code pulse is received by the inverse code track relay SATB., as previously described. The auto-reactor ZETA is constructed and is controlled by the retarded contact 28 of relay ZTPA in exactly the same way as described for the auto-reactor SRT used to control the driven code pulses. In other words, the advanced contact 2| of relay ZTPA may be constructed of suitable low resistance material, such as silver, since only a relatively low potential and current is controlled by this contact, while the retarded contact 28 may be constructed of suitable high resistance contact material, such as tungsten, for reasons previously explained. The current controlled by the contact 28 is relatively low in View of the winding ratio of the auto-reactor 2RTA, and the associated resonating condenser 29 acts to absorb any are at the contact 28 when it is broken at the end of the inverse code impulse period. It can be seen from the above that each inverse code pulse period is of a yduration equal to the pick up period of the relay 2TPB together with the drop away period of the relay ZTPA, and these values are so chosen, as above mentioned, that the inverse code pulse will cease in plenty of time before the driven code pulse is applied at the opposite end of the track section.

Although for the purposes of this particular embodiment of the present invention, auto-reactors, such as SRT and 2R'IA are used for controlling the driven code pulses, and for controlling the application of the inverse code pulses, it

should be understood that a usual transformer with separate primary and secondary windings could be just as well employed and still accomplish the functions of the present invention. Such an organization is shown in Fig. 1B, where the primary winding of such a transformer SRTl is connected in the input of the rectier 3R the same as winding 6 of Fig. 1; while its secondary has the condenser 9 connected across its outer terminals, and such outer terminals are shunted and unshunted by the contact 8 of the transmitter relay SCP. Since the characteristics of the secondary load are transferred to the primary of a transformer, the condenser 9 connected across the secondary has such a value as to resonate the transformer and also to act to absorb or suppress any arcing from the associated controlling contact. The operation of such a modication is exactly the same as that already described. Although the auto -reactor has been disclosed as a preferred form, it is to be understood that any embodiment of the invention using a transformer having separate primary and secondary windings is intended to be within the scope of the present invention.

As above mentioned, the inverse code receivf ing track relays, such as 3ATR for example, are preferably made slow acting in being actuated to their lower or dropped away positions. In Fig. l. this is acomplished by the provision of a front contact shunting the upper winding of the relay. But it is to be understood that this may be accomplished in different ways such as shown for example in Fig. 1A, where a rectifier unit 3@ ,is shown as shunting the upper winding of relay ZATRI. This rectifier 3B is included in the shunting circuit for this upper winding in such a direction that the inductive impedance of this upper winding is effective when the lower winding is energized in a direction to actuate the contacts to their lower positions, but is 'not effective (due to its high resistance to current ow in a backward direction) when the intermediate winding of the relay is energized by an inverse code pulse. The complete circuits have not been shown in Fig. 1A, since it is to be understood that this relay SATR1 may be directly inserted in Fig. 1 in place of the relay SATR.

Fig. 2 form of the inventionitfith reference to the accompanying Fig. 2 of the drawings, a stretch of track has been divided into track sections by suitable insulated joints of which the track secton '5T has been shown completely and track sections 41T and ET in part only. Color light type signals 5 and 6 are shown at the entrance ends of track sections 5T and 6T respectively. These signals can of course be of any suitable desired type.

At the exit end of each track section is suitable driven code transmitting apparatus governed by the code receiving apparatus for the entrance end of the next adjacent track section in advance, so as to apply different driven codes. in accordance with traffic conditions in advance. At the entering end of each track section is r suitable code receiving organization indicated in the drawings as including a track relay ETR of the polarized biased type, this is, this relay ERT responds to only a particular polarity to be actuated to an operating position, and is biased to a normal position.

Each code following track relay, such as relay ETR, governs suitable decoding apparatus of any well-known construction, such as shown for example in the Patent No. 2,342,489 granted to N. D. Preston February 22, 1944, and such decoding apparatus has been diagrammatically illustrated as including a decoding transformer di] which has a mid-tapped primary winding controlled by contact 4i of the track relay STR so that this transformer is energized in opposite directions alternately as the Contact il of the track relay ETR is operated to its opposite positions in response to driven code pulses. lThe secondary winding of this decoding transformer 43 is midtapped and connected to the home relay 5H in combination with a rectifying contact i2 so that the relay 5H is picked up whenever the track relay ETR is receiving driven code pulses of either the clear or caution code rates, but is dropped away whenever there is an absence of such code pulses. A suitable tuned decoding transformer 38 has its primary connected to another secondary winding of the transformer 4D, while its secondary is connected through the rectifier Aunit 113 to the distance relay D. This circuit is tuned by the condenser 3S so as to pick up the relay 5D only when the track relay 5TR is operating at the clear code rate which for the purposes of this disclosure is to be pulses per minute.

