US 3865042 A
A method and apparatus for controlling the positioning of switches in a railway classification yard so as to route successive cuts from a train, as they are uncoupled at the hump of the yard, to their respective destination tracks. A digital computer receives information respecting the location of the various cuts as they are traveling through the yard and operates the various switches in the yard to safely route each of the cuts to its destination track. Protection is provided to handle blocked and fouled tracks and also to detect stalled cars and prevent cornering. The computer is responsive to information received from a variety of sensing devices placed throughout the yard and means are further provided to detect failures of these sensing devices in order to enable the system to operate in spite of such failures. The apparatus is so arranged that it can be applied to a wide variety of classification yards with a minimum amount of modification. In particular, the yard characteristics are separately stored in a storage means. To modify the apparatus to control a classification yard with differing characteristics, it is only necessary to modify the yard characteristic data stored in the storage means and the apparatus can be operated in a virtually unchanged manner.
Description (OCR text may contain errors)
Ilnite tates tent [191 DePaola et a1.
l ll 3,%5,4
[451 Feb. it, 1975 AUTOMATIC SWITCHING CONTROL SYSTEM lFOR RAILWAY CLASSIFICATION YARDS  Inventors: John J. DePaola, Penfield; Charles W. Morse, Rochester, both of NY.
 Assignee: General Signal Corporation,
22 Filed: Apr. 4, 1973 21 Appl. No.: 348,376
Primary ExaminerM. Henson Wood, Jr.
Assistant Examiner-Reinhard .1. Eisenzopf Attorney, Agent, or Firm-Stanley B. Green; Milton E. Kleinman ABSTRACT A method and apparatus for controlling the positioning of switches in a railway classification yard so as to route successive cuts from a train, as they are uncoupled at the hump of the yard, to their respective destination tracks. A digital computer receives information respecting the location of the various cuts as they are traveling through the yard and operates the various switches in the yard to safely route each of the cuts to its destination track, Protection is provided to handle blocked and fouled tracks and also to detect stalled cars and prevent cornering. The computer is responsive to information received from a variety of sensing devices placed throughout the yard and means are further provided to detect failures of these sensing devices in order to enable the system to operate in spite of such failures. The apparatus is so arranged that it can be applied to a wide variety of classification yards with a minimum amount of modification. in particular, the yard characteristics are separately stored in a storage means. To modify the apparatus to control a classification yard with differing characteristics, it is only necessary to modify the yard characteristic data stored in the storage means and the apparatus can be operated in a virtually unchanged manner.
16 Claims, 22 Drawing Figures PATENIEDFEBHIBYE- 3.865.042
sum U101 14 1 5/ FIG. 2B. P N
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sum cm 147 FIG. 3B.
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Output To Throw Switch Sig? No Re tu rn) Store Car Parameters Reset PATENTEBFEB A i 3;8e5'.@42
-SHEET CHEF 14 I n DACT List Y 72 Message es gy (Turn Off) T Add 73 Yes ne 0 Tem 262 AXLE Ont f a wo pci j t fin Lights No et 76 Swlfch Prefect 77 St 78 I Y e 2 W e5 LOODFGII Defect No SWOCC hisN es 'g SWOCC C Ajiled FIG. 5A.
PATENTEI] FEB] 1 1975 Flag As MISRT SHEET CB [IF M DEST eet DEER I09 mc Determine 4/ 98 Hlgh And Low Gei Aciocent Truck Reochoble Truck I IIO s 99 Track N0 Blogk Yes PATENTEDFEBI 1 i915 3.865.042
sum 10 0F 1 4 com s GE) I lGefCU T Ace! I Add Sw.Grodel I65 Decrement DESTB I25 Get Prev. Switch No. And Store lncremenfl/ DESTB Use This J/ITI Swi fch AS SWXX Us e EsfMuster Exi H-B As VF I33 I Add Ave Ref. Time To T Increment Poss No.,
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PATENTED 1 I975 3.8651342 SHEEI 120F14 GetCulc. 188 V Next Front 178 Sfore' CUT I89 Add ForCUTB USeAS v l Of CUT B Resfo'reP ev. Saved In 0.
