Vital relay operating circuit
AssigneeGeneral Signal Corporation
InventorsJohn H. Auer, Jr., Henry C. Sibley
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Abstract
There is disclosed a circuit for energizing a vital relay in response to an input signal that is modulated between two frequencies. A discriminator circuit responds to the modulated frequencies and alternately produces an output patented of one polarity and then a reverse polarity in response to the modulated signals. Coupled between the discriminator and the vital relay is a relay driver which responds to the output of the discriminator and energizes the vital relay. A d.c. power supply is coupled to the relay driver. The vital relay includes two windings. Failure of the modulation, the d.c. source or virtually any circuit element, will result in release of the vital relay. The disclosed embodiment uses photoresistors as switching elements.
Claims18
Fail safe relay actuating means comprising in combination:
- (a) an a.c. signal source modulated at a predetermined rate to signals of first and second frequencies;
- (b) discriminator means coupled to said signal source rectifying said signals of said first and second frequencies for producing an output potential, between a pair of terminals, which reverses polarity at said predetermined rate in response to the modulation of said a.c. signal source;
- and
- (c) first and second polarity responsive means coupled in parallel between said pair of terminals for producing relay control signals in response to said polarity reversals.
A circuit for actuating a vital relay in response to an a.c. signal being alternately modulated to signals of first and second frequencies and comprising in combination:
- (a) first and second rectification means responsive to said first and second frequencies for producing first and second d.c. output potentials, respectively;
- (b) said first and second d.c. output potentials coupled in series opposition across a terminal pair for producing an output potential having the polarity of the dominant one of said first and second d.c. output potentials;
- (c) first and second polarity responsive control means bridged in parallel across said terminal pair for producing first and second signals and second and first signals, respectively, when the potential across said terminal pair is of the polarity of said first and second d.c. output potentials, respectively;
- (d) first and second switching means coupled to said first and second polarity responsive control means, respectively, and responsive to said first signals for rendering said first and second switching means conducting;
- and responsive to said second signals for rendering said first and second switching means relatively nonconducting;
- and wherein
- (e) said first and second switching means control the flow of current to the vital relay.
Dependencies are inferred from the claim text.