Humidified gases delivery apparatus and methods for controlling same

1. A method of determining an amount of water amount in a humidification chamber within a humidified gases delivery system, said method comprising:

delivering power to a heater used to heat contents of a humidification chamber;

varying the delivered power to the heater over a period of time;

determining a plurality of temperature measurements from a temperature sensor over the period of time in the humidification chamber responsive to varying the delivered power;

determining a temperature change trend from the plurality of temperature measurements over the period of time;

determine a flow rate of air flowing through the humidification chamber from a flow sensor or a pressure sensor;

calculating an evaporation rate of water in the humidification chamber over the period of time based on the flow rate of air flowing through the humidification chamber and the temperature change trend;

comparing the evaporation rate with a predetermined trend comprising a look up table storing a plurality of values corresponding to a relationship between the evaporation rate and known water amounts in the humidification chamber; and

determining the amount of water within the humidification chamber based on said comparison.

2. The method of claim 1 , wherein the temperature change trend comprises a rate of temperature increase.

3. The method of claim 1 , wherein the plurality of temperature measurements comprise an initial temperature of the humidification chamber contents at start up, a final temperature of the chamber contents after said time period has elapsed.

4. The method of claim 1 , wherein the amount comprises volume.

5. The method of claim 1 , wherein the amount comprises mass.

6. A method of determining a water amount in a humidification chamber within a humidified gases delivery system wherein the method comprises:

delivering power at a first power level to a heater to heat contents of the chamber;

changing power to a second power level to the heater for a period of time, said second power level is different than the first power level;

determining a plurality of temperature measurements over the period of time in the humidification chamber responsive to the change of power;

determining a temperature change trend from the plurality of temperature measurements from a temperature sensor over the period of time responsive to the change of power to the second power level;

determine a flow rate of air flowing through the humidification chamber from at least one of the following sensors: a flow sensor or a pressure sensor;

calculating an evaporation rate based on the flow rate of air flowing through the humidification chamber and the temperature change trend;

comparing the evaporation rate with predetermined values stored in a look up table, said predetermined values include evaporation rates for known water amounts in the humidification chamber; and

determining the water amount within the humidification chamber based on said comparison.

7. The method of claim 6 , wherein the temperature change trend comprises a rate of temperature decrease.

8. The method of claim 6 , wherein the plurality of temperature measurements comprise measuring a temperature of the chamber prior to reducing power to the heater, and measuring a temperature after the period of time.

9. The method of claim 6 , wherein the amount comprises volume.

10. The method of claim 6 , wherein the amount comprises mass.

11. A humidification apparatus adapted to humidify a stream of gases, the humidification apparatus comprising:

a humidification chamber adapted to hold a volume of water, the humidification chamber including an inlet adapted to receive the stream of gases and an outlet, a heater plate, in use, in contact with the humidification chamber, the heater plate adapted to heat the humidification chamber and contents within the humidification chamber to create water vapour within the humidification chamber;

an electronic controller adapted to control power supplied to the heater plate;

the electronic controller adapted to:

deliver power to the heater plate used to heat the contents of the humidification chamber;

vary the delivered power to the heater over a period of time;

determine a plurality of temperature measurements from a temperature sensor over the period of time in the humidification chamber responsive to varying the delivered power;

determine a flow rate of air flowing through the humidification chamber from a flow sensor or a pressure sensor;

calculate an evaporation rate of water in the humidification chamber over the period of time based on the flow rate of air flowing through the humidification chamber and the plurality of temperature measurements;

compare the evaporation rate with a predetermined trend stored in a look up table, wherein the predetermined trend comprises a relationship between evaporation rates and known water amounts in the humidification chamber; and

determine the volume of water within the humidification chamber based on the comparison.

12. A humidification apparatus adapted to humidify a stream of gases, the humidification apparatus comprising:

a humidification chamber adapted to hold a volume of water, the humidification chamber including an inlet adapted to receive the stream of gases and an outlet, a heater plate, in use, in contact with the humidification chamber, the heater plate adapted to heat the humidification chamber and contents within the humidification chamber to create water vapour within the humidification chamber,

an electronic controller adapted to control power supplied to the heater plate;

the electronic controller adapted to:

deliver power to the heater plate to heat the contents of the humidification chamber;

change the delivered power to the heater plate for a period of time;

determine a plurality of temperature measurements from a temperature sensor;

determine a temperature change trend from the plurality of temperature measurements over the period of time in response to said change of power;

determine a flow rate from a flow sensor or a pressure sensor;

calculate an evaporation rate based on the flow rate of air flowing through the humidification chamber and the temperature change trend;

compare the evaporation rate with predetermined values stored in a look up table, said predetermined values include evaporation trend for known water amounts in the humidification chamber; and

determine the volume of water within the humidification chamber based on said comparison.