F As N 1 I94 A Cl ronc Poss Use Vel. I95
use Mosrer' Group Of CUT Exit Speed EXIT Speed Add Possible ConfrolError '/|B6 UseColc. Findlvelocity PATENTED FEB] I I975 SHEET l bUF14 mum 6E; wEBum 22265 o8 E a AUTOMATIC SWITCHING CONTROL SYSTEM FOR RAILWAY CLASSIFICATION YARDS BACKGROUND OF THE INVENTION Typically, railway classification yards perform a sorting function. A train of cars is received and pushed up to the hump of the yard. At the hump, the cars are uncoupled and allowed to roll down the hump and the switches in the yard are positioned so as to route each of the diffferent cuts taken from the train, to its destination track. The cars in the train may have originated from a single location but commonly have ultimate destinations at widely separate locations. The railway classification yard segregates the train into a number of different groups, each of the groups having cars with the same or nearby ultimate destinations. A typical railway classification yard is shown, in plan view, in FIG. 1. This shows a yard with eight destination tracks so that the incoming train can be broken up into as many as eight different groups of cars. FIG. 2 shows an elevation view of the yard showing one typical route through the yard.
In the earlier days of use of railway classification yards, the switching functions were manually controlled. That is, an operator, stationed in a control tower, manually positioned the switches in the yard so as to properly route a particular cut to its destination track. However, the period of time during which a car may be traveling from the crest to its destination track can be appreciable and, in order to avoid conflicts, these manually controlled yards were used limited to only one or two cars actually rolling through the yard at the same time. In an attempt to increase the capacity of these railway classification yards, automatic control apparatus, based on relays, was provided so as follow a particular cut through the yard and properly position the switches immediately ahead of it as necessary to route the cut to its destination track. This enables a plurality of cars to be rolling through the yard at the same time and avoids routing conflicts. However, these control units were large, costly, and complex. A prime factor in the large cost of these control systems was the fact that each one had to be specially designed to fit the characteristics of the particular yard for which it was intended. For instance, such a system for a yard with eight destination tracks could hardly be sufficient to control a yard with 16 destination tracks. Even two yards with the same number of destination tracks might not be able to use identical control apparatus due to differences in the switching arrangement within the yard.
With the advent of the digital computer and associated technology, it became apparent that application of this technology to the railway classification yard control problem could reduce the cost and the complexity of the control equipment required. Instead of tailor making a relay control system for each yard, it would only be necessary to devise a program for the digital computer, fitted to the yard to cooperate with the sensing and control apparatus in order to properly operate the various switches so as to achieve the functions of the railway classification yard. This approach has proved fruitful and there are a number of digital computer controlled railway classification yards now in operation.
The advent of the computer, with its increased decision-making capabilities over the relay control systems also allowed the control system to respond to a number of poptentially dangerous situations and to control the apparatus in the yard to avoid these dangers. For instance, a cut may become stalled at an intermediate position in the yard. This is a condition which must be recognized and responded to by the control system so as not to route additional cuts into the same track in which another cut is stalled. Furthermore, one of the most potentially dangerous situations in a railway classification yard is cornering. Railway cars are designed to withstand substantial shocks when applied at the car coupler. However, the superstructure of many cars is not designed to withstand similar impacts, and if impacted, will be severely damaged. If one cut traverses a switch in one position and a following cut traverses the same switch in a different position, a potential cornering situation is present. If the second cut is traveling faster than the first cut, the front corner of the second cut may impact the rear corner of thefirst cut causing damage to both. To prevent cornering, the control system must respond to potential cornering situations by maintaining the switch in its original position for a sufficient period of time to ensure that this cornering cannot occur.
Although the advent of digital computer technology enabled the reduction in costs of fabricating a control system substantially, the complexity of the control problem, of course, was not reduced. A program devised to control the railway classification yard was still costly and complex to develop. Applicants believed it desirable to provide a system in which a digital computer controlled a railway classification yard with a program that was easily modifiable to control a wide variety of classification yards. In particular, applicants sought to devise such a system wherein the logical or decision making functions was segregated from the data which defined the yard characteristics. The system disclosed in this application accomplished this objective and is thus adaptable to almost any classification yard. That is, the logical portions of the program can be applied to any classification yard and the tables which define the yard characteristics need only be modified in accordance with the characteristics of the yard to which the program is to be applied.
