WIRE HEATED TUBE WITH TEMPERATURE CONTROL SYSTEM, TUBE TYPE DETECTION, AND ACTIVE OVER TEMPERATURE PROTECTION FOR HUMIDIFIER FOR RESPIRATORY APPARATUS

• US 20110023874A1
• Filed: 07/30/2010
• Published: 02/03/2011
• Est. Priority Date: 07/31/2009
• Status: Active Grant

• Current Assignee: ResMed Pty Ltd. (ResMed Incorporated)
• Original Assignee: Resmed Limited (ResMed Incorporated)
• Inventors: Zhu, Jianhua, BATH, Andrew Roderick, Huby, Ronald James, Row, Nathan John, Shadie, Timothy Nicholas, Dujmovic, Ivan, Richmond, Donald Angus
• Granted Patent: US 8,733,349 B2
• Time in Patent Office: Days
• US Class Current: 128/202.22
• CPC Class Codes: A61M 16/0003 Accessories therefor, e.g. sensors, vibrators, negative pressure
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/0066 Blowers or centrifugal pumps
• CPC Class Codes: A61M 16/0069 the speed thereof being controlled by respiratory parameters, e.g. by inhalation
• CPC Class Codes: A61M 16/024 including calculation means, e.g. using a processor
• CPC Class Codes: A61M 16/06 Respiratory or anaesthetic masks
• CPC Class Codes: A61M 16/0605 Means for improving the adaptation of the mask to the patient
• CPC Class Codes: A61M 16/065 in the form of a pivot
• CPC Class Codes: A61M 16/0816 Joints or connectors
• CPC Class Codes: A61M 16/0875 Connecting tubes
• CPC Class Codes: A61M 16/1075 by influencing the temperature A61M16/1045 takes precedence
• CPC Class Codes: A61M 16/109 the humidifying liquid or the beneficial agent
• CPC Class Codes: A61M 16/1095 in the connecting tubes
• CPC Class Codes: A61M 16/16 Devices to humidify the respiration air A61M16/1045 takes precedence
• CPC Class Codes: A61M 16/161 with means for measuring the humidity
• CPC Class Codes: A61M 2016/0021 with a proportional output signal, e.g. from a thermistor
• CPC Class Codes: A61M 2016/0027 pressure meter
• CPC Class Codes: A61M 2016/0039 in the inspiratory circuit
• CPC Class Codes: A61M 2205/051 with radiation therapy
• CPC Class Codes: A61M 2205/18 with alarm
• CPC Class Codes: A61M 2205/3306 : Optical measuring means
• CPC Class Codes: A61M 2205/3368 : Temperature
• CPC Class Codes: A61M 2205/3375 : Acoustical, e.g. ultrasonic, measuring means
• CPC Class Codes: A61M 2205/42 : Reducing noise
• CPC Class Codes: A61M 2205/502 : User interfaces, e.g. screens or keyboards
• CPC Class Codes: A61M 2205/581 : by audible feedback
• CPC Class Codes: A61M 2205/582 : by tactile feedback
• CPC Class Codes: A61M 2205/584 : having a color code
• CPC Class Codes: A61M 2205/6018 : providing set-up signals for the apparatus configuration
• CPC Class Codes: A61M 2230/205 : partial oxygen pressure (P-O2)
• CPC Class Codes: A61M 2230/62 : Posture

Abstract

A PAP system for delivering breathable gas to a patient includes a flow generator to generate a supply of breathable gas to be delivered to the patient; a humidifier including a heating plate to vaporize water and deliver water vapor to humidify the supply of breathable gas; a heated tube configured to heat and deliver the humidified supply of breathable gas to the patient; a power supply configured to supply power to the heating plate and the heated tube; and a controller configured to control the power supply to prevent overheating of the heating plate and the heated tube.

Claims

1. A control system for a heated conduit for use in a respiratory apparatus, the control system comprising:

a power supply to provide power to the heated conduit;

an over-temperature control circuit to prevent the overheating of the heated conduit;

a heating control circuit configured to control heating to obtain a predetermined temperature;

a sensing circuit including a sensing resistor configured to indicate the temperature of a sensor positioned in the heated conduit; and

a bias generator circuit configured to provide a first source voltage to the sensing circuit so that the temperature of the heated conduit is continuously monitored.

2. A control system according to claim 1, wherein the over-temperature control circuit comprises a first transistor switch that is turned on when the temperature is below the predetermined temperature and is turned off when the temperature is at or above the predetermined temperature.

3. A control system according to claim 2, wherein the predetermined temperature is between the range of about 30°

C. and about 45°

C.

4. A control system according to claim 2, wherein the over-temperature control circuit further comprises a first comparator that controls the switching of the first transistor switch by comparing a reference voltage representing the predetermined temperature to a voltage determined from a first amplifier of the sensing circuit.

5. A control system according to claim 4, further comprising a multiplexer to multiplex the output of the first amplifier.