These home and distant relays 5H and 5D govern the indications of the associated signal 5, as will vbe readily understood from the drawings, while the home relay 5H also acts to select between the particular coding contacts which are to govern the driven code rate for the transmitting relay for the section next in the rear (not shown). Such coding contacts SSC and 75C have been shown as associated with the signal 6, and these contacts are assumed to be operating 180 times per minute and '75 times per minute respectively to provide the usual code rates, but it will be readily appreciated that various other rates may be selected if desired. These coding contacts 180C and 75C may be of any 11 suitable type, that is, they may be motor driven, or they may be code oscillators of the type dis closed in the patent to O. S. Field No. 2,351,532?. dated June 20, 1944.

At the exit end of each track section, such as shown for the track section T, a transformn er ETFA has its primary winding energized from the opposite terminals (BX) and (CX) of a suit able alternating current supply; while its secondary Winding is connected in series with the secondary winding of a like transformer STIPB across the opposite terminals of the input of e. full-wave rectifier 5R. The output of the rectifier GR is connected through the limiting resistor 44 to the rails of the track section 5T.

The primary winding of the transformer STF@ is supplied with alternating current from the same source as transformer G'IFA when the back contact 45 of relay GCP is closed. Since the primary-secondary Winding ratios of the trans-- formers ETFA and G'IFB are substantially iden-- tical, and since the windings of the transformers are so connected that the output potentials of their secondaries are in opposition, there is no potential applied to the rectifier 5R under such condition. On the other hand, when the conu tact 45 of the relay BCP is picked up, the alternating current energy is removed from the primary winding of the transformer 'IFB, and such primary winding is also shunted through front contact 45. This not only removes the opposing potential of the secondary winding from the series circuit across the rectifier, but also substantially removes the inductive reactance of such transformer so that a potential, as supplied by the secondary winding of the transformer G'IFA, is applied to the opposite terminals of the rectier 6R. The output of the rectifier 5R is fed to the rails of the track section to energize relay 5'IR at the entering end. It is noted here that the track relay 5TH, at the entering end is connected across the track rails through limiting resistor 46 and back contact 4T of relay 5TPC.

The condenser 48 and a series resistor 49 are connected across the opposite terminals of the secondary of transformer GTFB and in multiple with front contact 45 of relay SCP so as to act as an arc suppressing unit for the front contact 45. It should be noted that condenser 48 does not resonate transformer WIFE, nor does it materialf 1y affect the phase of the output of the secondary of transformer GTFB because of the low capacity of such condenser.

The code transmitting relay SCP is controlled through front and back points 50 of relay 6H so as to be operated at the selected code rate, and while front contact 45 of relay GCP is closed, code pulse energy is supplied to the track section 5T, :but when back contact 45 is closed, the opposing potential of the secondary of transformer STFB prevents the flow of current to the track rails of section 5T. In this way, code pulses are applied to the rails of the track section 5T at the particular selected code rate.

Each track section has associated therewith an inverse code receiving relay ATR at the leaving end and suitable inverse code transmitting apparatus at the entering end of the track section including a rectifier SRA, a transformer ETFA and a transformer `ETFB, as well as a transmitting relay 5TPC controlled through repeater relays 5TPA and 5TPB as will presently be described.

Since it is desired to first point out the operation of the driven code transmitting apparatus,

it will be assumed for the present that only a driven code is being transmitted through the track section. It will be apparent that the current supplied through back contact 45 to the transformer G'IFB is merely of a suicient amount to supply the power losses of such transformer, and that the closure of front contact 45 causes a current flow through it, although the actual current of the driven code pulse is supplied by transformer ISTFA. The front contact 45 and circuit shunting the primary of transformer TFB will carry a current having a Value dependent upon the potential drop across the secondary of the transformer GTFB and dependent upon the ratio of turns between the primary and secondary windings. Since this is a short circuit condition for thetransfcrmer E'IFB, the potential across the secondary winding of this transformer will be fairly low because of the impedance of the track circuit load, so that the current through front contact 45 is not excessive. But since there will be some magnetic uX change in the transformer due to the opening of front contact 45 at the end of the impulse period, it is desirable to employ the condenser 48 and the series resistor 49 connected in multiple therewith to absorb any sudden changes in current conditions produced by the opening of front contact 45. In other words, although the arrangement of the transformers provides for a minimum of arcing at the contact 45, it is desirable to further reduce this arcing by the use of condenser 48. The series resistor 49 is included so that should the condenser 48 be substantially charged during the change-over of the contact 45 from a back point to a front point, the discharged current of the condenser will be limited by the series resistor 49.

