Patent ID: 6810906
Filing Date: 2004-11-02
Classification: G05D,Y10T

Abstract:
A flow control device including:a flow control valve controlling a flow of liquid; first and second linear variable differential transformers which are equipped with a core moving in a same direction as a cylinder of said flow control valve and which detect a position of said valve cylinder; first and second servo controllers generating control signals to control a lift of said flow control valve based on signals detected individually by said first and second linear variable differential transformers; and a switch selecting one of the control signals output individually from said first and second servo controllers so that the selected control signal is supplied to said flow control valve; wherein said first and second linear variable differential transformers each comprise: said core; a primary coil fed with an alternating current voltage; and two, first and second, secondary coils, connected in parallel, where voltages are induced in accordance with the position of said core when said primary coil is energized with a voltage; wherein said first servo controller monitors voltages which are generated individually in said primary coil, said first secondary coil and said second secondary coil provided in said first linear variable differential transformer, and said second servo controller monitors voltages generated individually in said primary coil, said first secondary coil and said second secondary coil provided in said second linear variable differential transformer; and while the control signal transmitted from said first servo controller is being selected by said switch and when it is confirmed that at least one of said primary coil, said first secondary coil and said second secondary coil provided in said first linear variable differential transformer outputs a voltage out of a range of normal performance, said switch stops selecting the control signal from said first servo controller; and while the control signal transmitted from said second servo controller is being selected by said switch and when it is confirmed that at least one of said primary coil, said first secondary coil and said second secondary coil provided in said second linear variable differential transformer outputs voltage out of a range of normal performance, said switch stops selecting the control signal from said second servo controller.