US2043768A - Railway traffic controlling apparatus - Google Patents

Description

June 9, 1936.

F. H. NICHOLSON ET AL RAILWAY TRAFFIC CONTROLLING APPARATUs Filed Dec. 28, 1953 3 Sheets-Sheet 1 CODE C C0DE5 5 INVENTORS Frank HJVZCIIOLSOH and Herman G.Bloser.

THEIR ATTORNEY June 9, 1936. F. H. NICHOLSON ET 'AL 2,043,768

RAILWAY TRAFFIC CONTROLLING APPARATUS Filed Deal 28, 1935 3 Sheets-Sheet 2 d fi w m R n on wqab mw Edn w vmmfi 7 MG H m Y B I V 1 h THEIR A TTORNEY wmmow N HQQ m W NQQ M WHQQU June 9, 1936. F. H. NICHOLSON ET AL 2,043,768

RAILWAY TRAFFIC CONTROLLING APPARATUS Filed Dec. 28, 1933 3 Sheets-Sheet 3 INVENTORS Fran]: liNwlzolson and y flerm fiqgBlgssop' THEIR ATTORNEY SBLEQ W g m F W a, w x m w m M j n MQQ m WQQ w H QU w 5v Patented June 9, 1936 RAILWAY TRAFFIC CONTROLLING APPARATUS Frank H. Nicholson, Edgewood, and Herman G. Blosser, Pittsburgh, Pa., assignors to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application December 28, 1933, Scrial No. 704,324 22 Claims. (01. 246-34) Our invention relates to railway trafiic controlling apparatus, and more specifically to apparatus for providing broken down insulated rail joint protection in trafiic governing systems which utilize coded rail current for controlling wayside and/or cab signals.

We will describe four forms of railway trafiic controlling apparatus embodying our invention, and will then point out the novel features thereof in claims,

Fig. 1 of the accompanying drawings is a diagrammatic view showing one form of apparatus embodying our invention. Fig. 2 is a diagrammatic View illustrating some codes which may be used with apparatus embodying our invention. Figs. 3, 4 and 5 are diagrammatic views showing modified forms of apparatus also embodying our invention.

Similar reference characters refer to similar parts in each of the several views.

For reasons of economy, it is desirable that a signaling system have a minimum number of line wires. Therefore, other factors being equal, a system employing the single element type of track relay is to be preferred to one in which a two-element relay with its attendant line wires is used. However, in signaling systems using a single element track relay, broken down insulated rail joints may result in current from one track circuit flowing to the track'relay of an occupied track circuit in advance, thereby creating a potential false clear condition unless some protective means are provided. Since broken down rail joint protection is but one phase of the coded wayside and cab signalingproblem, there being numerous other factors and operating conditions which require that protective features be incorporated in any system which can be accepted as being safe and practicable, it is highly desirable that the solution for the broken down rail joint problem be of a type which can be readily assimilated into existing systems without necessitating extensive and costly changes.

Referring to Fig. 1, the apparatus shown therein can be used for providing protection to traflic moving from left to right, in the direction of the arrow. Section I2, as well as sections to the right and to the left thereof are supplied with coded rail current of what is known as the usual or unmodified frequency code, shown diagrammatically as code C of Fig. 2. This code comprises carrier current which may be either direct or alternating in character, upon which are impressed regular periodic variations recurring at any one of several code frequencies determined in accord.-

ance with traffic conditions in advance. Code frequencies of 180, 120 and impulses per minute will be assumed for purposes of illustration.

The code current for section l2 is supplied from a track transformer T energized from a 5 suitable code transmitter and code-selecting apparatus which are not shown, but which are similar to the corresponding apparatus located at the entering end of section l-2. Track relay TR which is energized through the relay transformer RT andrectifier R ,is designed to follow the impulses of the code, alternately closing contacts 9-H] and 9-4 I. These contacts periodically reverse the flow of direct current from a source BC, in the primary of decoding transformer DT thereby inducing an alternating voltage of the same code frequency in the secondary of this transformen, Decoding relay H which is energized through, the rectifier RH is non-selective as to the various codes-and will therefore be energized by current of any one of the three code frequencies which have been assumed. Relay E energized through the decoding unit DE is selective to code; and relay F energized through the decoding unit DF is selective to code. Units DE and DF are the usual code-tuning units and comprise a rectifier energized from a reactor and condenser circuit tuned to the desired code frequency. Relay H being non-tuned, will ordinarily pick up much more rapidly than either of the tuned relays E or F The apparatus described thus far is well known in coded wayside and cab signaling circuits and requires no further detailed description.