The voltage supplied to the primary winding of the transformer GTFB may be of any suitable Value, such as a commercial volt supply, but since this value is usually a relatively high potential, as compared to the track circuit potentials Which may be in the order of S volts, for example, the contact 45 can be readily constructed of a relatively high resistance material, such as tungsten, and thus provide for long and reliable service. In other words, higher contact resistance materials may be used in such a circuit, since the potential is suflicient to break down any contact resistance and thus reliably supply the required current.

Assuming that each track section of a block signalling system is organized as above described, and that a clear code is being received over the track section 6T so that the home relay `(SH is picked up, then the relay GCP is being operated at the 180 code rate, and the signal 5 is of course indicating green or proceed. On the other hand, if the relay 6H were deenergized due to the absence of code in the track section 5T, the relay SCP would be operated at the 75 code rate and driven code pulses would be applied to the track section 5T in a manner above described. These impulses would be received by the track relay 5'IR causing the signal 5 to be controlled in accordance with such codes.

When a 180 code is received at the signal 5, the track relay 5'IR operates contact 4| at the 180 code rate so that should a train approach this signal and cause the deenergization of the approach decoding relay 5AII and close back contact 5l, then the signal 5 would indicate green by reason of a circuit from (-1-) closed through back contact 5l of relay 5AI-I, front contact 52 of relay H, front contact 53 of relay 5D, lamp of signal 5, to But if a 75 code is being received, then the relay 5D will be dropped away and the yellow lamp Y will be energized through back contact 53. On the other hand, if there is no code being received at signal 5 due to the presence of a train in track section 5T, both relay 5D and 5H will be dropped away, so that the red lamp will be energized through back contact 52 of relay 5H.

The transmission and reception of inverse code pulses will now be considered. More speciiically, upon the reception of each driven code pulse, the relay 5TR is picked up closing front cotnact 4l which causes vcurrent to flow through the upper half of the primary winding of the transformer 30. When this contact 4l assumes its lower or dropped away poistion upon the end of the driven code pulse, then the inductive reactance of the transformer 4B causes a surge of energy to charge the condenser 54 and in so doing causes a current fiow through the upper winding of the relay 5TPC of sufficient value and in a direction proper to pick up its contacts. Since the relay ETPC is of the magnetic stick type, its contacts remain in picked up positions after the surge of current through its upper windings has ceased.

At substantially the same time, the closure of back contact @l causes current to flow through rectifier unit 55 and through the relays 5TPA and 5'I`PB in multiple, the circuit for relay 5'IPB including back contact 5S of relay 5TPA. The relay BTPB picks up after a short interval of time followed by the picking up of the relay BTPA which opens the circuit for relay 5'I'PB at back contact 56. In other words, the relay STPA is slightly slower to pick up than the relay 5TPB, and this can be accomplished by adding a suitable resistor in multiple with the relay 5TPA.

After a short interval of time, the relay STPB releases, and this interval of time can be made of suitable value by adding a rectifier unit in multiple with its windings, and thus slightly delay its drop away. But when the relay 5TPB drops away, the relay STPA is still picked up, so that there is a circuit from (-l) through front contact 5l of relay S'IPA, back contact 58 of relay 5TPB, front contact 59 of relay 5TPC, lower winding of relay ETPC, to The current which iiows in this circuit is of such a direction as to cause the contacts of the magnetic stick type relay BIPC to be actuated to their lower positions to open contact 59 and immediately break such circuit. This happens before the end of the off period between two successive driven code pulses. In order to suppress any arcing which may occur at contact 59, a suitable condenser B may be placed in multiple with the lower winding or relay ETPC.

Thus, it can be seen that at the end of each driven code pulse, the relay STPC is actuated to a picked up position to apply an inverse code pulse to the track section 5T, and after a short period of time is restored to mark the end of the inverse code pulse.

