Methods and systems for controlling oxygen delivery in a flow therapy apparatus

A respiratory apparatus that provides a flow of gases to a patient, the respiratory apparatus comprising:

• an ambient air inlet;
• a supplemental inlet for receiving supplemental gases from a supplemental gases source;
• a valve, wherein the valve requires a minimum amount of current in order to open;
• a gases composition sensor configured to measure gases composition of mixed flow of ambient air and supplemental gases;
• a main controller configured to control delivery of gases to the patient, the controller configured to:
• adjust actuation of a valve opening by controlling valve current;
• and
• activate a coarse controller when a target flow rate of supplemental gas is increased from zero;
• a coarse controller configured to:
• control actuation of the valve opening by controlling the valve current, wherein the main controller or the coarse controller can control the valve current;
• iteratively increases current supplied to the valve;
• and
• switch control of the actuation of the valve to the main controller after flow through the valve is detected.