Importance

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Abstract

A voltage fault detector (10) for producing a trip signal causing switching from a first AC voltage source (12) to a second AC voltage source (14) is disclosed. A plurality of comparators (18,20,22) monitor a signal which is proportional to the magnitude of the voltage of a first AC voltage source (12) to determine if sample values fall within predetermined ranges. A counter (30) counts the number of samples falling outside the predetermined range to generate the trip signal when the count reaches a predetermined limit. The counter (30) is augmented for each sample which is outside the predetermined range and decremented for each sample which is within the predetermined range. A plurality of latches (24,26,28) are respectively coupled to a different one of the comparators for applying the output level signal from one of the comparators to the counter at predetermined times under the control of clock signal pulse trains generated by a combinational logic circuit (32) which are respectively applied to a different one of the plurality of latches. The voltage fault detector (10) may be used to monitor the condition of one or more phases of a backup voltage source.

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First Claim