Control of humidifier chamber temperature for accurate humidity control

A breathing assistance system for delivering a flow of gases to a user for therapeutic purposes, comprising:

• a humidifier unit that has an inlet port and an exit port, said humidifier unit adapted to in use receive said flow of gases from a gases source via said inlet port, said humidifier unit further adapted to hold and heat a volume of water in use, in use said flow of gases passing through said humidifier unit and becoming heated and humidified, said heated and humidified flow of gases exiting said humidifier unit via said humidifier unit exit port;
• an exit port temperature sensor adapted to measure the temperature of said flow of gases exiting said humidifier unit;
• an ambient temperature sensor adapted to measure the temperature of said flow of gases at a point before said gases enter said humidifier unit;
• a flow sensor adapted to measure the actual flow rate of said flow of gases through said system;
• and
• a controller adapted to:
• receive data from said ambient temperature sensor relating to the measured temperature, data from said exit port temperature sensor relating to the measured temperature, and data from said flow sensor relating to said actual flow rate;
• determine a target temperature for said flow of gases passing through said exit port based on at least the data from said ambient temperature sensor and said flow sensor;
• compare said target temperature to data from said exit port temperature sensor relating to the measured temperature of said flow of gases;
• and
• adjust the power to said humidifier unit to achieve said target temperature for said flow of gases passing through said humidifier unit exit port.