The operation of relay LP which provides the broken down rail joint protection will become apparent from the description which follows. It should be noted that relay LP receives energy over a front point of contact l2 of relay TR and a front point of-contact I3 of relay H Relay LP is sufficiently slow releasing to bridge the open interval of contact [2 when relay TR is following the lowest code frequency, assumed to be 80. Relay LP is also slightly slow to pick up for reasons which will become clear as the 45 description progresses. The indications of signal S are selectively controlled by the group of relays H LP E and F in a manner which will be obvious from the drawings, and it is deemed unnecessary to trace the signal control circuits in detail.

In normal operation, if current of 180 code is supplied to section l--2, 180 code will also be supplied to the rear section over a circuit which includes the following: terminal BX of a suitable source, contact 1 8|] of code transmitter GT front point of contact M of relay F back point of contact iii of relay E front contact l6 of relay LP and front point of contact I! of relay H and the winding of track transformer T for the rear section. If the code is I20, the rear section will again receive 180 code over the same circuit as above, with the exception that the circuit from terminal BX and contact 580 of the code transmitter will pass directly over the front point of contact l5 of relay E without including contact I 4 of relay F If code is supplied to section l2, code will be supplied to the rear section over a circuit which includes terminal BX,- contact 120 of transmitter CT back point of contact 14 of relay F and back point of contact [5 of relay E the remainder of the circuit being the same as previously traced. If a train is occupying section I2, relay H will be deenergized, and 80 code will be supplied to the rear section from terminal BX, contact 89 of transmitter 0T and back point of contact I! of relay H to the track transformer T.

From the foregoing description, it will be observed that relay LP must be energized before a code higher than 80 can be supplied to transformer T of the rear section. The slow pick up feature of relay LP aids in delaying the application of the 120 and codes to the rear section when changes in traffic conditions in advance sections warrant the application of these codes.

Without relay LP if the rail joints at location I should be broken down at the sametime that a train occupies the right-hand end of section l2, relay TR might follow 80 code from transformer T, energizing relay H and causing 120 code to be supplied to transformer T. The 120 code might cause relay E to become energized causing 180 code to be supplied to transformer T, with the possibility of relay F becoming falsely energized. In this manner, by successive stages, a false proceed indication might finally be displayed by signal S in the occupied section l2. Relay LP provides the required protection by preventing the occurrence of the first step in the sequence of operations just described, that is, it prevents the stepping up of the code in the rear section from 80 to 120 when section I 2 is occupied.

If the rail joints at location I are broken down at the same time that a train occupies the righthand end of section I2, and relay TR begins to follow 80 code from the rear section, relay H may become temporarily energized, but as soon as relay H picks up, all energy will be disconnected from transformer T at the back point of contact l1, whereupon relay TR will immediately release, releasing relay H in turn, to repeat the above cycle periodically. Relay Ll? is so designed that the short time interval during which front contacts 12 and I3 of relays TR and H respectively are closed simultaneously is insuflicient for pickup of relay LP Therefore, neither 120 nor 180 code can be fed to transformer T under the above condition, as a result of which it will be impossible for signal S to display a permissive indication. Furthermore, since relay H will pick up and release alternately, the restrictive indication displayed by signal S will be flashing in character, thus providing an indication of the defective rail joint condition.