The system disclosed herein also provides improved cornering protection. The cornering protection system is capable of searching through the portion of the yard behind any particular cut to search for another out which is destined for the same switch. The second cuts present velocity is determined and then the velocity is projected so as to determine the velocity of the second cut at the switch where a potential cornering problem exists. The system then computes the times necessary for both cuts to reach a point beyond which cornering is no longer possible. The switch is then held in its original position for a time sufficient to ensure that no cornering can take place. If the second identified cut reaches the switch before the expiration of this protection time, it is routed to follow the first cut which will of course make cornering impossible.
In addition, the system is designed to respond to and safely handle failures in sensing device operation without creating dangerous conditions.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a plan view of a typical railway classification yard, schematically illustrating the placement of sensing apparatus of the control system;
FIG. 2A is an elevation view of a typical route in a railway classification yard shown in FIG. 1, identifying major routines which are performed when a cut is sensed at that specific location in the route;
FIG. 2B is a schematic showing of the interrelationship between the digital computer and the various sensing and control devices in the yard;
FIG. 3A and FIG. 3C, taken together, are a flow diagram for the routine entitled CARDET;
FIG. 3B is a flow diagram for the routine entitled FORW;
FIG. 4 is a flow diagram for the routine entitled POSSW;
FIG. 5A is a flow diagram for the routine entitled SWWD;
FIG. 5B is a flow diagram for the routine entitled SWOCC;
FIG. 5C is a flow diagram for the routine entitled DESEN;
FIG. 5D is a flow diagram for the routine entitled DEST;
FIG. SE is a flow diagram for the routine entitled CALARV;
FIG. 5F, FIG. 56, FIG. 5H, and FIG. 5K, taken together, are a flow diagram for the routine entitled CP;
FIG. 5[ is a flow diagram for the routine entitled COMPS;
FIG. 5.] is a flow diagram for the routine entitled LOST;
FIG. 6A and FIG. 6B, taken together, are a flow diagram for the routine entitled SUN;
FIG. 6C is a flow diagram for the routine entitled REMOV;
FIG. 7 is a flow diagram for the routine entitled CTC.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In a railway classification yard, a train of incoming cars is pushed up to the crest or hump of the yard and then the cars are uncoupled and allowed to roll down the crest and through the yard to their intended destination tracks. Destination tracks for each of the cars of the train are assigned with respect to the ultimate destination of each of the cars. When adjacent cars of a train have the same ultimate destination or nearby ultimate destinations, they may be assigned identical destination tracks. In this case, the adjacent cars remain coupled and such cars are called a cut. For the purposes of this description we shall refer only to a cut, and a cut may comprise one or more than one car intended for the same destination track.
At or before the time of arrival of the train into the railway classification yard, a consist will be available. The consist is merely a list of the cars in the train in the order in which they will arrive, identifying the car by its owner and serial number, the number of axles in the car, and, most importantly, its intended destination track. After a cut is uncoupled from the train and allowed to roll down the hump, the apparatus disclosed herein will properly position the switches in its path so as to route the cut to the correct one of the destination tracks in the yard.
FIG. 1 shows an illustrative railway classification yard with eight destination tracks, Tl-T8. It will, of course, be understood that the number of destination tracks in an actual railway classification yard can vary, being either more or less than the number of destination tracks shown in FIG. 1.
Located at the crest is wheel detector 1 (WDl which actually comprises a pair of wheel detectors WDla and WBlb. Additional wheel detectors, WD2 through WD8, are located prior to each switch in the classification yard. FIG. 1 shows seven switches in the classification yard, Sl-S7. Also adjacent each of the switches in the yard is a presence detector, P2-P8. Both the wheel detectors WDl-WD8 and the presence detectors P2-P8 sense the presence of a cut. Each of the wheel detectors produces a signal whenever a wheel (also referred to as an axle) passes thereover. On the other hand, each of the presence detectors produces a signal when a cut is in the space defined by the presence detectors. Both the wheel detectors and the presence detectors provide real time information as to the location of the various cuts throughout the yard at any instant of time. In addition to detectors WDla and WDlbat the crest, a further detector CL is also located adjacent the crest. This comprises a light source and a light detector which are located on opposite sides of the track at the height of the railway car couplers. The light detector is so located with respect to wheel detectors WDla and WDlb that when there is only one car in a cut, the previously interrupted light path will be restored after passage of the car. However, when a cut is made up of more than one car, the light path will continue to be interrupted by the coupler of the second car.
