CA1162630A - Dual signal frequency motion monitor and broken rail detector - Google Patents
Dual signal frequency motion monitor and broken rail detectorInfo
- Publication number
- CA1162630A CA1162630A CA000371518A CA371518A CA1162630A CA 1162630 A CA1162630 A CA 1162630A CA 000371518 A CA000371518 A CA 000371518A CA 371518 A CA371518 A CA 371518A CA 1162630 A CA1162630 A CA 1162630A
- Authority
- CA
- Canada
- Prior art keywords
- impedance
- low frequency
- track
- high frequency
- rail
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B61—RAILWAYS
- B61L—GUIDING RAILWAY TRAFFIC; ENSURING THE SAFETY OF RAILWAY TRAFFIC
- B61L23/00—Control, warning, or like safety means along the route or between vehicles or vehicle trains
- B61L23/04—Control, warning, or like safety means along the route or between vehicles or vehicle trains for monitoring the mechanical state of the route
- B61L23/042—Track changes detection
- B61L23/044—Broken rails
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B61—RAILWAYS
- B61L—GUIDING RAILWAY TRAFFIC; ENSURING THE SAFETY OF RAILWAY TRAFFIC
- B61L29/00—Safety means for rail/road crossing traffic
- B61L29/24—Means for warning road traffic that a gate is closed or closing, or that rail traffic is approaching, e.g. for visible or audible warning
- B61L29/28—Means for warning road traffic that a gate is closed or closing, or that rail traffic is approaching, e.g. for visible or audible warning electrically operated
- B61L29/32—Timing, e.g. advance warning of approaching train
Abstract
(Case No. 7073) ABSTRACT OF THE DISCLOSURE
A highway crossing warning system for monitoring the motion and predicting the time of arrival of an approaching train at the highway crossing and for detecting the presence of a broken rail in the approach zone by feeding dual fre-quency signals into the track rails and measuring the track impedances at the two frequencies and the phase angle of the lower of the two frequencies.
A highway crossing warning system for monitoring the motion and predicting the time of arrival of an approaching train at the highway crossing and for detecting the presence of a broken rail in the approach zone by feeding dual fre-quency signals into the track rails and measuring the track impedances at the two frequencies and the phase angle of the lower of the two frequencies.
Description
(Case No. 7073) .lI6263n DUAL SIGNAL FREQUENC~ MOTION MONITOR
AND ~ROKEN RAI~ DETECTOR
FIELD OF THE INVENTION
_ Thi~ invention relate~ to a dual signal freguency motion monitor and broken rail detector and more particularly to a railway highway crossing warning system for sensing an approaching train and for detecting a broken rail to cause the initiation of a warning device.
BAC~GROUWD OF THE INVENTION
In former railway grade crossing protection arrangements, it was conventional practice to detect motion o oncoming trains by continuously monitoring the track impedance and by sensing a change in the impedance. It will be appreciated that the reliability of the motion sensing and the accuracy of the time of arrival prediction are dependent upon a linear relationship between the track impedance and the distance to a train. That is, under certain conditions, the distance that a train is from the highway crossing is directly pro-portional to the Lmpedance a~ross the track rails. However, when a broken rail exists in the approach zone, the impedance at the crossing i8 proportional to the distance to a train only as far as the break. Thus, a train cannot be detected beyond the point of the broken rail. It has been found that when a partial break of several ohms resistance occurs, the presence of a train just beyond the point of fracture appears to be several thousand feet further away. Thus, the result 1 162~3p of a partial a~ well aa total break in the approach track~
can ~ignlficantly reduce the amount of warning time given to motorists and pedestrians at the highway crossing. In order to avoid such a potentially dangerous sltuation, it is mandatory to detect any broken rail in the approach zones 80 that appropriate action can be taken to protect the lives and property of individuals. Presently, railroad crossing warning sy3tems employ one of two techniques for detecting broken rails, namely, either a wrap-around circuit or a high level detector. ~he wrap-around circuit employs an audio frequency overlay (AF0) track circuit which extends along the entire length of the approach zones. In practice, the APO wrap-around circuit functions to provide an initial train entrance into the approach zone and therea~ter transfers the control of the highway crossing warning apparatus to the motion detector. That is, only after the preaence of a train is recognized by the AE0 circuit is the motion detector activated to measure the distance to the approaching train.
Thus, the use of the AF0 wrap-around track circuit insures the cro~sing warning time will not be shortened or reduced due to the occurrence of a broken rail in the approach zones.
However, the additional hardware required to implement AF0 train detection results in a significant increase in the overall coRt of the highway crossing protection system.
The high level detector-arrangement employs a threshold detecting circuit incorporated with the motion sensing ~ 1~2~30 apparatus. In casq a high resistance break in a rail occur~
near the cros~ing area, the track impedance increases beyond the normal operating limits of the apparatus. Thus, the high impedance level is detected and the cro~ing warning devices are activated under such a broken rail condition.
However, while the threshold detector provides some minimum amount of warnin~ time, in some instances, there may be a significant reduction in the cros~ing warning time. Accord-ingly, such a proposal i8 not ent~rely satisfactory since the hazard of a broken rail is not completely eliminated.
OBJECTS OF THE INVENTIo~
Accordingly, it is an object of thi~ invention to provide a n~w and improved railway highway crossing protec-tion system.
A further object of this invention is to provide a unique railroad crossing warning system including motion monitoring and broken rail detection.
Another object of this invention is to provide a novel dual frequency motion sensor and broken rail detector.
Still a further object of this invention is to provide an improved railroad crossing warning system having a motion monitor and broken rail detection for activating an alarm when an approaching train is within a given time from the crossing or when a broken rail exists in the approach zone.
Still another object of this invention is to provide a superior motion sensor and broken rail indicator for a railroad highway warning system.
1 l6~n Yet a further object of the invention is to provide a railway crossing warning system for monitoring the motion of vehicles approaching a highway crossing and for detecting a broken rail in an approach zone comprising, means for sensing high and low frequency voltage signals, means for sensing high and low frequency current signals, means for filtering and separating the high and low frequency voltage signals into a discrete high frequency voltage signal and a discrete low frequency voltage signal, means for filtering and separating the high and low frequency current signals into a discrete high frequency current signal and a discrete low frequency current signal, means for calculating the act-ual high frequency impedance of the discrete high frequency current and voltage signals, means for detecting the level of said discrete high frequency current signal, means for cal-culating the actual low frequency impedance of the discrete low frequency current and voltage signals, means for detecting the phase angle of the discrete low frequency current and vol-tage signals, means for detecting motion by initially storing and sequentially updating the actual low frequency impedance and phase angle to determine an approaching vehicle, means for calculating rail integrity of the track by multiplying the actual low frequency impedance with a function of the phase angle to obtain an estimated high frequency impedance, means for comparing the estimated high frequency impedance with the actual high frequency impedance to determine the integrity of the rails of the track and means responsive to 1 1~263~
the motion detecting means and the rail integrity comparing means for providlng a warnlng of an approachlng vehlcle or an existing broken rail.
SUMMARY OF TB INVENTION
In accordance wlth the pre3ent invention, thers i8 provided a railroad highway crossing protection system for monitoring the motion of an approaching train and for detec_ ting a broken rail in an approach zone. A pair of conductors i8 directly connected to the track rails for injecting high and low frequency constant voltage signals in$o the trackway.
