Processing system for grade crossing warning

• US 4,581,700 A
• Filed: 08/06/1984
• Issued: 04/08/1986
• Est. Priority Date: 08/07/1981
• Status: Expired due to Term

• Current Assignee: Harmon Industries, Inc. (GE Aerospace)
• Original Assignee: SAB Harmon Industries Incorporated
• Inventors: Ballinger, Forrest H., Farnham, Wilfred L., Wheeler, Wayne N., Garrison, Lynn R.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Lastova, John R.
• Application Number:
  US06/637,911
• Time in Patent Office: 610 Days
• Field of Search: 364/184, 364/185-186, 364/436, 364/200, 364/900, 246/125, 246/130, 246/34 R, 246/34 A, 246/34 CT, 246/121-122 R, 340/38 L, 340/931, 340/938, 340/941, 371/3, 371/14
• US Class Current: 700/80
• CPC Class Codes: B61L 29/226 using track-circuits, closed or short-circuited by train or using isolated rail-sections
• CPC Class Codes: B61L 29/284 using rail-contacts, rail microphones, or the like, controlled by the vehicle
• CPC Class Codes: B61L 29/30 Supervision, e.g. monitoring arrangements

Abstract

A railroad train moving along an approach to a grade crossing (or other location of interest) is detected by apparatus that is responsive to the change in effective track impedance caused by the moving shunt. A constant current AC signal is applied to the track adjacent the crossing, and the resulting voltage changed in amplitude and phase is picked off by a receiver on the opposite side of the crossing. Voltage and current information derived from these signals is inputted to a microcomputer which calculates the track impedance and determines whether or not a warning device or devices at the crossing should be activated. Such determination is made on a repetitive basis in accordance with a repeating program loop and stored in memory. To assure that the system is failsafe, the program loop is interrupted at predetermined intervals and an interrupt service routine checks the memory address at which the determination is stored and causes an independent computer output to change state each time the memory is checked and activation of the warning is not required. Accordingly, the independent output is toggled to produce an AC output signal, the loss of which initiates activation of the warning. The program executes each loop in a fixed time period which is monitored, and if the program is not executed within such period, the system is forced to reset and the warning is activated until the proper time constraints are again met. A self check also assures that the system will respond to the loss of the AC output signal.

Claims

1. A method of operating a digital computer in a fail-safe manner in order to activate a warning device when a train on a railroad track is moving along an approach to a given location, said method comprising the steps of:

deriving information indicative of the impedance of said track adjacent said location and inputing said information to said computer;

providing said computer with a repeating program loop that causes the computer on each program repetition to determine from said information whether or not activation of the warning device is required and to retain such determination in a memory;

repetitively interrupting said program loop to enter an interrupt program which checks said determination in memory and

(1) if activation of the warning device is not required, causes an output of said computer to undergo a change of state and then returns control of the computer to said program loop, or

(2) if activation of the warning device is required, returns control of the computer to said program loop without altering the previous state of said output,

whereby said output repeatedly changes state until activation of the warning device is required or a system failure disables the computer;

sensing the condition of said output to maintain said warning device deactivated in response to repeated changes of the state of said output, and activating said warning device with electrically responsive activating means when the state of said output remains constant for a predetermined period of time;

periodically momentarily disabling said output so its state cannot change;

checking the operability of said activating means in response to said momentary disability; and

activating said warning device if the activating means fails to respond to said momentary disability.

2. The method as claimed in claim 1, further comprising the steps of:

monitoring the execution time of said repeating program loop; and

activating said warning device if each execution is not completed in a predetermined time period.

3. A method of operating a digital computer in a fail-safe manner in order to activate a warning device when a train on a railroad track is moving along an approach to a given location, said method comprising the steps of:

deriving information indicative of the impedance of said track adjacent said location and inputing said information to said computer;

providing said computer with a repeating program loop that causes the computer on each program repetition to determine from said information whether or not activation of the warning device is required and to retain such determination in a memory;

repetitively interrupting said program loop to enter an interrupt program which checks said determination in memory and

(1) if activation of the warning device is not required, causes an output of said computer to undergo a change of state and then returns control of the computer to said program loop, or

(2) if activation of the warning device is required, returns control of the computer to said program loop without altering the previous state of said output,

whereby said output repeatedly changes state until activation of the warning device is required or a system failure disables the computer;

inputing said computer output to a filter which blocks signals other than those having a time-varying characteristic, whereby an output signal is delivered by said filter only when said computer output repeatedly changes state; and

activating said warning device in response to an absence of the output signal from said filter.

4. A method of operating a digital computer in a fail-safe manner in order to activate a warning device when a train on a railroad track is moving along an approach to a given location, said method comprising the steps of:

deriving information indicative of the impedance of said track adjacent said location and inputing said information to said computer;

providing said computer with a repeating program loop that causes the computer on each program repetition to determine from said information whether or not activation of the warning device is required and to retain such determination in a memory;

repetitively interrupting said program loop to enter an interrupt program which checks said determination in memory and

(1) if activation of the warning device is not required, causes an output of said computer to undergo a change of state and then returns control of the computer to said program loop, or

(2) if activation of the warning device is required, returns control of the computer to said program loop without altering the previous state of said output,

whereby said output repeatedly changes state until activation of the warning device is required or a system failure disables the computer;

sensing the condition of said output to maintain said warning device deactivated in response to repeated changes of the state of said output, and activating said warning device with electrically responsive activating means when the state of said output remains constant for a predetermined period of time;

providing said program loop with a routine that periodically momentarily disables said output so its state cannot change;

checking the operability of said activating means in response to said momentary disability; and

activating said warning device if the activating means fails to respond to said momentary disability.

5. A method of operating a digital computer in a fail-safe manner in order to activate a warning device when a train on a railroad track is moving along an approach to a given location, said method comprising the steps of:

deriving information indicative of the impedance of said track adjacent said location and inputing said information to said computer;

providing said computer with a repeating program loop that causes the computer on each program repetition to determine from said information whether or not activation of the warning device is required and to retain such determination in a memory;

repetitively interrupting said program loop to enter an interrupt program which checks said determination in memory and

(1) if activation of the warning device is not required, causes an output of said computer to undergo a change of state and then returns control of the computer to said program loop, or

(2) if activation of the warning device is required, returns control of the computer to said program loop without altering the previous state of said output,

whereby said output repeatedly changes state until activation of the warning device is required or a system failure disables the computer;

sensing the condition of said output to maintain said warning device deactivated in response to repeated changes of the state of said output, and activating said warning device when the state of said output remains constant for a predetermined period of time, said activating of the warning device being effected by control means responsive to the presence or absence of electrical excitation;

providing said program loop with a routine that periodically momentarily disables said output so its state cannot change;

interposing a motion detector gate between a source of said electrical excitation and said control means;

maintaining said motion detector gate in conduction so long as said output repeatedly changes state;

providing a self-check gate in series with said motion detector gate between said source and said control means;

in response to each momentary disability of said output, maintaining said self-check gate in conduction for a limited time period greater than the interval from one momentary disability to the next; and

holding said motion detector gate in conduction during said momentary disability, whereby both of said gates remain in conduction upon proper response to said disability, whereas failure to so respond causes said self-check gate to cease conduction and remove excitation from said control means to activate said warning device.