In order to properly control the switches of the railway classification yard, the apparatus of the present invention employs a digital computer which is loaded with the program illustrated in FIGS. 3-7. The program itself and the manner in which it operates will be discussed in detail with respect to FIGS. 3-7. However, FIG. 2B shows the information flow paths both to and from the computer. The first class of information that the computer receives, after being loaded with the program and the tables defining the yard characteristics, is the train consist which, as explained above, is a sequential list of the cars of the train as they will appear at the crest along with data with respect to each of the cars. As the cars are uncoupled at the crest, detectors WDla, WDlb and CL provide sufficient information to determine the number of cars in the cut and the number of axles in each cut.
The remaining information received by the computer consists of real time information related to the status of sensing devices throughout the yard which 52 reflect the changing conditions of the yard. In particular, indications are received from detectors CL and WDla and WDlb, located at the crest. Further information is received from wheel detectors WD2-WD8 and also the presence detectors P2-P8. These sensors indicate the passage of cuts and the identification of a cut as either single or multi-car. Furthermore, the computer receives switch indications from each of the switches in the yard. Each switch may be indicating either normal, reverse, or neither of the two. This latter case is possible if for some reason the switch cannot be fully thrown to one or the other of its positions by reason of some physical blockage or failure in the switching equipment.
In accordance with the available information and based on the logic found in the program, the computer determines the required position for the switches and transmits these switch calls to the field to control the positioning of the switches.
FIG. 2A is an elevational view of the yard showing the crest at the left and the path of one typical route to a particular destination track. Four switches have been shown in the route in accordance with FIG. 1. The switches are unidentified to make the view completely general. In addition, two car retarders, RH, the hump,
retarder, and RG, a group retarder, are shown, for illustrative purposes, since the system disclosed herein does not control the retarders. A related application Ser. No. 339,473, entitled Car Retarder Control System, filed Mar. 8, i973, discloses a system that is useful for controlling retarders in a railway classification yard.
Illustrated in FIG. 2A adjacent each switch and the crest of the yard is a listing of some of the relevant routines which are called into play by the presence ofa cut at the identified location. For instance, when a cut is detected at the crest, the routines CARDET, POSSW and RETOT are called into play. The routine CARDET responds to the signals produced by detectors WDla, WDlb, and the cut light detector CL to identify the make-up of each of the cuts. This routine will be discussed in detail with reference to FIG. 3A. The next routine in FIG. 2A,, POSSW, determines the positioning of the first switch in the yard in accordance with the intended destination track of the out which is at the crest and will cause that switch to be thrown to the proper position so long as the switch can be thrown without violating any of the safety rules. The subroutine RETOT merely involves a transfer of information with respect to the cut to the car retarder operating system. Since the car retarding operation system does not form any part of the instant invention, this subroutine will not be further discussed.
Located at the first switch, the subroutine SWWD services the switch wheel detector. Upon the detection of a wheel detector actuation at any switch in the yard, the routine SWWD is called. This routine searches for an entry in a table associated with the switch at which the wheel detector is actuated in order to determine the identity of the cut approaching the switch. If no entry is found, the routine LOST is called to handle the situation. LOST is discussed with reference to FIG. 5].
Assuming there is an entry at the table associated with the switch, upon the first wheel detector actuation, an entry is made in a software file to prohibit the throwing of this particular switch. Uppon the second wheel detector actuation, at this switch, the routine SWOCC is called to determine the positioning of the switch in order to identify whether or not a misroute has occurred. If a misroute has occurred, a new destination is determined for this cut in light of existing conditions. Then, the subsequent portions of the route for the cut are checked to determine whether the intended destination is achievable, and if it is, an entry is made in the table for the next switch in the route to identify this cut. At this time, the routine POSSW will throw this next switch, if such action is achievable.