An i~pedance bond i8 connected across the tra~k rail at a remote point which establishes the outer limit of an approach zone. A pidkup coil is disposed alongside one of the track rails at a given distance from the highway crossing to estab-lish a positive protection island zone. The pickup coil sense~ high and low frequency current signals flowing in the track rails. The high and low voltage signals in the track rails are conveyed to a first pair of high and low frequency filters which separate the voltage signals into a discrete high frequency voltage signal and a discrete low fre~uency voltage signal. The current signal~ induced into the pickup coil are conveyed to a second pair of high and low frequency filters which separate the current signals into a discrete high frequency current signal and a discrete low frequency current signal. The discrete low frequency ~oltage and current signals are fed to an impedance ~ ~ B~n calculator which produces an output signal proportional to the actual low fre~uency impedance. The di~crete low fre_ quency voltage and current signals are al~o fed to a phase detector whlch produces an output signal proportional to the low frequency pha~e angle. The discrete hlgh frequency voltage and current signals are fed to an impedance calcu-lator which produces an output signal proportional to the actual high frequency impedance. The discrete high fre-quency current signal is al80 fed to a threshold level deteetor which produces an output signal when the absolute value of the track current exceed~ a predetermined amount.
The low frequency impedance and phase angle signals are fed to a motion detector which samples, stores and updates the impedance and phase angle signals to determine whether or not an approaching train is in the approach zone. The low frequency impedance and phase angle impedance are al80 fed to a rail integrity calculator which produces an estimated high frequency impedance signal by multiplying the actual low frequency impedance outpu~ signal with a function of the low frequency phase angle output signal. The estimated and actual high frequency impedance signals are fed to a rail integrity comparatox which compares the value of the astimated high frequency impedance signal to the value of the actual high impedance signal to determine whether or not a broken rail exists in the approach zone. A three-input AND gate coupled to the outputs of the motion 1 152~3~
detector, rail integxlty comparator and level det~ctor which normally keep~ a vital relay enargized to maintain the highway cros~ing warning devices deactivated unle~
an approaching train is a gi~en distance and velocity from the highway cro~sing, a broken rail exi~ts in the approach zone and/or the output signal of the level detector di~-appears.
DESCRIPTION OP ~HE DRAWI~G~
The foregoing objects and other attendant features and advantages of the subject invention will become more fully apparent from the following detailed de~cription when read in conjunction with the accompanying drawings wherein:
FIG. 1 of the drawings illustrates a schematic circuit block diagram of a railway crossing warning system including motion monitoring and broken rail detecting apparatus.
FIGS. 2, 3, 4 and 5 are graphic curves to be used in the description o~ the embodiment of FIG. 1 and in the understanding of the theory of operation of the present invention.
Referring now to FIG. 1 of the drawings, there is shown a grade crossing protection system for alerting the highway users of oncoming trains.
As shown, a highway or roadway HC is intersected or crossed by a track or trackway which includes a pair of running rails 1 and 2. It has been found that in order ~ 16263~
to provide the highest degree o~ ~a~ety and protection to pedestrian~ and motorists, it i8 advisable to design the end of the approach zones as long as pos~ible from the highwa~ crossing and to provide an island zone around the highway crossing to establish a po~itive protection area.
In practice, it i8 highly de~irable to provide a constant warning time in activating the cautionary 6ignals, such as, sounding the bell, flashing the lights, and/or lowering the barrier gates, when a train or transit vehicle enters the approach zones. It will be appreciated that the speeds ~f train~ entering the approach zone may range from a maximum to a minimum value so that the time of arrival at the high-way crossing may vary over a wide interval. Thus, in order to effectively alert motoris~s and pedestrians of the ensuing peril, it is necessary to detect the presence and to discern the speed of an oncoming train ih the approach zone to accu-rately predict its time of arrival at the highway crossing.
As mentioned above, it is common practice to provide a posi-tive protection area or section at the highway crossing HC
so that when a train or transit vehicle is within the island zone, the warning apparatus is constantly activated until such time as the last vehicle exits the island zone and its rear wheels clear the insulated joints IJl and IJ2.
For the purpo~e of convenience, it will be presently assumed that the trains or transit vehicles travel in the direction as shown by arrow A so that they enter the ~ 16263P
approach zone at the right in viewing the drawing. As shown, a.c. signals are connected to the track circuit TC vla a pair of conductive leads Ll and L2 which are coupled to a suitable a.c. transmitter. In practice, the a.c. tran~-mitter consists of two oscillator~, an amplifier and a dualfrequency filter. One of the two o~cillators generate~ a high frequency audio signal while the other of the two oscillators generates a low freguency audio ~ignal. The oscillators are ~olid_state crystal controlled circuits to assure a precise freguency of oscillat~ons. me fre-quency of the low frequency signal i8 in the range of 150 Hz to 600 Hz while ~he frequency of the hiyh frequency signals may be in ~he range of 600 Hz to ~,000 Hz. The high and low frequency signals are combined and are amplified to an amplitude sufficient to operate the ~ystem with some arbi-trary noi~e and interference ~mmunity. The amplified signals are fed to the dual frequency filter cixcuit which reduces the harmonics and provides isolation from any coded signals in the track. The dual frequency voltage signals are con-veyed to the track rails 1 and 2 and are also fed to a pairof band-pas~ filters which will be described hereinafter.
m e lumped ballast leakage resistance is illustrated by a phantom resistive or impedance element R which occurs at the crossing area due to the accumulation or buildup of snow, mud, salt, cinders and other ~oreign substance which takes place during the winter ~oa~on. A ~hunt lmpedance Z
is connected between the track rails 1 and 2 at a distance location from the highway crossing HC to establish an approach zone. A pickup coil PC i# disposed a given distance from the highway crossing HC and is situated adjacent track rail 2.
It will be noted that the island zone is defined as the distance between transmitted rail connections and the posi-tion of the pickup coil. Further, the approach zone is determined by the position of the a.c. shunt impedance Z
which is welded between the rails 1 and 2. The shunt impe-dance Z is preferably a narrow band, sharply tuned, resonant circuit which is hard-wired connected to the rails 1 and 2 when used in coded signal territory. However, it is under-stood that in nonsignal territory, the shunt Z may be a quitable wide band a.c. element, such as, a capacitor or a length of wire.
It will be noted that the pickup coil PC senses the amount of high and low frequency current which is actually flowing through the track rails 1 and 2. The signals induced in pickup coil PC are fed to suitable high and low freguency filters HFC and LFC, respectively. As shown, one end of pickup coil PC is connected to the input of low band-pass filter LFC by lead L3 and is connected to the input of low band-pass filter LFC by lead L5 and is connected to the input of high band-pass filter HFC by leads L6 and L4. It will be seen that the voltage developed across the track rails 1 and 2 _ 10 --t ~ 6 ~
ls also sensed and is ed to suitable high and low frequency filters HFV and LFV, respectively. A~ shown, one input of the low frequency band-pas~ filter LFV is connected by lead ~7 to the track lead Ll while one input of the high ~re_ quency band-paqs filter HFV i8 connected by lead L8 to the traek lead ~1. The other input o~ the low fre~uency band-pass filter LFV i~ connected by lead L9 to the track lead L2 while the other input of the high frequeney band-pass filter is connected by lead L10 to the track lead L2.
It will be noted that the low freguency current signals passed by filter eircuit LFC are fed to the current input of an appropriate impedance calculator ICL via lead IL
and to the current input of a suitable phase detector PDL.
