Fail-safe time delay circuit
AssigneeWestinghouse Air Brake Company
InventorDick J. Kolkman
Life of this patent
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Abstract
A fail-safe time delay circuit comprising a detection relay for sensing the presence and absence of an input signal, a switching relay for assuming a first and a second condition in accordance with the presence and absence of the input signal, and a programmable unijunction transistor oscillating circuit, a silicon controlled rectifier gating circuit and a d.c. making circuit including a solid-state Colpitts oscillator and half-wave rectifier controlled by the second condition of the switching relay for providing a predetermined time delay period between the disappearance and the reappearance of the input signal prior to permitting the switching relay reassume its first condition.
Claims10
A fail-safe time delay circuit comprising, detection means for sensing the presence and absence of an input signal on a pair of terminals, switching means connectable between said pair of input signal terminals and a pair of d.c. supply terminals, said switching means assuming a first and a second condition in accordance with the presence and absence of the input signal on said pair of input signal terminals, oscillating means connectable to said pair of d.c. supply terminals, gating means connected to said oscillating means, and d.c. making means connectable to said pair of d.c. supply terminals, and said oscillating, gating and d.c. making means controlled by the second condition of said switching means for providing a time delay period between the disappearance and the reappearance of the input signal on said pair of input signal terminals prior to said switch means reassuming the first condition.
Dependencies are inferred from the claim text.