The circuit of Fig. 1 is sui'ficient to provide protection to a train moving in the normal trafiic direction, as indicated. However, under certain traffic conditions, this circuit may prove inadequate. For example, should the joints at loca- 'l--2 will not receive 120 or 180 code over the joints because relay LP will not pick up, as explained above. However, if section l2 is already receiving code prior to the time that the joints break down, then since relay LP is energized, there is nothing further to prevent the application of the 120 or 180 code. Therefore, a train hacking into section l-2 or entering the section from a siding without effectively shunting the track might fail to cancel the permissive indication of signal S The circuits of Figs. 3, 4 and 5 provide against conditions such as the one just described, and represent modified forms of the circuit of Fig. 1. These circuitsare adapted to use codes such as A and B of Fig. 2 in alternate track sections. Codes A and B are essentially the same as code C in that the same wayside and cab signal response is obtainable therewith as with code C, but these codes are modified by interposing a relatively long on interval periodically in code A, and a relathe proper code contacts, thus cancelling the off intervals 0. and the on intervals 1) shown dotted in Fig. 2. For reasons which will become clear as the description of Figs. 3, 4 and 5 progresses, it is not necessary that the long on or long off intervals be present in each of the 180, 120 and 80 code frequencies of codes A and B, as it is sufficient merely to modify the 180 code for preventing a false clear signal, the 120 and 80 codes remaining unmodified and being therefore similar to code C of Fig. 2.

Referring now to Fig. 3, adjoining track sections of this figure have staggered codes, that is, section 3% is supplied with code A having a long on interval, and the adjoining section to the left as Well as the section to the right thereof are supplied with code B having a long off interval, it being understood that codes of additional adjoining sections, which are not shown, will be alternated or staggered in a similar manner throughout the stretch. The stagger will be present in the 180 code only, the 120 and 80 codes of adjoining sections being unmodified, that is, identical for all sections of the stretch.

The normal operation of the system of Fig. 3 is identical with that of the system of Fig. 1, in that the decoding relay H will remain energized on any one of the three code frequencies, and the tuned decoding relays E or F will be energized on 120 or 180 code, respectively. The circuits for signal S are not shown extended to the signal location in order to simplify the drawings. The manner in which the decoding relays control the indications of signal S under normal conditions, being well known, will not be described in detail.

Relay 'IP is the protective relay in Fig. 3, and performs a function analogous to that of the LP relay of Fig. 1. It will be noted that the front contact 18 of relay TP is included in the circuits which feed 180 and 120 code to track transformer T Therefore, it is necessary that relay TP be energized before any code higher than 80' can be fed to the rear section. If 80 or 120 code is applied to section 3-4, relay TF will be energized over front contact IQ of relay H and the back point of contact 20 of relay F following 180 codehaving the long on interval, the energizing circuit for relay 'I'P will include front contact IQ of relay H front point of contact 20 of relay F front contact 2| of relay TR and front contact 22 of relay TF Relay TP is quick to pick up but is sufiiciently slow releasing to bridge the normal periodic opening of front contact 2| of relay TR on 180 code such as is pro vided by code A of 180 code frequency.

We shall now assume that while code B of 180 code frequencyis being fed to the rear section and the rail joints at location 3 are broken down, a train enters section 3-4 from a siding, or a switch is thrown in the section, thus cutting off the normal supply of current to section 3-4. Should relay TR operate on current of code B entering over the rail joints, relays F and H will be held energized momentarily, but the first long off interval of the code B of 180 code frequency will cause relay IT to release, by virtue of the prolonged open circuit time of front contact 2!. Thereupon, all code will be disconnected temporarily from the rear-section, causing a release of the decoding relays F and H and causing signal S to display-its most restrictive indication.

Upon the release of relay H 80 code will be fed tothe rear section over the back points of contacts l8 and 23 of relays TF and H If the nect the modified 180 code with the long off interval to the rear'section, thus releasing relay TP -again, only to cause aperiodic repetition of "the above cycle of operation.

It will be apparent from the foregoing that whenever conditions are such that a false clear signal might be displayed by leakage of the 180 code from an adjoining section, the I? relay becomes deenergized and deenergizes the decoding apparatus, thus preventing a clear signal. With the apparatus of Fig. '3, if the rail joints break down, the signal indications will be stepped up in repeated and rap-id succession from the indication corresponding to no code, through the indications corresponding to the 80 and 120 codes up to, but not including, the sustained clear indication which corresponds to 180 code. The flashing aspect of the signal may be used to provide a distinctive indication of the particular type of failure which has occurred.