As shown, the low frequeney voltage signals passed by fllter eireuit LFV are fed to the voltage input of the impedanee calculator ICL via lead VL and to the voltage input of ~h~se detector PDL. The output of the impedanee calcula-tor takes the form of a d.c. voltage whieh is proportional to low frequeney voltage divided by the low frequency current, namely, ~LOW ELOW
ILow The output of the phase detector represents the relative pha~e shift between the low freguency track voltage and rail current, namely, the phase angle ~LOW-I lS2~
It will be ob~erved that the hlgh frequency currentsignal~ pa3sed by the filter circuit HFC are fed to the current input o~ an appropriate impedance calculator ICH via lead IH
and are also fed to the input of a suitable level detector ~D
via lead IHlo A~ shown, the high frequency voltage signal~
pa~sed by the filter circuit HFV are fed to the voltage input of the impedance calculator ICH via lead VU. Like impedanc0 calculator produces a d.c. output voltage which is proportional to tho high frequency voltage divided by the high freguency current, namely, ~IG~ = E~IGH
IHIGH
The d.c. voltage ZLoW developed by the impedance calcula-tor ICL is fed to the low impedance input of a motion detector MD via lead Zl and is also fed to the low impedance input of a rail integrity calculator RIC via lead ZLl. The output 0Low of phase detector PDL is fed to the phase angle input of the rail integrity calculator RIC via lead ~L and is also fed to the phase angle input of the motion detector MD via lead 0Ll.
The motion detection is achieved by measuring the linearized track impedance and sensing any change in this impedance as an indication of train movement. As shown, the output of the motion detector MD is connected by lead MDL to one input of a three-input D gate AG. The rail integrity calculator RIC
predict~ and calculates the rail integrity by multiplying the low freguency impedance input on lead ZLl by a function of the 1 ~62630 low frequency phase angle on lead 0L to obtain an estimated high ~requency impedance value. The actual mea~ured high fre-quency impedance i8 ~onveyed by lead ZHA to a rail integrity comparator RICOM, and the estimated calculated high frequency S impedancP is conveyed by lead ZHE to the rail integrity com~
parator RICOM. The output of the rail integrity comparator RICOM is connected by lead RICL to a second input of the three-input A~D gate AG. The third input of the D gate AG is connected by lead LDL to the output of the level detector LD.
m e output of the AND gate AG i9 connected by lead AGL to a vital relay VR which i8 normally energized during the absence of a train in the approach and island zones to cause the elec-trical contacts to the power circuit for the light~, bell, and/or gate mechanism to assume an open position so that no warning signal is conveyed to the general public.
Referring now to FIG. 2, there is shown in the upper graph the track impedance (Z) versus the distance (D) to a train and in the lower graph the phase angle (0) versus the distance (D) to a train. It will be seen that the track impedance can be used to measure the distance to a train since rail impedance is directly proportional to the length of the track circuit. In viewing FIG. 2, it will be noted that under a dry ballast condition Rb = 100 ~L , the track impedance is approximately equal to the rail impedance over the desired approach distance. However, under a wet ballast condition Rb = 1 ~ or R = 5 Q , the track impedance curves are not linear beyond a given point so that track impedance _ 13 -~ l~26~n i~ no longer directly proportlonal to th~ dl~tance to a traln In examining the curves on the upper graph of FIG. 2, it will be noted that the bottom curve Rb ~ which i8 repregenta_ tive of one ohm per thousand feet of ballast, the track impedance is significantly nonlinear beyond one thousand ~eet Thus, it i8 impractical to base motion ~en~ing on track impe-danca alone beyond the thousand-foot point. However, in viewing the curves on the lower graph of FIG. 2, it will be ob~erved that the Rb = 11~ curve continues totchange rapidly out to a distance of about two thousand feet. The use of the phase angle information can be utilized to improve the accuracy of the motion ~en~ing so that the maximum feasible approach distance can be significantly increased. As shown in FIG. 3, the track impedance can be linearized by multiplying the measured impedance by a second order function derived from the phase angle. It has been found that for the curves shown in FIG. 2, the linearized function would take the form of:
Zlin = Z(3.103 - .044230 + .000227402) .
Thus, it can be seen that the linearized impedance for Rb =
1~ curve makes it possible to sense motion up to approxi-mately 1700 feet, and that the Rb o 5 ~ linearized curve is almost a ~traight line up to the 3500-foot point.
However, it has been found that both the track impedance and phase angle information is still insufficient to detect a broken rail under all conditions of ballast leakage, break location and break resistance. For example, a rail break of several ohms with moderate ballast conditions can result in _ 14 -1 162~3P
the same track impedance and phase angle as a track circuit at low balla~t with the rail intact. Thus, the technique has been developed to detect broken rails by utilizing the track impedance at two different audio frequencie~, and the phase angle of the impedance at the lower of these two ~requencie~.
It will be appreciated that when the frequency of track voltage is increased, the impedance of track circuit increases due to the inductive char-acteristics exhibited by the track rails. The ratio of the impedance which is measured at the two frequencies as a function of the distance to a train can be approximated by a ~olynominal derived from the phase angle of the track impedance at the lower of the two operating fre-quencies. This may be demonstrated mathematically as a simple algebraic manipulation of the apprOXimat~Qn equation:
ZHIGH ^J F (0LOW) ~ow wherein ZHIGH i~ the impedance value at the high operating fre_ quency, ZLOW is the impedance value at the low operating fre-quency, and 0LOW is the phase angle value at the low operating frequency.
If we now multiply through by the low frequency track impedance, the following results:
ZHIGH ZL~W X F (0LOW) This latter equation is now used to predic~ the estimated high frequency impedance from the low frequency data. The _ 15 -~ 162~3~
estimated high frequency impedance i~ then compared to the measured hlgh frequency impedance to a~ure the integrity of the track rail~.
m e approximated polynominal i8 derived by performing the following stepq:
(a) Establish and examine a set of curves of the track impedance and phase angle versus the distance to a train for a number of different ballast resistance values at each of the two operating frequencies, such as, shown in FIG. 4, and (b) judiciously choose a number of data point~ at which the approximation will give an exact prediction of the high frequency track impedance.
It will be ~ppreciated that for an nth order approxLma-tion of the form, F(0) = (C0 + Cl~ + C20 + ''' + Cn0 ) n + 1 data points must be chosen. Thus, the n + 1 data values establish n + 1 simultaneous equations which that the form, ZHIGH = ZLOW (C0 + C~ + C2~2 + '~' + Cn~) which are then solved for the coefficients C0, Cl, C2, etc.
While in many cases,a sufficiently accurate approximation can be obtained with only a second order polynominal, it has been found that the response of the system to a broken rail using such a simple approximation will not guarantee detection of a rail break at all times. It will be noted that the _ 16 _ ~ 162~3~
requirements for the approximation polynomlnal for u~e in broken rail detection are that a rail break of suficient magnitude occurring anywhere in the approach zone which cauEes a ~ignificant reduction in the warning time must be detectable over the entire operatin~ range of balla~t leakage. It has been found that the following fourth order polynominal, F(0)- -Co + Cl~:- C2~ ~ C30 - C4~
provides the required system response where the coefficients are positive real numbers.