Subsequently, CALARV calculates the arrival time for the front of this cut at the next switch. This is required in order to detect stalled cuts, that is, if the cut does not arrive at the next switch within the computed time, the cut is identified as stalled and appropriate protective action is taken.
When the next to the last axle in the cut causes a wheel detector actuation, the routine CP is called which will prevent cornering. Subsequently, a further entry is made in a software file to indicate that the cut has arrived at the switch. Since there is only one remaining axle to be counted in the cut, it is assumed that all cars of the cut have arrived at the switch.
If two excess wheel detector actuations are detected at a switch, it is assumed that a catch-up condition has occurred. That is, a following cut had caught up to a preceding cut and it must be determined whether or not the following cut was misrouted in following the first cut over the switch which was positioned in accordance with the first cuts destination, and not necessarily the second cuts destination.
The same functions are performed as each cut is identified at each succeeding switch in its travel through the yard.
There are two additional routines which are performed, although neither is related to the arrival of a cut at a switch. The wheel detectors signal the arrival of a cut at a switch, the presence detectors, P2-P8, when their status changes from indicating the presence of a cut to indicating the absence of a cut, indicate that a cut has left the switch. When this occurs, it may be possible to remove the identification of the cut from the table associated with the switch whose presence detector went unoccupied. In particular, this function can be achieved when the software file indicates that the cut has arrived. This is performed by SUN which also detects wheel detector failures inasmuch as if the indicated change occurs without the previous occurrence of a number of wheel detector actuations, it can safely be assumed that the wheel detector has failed. Furthermore, when a cut has arrived at a switch, the tables for all the previous switches in the cuts route are checked to make sure they no longer contain the identification of this cut. If they do, there may have been other presence detectors or wheel detectors which have failed and appropriate action is taken.
Another routine which is performed without relation to specific indication changes is CTC. This routine checks a number of timer functions which are provided to check for stalled cuts, blocked or fouled tracks, and provide cornering protection. This routine will also detect wheel detector failures and, when such occurrence is indicated, will cause the removal of a cuts identity from tables associated with affected switches.
Before one can understand the manner in which the entire system operates, one must understand how each of the particular routines operates and how that operation is interfaced with the operation of the remaining routines. An essential starting point for understanding of the operation of the particular routines is an understanding of the information that is stored in the computer and the manner in which that information is stored. Therefore, prior to describing any of the routines in detail, we shall first describe some of the .tables which are created by the program and referred to by the program to obtain essential information.
One table that is created by the program as the system operates is called the cut statistics (hereinafter referred to as CUTST). The basis for the cut statistics is found in the train consist which is stored in the machine prior to the arrival of the train. As each cut is uncoupled from the train and detected as an entity by CARDET, the information from the consist for the particular cars in the cut is stored at a particular location which is thereinafter referred to as that cut. The stored data comprises the identifying designation for each of the cars in the cut, the total number of axles in the cut and other information which is available from the consist including the destination track. As the cut proceeds through the yard, entries are made into CUTST with respect to that cut such as velocities and expected times of arrival at various points in the yard. At other times, the program refers to CUTST for the particular cut in question to obtain information which has previously been stored therein. For instance, if at some point it is necessary to determine whether or not all of the axles of a out have passed a given point, it is only necessary to compare the number of signals received from a particular wheel detector with the total number of axles that are known to be in that cut. If the number of counts from the wheel detector is less than the total number of the axles of the cut, one knows that the entire cut has not yet passed that point. On the other hand, if the total number of counts from the wheel detector is greater than the number of axles contained in that cut, then the system has determined a catch-up condition in which a following out has caught up to a preceding cut.
Another table which is relied on by the system is entitled destination (hereinafter referred to as DESTB). In this table are stored entries for each destination track in the yard. A portion of a typical DESTB is represented below in Table l. The entry for each destination track is made up of a number of words equal to the number of switches in the route from the crest to the particular destination track. Thus, referring to the typical entries in Table 1, both destination tracks 5 and 6 are made up of four words and therefore there are four switches which are traversed from the crest of the classification yard to each of destination tracks 5 and 6. The last two columns in DESTB each represent multibit entries. Thus, the last column switch number would require at least 6 bits. Five bits are required to count up to 32, an additional sixth bit is required for the negative indicator which designates the end of the entry for the particular destination track. Another column with which requires multi-bit entries is the retarder number column. This identifies the retarder which precedes the particular switch. Of course, a entry in this column indicates that no retarder precedes this switch.