The decoding apparatus for the rear section adjoining section 3-4 has not been shown since it is identical with the apparatus of section 3-4 with the exception that, since the TP relay for the rear section must release during a long on interval, this relay will be controlled over a back contact of the code-following track relay, corresponding to the front contact 2| of relay TR It is understood that if desired, the 120 and 80 LP relay circuit of Fig. 1 with the protective fea- If relay TB. is

tures of the TP relay circuit of Fig. 3. The LP relay of Fig. 1 insures that once the signal is caused to indicate danger as a result of defective rail joints, the danger indication will be maintained. However, should the dangerous condition arise while the signal is displaying a proceed indication, the LP relay will not provide the required protection. On the other hand, the '1? relay of Fig. 3 will provide the desired protection against a false clear signal, but

will not maintain a steady danger indication, which in most cases is to be desired. By incorporating both LP and 'I'P relays in Fig. 4, a circuit is obtained in which, if the rail joints break down and the normal code supply is cut off from the track section'for any reason, the T? relay will cause the associated signal to indicate danger, and the LP relay will cause this indication to be maintained until the defect is cured.

The 180 code supplied to section 5-6 contains a periodic long on interval (Code A of Fig. 2), and the 180 code supplied to section 6-! contains a periodic long off interval (Code B of Fig. 2), the 120 and 80 codes for both sections being unmodified, as in Fig. 3. If section 6-! is deprived of code, that is, if a train enters this section from a siding for example at a time when the rail joints at location 6 are broken down and section 5-6 is being supplied with code A of 180 code frequency, relays H and P will be energized momentarily, but relay TP which was picked up following the pickup of relay H will release uponthe occurrence of the first long on. interval of code A, since it is controlled over the back point of contact 24 of relay PR This will occur because during the long on interval the back point of contact 24 will remain open, and the retardation of relay TIP is insufficient to bridge this interval. During the release interval of relay TP and the subsequent release interval of relay H no code will be fed to section 5-6 because as soon as the front point of contact 3 of relay TP opens, the

120 or 180 code is disconnected, and until the back point of contact [8 and the back point of contact 23 of relay H are both closed, 80 code can not be supplied to the rear section.

As soon as the back point of contact 23 of relay H closes, 80 code will be supplied to section 5-6. i

The 80 code will operate relay TR, causing relay H to pick up, again cutting off the 80 code at the back point of contact 23. Since relay LP which controls the application of 120 code to section 5-6, requires that front contacts l9 and 24 of relays H and TR be both closed for an appreciable time interval in order that relay LP may pick up, therefore. as previously described in connection with Fig. 1, relay LP will not pick up when 80 code enters from an adjoining section. Consequently, signal I S will continue to indicate danger, as will be apparent from an inspection of the signal control circuits, which are self-explanatory. That is, the danger indication will be momentarily interrupted each time that relay H picks up, open- 7 than 80 can subsequently enter section 6-! from the rear section, with the result that after a momentary signal flash, the danger indication will be maintained even though this indication is periodically interrupted.

Referring to Fig. 5 which represents a simplification of the circuit of Fig. 4, it will be noted that the single relay AP replaces the two relays LP and TP of Fig. e, and combines the protective features of each. Considering section 9l0, under normal conditions relay AP will remain energized on any of the codes supplied to the section by transformer T That is, if the code is89, relay I-l will be energized, and relay AP will be picked up over a circuit which includes back contact 25 of relay F front point of contact 24 of relay PR and front contact IQ of relay H If the code is 129, no change in the above energizing circuit for relay AP will occur. If the code is 180, code B being understood, then the energizing circuit for relay AP will include front contact 26 of relay AP front point of contact 27 of relay F back point of contact 2 3 of relay TR and front contact IQ of relay H With a train occupying the right-hand end of section 9-49, if 180 code A from the rear section passes over the joints and operates relay T129, the long on interval of this code will hold the back point of contact 2d of relay TR. open for a sufiicient period to release relay AP 'which in opening its front contact 28 will release relay F immediately, thus shortening the duration of the signal flash and accelerating the display of the danger indication. The release of relay AP will cut off all code from section 89, causing relay H to release. When relay H releases, code will be fed to section 8--9 over the back point of contact 23, picking up relay H momentarily, thus cutting on; the code, as described previously. Relay AP is so designed that it will not pick up during the short interval that front contacts l9 and 24 of relays H and TR are simultaneously closed, in the above operation. Therefore, signal S will continue to indicate danger. If code from section 8-9 operates relay TR relay E will pick up and will apply code A to the rear section, which code will, in turn, release relay AP".

claim is:

'1. In combination, two adjoining sections of railway track, a source of code current and a code-following track relay connected with the rails of one of said sections, a decoding relay responsive to code operation of said track relay, a protection relay controlled by both said track relay and said decoding relay, a signal govrned by said protection relay, and means governed by said decoding relay for controlling the supply of rail current to the other of said two sections.