In viewing the graph of FIG. 5, it will be noted that a curve of F(0) versus phase angle at the low frequency of 400 Hz and high frequency of 1000 Hz is derived from the curves of FIG. 4. In practice, the fourth order approximation is:
F(0) = -9.506 + 78460 - 02119~ + 2.526 x 10 - 1.09 x 10 It will be seen in FIG. 4 that the impedance curves at a nominal ballast resistance of 5 ohms per 1000 feet are used and the range of the phase angle is salected to be from 60 to 75 degrees. mis frequency range is divided into five degree increments of 60-65 , 65 -70 and 70 -75 which are centered at 62.5- 67.5 and 72.5 ~ respectively. In plotting the phase angles of 72.5, 67.5 and 62.5 , it will be seen that dis-tances to a train are 1400 feet, 1850 feet and 2200 feet, respectively. At an audio frequency of 400 Hz, these distances result in track impedances of 1.63~ , 2.00 ~L and 2.24 S~
while at an audio frequency of 1000 Hz, these distances result 1 ~62~Q
ln track impedances of 3.52 ~, 4.00-~ and 4.13-~. In u~ng the a~uation, F(~) 5 ZHI&EI
2Low the values of F(0) are 1.84, 2.00 and 2.16 at the phase angles of 62.5, 67.5 and 72.5 , respectively. It will be seen that the approximated values of F(~) taken from the curve of FIG. 5 are 1.82, 1.98 and 2.14 for pha~e angles 62.5, 67.5 and 72.5, respectively. Thu8, it will be seen that the fourth order polynominal i8 su~ficiently accurate to effectively detect a broken rail.
Turning now to FIG. 1, let us assume that no broken rail exists and that a train has entered the remote end of the approach zone. As the train approaches the highway crossing HC, the distance to the train and its ~elocity and accelera-tion are utilized to provide a constant warning time. ~he low fre~uency impedance and phase angle information are employ-ed to generate the linearized track impedance curves, as shown in FI&. 3. As the train is approaching, the distance and impedance data are sampled and stored in the motion detector MD. m e data is then repeatedly updated at a given time interval to determine the predicted time of arrival from the distance velocity and acceleration. The predicted time of arrival is then compared to the desired advance warning time.
When the predicted time is less than the desired time, the motion detector removes the output signal from lead MDL so that the AND gate ~G is turned off. The turning off of gate _ 18 _ ~ 16263P
AG causes t.he deenergization of vital relay VR which reqults in the activation of the highway crossing warning devices to alert motorists and pedestrians that a train is approaching the highway crossing HC. Now when the leading wheels of the train enter thc positive protection area, namely, the island zone, the voltage track signals from the transmitter are shunted so that no ~urrent signals are induced into pic~u~
coil PC. Thus, two inputs to the AND gate A& are removed so that warning device~ will continue to be energized 80 long as the train occupies the island zone. Now when the last wheels of the receding train pass over the insulated joints IJl and I~2 and no other train is within the confine~ of the detection area, the warning devices are deactivated to allow the free passage of the general public. m us, the system reverts to normal operation to monitor train movement and to check rail integrity.
As previously mentioned, broken rail detection is achieved by calculating an estimated high frequency impedance from low frequency data and, in turn, comparing the estimated high fre-quency impedance with the measured high frequency impedance.Thus, if the difference between estimated and measured impe-dance values exceeds a certain amount, which may be, for example, 25 percent, the output signal of the comparator RICOM is removed. The AND gate AG is triggered to its off condition since no input signal is present on lead RICL, and thus deenergizes relay VR which causes the actua~ion of the warning devices. It will be appreciated that the dual ._ 19 _ l 162S~P
frequency technique has several other advantages beeide~ broken rail detection. For example, any discontlnuity in the approach track circuit i8 recognized by the broken rail detection system. As a result of this, any load on the track which presents a substantially different impedance at one o the two operating frequencies from the impedance at the other fre~uency is detected as if it was a broken rail. mis char-acteristic may be used to advantage when filters are required in the track circuit systems to reduce or eliminate interfer-ence to the motion sensors produced by coded track circuits.Th~ use of a single inductor filter i8 relatively safe; however, an inductor, which is large enough to eliminate noise or inter-ference, has a detrimental effect on the operation of the coded track signaling circuit. While the use of a single L_C
~5 parallel tuned circuit permits interference-free operation of the coded track circuit and motion monitor, it will be appre_ ciated that if the filter capacitor becomes shorted, there is a possibility that such a failure may not be detected and the safety of the motion detection system may be jeopardized. The use of two operating frequencies allows the utilization of a double L_C parallel tuned filter~ In this case, a failure of any of the filter components results in the activation of the crossing warning apparatus since the motion sensor detects the failure as if it was a broken rail. In this way, the presently disclosed system is afforded additional security.
Another advantage of using a dual frequency broken rail detection system is that not only the integrity of the approach ~ 162~
track circuit i~ as~ured but also the sae operation of the internal circuitry Qf the motion ~ensor i8 guaranteed. It will be eeen that any single internal failure of the system up to the point where the e~timated and measured impedance comparicon is made will xe~ult in a ~ufficient impedance di~ferential which will be detected by the comparator RICOM.
Thu8, the design of the subject highway cros~ing protection system has been directed at economy and reliability whereLn nonvital circuits are combined in such a way that vital opera-tion i8 achie~ed.
It will be appreciated that various changes, modifica_tions and alterations may be made by persons skilled in $he art without departing from the spirit and scope of the present invention. For example, the system may be used at a crossing which has bidirectional train movement. In such a situation, the insulated joints are removed and a second pickup coil is suitably located adjacent the track at a safe distance on the left side of the highway crossing HC a~ viewed in FIG. 1. The additional pickup coil is connected to separate high and low frequency filtering circuits which, in turn, are connected to the low frequency current inputs of a supplementary phase detector and impedance calculator. The low frequency voltage inputs of the added phase detector and impedance calculator are connected to the track circuit via the l~w frequency voltage filter LFV. An additional high impedance calculator has its high frequency voltage input connected to the track circuit via filter HFV and has its high frequency current input coupled 63~
to the added pickup coil via the supplementary high frequency filter. A level detector which i~ ~imilar to detector LD
measures the ~bsolute value of the current flowing in the left s~de of the track circuit. The u~e of the two pickup coils permits the separate measurement of the track circuit para-meter~ associated with each approach zone independently. It will be appreciated that an additional impedance bond is con-nected across the track rails at a remote location to define the outer limit of the left approach zone while the island zone is defined as the distance between the two pickup coils.
It will be appreciated that with the advent of microprocessors, the function of the calculator, detector comparator and gating circuits, may be accomplished in a suitably programmed digital microcomputer. In addition, it is understood that the "window"
of comparator RICOM between the estimated and measured high frequency impedance may vary over a wide range, such as, O to 50 percent, dependent upon the circumstances. Further, it ~ill be apparent that various other variations and ramifications may be made to the subject invention and, therefore, it is under-stood that all changes, modifications and equivalents withinthe spirit and scope of the present invention are herein meant to be encompassed in the appended claims.
AND ~ROKEN RAI~ DETECTOR
FIELD OF THE INVENTION
_ Thi~ invention relate~ to a dual signal freguency motion monitor and broken rail detector and more particularly to a railway highway crossing warning system for sensing an approaching train and for detecting a broken rail to cause the initiation of a warning device.
BAC~GROUWD OF THE INVENTION
In former railway grade crossing protection arrangements, it was conventional practice to detect motion o oncoming trains by continuously monitoring the track impedance and by sensing a change in the impedance. It will be appreciated that the reliability of the motion sensing and the accuracy of the time of arrival prediction are dependent upon a linear relationship between the track impedance and the distance to a train. That is, under certain conditions, the distance that a train is from the highway crossing is directly pro-portional to the Lmpedance a~ross the track rails. However, when a broken rail exists in the approach zone, the impedance at the crossing i8 proportional to the distance to a train only as far as the break. Thus, a train cannot be detected beyond the point of the broken rail. It has been found that when a partial break of several ohms resistance occurs, the presence of a train just beyond the point of fracture appears to be several thousand feet further away. Thus, the result 1 162~3p of a partial a~ well aa total break in the approach track~
can ~ignlficantly reduce the amount of warning time given to motorists and pedestrians at the highway crossing. In order to avoid such a potentially dangerous sltuation, it is mandatory to detect any broken rail in the approach zones 80 that appropriate action can be taken to protect the lives and property of individuals. Presently, railroad crossing warning sy3tems employ one of two techniques for detecting broken rails, namely, either a wrap-around circuit or a high level detector. ~he wrap-around circuit employs an audio frequency overlay (AF0) track circuit which extends along the entire length of the approach zones. In practice, the APO wrap-around circuit functions to provide an initial train entrance into the approach zone and therea~ter transfers the control of the highway crossing warning apparatus to the motion detector. That is, only after the preaence of a train is recognized by the AE0 circuit is the motion detector activated to measure the distance to the approaching train.
