Monitoring device for airfield lighting system

Claim 1

An electrical circuit for monitoring the operation of a plurality of lights, comprising: power source means for supplying constant current AC power; a plurality of isolation transformer means, each of said transformers plurality having serially interconnected primary circuitry, said interconnected primary circuitry coupled to said power source means forming a circuit loop, each of said transformer plurality having secondary circuitry electrically coupled to a corresponding one of the plurality of lights; monitoring current transformer means having a magnetic core with a primary circuit serially coupled to said circuit loop such that said core magnetically saturates in response to current flowing through said circuit loop, said monitoring current transformer means having a secondary circuit in a substantially open circuit condition for generating a monitoring signal in response to each inversion of current in said circuit loop; enabling circuit means coupled to receive said monitoring signal for providing an output window signal having a duration corresponding to the time said monitoring signal amplitude is within a predetermined range; means coupled to said circuit loop for providing signals indicative of the voltage across said serially interconnected isolation transformer means primary circuitry; integrating circuit means receiving said voltage indicating signals and said output window signals, for providing an integrated voltage signal during the presence of said output window signal; and subtracting circuit means coupled to receive said integrated voltage signal and a reference voltage signal indicative of current loop voltage when all of the plurality of lights are operative, for providing a difference signal indicative the number of defective lights in the loop.

Claim 7

A method for monitoring the operation of a plurality of electrical lights, comprising the steps of: providing a constant current AC power source; serially connecting the primary windings of a plurality of isolation transformers to said AC power source to form a circuit loop; coupling the secondary windings of each of said isolation transformers to a corresponding lamp; providing a monitoring current transformer having a magnetic core with a primary circuit serially coupled to said circuit loop and a secondary circuit in substantially open circuit condition, such that said core magnetically saturates in response to current flowing through said circuit loop to generate a monitoring signal in response to each inversion of current in said circuit loop; coupling said monitoring signal to an enabling circuit for producing an output window signal during a time period when said monitoring signal amplitude is within a predetermined range; determining the voltage across the serially connected primaries of said isolation transformers; integrating said determined voltage during the occurrence of said output window signal; and subtracting said integrated voltage signal from a reference signal indicative of the voltage across the serially connected primaries of said isolation transformers when all of the plurality of lights are operative, thereby providing a difference signal indicative of the number of defective lamps in the loop.

Claim 8

A method for monitoring the operation of a plurality of electrical lights, comprising the steps of: providing a constant current AC power source; serially connecting the primary windings of a plurality of isolation transformers to said AC power source to form a circuit loop; coupling the secondary windings of each of said isolation transformers to a corresponding lamp; providing a monitoring current transformer having a magnetic core with a primary circuit serially coupled to said circuit loop and a secondary circuit in substantially open circuit condition, such that said core magnetically saturates in response to current flowing through said circuit loop to generate a monitoring signal in response to each inversion of current in said circuit loop; coupling said monitoring signal to an enabling circuit for producing an output window signal during a time period when said monitoring signal amplitude is within a predetermined range; determining the voltage across the serially connected primaries of said isolation transformers; integrating said determined voltage during the occurrence of said output window signal; and subtracting said integrated voltage signal from a reference signal indicative of the voltage across the serially connected primaries of said isolation transformers when all of the plurality of lights are operative, thereby providing a difference signal indicative of the number of defective lamps in the loop.