Abstract: A method and apparatus for driving a stepper motor such that when the motor is stepped, the velocity of the motor is substantially zero upon reaching a new stepped position, thereby eliminating overshoot and ringing, and the wasted energy associated with these effects. The method comprises energizing at least one of the stepper motor windings at a predetermined current level for a predetermined step time, wherein the current level is determined as a function of the step time and dynamic single-step response characteristics of the stepper motor and load so that the motor velocity is substantially zero when the adjacent stepped position is reached. At this point, the stepper motor windings that were energized to make the rotor of the motor move are de-energized, whereupon the rotor is held in place by the inherent detent torque of the stepper motor. Since the velocity of the motor is substantially zero when the adjacent stepped position is achieved, there is no overshoot, and thus ringing is eliminated.

Abstract: A method and apparatus for determining leakage, particularly of valves, in a pump assembly. A pump assembly (20) includes a primary valve (34) and a secondary valve (36), which may be selectively activated to control the source of fluid input to the pump assembly. The pump assembly also includes an inlet valve (42) and an outlet valve (50) disposed on each side of the pumping chamber (46). Downstream of the outlet valve is disposed a pressure sensor (54), which produces a signal indicative of the pressure of fluid within the pump assembly at that point. Leakage in the inlet or outlet valves is detected in the inlet or outlet valves by filling the pumping chamber with fluid, closing the inlet and outlet valves, and equalizing the pressure in the pump assembly distal to the inlet valve. After the pressure has been equalized, the outlet valve is opened and a reference pulse is determined as a function of the signal produced by the pressure sensor.

Abstract: Risk of hydrodynamic pressure noise interference with a valve leakage test conducted upon a plurality of valves within a pump assembly is minimized. A pressure sensor within the pump assembly produces a signal indicative of hydrodynamic pressure in fluid distal of an outlet valve of the pump. The signal produced by the pressure sensor is input to a microcontroller that controls the pump assembly. Prior to conducting the valve leakage test, the hydrodynamic pressure level of the fluid is sampled at a frequency that is at least twice that of the hydrodynamic noise. The microcontroller determines if a maximum of the samples of the hydrodynamic pressure level taken during a data interval is above a predetermined threshold. If so, the valve leakage test is suppressed until the maximum pressure level is below the predetermined threshold during a successive data interval.