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The present invention provides for an improved method of determining a water out condition in a humidified gases supply apparatus. The method includes a two step process including a primary determination of a water out condition and a secondary determination of a water out condition. This primary de

The present invention provides for an improved method of determining a water out condition in a humidified gases supply apparatus. The method includes a two step process including a primary determination of a water out condition and a secondary determination of a water out condition. This primary determination is made during observation of the normal operation of the apparatus. During the secondary determination the method takes temporary control over the humidifying part of the apparatus. The secondary determination confirms or contradicts the primary determination.

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1. An apparatus for preparing a flow of gases, the apparatus comprising: a heater configured to heat a reservoir,a temperature sensor in thermal communication with the heater to read a temperature of the heater,a hardware controller configured to apply a first power from a power supply to the heater

1. An apparatus for preparing a flow of gases, the apparatus comprising: a heater configured to heat a reservoir,a temperature sensor in thermal communication with the heater to read a temperature of the heater,a hardware controller configured to apply a first power from a power supply to the heater, the controller further configured to monitor system conditions during operation, determine, according to a first determination method, a possible absence of water in the reservoir from at least some of the monitored system conditions and, following a determination of a possible absence of water condition according to the first determination method, determine according to a second determination method, an absence of water in the reservoir, the second determination method being different than the first determination method and comprising applying a second power that is different than the first power. 2. The apparatus of claim 1, wherein the hardware controller is further configured to determine, following the determination of the possible absence of water condition and applying the second power that is different than the first power, whether a resulting rise in temperature of the heater is indicative of a water out condition. 3. The apparatus of claim 2, wherein the hardware controller, in determining whether the resulting rise in temperature of the heater is indicative of a water out condition, is further configured to compare the heater temperature against a threshold temperature and determine a water out condition where the rise in temperature of the heater exceeds the predetermined threshold temperature. 4. The apparatus of claim 3, wherein the hardware controller is configured to determine the water out condition when the resulting rise in temperature exceeds the predetermined threshold temperature within a predetermined period of time. 5. The apparatus of claim 4, wherein the hardware controller is configured to reduce an amount of power supplied from the power supply to the heater when a water out condition is determined. 6. The apparatus of claim 1, wherein the hardware controller is configured to apply the second power that is a maximum available power to the heater following a determination of a possible absence of water condition. 7. The apparatus of claim 1, wherein the hardware controller is configured to apply the second power that is a predetermined amount of power to the heater following a determination of a possible absence of water condition. 8. The apparatus of claim 1, wherein the hardware controller is configured to apply the second power that is an amount of power to the heater that would elevate the temperature of the heater in the absence of water to a temperature that exceeds any temperature that the heater temperature would reach with water present in the chamber following a determination of a possible absence of water condition. 9. The apparatus of claim 1, wherein the heater comprises a heater plate and the apparatus includes a clamp for holding a removable chamber against the heater plate. 10. The apparatus of claim 9, wherein the temperature sensor is attached to the heater plate. 11. The apparatus of claim 10 further comprising a blower for generating a flow of gases and a humidifier incorporating the heater and the reservoir, an outlet of the blower leading to an inlet of the humidifier. 12. The apparatus of claim 1, wherein the system conditions monitored by the hardware controller during operation include a temperature of gases leaving the reservoir and the first power applied to the heater; wherein the hardware controller is configured to determine the possible absence of water condition based on a function of the temperature of gases leaving the reservoir and the first power applied to the heater. 13. The apparatus of claim 12, wherein the function used by the hardware controller comprises a ratio of the temperature of the gases leaving the humidifier to the first power applied to the heater. 14. The apparatus of claim 13, wherein the hardware controller is further configured to determine the possible absence of water in the reservoir by comparing a result of the function against a predetermined threshold. 15. The apparatus of claim 1 wherein when the hardware controller applies the second power to the heater plate, the hardware controller increases the heater plate duty cycle to a maximum available duty cycle and applies full power to the heater plate. 16. The apparatus of claim 15 wherein the hardware controller is configured to make a determination of a water out condition by monitoring a rate of increase in the heater temperature, wherein if the rate of increase of the heater temperature exceeds a threshold rate, a water out condition is confirmed. 17. The apparatus of claim 1 wherein the hardware controller monitors an amount of time the heater temperature exceeds a threshold temperature for a predetermined time limit and confirms a water out condition if the heater temperature exceeds the threshold temperature for a predetermined time limit. 18. The apparatus as claimed in claim 17 wherein the hardware controller has a threshold temperature of 125 degrees Celsius and a predetermined time limit of at least 30 seconds. 19. The apparatus of claim 1 wherein the temperature sensor is configured to measure the heater temperature every 90 seconds or less. 20. The apparatus of claim 1 wherein the hardware controller is configured to determine according to the second determination method, an absence of water in the reservoir, wherein the second determination method further comprises: sensing the heater temperature using the temperature sensor;comparing the heater temperature to a temperature that would occur in the absence of water when the second power is applied to the heater; andreducing the power supplied to the heater following a determination of an absence of water according to the second determination method. 21. The apparatus of claim 20 wherein the hardware controller is configured to determine according to the second determination method, an absence of water in the reservoir, wherein the sensing the heater temperature using the temperature sensor further comprises determining a rise in a heater plate temperature. 22. A system for preparing a flow of gases, the system comprising: a humidifier including a reservoir and a heater for heating the reservoir,a temperature sensor in thermal communication with the heater and configured to read a temperature of the heater,a hardware controller configured to apply a first power from a power supply to the heater, the hardware controller configured to monitor system conditions during operation and determine, according to a first determination method, the existence of a possible absence of water condition in the reservoir based on at least some of the monitored system conditions;wherein the hardware controller is further configured to apply a second power that is different from the first power, according to a second determination method that is different from the first determination method, from the power supply to the heater following a determination of a possible absence of water condition and confirm an absence of water condition if the temperature read by the temperature sensor exceeds a predetermined threshold for a predetermined period of time. 23. The system of claim 22, wherein the hardware controller is further configured to reduce power supplied from the power supply to the heater if an absence of water condition is confirmed. 24. The system of claim 22, wherein the hardware controller is further configured to provide an output indicating a water out condition if an absence of water condition is confirmed.