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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
First Claim
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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.

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