Humidity sensor

A system for interpolating the output of an absolute humidity sensing apparatus for sensing the absolute humidity of a flow of respiratory gas comprising:

• a humidity transducer providing a first signal, said first signal indicative of the relative humidity of said flow of gas;
• a heater associated with or in substantial thermal contact with said humidity transducer and adapted to heat at least a portion of said humidity transducer depending on energisation power supplied thereto;
• a temperature sensor associated with or in substantial thermal contact with said humidity transducer and providing a second signal, said second signal indicative of the temperature of said humidity transducer
• a flow sensor configured in use to provide an indication of the flow rate of said gas and having a response tune significantly lower than said humidity transducer or said temperature sensor, and;
• a controller or processor configured to:
• (i) provide a first said energisation power to said heater to heat said humidity transducer to an operating temperature;
• (ii) receive said first signal and said second signal;
• (iii) calculate an estimate of the absolute humidity of said flow of gas based on said first signal and/or said second signal;
• (iv) store information on said absolute humidity over a period of time;
• (v) sense the flow rate of said flow of gas;
• (vi) store information on said flow rate of said gas over said period of time;
• and
• (vii) interpolate absolute humidity values for said flow of gas during a portion of said period of time based on said stored flow rate of gas during said portion of said period of time and said stored absolute humidity during said portion of said period of time.

A system for automatically testing the accuracy of an absolute humidity sensing apparatus for sensing the absolute humidity of respiratory gas comprising:

• a humidity transducer providing a first signal, said first signal indicative of the relative humidity of said gas,
• a heater associated with or in substantial thermal contact with said humidity transducer and adapted to heat at least a portion of said humidity transducer depending on energisation power supplied thereto,
• a temperature sensor associated with or in substantial thermal contact with said humidity transducer and providing a second signal, said second signal indicative of the temperature of said humidity transducer, and
• a controller or processor configured to provide energisation power to said heater to heat said humidity transducer to at least two different calibration temperatures, receive said first signal and said second signal and calculate an estimate of the absolute humidity of said gas at each different calibration temperature based thereon, and detect or determine whether the apparatus is operating correctly, based on whether said absolute humidity is consistent over said temperatures.

A system as claimed in 9 wherein said detection of liquid water comprises the steps:

• a) storing absolute humidity values during normal operation;
• b) providing a third said energisation power to said heater to heat said humidity transducer to the dewpoint of said gas (where the relative humidity just reaches 100%);
• c) comparing the absolute humidity reading at dew point with that during normal operating (stored in step (a));
• and if there is a substantial difference providing a fourth signal indicative of incorrect or faulty operation.

A system for locating an absolute humidity sensor within a gas delivery apparatus for suppling a flow of respiratory gas to a patient comprising:

• a gas supply adapted to provide a flow of gas at a desired pressure,
• a humidifier having an inlet and an outlet, said inlet adapted to be in fluid communication with said gas supply and said humidifier thereby providing water vapour to humidify said flow of gas as they pass through said humidifier,
• a conduit in use adapted to be connected to said outlet and accepting said flow of gas there from, said conduit including an interior and an exterior, said conduit in use conveying said flow of gas through said interior, in use a portion of said conduit adjacent said outlet being substantially vertical and including a protrusion within the interior of said substantially vertical portion, and
• a humidity sensor adapted to be located in said interior providing an estimate of the absolute humidity of said flow of gas, said humidity sensor juxtapositioned below said protrusion, said protrusion thereby substantially preventing any liquid water from flowing down said conduit onto said humidity sensor.

A method of automatically disinfecting an absolute humidity sensor for respiratory gas comprising the steps:

• operating in an absolute humidity measurement mode comprising the steps of
• using a humidity transducer to sense the relative humidity of said gas;
• heating at least a portion of said humidity transducer to an operating temperature and sensing the temperature of said humidity transducer, and
• determining an estimate of the absolute humidity of said gas based on said temperature and said relative humidity;
• operating in a disinfecting mode comprising the step of
• heating said humidity transducer to a predetermined disinfection temperature, said disinfection temperature being higher than said operating temperature and adequate to substantially kill the majority of any common pathogens present on said humidity transducer.

A method of interpolating the output of an absolute humidity sensor of respiratory gas comprising the steps:

• using a humidity sensor to sense the relative humidity of said gas,
• heating at least a portion of said humidity sensor to an operating temperature,
• determining an estimate of the absolute humidity of said flow of gas based on said relative humidity and temperature, said absolute humidity determination having a response time,
• storing said relative or absolute humidity over a period of time,
• sensing the flow rate of said gas, said flow rate having a response time significantly lower than said humidity,
• storing said flow rate over said period of time, and
• interpolating values for absolute humidity during a portion of said period of time based on said stored flow rate and said stored absolute humidity.

A method of automatically testing the accuracy of an absolute humidity sensor for respiratory gas comprising the steps:

• using a humidity sensor to sense the relative humidity of said gas at each temperature,
• heating at least a portion of said humidity sensor to at least two different calibration temperatures,
• calculating an estimate of the absolute humidity of said gas at each temperature based on said relative humidities and said temperatures,
• detecting or determining whether the apparatus is operating correctly, based on whether said absolute humidity is substantially consistent over said temperatures.

A method of locating an absolute humidity sensor for respiratory gas comprising the steps:

• providing a flow of gas at a desired pressure,
• humidifying said flow of gas,
• conveying said flow of gas through the said interior of a conduit and providing at least a portion of said conduit substantially vertical with a protrusion in said interior of said substantially vertical portion,
• positioning a humidity sensor within the flow of gas below said protrusion, said protrusion thereby substantially preventing any liquid water from flowing down said interior onto said humidity sensor, and
• providing an estimate of the absolute humidity of said flow of gas, based on the temperature and relative humidity of said gas from said humidity sensor.