More specifically, when the relay 5'IPC is picked up it opens back contact 4T to disconnect the track relay STR, and closes front lcontact 4l to connect the output of the rectifier unit 5RA through the limiting resistor S2 across the rails of the track section 5T. rlhe opening of back contact 53 of relay 5TPB disconnects the source of energy from the primary of the transformer S'IFB, and shunts such winding through front contact 53 to remove the inductive reactance of this transformer from the input circuit of the rectifier 5RA so that it can receive the necessary energy from the secondary of transformer 5'IFA. The back contact 63 of relay 5TPB is opened and its front contact is closed vslightly after the front contact 4l of relay 5TPC is closed. On the other hand, the relay 5TPB must drop to close its back contact 58 before the relay 5TPC is actuated to its lower position, thus, the back contact t3 is closed applying a potential in opposition to the potential produced by the secondary winding of transformer 5TFA before the front contact 4i is opened and the back contact 47 closed. In this way, the contact lll is used to commutate the track relay and inverse code energy applying circuit across the track rails at times at Iwhich there is no energy iiow to the track trails. For this reason, there is no arcing at the front and back points of the contact 47, and these contacts may be of suitable low resistance contact material, such as silver for example. The energy controlling contact 63 may be. constructed of suitable high resistance contact material, such as tungsten, since it controls the losses in the transformer 5TFB at a relatively high voltage, as described in connection lwith contact "l5 of the relay SCP.

he application of an inverse code pulse to the track section 5T occurs at a time when the driven code transmitting relay GCP is dropped away, so that there is no potential across the input terminals of the rectifier 6R. The inverse code energy iiows from the lower track rail through the rectifier unit GR and the limiting resistor 411 to the upper track rail. This produces a potential drop across the rectifier and the limiting resistor All so that a current flow is produced in the lower winding of the relay EATR to the right and through back contact 64 of the transmitting relay BCP to the upper terminal of resistor 41S. rThis causes the contacts of the inverse code receiving track relay SATR to he picked up, and since this is a magnetic stick type relay. its contacts remain picked up although the inverse code pulse ceases. It should be noted in this connection, that the potential across the lower winding of relay GATR is during an inverse code pulse substantially the same as that across the track rails, except perhaps for the potential drop that is caused in the lead wires from the track. Although the rectifier unit SR and limiting resistor lili are shunted across the track rails of section 5T under such a condition, it should be recognized that such a shunt has a higher effective resistance than would at first be apparent, because the relatively low potential at this end of the track circuit iinds that the forward resistance of the rectiner unit 6R is relatively high, which forward resistance is added to the particular adjustment of the limiting resistor 44. In other Words, rectifier units, especially those of the copper oxide type and the like, have a relatively high forward resistance for low potential and current values. The rectifier units when employed for applying energy te the track circuit are dealing with higher potentials and the forward resistance is relatively low, but when used to receive energy over the track rails at very low potential, the resistance is higher accordingly, and this factor should be taken into consideration in considering the potential drop across the low;r winding of the relay SATR upon the reception of inverse code pulses.

Upon the following driven code pulse, the rela-y tCP is picked up closing front contact 64 so that the lower winding of relay A'IR is connected through limiting resistor 55 to the output terminals of the rectifier unit 5R, causing cui rent to now in a left-hand direction through the lower winding of relayT SA'IR actuating its contacts to their lower or dropped away positions. In this way, the relay SATR is picked up upon each inverse code pulse and is caused to be dropped away upon each driven code pulse by reason of a local circuit. The actuation of the contacts of relay @ATR to their lower positions is caused to be retarded by reason of its upper winding being shunted by front contact 99. This is so that the contacts of the relay tATR will be in their upper and lower positions substantially the same length of time even if the inverse code pulses are of relatively short duration.

It will be readily apparent how a stretch of track having its several track sections equipped with coded track circuit apparatus as disclosed herein will provide for the control of the signals to give three indication signalling for the passage of tra-flic in an east bound direction, so that a detailed consideration of the passage of a train will not be given, and especially since it is believed that the above description clearly points out the condition of the signals during the presence and absence of a train and the dif ferent code rates.