2. In, combination, two adjoining sections of railway track, a source of code current and a code-following track relay connected with the rails of one of said sections, a decoding relay responsive to code operation of said track relay, a protection relay controlled by both said track relay and said decoding relay, and means governed by said decoding relay and said protection relay for controlling the supply of rail current to the other of said two sections.

. 3. In combination, two adjoining sections of railway track, a source of code current and a code-following track relay connected with the rails of one of said sections, a decoding relay which becomes energized in response to code operation of said track relay, a protection relay, an energizing circuit for said protection relay including a front contact of said track relay and 1 a front contact of said decoding relay, a signal governed by said protection relay, and means including a back contact of said decoding relay for supplying rail current to the other of said two sections. 2

4. In combination, two adjoining sections of railway track, a source of code current and a code-following track relay connected with the rails of one of said sections, a decoding relay which becomes energized in response to code operation of said track relay, a protection relay energized over a front contact of said track relay and a front contact of said decoding relay, and means including a front contact of said decoding relay and a front contact of said protection relay 2- for controlling the supply of rail current to the other of said two sections.

5. In combination, two adjoining sections of railway track, a source of code current and a code-following track relay connected with the 3 rails of one of said sections, a decoding relay which becomes energized in response to code operation of said track relay, a circuit including a back contact of said decoding relay for supplying rail current to the other of said two sections, 4 and a protection relay energized over a front contact of said track relay as well as a front con: tact of said decoding relay and having a time interval suificiently long for bridging the code operation of said track relay, said time interval be- 4 ing sumciently short to permit said relay to release if said track relay becomes operated by current supplied to said other section, thereby providing an indication that rail current from said other section is flowing in said one section. 5

6. In combination, a firstsection of railway track, a second section of railway track adjoining therewith, means for supplying said first section with rail current varied according to a first code, a code-following track relay for said first section, a decoding relay-responsive to code operation of said track relay, a source of current varied according to a second code, a protection relay controlled by said track relay and said decoding relay in such manner as to assume one condition when the track relay is following current varied according to said first code and another condition when the track relay is following current from said source varied according to said second code, and means controlled in 0 accordance with the condition of said protection relay for supplying current from said source to the rails of said second section.

7. In combination, a first section of railway track, a second section of railway track adjoin- 7 ing therewith, means for supplying said first section with a first code having a periodically recurrent on interval of relatively long duration, means for supplying said second section with a second code having a periodically recur- 7 rent off interval of' relatively longduration, a code-following track relay for said first section, a decoding relay responsive to code operation of said track relay, a protection relay controlled by said track relay and said decoding relay in such manner as to assume a first or a second condition according as said track relay is following said first or said second code respectively, and means effective when the protection relay occupies said second condition for preventing the supply of said second code to said second section.

8. In combination, a first section of railway track, a second section of railway track adjoining therewith, means for supplying said first section with a, first code having .a periodically recurrent on interval of relatively long duration, means for supplying said second section with a second code having a periodically recurrent/o interval of relatively long duration, a code-following track relay for said first section, a decoding relay which maintains its energized condition in response to code operation of said track relay, a protection relay energized over a front contact of said decoding relay and having ,a. release time insufiicient to bridge the long off interval of said second code, and

means effective when the protection relay is deenergized for preventing the supply of said second code to said second section.

9. In combination, a first section of railway track, a second section of railway track adjoining therewith, means for supplying rail current of a first and of a second code to said first and said second section respectively, a code-following track relay for said first section, a decoding relay which becomes energized in response to code operation of said track relay, a protection relay, a pickup circuit for said protection relay including a front contact of said decoding relay, astick circuit for said protection relay including a front contact of said track relay and a front .contact of said decoding relay, the release time of said protection relay with respect to the duration of impulses of said second code being such that said protection relay will release if said ,track relay is following said second code, and

means controlled by said protection 'relay for governing the supply of said second code to said second section.