Thus, the use of the AF0 wrap-around track circuit insures the cro~sing warning time will not be shortened or reduced due to the occurrence of a broken rail in the approach zones.
However, the additional hardware required to implement AF0 train detection results in a significant increase in the overall coRt of the highway crossing protection system.
The high level detector-arrangement employs a threshold detecting circuit incorporated with the motion sensing ~ 1~2~30 apparatus. In casq a high resistance break in a rail occur~
near the cros~ing area, the track impedance increases beyond the normal operating limits of the apparatus. Thus, the high impedance level is detected and the cro~ing warning devices are activated under such a broken rail condition.
However, while the threshold detector provides some minimum amount of warnin~ time, in some instances, there may be a significant reduction in the cros~ing warning time. Accord-ingly, such a proposal i8 not ent~rely satisfactory since the hazard of a broken rail is not completely eliminated.
OBJECTS OF THE INVENTIo~
Accordingly, it is an object of thi~ invention to provide a n~w and improved railway highway crossing protec-tion system.
A further object of this invention is to provide a unique railroad crossing warning system including motion monitoring and broken rail detection.
Another object of this invention is to provide a novel dual frequency motion sensor and broken rail detector.
Still a further object of this invention is to provide an improved railroad crossing warning system having a motion monitor and broken rail detection for activating an alarm when an approaching train is within a given time from the crossing or when a broken rail exists in the approach zone.
Still another object of this invention is to provide a superior motion sensor and broken rail indicator for a railroad highway warning system.
1 l6~n Yet a further object of the invention is to provide a railway crossing warning system for monitoring the motion of vehicles approaching a highway crossing and for detecting a broken rail in an approach zone comprising, means for sensing high and low frequency voltage signals, means for sensing high and low frequency current signals, means for filtering and separating the high and low frequency voltage signals into a discrete high frequency voltage signal and a discrete low frequency voltage signal, means for filtering and separating the high and low frequency current signals into a discrete high frequency current signal and a discrete low frequency current signal, means for calculating the act-ual high frequency impedance of the discrete high frequency current and voltage signals, means for detecting the level of said discrete high frequency current signal, means for cal-culating the actual low frequency impedance of the discrete low frequency current and voltage signals, means for detecting the phase angle of the discrete low frequency current and vol-tage signals, means for detecting motion by initially storing and sequentially updating the actual low frequency impedance and phase angle to determine an approaching vehicle, means for calculating rail integrity of the track by multiplying the actual low frequency impedance with a function of the phase angle to obtain an estimated high frequency impedance, means for comparing the estimated high frequency impedance with the actual high frequency impedance to determine the integrity of the rails of the track and means responsive to 1 1~263~
the motion detecting means and the rail integrity comparing means for providlng a warnlng of an approachlng vehlcle or an existing broken rail.
SUMMARY OF TB INVENTION
In accordance wlth the pre3ent invention, thers i8 provided a railroad highway crossing protection system for monitoring the motion of an approaching train and for detec_ ting a broken rail in an approach zone. A pair of conductors i8 directly connected to the track rails for injecting high and low frequency constant voltage signals in$o the trackway.
An i~pedance bond i8 connected across the tra~k rail at a remote point which establishes the outer limit of an approach zone. A pidkup coil is disposed alongside one of the track rails at a given distance from the highway crossing to estab-lish a positive protection island zone. The pickup coil sense~ high and low frequency current signals flowing in the track rails. The high and low voltage signals in the track rails are conveyed to a first pair of high and low frequency filters which separate the voltage signals into a discrete high frequency voltage signal and a discrete low fre~uency voltage signal. The current signal~ induced into the pickup coil are conveyed to a second pair of high and low frequency filters which separate the current signals into a discrete high frequency current signal and a discrete low frequency current signal. The discrete low frequency ~oltage and current signals are fed to an impedance ~ ~ B~n calculator which produces an output signal proportional to the actual low fre~uency impedance. The di~crete low fre_ quency voltage and current signals are al~o fed to a phase detector whlch produces an output signal proportional to the low frequency pha~e angle. The discrete hlgh frequency voltage and current signals are fed to an impedance calcu-lator which produces an output signal proportional to the actual high frequency impedance. The discrete high fre-quency current signal is al80 fed to a threshold level deteetor which produces an output signal when the absolute value of the track current exceed~ a predetermined amount.
The low frequency impedance and phase angle signals are fed to a motion detector which samples, stores and updates the impedance and phase angle signals to determine whether or not an approaching train is in the approach zone. The low frequency impedance and phase angle impedance are al80 fed to a rail integrity calculator which produces an estimated high frequency impedance signal by multiplying the actual low frequency impedance outpu~ signal with a function of the low frequency phase angle output signal. The estimated and actual high frequency impedance signals are fed to a rail integrity comparatox which compares the value of the astimated high frequency impedance signal to the value of the actual high impedance signal to determine whether or not a broken rail exists in the approach zone. A three-input AND gate coupled to the outputs of the motion 1 152~3~
detector, rail integxlty comparator and level det~ctor which normally keep~ a vital relay enargized to maintain the highway cros~ing warning devices deactivated unle~
an approaching train is a gi~en distance and velocity from the highway cro~sing, a broken rail exi~ts in the approach zone and/or the output signal of the level detector di~-appears.
DESCRIPTION OP ~HE DRAWI~G~
The foregoing objects and other attendant features and advantages of the subject invention will become more fully apparent from the following detailed de~cription when read in conjunction with the accompanying drawings wherein:
FIG. 1 of the drawings illustrates a schematic circuit block diagram of a railway crossing warning system including motion monitoring and broken rail detecting apparatus.
FIGS. 2, 3, 4 and 5 are graphic curves to be used in the description o~ the embodiment of FIG. 1 and in the understanding of the theory of operation of the present invention.
Referring now to FIG. 1 of the drawings, there is shown a grade crossing protection system for alerting the highway users of oncoming trains.
As shown, a highway or roadway HC is intersected or crossed by a track or trackway which includes a pair of running rails 1 and 2. It has been found that in order ~ 16263~
to provide the highest degree o~ ~a~ety and protection to pedestrian~ and motorists, it i8 advisable to design the end of the approach zones as long as pos~ible from the highwa~ crossing and to provide an island zone around the highway crossing to establish a po~itive protection area.
In practice, it i8 highly de~irable to provide a constant warning time in activating the cautionary 6ignals, such as, sounding the bell, flashing the lights, and/or lowering the barrier gates, when a train or transit vehicle enters the approach zones. It will be appreciated that the speeds ~f train~ entering the approach zone may range from a maximum to a minimum value so that the time of arrival at the high-way crossing may vary over a wide interval. Thus, in order to effectively alert motoris~s and pedestrians of the ensuing peril, it is necessary to detect the presence and to discern the speed of an oncoming train ih the approach zone to accu-rately predict its time of arrival at the highway crossing.
