Patent ID: 8317156

Claim:
A method of controlling the operation of a metering valve driven by a stepper motor, a position sensor normally providing position information to allow control over the metering valve in a closed loop manner, the method comprising the steps of: performing a calibration operation to derive a relationship between stepper motor position and metering valve position; controlling the operation of the metering valve in a closed loop manner; and controlling the operation of the metering valve in an open loop manner in the event that the position sensor output is thought to be unreliable; wherein the step of performing a calibration operation involves sweeping the metering valve through its range of normal movement between a fully open position and a fully closed position while monitoring the output of the position sensor and calculating a gain value as a ratio of the movement of the stepper motor to the change in the output of the position sensor; and wherein allowance is made for potential backlash in the drive train between the stepper motor and the metering valve.