The normal column in DESTB indicates whether or not that particular switch should be reversed or normal in order to route the cut to its particular destination track. Thus, assuming an entry of l designates a normal switch and an entry of 0 designates a reverse switch, the route for destination track would consist of, in sequence, switch 8 normal, switch 32 reverse,
' bk ,1 6 switch 6 normal, and switch 5 normal. The retarder column indicates, when a l is present, that the switch follows a retarder.
An explanation of the meanings of the continue" and do not throw columns requires an explanation of the use of lap switches in classification yards. Where two switches are so close together that it would be unsafe to throw one while the other is occupied, the switches are considered lap switches. The one bit in the continue column for a switch indicates that the switch is the first switch ofa lap switch. The one bit in the do not throw column indicates that the switch is the unused second switch of a lap switch. From DESTB we can determine that switch 8 is the first switch of a lap switch and, when it is in the normal position, switch 32 is the unused second half of the lap switch and it has been set to the reverse position.
The l in the switch number column indicates the end of an entry for a particular destination track. DESTB is one of the tables which defines the characteristics of the yard.
An additional table which is related to the characteristics of the yard is entitled NEXTB for next best. For various reasons, either related to a simple malfunction, or the prohibition against throwing a switch when such action is unsafe, a cut may be misrouted at any point in the route. If this occurs, it is important for the system to recognize that a cut has been misrouted. It is equally important to determine a new destination track for the particular cut so that it may be supervised in its travel through the remaining portion of the classification yard. In order to select a new destination track for a misrouted cut, the table NEXTB is provided. For each destination track, there is an entry for each switch in the route and related thereto a different destination track. Therefore, ifa cut becomes misrouted, it is only necessary to determine the original destination track and the switch at which it became misrouted to determine, from the table NEXTB, the next best destination track for that cut. Other tables related to the yard characteristics define, for each switch, the distance and grade to each next possible switch in a route. Since the make-up of these tables is not vital, they are not further described here.
Through the use of these tables, one of the important objects of the present invention is achieved. The entries in these tables uniquely define the classification yard characteristics. Thus, to apply the system disclosed in the present application to a classification yard different than the one for which it was designed, it is only necessary to modify these tables in accordance with the characteristics of the yard to which the system is to be applied. The remaining portions of the system are applicable to any classification yard.
For each switch in the classification yard, there is an additional table entitled ADDSW. These tables are created as the system operates and, when the classification yard is not in operation, each of these tables is empty. Each table is capable of holding a number which designates the address of the location in CUTST where information respecting an approaching cut can be located. When the first cut is detected at the crest of the classification yard, the address of CUTST for that cut is loaded in the ADDSW for the first switch in the yard. When the first cut reaches the first switch, the address which had been in ADDSW with respect to the first switch is transmitted to the next ADDSW table for the switch next to the route to the destination track for that cut. As the cut proceeds through the classification yard, the CUTST address for that cut is transmitted from ADDSW table to ADDSW table preceding the cut. Thus an entry is made to an ADDSW table when the cut associated with that entry reaches the preceding switch. Because more than one cut may be traveling between two particular switches, each ADDSW table is capable of holding a multiplicity of entries. The sequence of the entries identifies the sequence of the cuts approaching the particular switch. It is from this address, stored in ADDSW, that the system can determine the destination track for a particular cut so that the switch may be properly positioned and the next switch in the route identified for receipt of the address identifying the location in CUTST where information respecting that cut may be found.