As mentioned above, it is common practice to provide a posi-tive protection area or section at the highway crossing HC
so that when a train or transit vehicle is within the island zone, the warning apparatus is constantly activated until such time as the last vehicle exits the island zone and its rear wheels clear the insulated joints IJl and IJ2.
For the purpo~e of convenience, it will be presently assumed that the trains or transit vehicles travel in the direction as shown by arrow A so that they enter the ~ 16263P
approach zone at the right in viewing the drawing. As shown, a.c. signals are connected to the track circuit TC vla a pair of conductive leads Ll and L2 which are coupled to a suitable a.c. transmitter. In practice, the a.c. tran~-mitter consists of two oscillator~, an amplifier and a dualfrequency filter. One of the two o~cillators generate~ a high frequency audio signal while the other of the two oscillators generates a low freguency audio ~ignal. The oscillators are ~olid_state crystal controlled circuits to assure a precise freguency of oscillat~ons. me fre-quency of the low frequency signal i8 in the range of 150 Hz to 600 Hz while ~he frequency of the hiyh frequency signals may be in ~he range of 600 Hz to ~,000 Hz. The high and low frequency signals are combined and are amplified to an amplitude sufficient to operate the ~ystem with some arbi-trary noi~e and interference ~mmunity. The amplified signals are fed to the dual frequency filter cixcuit which reduces the harmonics and provides isolation from any coded signals in the track. The dual frequency voltage signals are con-veyed to the track rails 1 and 2 and are also fed to a pairof band-pas~ filters which will be described hereinafter.
m e lumped ballast leakage resistance is illustrated by a phantom resistive or impedance element R which occurs at the crossing area due to the accumulation or buildup of snow, mud, salt, cinders and other ~oreign substance which takes place during the winter ~oa~on. A ~hunt lmpedance Z
is connected between the track rails 1 and 2 at a distance location from the highway crossing HC to establish an approach zone. A pickup coil PC i# disposed a given distance from the highway crossing HC and is situated adjacent track rail 2.
It will be noted that the island zone is defined as the distance between transmitted rail connections and the posi-tion of the pickup coil. Further, the approach zone is determined by the position of the a.c. shunt impedance Z
which is welded between the rails 1 and 2. The shunt impe-dance Z is preferably a narrow band, sharply tuned, resonant circuit which is hard-wired connected to the rails 1 and 2 when used in coded signal territory. However, it is under-stood that in nonsignal territory, the shunt Z may be a quitable wide band a.c. element, such as, a capacitor or a length of wire.
It will be noted that the pickup coil PC senses the amount of high and low frequency current which is actually flowing through the track rails 1 and 2. The signals induced in pickup coil PC are fed to suitable high and low freguency filters HFC and LFC, respectively. As shown, one end of pickup coil PC is connected to the input of low band-pass filter LFC by lead L3 and is connected to the input of low band-pass filter LFC by lead L5 and is connected to the input of high band-pass filter HFC by leads L6 and L4. It will be seen that the voltage developed across the track rails 1 and 2 _ 10 --t ~ 6 ~
ls also sensed and is ed to suitable high and low frequency filters HFV and LFV, respectively. A~ shown, one input of the low frequency band-pas~ filter LFV is connected by lead ~7 to the track lead Ll while one input of the high ~re_ quency band-paqs filter HFV i8 connected by lead L8 to the traek lead ~1. The other input o~ the low fre~uency band-pass filter LFV i~ connected by lead L9 to the track lead L2 while the other input of the high frequeney band-pass filter is connected by lead L10 to the track lead L2.
It will be noted that the low freguency current signals passed by filter eircuit LFC are fed to the current input of an appropriate impedance calculator ICL via lead IL
and to the current input of a suitable phase detector PDL.
As shown, the low frequeney voltage signals passed by fllter eireuit LFV are fed to the voltage input of the impedanee calculator ICL via lead VL and to the voltage input of ~h~se detector PDL. The output of the impedanee calcula-tor takes the form of a d.c. voltage whieh is proportional to low frequeney voltage divided by the low frequency current, namely, ~LOW ELOW
ILow The output of the phase detector represents the relative pha~e shift between the low freguency track voltage and rail current, namely, the phase angle ~LOW-I lS2~
It will be ob~erved that the hlgh frequency currentsignal~ pa3sed by the filter circuit HFC are fed to the current input o~ an appropriate impedance calculator ICH via lead IH
and are also fed to the input of a suitable level detector ~D
via lead IHlo A~ shown, the high frequency voltage signal~
pa~sed by the filter circuit HFV are fed to the voltage input of the impedance calculator ICH via lead VU. Like impedanc0 calculator produces a d.c. output voltage which is proportional to tho high frequency voltage divided by the high freguency current, namely, ~IG~ = E~IGH
IHIGH
The d.c. voltage ZLoW developed by the impedance calcula-tor ICL is fed to the low impedance input of a motion detector MD via lead Zl and is also fed to the low impedance input of a rail integrity calculator RIC via lead ZLl. The output 0Low of phase detector PDL is fed to the phase angle input of the rail integrity calculator RIC via lead ~L and is also fed to the phase angle input of the motion detector MD via lead 0Ll.
The motion detection is achieved by measuring the linearized track impedance and sensing any change in this impedance as an indication of train movement. As shown, the output of the motion detector MD is connected by lead MDL to one input of a three-input D gate AG. The rail integrity calculator RIC
predict~ and calculates the rail integrity by multiplying the low freguency impedance input on lead ZLl by a function of the 1 ~62630 low frequency phase angle on lead 0L to obtain an estimated high ~requency impedance value. The actual mea~ured high fre-quency impedance i8 ~onveyed by lead ZHA to a rail integrity comparator RICOM, and the estimated calculated high frequency S impedancP is conveyed by lead ZHE to the rail integrity com~
parator RICOM. The output of the rail integrity comparator RICOM is connected by lead RICL to a second input of the three-input A~D gate AG. The third input of the D gate AG is connected by lead LDL to the output of the level detector LD.
m e output of the AND gate AG i9 connected by lead AGL to a vital relay VR which i8 normally energized during the absence of a train in the approach and island zones to cause the elec-trical contacts to the power circuit for the light~, bell, and/or gate mechanism to assume an open position so that no warning signal is conveyed to the general public.
Referring now to FIG. 2, there is shown in the upper graph the track impedance (Z) versus the distance (D) to a train and in the lower graph the phase angle (0) versus the distance (D) to a train. It will be seen that the track impedance can be used to measure the distance to a train since rail impedance is directly proportional to the length of the track circuit. In viewing FIG. 2, it will be noted that under a dry ballast condition Rb = 100 ~L , the track impedance is approximately equal to the rail impedance over the desired approach distance. However, under a wet ballast condition Rb = 1 ~ or R = 5 Q , the track impedance curves are not linear beyond a given point so that track impedance _ 13 -~ l~26~n i~ no longer directly proportlonal to th~ dl~tance to a traln In examining the curves on the upper graph of FIG. 2, it will be noted that the bottom curve Rb ~ which i8 repregenta_ tive of one ohm per thousand feet of ballast, the track impedance is significantly nonlinear beyond one thousand ~eet Thus, it i8 impractical to base motion ~en~ing on track impe-danca alone beyond the thousand-foot point. However, in viewing the curves on the lower graph of FIG. 2, it will be ob~erved that the Rb = 11~ curve continues totchange rapidly out to a distance of about two thousand feet. The use of the phase angle information can be utilized to improve the accuracy of the motion ~en~ing so that the maximum feasible approach distance can be significantly increased. As shown in FIG. 3, the track impedance can be linearized by multiplying the measured impedance by a second order function derived from the phase angle. It has been found that for the curves shown in FIG. 2, the linearized function would take the form of:
Zlin = Z(3.103 - .044230 + .000227402) .
