Patent ID: 7950294
Filing Date: 2011-05-31
Classification: G01M

Abstract:
1. A valve system comprising: a valve, including a valve body and a motor configured to apply a torque to the valve body in response to a drive current so as to cause the valve body to move between an open position that allows a flow of a fluid, and a closed position that prevents the flow of the fluid, wherein the motor is a two-phase stepper motor; and a controller for the valve, the controller configured to control the application of the drive current to the motor and wherein the controller is configured to apply one or more phase currents to the stepper motor in each of the two phases of the stepper motor, the controller being configured (a) to determine the torque delivered by the motor to the valve body as a function of the voltage applied to the motor and compare the value of the determined torque with a threshold value, wherein determining the torque comprises computing a phase voltage in each phase of the stepper motor based on the currents applied to the stepper motor in each phase, computing the angle between the phase current and the phase voltage in each phase of the stepper motor, then computing the delivered torque as a product of a peak value of the phase current, the cosine of the angle, and a back emf constant, and (b) to detect when there is a need by the valve system for preventive maintenance when the value of the determined torque is substantially equal to the threshold value.