Having described two forms of a coded track circuit block signalling system employing code transmitting apparatus organized to give a minimum amount of arcing at the code transmitting contacts as embodying the present invention, it is desired to be understood that the invention is shown in this connection for the purpose of facilitating its disclosure, and that it can be applied to systems of various other types. Although the invention has been shown embodied in two diiferent forms, it to be understood that other specinc embodiments and modi-- iications of the invention may be made, and that various adaptations and alterations may be re- ,i

quired to meet the problems of practice without in any manner departing from the spirit or scope of the present invention except as limited by the appended claims.

What I claim is:

l. In a coded track circuit signalling system for a section of railway track, a code transmitter comprising, a source of alternating current, a rectier unit, an inductive reactor unit including windings, circuit means connecting said alternating current source across the rails of said section through a portion of said reactor windings and rectifier units in series, and a coding contact intermittently acting to shunt said reactor windings to thereby permit the intermittent application of direct current code pulses to said section of track.

2. In a coded track circuit for railroads, a driven code transmitter comprising, a code transmitter relay having a contact intermittently operated to its opposite positions in accordance with different selected code rates, a full-wave rectifier unit having input and output terminals, circuit means effective to connect the output terminals of said rectifier across the rails of said track section, a reactor unit of the auto-transformer type having a condenser connected across its outer terminals to effect .its resonance at a particular frequency, and having a mid tap connected to one input terminal of said rectifier. a source of alternating current connected to the other input terminal of said rectifier and one outer terminal of said auto-transformer, and circuit means including said contact of said transmitter relay for intermittently shunting the outer terminals of said auto-transformer, whereby a succession of driven code impulses are applied to said track rails which impulses are controlled by said contact of said transmitter relay at a potential substantially higher than the actual potential applied to said track rails.

3. In a code transmitting organization having driven code pulses transmitted at different code rates, a code transmitting relay intermittently operated to its opposite positions in accordance with diiferent selected code rates and having advanced and retarded contacts both being closed in theJ same position, but said advanced contact being closed slightly prior to the closure of said retarded contact and being opened slightly subsequent to the opening of said retarded Contact, a full-wave rectifier having input and output terminals, circuit means including said advanced contact for intermittently connecting said rectifier output terminals to a track circuit, a reactor unit, a source of alternating current connected to the input terminals of said rectifier through a portion of said reactor unit, and circuit means including said retarded contact for shunting said reactor unit during each period when said rectier output terminals are connected to the track circuit.

4. In a coded track circuit for railroads operable to transmit oiI-code current pulses in one direction during off intervals between driven code pulses transmitted in the opposite direction, code transmitting and receiving apparatus at the driven code transmitting end of the track section comprising, an off-code track relay responsive to off-code pulses, a full-wave rectier having input and output terminals, a transmitter relay intermittently energized and deenergiaed in accordance with diiferent driven code rates and including advanced and retarded contact means, circuit means including said advanced contact means operated by said transmitter relay for alternately connecting and disconnecting said 0ff code track relay and the output terminals of said rectier across the rails of said track circuit, and circuit means including an alternating current source and said retarded contact means on said transmitter relay for applying energy to the input terminals of said rectifier subsequent to each of its connections to said track rails, said circuit means being effective to remove energy from the input of said rectier prior to each of its disconnections from the track rails, whereby said advanced contact means is not required to make or break the load current supplied to said track rails during each driven pulse application.

MARCIAN A. SCHEG.

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

UNITED STATES PATENTS Number Name Date 959,548 Kettering May 31, 1910 1,320,125 Chubb Oct. 28, 1919 1,930,609 Davidsmeyer Oct. 17, 1933 1,930,616 Herman I Oct. 17, 1933 (other references on following page) 17 13 UNITED STATES PATENTS Number Name Date Number Name Date Rees 18, 2,162,393 Thompson June 13, 1939 2,365399 BlOSSel Dec- 26 1944 2,172,693 Thomas sept. 12, 1939 2,366,983 'Scheg Jam 9I 1945 2,204,810 M1115 June 18, 1940 5 2,366,984 Scheg et a1. Jan. 9, 1945 2,206,576 Place July 2, 1940 2,399,760 Rees May '7, 1946 2,277,473 Crooks Mar, 24, 1942 f'2,405,860 Thompson Aug- 13, 1946 2,280,016 Agnew App 14, 1942 '2,416,736 Buckley Mar. 4, 1947 2,332,874 staples et a1. oct. 26, 1943 2,425,570 Scheg et a1- Apr- 12I 1947 2,348,525 Cravath May 9, 1944 10

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