Thus, it can be seen that the linearized impedance for Rb =
1~ curve makes it possible to sense motion up to approxi-mately 1700 feet, and that the Rb o 5 ~ linearized curve is almost a ~traight line up to the 3500-foot point.
However, it has been found that both the track impedance and phase angle information is still insufficient to detect a broken rail under all conditions of ballast leakage, break location and break resistance. For example, a rail break of several ohms with moderate ballast conditions can result in _ 14 -1 162~3P
the same track impedance and phase angle as a track circuit at low balla~t with the rail intact. Thus, the technique has been developed to detect broken rails by utilizing the track impedance at two different audio frequencie~, and the phase angle of the impedance at the lower of these two ~requencie~.
It will be appreciated that when the frequency of track voltage is increased, the impedance of track circuit increases due to the inductive char-acteristics exhibited by the track rails. The ratio of the impedance which is measured at the two frequencies as a function of the distance to a train can be approximated by a ~olynominal derived from the phase angle of the track impedance at the lower of the two operating fre-quencies. This may be demonstrated mathematically as a simple algebraic manipulation of the apprOXimat~Qn equation:
ZHIGH ^J F (0LOW) ~ow wherein ZHIGH i~ the impedance value at the high operating fre_ quency, ZLOW is the impedance value at the low operating fre-quency, and 0LOW is the phase angle value at the low operating frequency.
If we now multiply through by the low frequency track impedance, the following results:
ZHIGH ZL~W X F (0LOW) This latter equation is now used to predic~ the estimated high frequency impedance from the low frequency data. The _ 15 -~ 162~3~
estimated high frequency impedance i~ then compared to the measured hlgh frequency impedance to a~ure the integrity of the track rail~.
m e approximated polynominal i8 derived by performing the following stepq:
(a) Establish and examine a set of curves of the track impedance and phase angle versus the distance to a train for a number of different ballast resistance values at each of the two operating frequencies, such as, shown in FIG. 4, and (b) judiciously choose a number of data point~ at which the approximation will give an exact prediction of the high frequency track impedance.
It will be ~ppreciated that for an nth order approxLma-tion of the form, F(0) = (C0 + Cl~ + C20 + ''' + Cn0 ) n + 1 data points must be chosen. Thus, the n + 1 data values establish n + 1 simultaneous equations which that the form, ZHIGH = ZLOW (C0 + C~ + C2~2 + '~' + Cn~) which are then solved for the coefficients C0, Cl, C2, etc.
While in many cases,a sufficiently accurate approximation can be obtained with only a second order polynominal, it has been found that the response of the system to a broken rail using such a simple approximation will not guarantee detection of a rail break at all times. It will be noted that the _ 16 _ ~ 162~3~
requirements for the approximation polynomlnal for u~e in broken rail detection are that a rail break of suficient magnitude occurring anywhere in the approach zone which cauEes a ~ignificant reduction in the warning time must be detectable over the entire operatin~ range of balla~t leakage. It has been found that the following fourth order polynominal, F(0)- -Co + Cl~:- C2~ ~ C30 - C4~
provides the required system response where the coefficients are positive real numbers.
In viewing the graph of FIG. 5, it will be noted that a curve of F(0) versus phase angle at the low frequency of 400 Hz and high frequency of 1000 Hz is derived from the curves of FIG. 4. In practice, the fourth order approximation is:
F(0) = -9.506 + 78460 - 02119~ + 2.526 x 10 - 1.09 x 10 It will be seen in FIG. 4 that the impedance curves at a nominal ballast resistance of 5 ohms per 1000 feet are used and the range of the phase angle is salected to be from 60 to 75 degrees. mis frequency range is divided into five degree increments of 60-65 , 65 -70 and 70 -75 which are centered at 62.5- 67.5 and 72.5 ~ respectively. In plotting the phase angles of 72.5, 67.5 and 62.5 , it will be seen that dis-tances to a train are 1400 feet, 1850 feet and 2200 feet, respectively. At an audio frequency of 400 Hz, these distances result in track impedances of 1.63~ , 2.00 ~L and 2.24 S~
while at an audio frequency of 1000 Hz, these distances result 1 ~62~Q
ln track impedances of 3.52 ~, 4.00-~ and 4.13-~. In u~ng the a~uation, F(~) 5 ZHI&EI
2Low the values of F(0) are 1.84, 2.00 and 2.16 at the phase angles of 62.5, 67.5 and 72.5 , respectively. It will be seen that the approximated values of F(~) taken from the curve of FIG. 5 are 1.82, 1.98 and 2.14 for pha~e angles 62.5, 67.5 and 72.5, respectively. Thu8, it will be seen that the fourth order polynominal i8 su~ficiently accurate to effectively detect a broken rail.
Turning now to FIG. 1, let us assume that no broken rail exists and that a train has entered the remote end of the approach zone. As the train approaches the highway crossing HC, the distance to the train and its ~elocity and accelera-tion are utilized to provide a constant warning time. ~he low fre~uency impedance and phase angle information are employ-ed to generate the linearized track impedance curves, as shown in FI&. 3. As the train is approaching, the distance and impedance data are sampled and stored in the motion detector MD. m e data is then repeatedly updated at a given time interval to determine the predicted time of arrival from the distance velocity and acceleration. The predicted time of arrival is then compared to the desired advance warning time.
When the predicted time is less than the desired time, the motion detector removes the output signal from lead MDL so that the AND gate ~G is turned off. The turning off of gate _ 18 _ ~ 16263P
AG causes t.he deenergization of vital relay VR which reqults in the activation of the highway crossing warning devices to alert motorists and pedestrians that a train is approaching the highway crossing HC. Now when the leading wheels of the train enter thc positive protection area, namely, the island zone, the voltage track signals from the transmitter are shunted so that no ~urrent signals are induced into pic~u~
coil PC. Thus, two inputs to the AND gate A& are removed so that warning device~ will continue to be energized 80 long as the train occupies the island zone. Now when the last wheels of the receding train pass over the insulated joints IJl and I~2 and no other train is within the confine~ of the detection area, the warning devices are deactivated to allow the free passage of the general public. m us, the system reverts to normal operation to monitor train movement and to check rail integrity.
As previously mentioned, broken rail detection is achieved by calculating an estimated high frequency impedance from low frequency data and, in turn, comparing the estimated high fre-quency impedance with the measured high frequency impedance.Thus, if the difference between estimated and measured impe-dance values exceeds a certain amount, which may be, for example, 25 percent, the output signal of the comparator RICOM is removed. The AND gate AG is triggered to its off condition since no input signal is present on lead RICL, and thus deenergizes relay VR which causes the actua~ion of the warning devices. It will be appreciated that the dual ._ 19 _ l 162S~P
frequency technique has several other advantages beeide~ broken rail detection. For example, any discontlnuity in the approach track circuit i8 recognized by the broken rail detection system. As a result of this, any load on the track which presents a substantially different impedance at one o the two operating frequencies from the impedance at the other fre~uency is detected as if it was a broken rail. mis char-acteristic may be used to advantage when filters are required in the track circuit systems to reduce or eliminate interfer-ence to the motion sensors produced by coded track circuits.Th~ use of a single inductor filter i8 relatively safe; however, an inductor, which is large enough to eliminate noise or inter-ference, has a detrimental effect on the operation of the coded track signaling circuit. While the use of a single L_C
~5 parallel tuned circuit permits interference-free operation of the coded track circuit and motion monitor, it will be appre_ ciated that if the filter capacitor becomes shorted, there is a possibility that such a failure may not be detected and the safety of the motion detection system may be jeopardized. The use of two operating frequencies allows the utilization of a double L_C parallel tuned filter~ In this case, a failure of any of the filter components results in the activation of the crossing warning apparatus since the motion sensor detects the failure as if it was a broken rail. In this way, the presently disclosed system is afforded additional security.