.lay which becomes energized in response to code operation of said track relay, a protection relay, a pickup circuit for said protection relay including a front contact of said decoding relay,

a stick circuit for said protection relay including a front contact of said track relay and a front contact of said decoding relay, the release time of said protection relay with respect to the duration of impulses of said second code being such that said protection relay will release if said track relay is following said second code, and a signal controlled by said protection relay.

11. In combination, a first section of railway track, a second section of railway track adjoining therewith, means for supplying said first section with rail current of a first or of a second code in accordance with trafiic conditions, means for supplying said second section with rail current of said first code or of a third code "in accordance with trafic conditions, a code-following track relay for said first section; a first and a second decoding relay, said first relay being energized in response to operation of said track relay on either said first or saidsecond code, and said second relay being energized only in response to operation of said track relay on said second code; a first and a second protection relay; apickup circuit for said first protection relay including a back contact of said second decoding relay, a front contact of said track relay, and a front contact of said first decoding relay; a pickup circuit for said second protection relay including a back contact of said second decoding relay and a front contact of said first decoding relay, a stick circuit for said second protection relay including a contact of said track relay and a front contact of said first decoding relay, said second protection relay having a release time suflioient to bridge the operation of said track relay on said first or said second code but not on said third code, means controlled by saidsecond protection relay for governing the supply of said third code to said second section, means including a back contact of said first decoding relay for preventing the pickup of said first protection relay if said track relay is following rail current of said first code supplied to said second section, and a signal governed by said first protection relay.

1 2. In combination, a first section of railway track, a second section of railway track adjoining therewith, means for supplying rail current of a. first and of a second code to said first and said sccondsection respectively, a code-following track relay ,for said first section, a protection relay, a pickup circuit for said protection relay including a front contact of said track relay; a stickcircuit for said protection relay including a back contact of said track relay, said protection relay having a release time sufiicient to bridge the p ation of said track relay on said first code but not on said second code; and means controlled by said protection relay for governing the supply of said second code to said second section. 13. In combination, a first section of railway track,,a second section of railway track adjoining therewith, means for supplying rail current of a first and of a second code to said'first and said second section respectively, a code-following track relay for said first section, a decoding relay energized in response to code operation of said track relay, a protection relay, a pickup circuit for said protection relay including a back contact of said decoding relay and afront contact of said track relay; a stick circuit for said protection relay including a front contact of said decoding relay and a contact of said track relay, said protection relay having a release time sufiicient to bridge the operation of said track relay on said first code but not on said second code; and means including a front contact of said protection relay for governing the supply of said second code to said second section.

14. In combination, afirst section of railway track, a second section of railway track adjoining therewith, means for supplying said first section with rail current of a first or of a second code in accordance with traffic conditions, means for supplying said second section with rail current of said first code .or of a third code in accordance with traffic conditions, a code-following track relay for said first section; a first anda second decoding relay, said first relay being energized in response to operation of said trackrelay on either said first or said second code, and said second relay being energized only in response to operation of said track relay on said second code; a protection relay; a pickup circuit for said protection relay including a back contact of said second decoding relay, a front contact of said track relay, and a front contact of said first decoding relay; a stick circuit for said protection relay including a front contact of said second decoding relay, a contact of said track relay, and a front contact of said first decoding relay, said protection relay having a release time suflicient to bridge the operation of said track relay on said first or said second code but not on said third code; means including a back contact of said first decoding relay for interrupting the supply of said first code to said second section, said protection relay having a pickup interval sufficiently long to prevent pickup if said track relay is following said first code supplied to said second section; and means controlled by said protection relay for governing the supply of said third code to said second section. 7

15. In combination, a first section of railway track, a second section of railway track adjoin,- ing therewith, means for supplying said first section with rail current of a first code characterized by a periodically recurrent long 01f interval, means for supplying said second section with rail current of 'a second code characterized by a periodically recurrent long on interval, a codefollowing track relay for said first section, a protection relay, a pickup circuit for said protection relay including a front contact of said track relay; a stick circuit for said protection relay controlled by said track relay in such manner as to become interrupted due to release of said protection relayif said track relay follows said long on interval of said second code; and means controlled by said protection relay for governing the supply of said secondiicode to said second section. 7