References to FIGS. 3A and 3B shows the subroutine CARDET. There are three real time inputs to the system related to this program. Two are received respectively from WDla and WDlb, located at the crest. These wheel detectors are spaced approximately eight feet apart. Since the inter-axle spacing on railway trucks is approximately 5 to 5% feet, WDla will be actuated by the second axle before WDlb is actuated by the first. For a two axle truck the wheel detector sequence will be WDla, WDla, Wdlb and WDlb. Furthermore, since the minimum inter-truck spacing of a railway car is 12 feet, the last axle of the first truck will actuate WDlb before the first axle of the second truck actuates WDla. In a like manner, in a multi-car cut, the last axle of the first car will actuate WDllb before the first axle of the second car actuates WDla. The third real time input to the system comes from CL or cut light. As is explained above, this is employed to determine the presence of a multi-car cut in combination with the signals from the wheel detector.
Before discussing the logic of CARDET in detail, attention is called to the fact that the routine sets up five registers entitled respective AXCNT, AXLES, AX- LESI, AXLES2, and SAVCNT. The routine also controls the conditioning of two flip-flops and at different portions of the routine responds to the conditions of these flip-flops. One is entitled A and can indicate either truck 1 or truck 2 depending on its condition; the other is entitled B and also can indicate either truck 1 or truck 2 depending on its condition.
When CARDET is called, the first decision point determines whether or not any wheel detector actuations have to be serviced. Since the subroutine itself contains a loop it is possible to reach decision point 20 when no wheel detector actuations are awaiting service. In that case, the subroutine is turned off. Assuming there is a wheel detector actuation to be serviced,
decision point 21 determines if the wheel detector that has been actuated is WDla. If, it is, then a reference is made to the flip-flop A, by decision point 22, to determine whether or not it is the first truck which has actuated the WDla. The manner in which the flip-flops A and B are set and reset to indicate truck 1 or truck 2 will be indicated as the discussion of FIG. 3A proceeds. It is only necessary to know that after the passage of a car, both A and B are set to truck l. Assuming that it is truck 1 which has actuated WDla, then function 23 resets the CCLD failure timer. After the passage of a car has been recorded, the CL detector is used to determine whether or not the cut is a multi-car cut or not. if CL does not detect a light signal, then the system assumes the reason is that a car coupler coupling the first and second cars of a cut has prevented the light from reaching the detector. However, the system is also designed so as to detect the failure of the light detector and uses a timer for this function. The timer is set when a car has passed the wheel detectors and no signal is detected. If the axles of a second car are detected, the timer is reset by function 23. If no second car of a cut is detected, then the system determines that the CCLD has failed.
Function 24 then increments the count in AXCNT, which had previously been set to 0. Function 25 increments the count in AXLES and decision point 26 determines if the count is legal. This is a logic function test on the operation of the system. Under proper system operation, the value stored in AXCNT will never exceed the value in AXLES by more than 2. Assuming the count is legal, the subroutine has recorded the first axle of a cut and proceeds to await further actuations to be serviced. At this time the register AXCNT has a count of l and so does the register AXLES, the other registers maintain their 0 counts, and the flip-flops are still set at truck 1.
The second axle of the first truck, when detected by WDla, traverses the identical portions of the subroutine, the only difference being that at the conclusion, AXCNT has a count of 2 as does AXLES.
The next wheel detector to be actuated will be WDlb, caused by passage of the first axle of the first truck. Thus, decision point 21 will determine that WDlb has been actuated and not WDla. This routes the routine through function 27 and the decision point 28 determines whether or not this is still truck 1. Since it is, function 29 decrements the count in AXLES and decision point 30 determines if this count is legal. Since the difference between the AXCNT count of 2 and the AXLES count of l is less than 2, the count is legal and decision point 31 determines if this is the last axle. The manner in which this is accomplished is merely a subtraction of the AXCNT from AXLES and since the difference is not 0, it is not the last axle and the subroutine proceeds to service further actuations. Assuming that no other wheel detector actuations remain to be serviced, decision point 20 will cause the subroutine to turn off. The next wheel detector actuation will be the second axle of the first truck actuating WDlb. As before, functions 20, 21, and 27 will bring the subroutine up to decision point 28 which will determine that this is still truck 1 and the count AXLES will be decremented by function 29. Decision point 30 determines whether or not this count is illegal. At this time, Axles has a count of 0 and AXCNT has a count of 2. Since the difference is not greater than 2, the count is not ille-