Importance

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Abstract

A system and methods to provide a desired operating area for a motor driving a fan for inducing a draft in a vent of a heating, ventilating and air conditioning system. The motor includes a stationary assembly and a rotatable assembly. The stationary assembly includes windings adapted to be energized in at least one preselected sequence. The rotatable assembly is in magnetic coupling relation to the stationary assembly and in driving relation to the fan. The system includes a commutating circuit responsive to a pressure signal representative of a minimum air pressure in the vent and a tachometer signal representative of the speed of the motor for controlling power switching devices. The power switching devices selectively connect a power supply to the windings to provide a motor current to the windings in the preselected sequence to produce an electromagnetic field for rotating the rotatable assembly at a motor operating speed. A control circuit limits the motor current provided to the windings by the power switching devices to a predetermined maximum current which is a function of the motor operating speed as represented by the tachometer signal. In this manner, the control circuit inhibits operation of the motor outside a pre-defined speed/current region by preventing the motor current at a particular motor operating speed from exceeding the predetermined maximum current. The predetermined maximum current is within the pre-defined speed/current region and corresponds to the particular motor operating speed so that excessive heat is not generated by the system.

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First Claim