16. In combination, a stretch of railway track divided into a plurality of track sections alternate ones of which are supplied with rail current of a first code and intervening ones of which are supplied with rail current of a second code, a, code- ,following track relay and a protection relay for each of said alternatessections and for each of said intervening sections, a pickup circuit for each of said protection relays including a front contact of the associated track relay, a stick circuit for each of .said protection relays controlled by the associated track relay in such manner as to become interrupted due to release of the protection relay in the event that the associated track relay is following the code supplied to an adjoining track section, and means controlled by each of said protection relays .for governing the supply of rail current to the rear section adjoining the section associated with the given protection relay. 17. In combination, a stretch of railway track divided into a plurality of track sections alternate ones of which are supplied with rail current of a first code characterized by a periodically recurrent long oif interval and intervening ones of which are supplied with rail current of a second code characterized by a periodically recurrent long on interval, a code following track relay and a protection relay for each of said alternate sections and for each of said intervening sections, a pickup circuit for each of said protection relays including a front contact of the associated track relay; a stick circuit for each of said protection relays controlled by the associated track relay in such manner as to become interrupted due to release of said protection relay if the associated track relay follows said long on interval of the second code or said long oif interval of the first code, respectively, according as the protection relay is associated with an alternate or an intervening track section; and means controlled by each of said protection relays for governing the supply of rail current to the rear section adjoining the section associated with the given protection relay.

18. In combination, a first section of railway track, a second section of railway track adjoining therewith, means for supplying rail current of a first and of a second code to said first and said second section respectively, a code-following track relay for said first section, a protection relay, a decoding relay energized in response to code operation of said track relay over a front P contact of said protection relay, means for controlling said protection relay by said track relay in such manner that the protection relay will remain energized if the track relay is following said first code but will release if said track relay is following said second code, means controlled by said protection relay for governing the supply of said second code to said second section, and a signal controlled by said decoding relay.

19. In combination, a first section of railway track, a second section of railway track adjoining therewith, means for supplying rail current of a first and of a second code to said first and said second section'respectively, a code-following track relay for said first section, a protection relay, a pickup circuit for said protection relay effective when said track relay is following code, a stick circuit for said protection relay controlled by said track relay in such manner as to remain effective when said protection relay is following said first code but not said second code, and means controlled by said protection relay for governing the supply of said second code to said second section.

20. In combination, a first section of railway track, a second section of railway track adjoining therewith, means for supplying rail current of a first and of a second code to said first and said second section respectively, a code-following track relay for said first section, a decoding relay energized in response to code operation of said track relay, a protection relay, a pickup circuit for said protection relay including a front contact of said decoding relay, 9, stick circuit for said protection relay including a front contact of said decoding relay and a contact of said track relay, said protection relay having a release time sufiicient to bridge the operation of said track relay on said first code but not on said second code, and means including a front contact of said protection relay for governing the supply of said second code to said second section.

21. In combination, two adjoining sections of railway track, a code-following track relay for the forward section, a, decoding relay controlled by said track relay in such manner as to assume an operated condition when the track relay is following code, means for supplying current to the rear section over a contact of said decoding relay which contact becomes opened when the decoding relay assumes said operated condition thereby causing an interruption in the supply of current to said rear section if said track relay becomes operated by the current supplied to said rear section, and a protection relay controlled by said decoding relay and said track relay in such manner that said protection relay will respond during said current interruption thereby providing an indication that rail current from said rear section is flowing in said forward section.

22. In combination, two adjoining sections of railway track, a code following track relay for the forward section, a decoding relay controlled to an energized condition by said track relay when the track relay is operated, means including a back contact of said decoding relay for supplying rail current to the rear section, and a protection relay controlled by said track relay and over a circuit including a front contact of said decoding relay whereby said protection relay will release during the interruption of said circuit which follows when said track relay is operated by current supplied to said rear section thereby providing an indication that rail current from said rear section is flowing in said forward section.

FRANK H. NICHOLSON. HERMAN G. BLOSSER.

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