Another advantage of using a dual frequency broken rail detection system is that not only the integrity of the approach ~ 162~
track circuit i~ as~ured but also the sae operation of the internal circuitry Qf the motion ~ensor i8 guaranteed. It will be eeen that any single internal failure of the system up to the point where the e~timated and measured impedance comparicon is made will xe~ult in a ~ufficient impedance di~ferential which will be detected by the comparator RICOM.
Thu8, the design of the subject highway cros~ing protection system has been directed at economy and reliability whereLn nonvital circuits are combined in such a way that vital opera-tion i8 achie~ed.
It will be appreciated that various changes, modifica_tions and alterations may be made by persons skilled in $he art without departing from the spirit and scope of the present invention. For example, the system may be used at a crossing which has bidirectional train movement. In such a situation, the insulated joints are removed and a second pickup coil is suitably located adjacent the track at a safe distance on the left side of the highway crossing HC a~ viewed in FIG. 1. The additional pickup coil is connected to separate high and low frequency filtering circuits which, in turn, are connected to the low frequency current inputs of a supplementary phase detector and impedance calculator. The low frequency voltage inputs of the added phase detector and impedance calculator are connected to the track circuit via the l~w frequency voltage filter LFV. An additional high impedance calculator has its high frequency voltage input connected to the track circuit via filter HFV and has its high frequency current input coupled 63~
to the added pickup coil via the supplementary high frequency filter. A level detector which i~ ~imilar to detector LD
measures the ~bsolute value of the current flowing in the left s~de of the track circuit. The u~e of the two pickup coils permits the separate measurement of the track circuit para-meter~ associated with each approach zone independently. It will be appreciated that an additional impedance bond is con-nected across the track rails at a remote location to define the outer limit of the left approach zone while the island zone is defined as the distance between the two pickup coils.
It will be appreciated that with the advent of microprocessors, the function of the calculator, detector comparator and gating circuits, may be accomplished in a suitably programmed digital microcomputer. In addition, it is understood that the "window"
of comparator RICOM between the estimated and measured high frequency impedance may vary over a wide range, such as, O to 50 percent, dependent upon the circumstances. Further, it ~ill be apparent that various other variations and ramifications may be made to the subject invention and, therefore, it is under-stood that all changes, modifications and equivalents withinthe spirit and scope of the present invention are herein meant to be encompassed in the appended claims.
Claims (5)
1. In a railway crossing warning system for monitoring the motion of vehicles approaching a highway crossing and for detecting a broken rail in an approach zone comprising, means for sensing high and low frequency voltage signals in the track, means for sensing high and low frequency current sig-nals in the track,means for filtering and separating said high and low frequency voltage signals into a discrete high fre-quency voltage signal and a discrete low frequency voltage sig-nal, means for filtering and separating said high and low fre-quency current signals into a discrete high frequency current signal and a discrete low frequency current signal, means for calculating the actual high frequency impedance of said dis-crete high frequency current and voltage signals, means for de-tecting the level of said discrete high frequency current sig-nal, means for calculating the actual low frequency impedance of said discrete low frequency current and voltage signals, means for detecting the phase angle of said discrete low fre-quency current and voltage signals, means for detecting motion by initially storing and sequentially updating said actual low frequency impedance and phase angle to determine an approach-ing vehicle,means for calculating rail integrity of the track by multiplying said actual low frequency impedance with a fun-ction of said phase angle to obtain an estimated high fre-quency impedance, means for comparing said estimated high frequency impedance with Raid actual high frequency impedance to determine the integrity of the rails of the track, and means responsive to said motion detecting means, said rail integrity comparing means and said level detecting means for providing a warning of an approaching vehicle or of an exist-ing broken rail.
2. The railway crossing warning system as defined in claim 1, wherein said means for sensing high and low frequency current signals is a pickup coil which is disposed adjacent the track.
3. The railway crossing warning system as defined in claim 1, wherein said means for calculating the estimated high frequency impedance follows the equation:
ZHIGH = ZLOW (-C0 + C10 - C202 + ''' + Cn0n) where ZHIGH is the estimated high frequency impedance, ZLOW is the actual low frequency impedance, 0 is the low frequency phase angle, and C0, C1, C2, ''', Cn are positive real number coefficients.
ZHIGH = ZLOW (-C0 + C10 - C202 + ''' + Cn0n) where ZHIGH is the estimated high frequency impedance, ZLOW is the actual low frequency impedance, 0 is the low frequency phase angle, and C0, C1, C2, ''', Cn are positive real number coefficients.
4. The railway crossing warning system as defined in claim 1, wherein said means responsive to said motion detec-ting means, said rail integrity comparing means and said level detecting means is a three-input AND gate which controls the electrical condition of a relay.
5. The railway crossing warning system as defined in claim 1, wherein said level detecting means includes a threshold device which senses the absolute value of the high frequency current signals.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/162,470 US4306694A (en) | 1980-06-24 | 1980-06-24 | Dual signal frequency motion monitor and broken rail detector |
| US162,470 | 1980-06-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1162630A true CA1162630A (en) | 1984-02-21 |
Family
ID=22585755
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000371518A Expired CA1162630A (en) | 1980-06-24 | 1981-02-23 | Dual signal frequency motion monitor and broken rail detector |
Country Status (3)
| Country | Link |
|---|---|
| US (1) | US4306694A (en) |
| CA (1) | CA1162630A (en) |
| IT (1) | IT1145161B (en) |
Families Citing this family (35)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4581700A (en) * | 1981-08-07 | 1986-04-08 | Sab Harmon Industries, Inc. | Processing system for grade crossing warning |
| US4723739A (en) * | 1985-07-16 | 1988-02-09 | American Standard Inc. | Synchronous rectification track circuit |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US3610920A (en) * | 1969-12-04 | 1971-10-05 | Gen Signal Corp | Apparatus and method for deriving a uniform time warning |
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| US3696243A (en) * | 1970-08-26 | 1972-10-03 | Marquardt Ind Products Co | Broken rail detector |
| US3777139A (en) * | 1970-12-03 | 1973-12-04 | R Peel | Motion sensor system |
| US3987989A (en) * | 1974-04-05 | 1976-10-26 | Erico Rail Products Company | Railway signal system |
| US3944173A (en) * | 1975-04-17 | 1976-03-16 | Saftran System Corporation | Railroad crossing motion sensing system |
| US3977634A (en) * | 1975-06-09 | 1976-08-31 | Safetran Systems Corporation | Computer for motion sensing device setup |
| US3974991A (en) * | 1975-08-27 | 1976-08-17 | Erico Rail Products Company | Railroad motion detecting and signalling system with repeater receiver |
-
1980
- 1980-06-24 US US06/162,470 patent/US4306694A/en not_active Expired - Lifetime
-
1981
- 1981-02-23 CA CA000371518A patent/CA1162630A/en not_active Expired
- 1981-06-23 IT IT67865/81A patent/IT1145161B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| US4306694A (en) | 1981-12-22 |
| IT1145161B (en) | 1986-11-05 |
| IT8167865A0 (en) | 1981-06-23 |
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