Patent ID: 7847276

Claim:
A method for determining a position of a movable flow sensor element of a flow sensor in a flow control system, the flow sensor being of a type having an axially-extending flow passageway for a liquid to be delivered by the flow control system, the movable sensor element being axially movable within the flow passageway in response to a first force exerted on the sensor element by the liquid as it passes through the flow passageway and in response to a second force exerted on the sensor element in a direction opposite the first force by a spring received within the flow passageway, the sensor reaching equilibrium position within the flow passageway when the magnitudes of the first and second forces are equal, the equilibrium position corresponding to a axial position within the flow passageway which varies with varying flow rate, the flow control system being of a type having a source of fluid driving pressure for driving the fluid through the flow passageway, the flow rate being responsive to variations in the fluid driving pressure, the method comprising: illuminating a photosensitive pixel array with a light source, the photosensitive pixel array extending axially along the flow passageway and the sensor element disposed in an optical path between the light source and the photosensitive pixel array to generate a first set of pixel intensity values for the photosensitive pixel array, the first set of pixel intensity values representative of a first sensor element position corresponding to a first flow rate; introducing an abrupt change in the fluid driving pressure; illuminating the photosensitive pixel array with the light source to generate a second set of pixel intensity values for the photosensitive pixel array, the second set of pixel intensity values representative of a second sensor element position corresponding to a second flow rate; calculating a difference between the first and second sets of pixel intensity values as a function of pixel position.