6. A control system according to claim 1, wherein the heating control circuit is configured to switch the power supply from the power supply and controller through a tube circuit of the heated conduit to a ground reference so that a temperature sensor of the tube circuit receives between zero volts and half a supply voltage of the power supply.

7. A control system according to claim 6, wherein power is supplied to the tube circuit from the power supply through a second transistor switch that is switched on and off to turn heating on and off, respectively, to the tube circuit.

8. A control system according to claim 7, wherein the second transistor switch is switched on and off with changes in a duty cycle.

9. A control system according to claim 7, wherein the second transistor switched is switched on to provide constant heating until the predetermined temperature is reached and is then switched off.

10. A control system according to claim 7, wherein when the second transistor switch is closed the first source voltage and half the supply voltage is applied to the sensing circuit and when the second transistor switch is open the first source voltage is applied to the sensing circuit.

11. A control system according to claim 7, wherein a signal from a temperature sensor of the tube circuit is provided to a first amplifier of the sensing circuit and the first amplifier produces a voltage that represents the temperature of the flow in the heated conduit, and the second transistor switch is open and closed to modulate the power supplied to the tube circuit to maintain the predetermined temperature.

12. A control system according to claim 11, further comprising a multiplexer to multiplex the output of the first amplifier.

13. A control system according to claim 1, wherein the control system is configured to detect an internal diameter of the heated conduit connected to the respiratory apparatus.

14. A control system according to claim 13, wherein the control system detects the internal diameter of the heated conduit based on a resistance value of a temperature sensor of a tube circuit of the heated conduit.

15. A control system according to claim 14, wherein the resistance values of the temperature sensor for differing internal diameters do not overlap within a specified operating temperature.

16. A control system according to claim 15, wherein the specified operating temperature is between the range of about −

5°

C. and about 50°

C.

17. A control system according to claim 11, further comprising a second comparator configured to compare the voltage across the sensing resistor sensed by the first amplifier with a reference voltage that identifies a heated conduit having a predetermined internal diameter corresponding to a predetermined resistance of the temperature sensor.

18. A control system according to claim 17, further comprising a second amplifier configured to add gain to the sensed voltage if the temperature sensor resistance corresponds to a first predetermined internal diameter and to add no gain to the sensed voltage if the temperature sensor resistance corresponds to a second predetermined internal diameter.

19. A control system according to claim 17, wherein the control system is configured to use a different reference voltage for each predetermined internal diameter.

20. A control system according to claim 18, wherein the first predetermined internal diameter is 19 mm and the second predetermined internal diameter is 15 mm.

21. A control system according to claim 17, wherein the control system is configured to control operation of a flow generator and/or a humidifier of the respiratory apparatus based on the detected internal diameter of the conduit.

22. A control system according to claim 21, wherein the control system is configured to adjust the amplitude of a signal generated by the temperature sensor based on the detected internal diameter of the conduit.

23. A control system according to claim 21, wherein the control system is configured to adjust a signal gain dependent on the detected internal diameter of the conduit to stop supplying power if the detected temperature exceeds the predetermined temperature.

24. A control system according to claim 1, further comprising a fault detection circuit configured to detect a fault in the connection of the conduit to the respiratory apparatus and/or a fault in a tube circuit of the conduit.

25. A control system according to claim 24, wherein the fault detection circuit comprises three resistors, a third comparator, a fourth comparator, and a second source voltage.

26. A control system according to claim 25, wherein the third and fourth comparators compare the voltage received from the first amplifier with threshold voltages across the three resistors.

27. A control system according to claim 24, wherein the fault may comprise a) a discontinuity in any of at least three wires of the conduit and/or b) arcing and/or a bad connection between the conduit and a flow generator and/or a humidifier of the respiratory apparatus and/or between the conduit and a patient interface and/or c) low voltage.

28. A control system according to claim 24, wherein the power supply and controller is configured to cease supplying power in the event of a fault in the temperature sensor.

29. A control system according to claim 1, wherein the sensing circuit comprises a signal wire configured to receive signal data from the sensor in the heated conduit and transmit control signals to the heated tube.

30. A control system according to claim 29, further comprising a modem to modulate the control signals and demodulate the signal data.

31. A control system according to claim 30, further comprising a multiplexer to multiplex the power supply to the signal wire.

32. A conduit for use in a respiratory apparatus for delivering breathable gas to a patient, the conduit comprising:

a tube;

a helical rib on an outer surface of the tube;

a tube circuit comprising at least three wires supported by the helical rib in contact with the outer surface of the tube and a temperature sensor connected to at least one of the three wires to provide a signal to a power supply and controller of the respiratory apparatus; and

a first cuff connected to a first end of the tube and a second cuff connected to a second end of the tube, the first cuff being configured to be connected to a patient interface of the respiratory apparatus and the second cuff being configured to be connected to a flow generator or humidifier of the respiratory apparatus.

33. A conduit according to claim 32, wherein the at least three wires are copper or enamelled copper.

34. A conduit according to claim 32, wherein the temperature sensor is provided in a fixture in the first cuff.

35. A conduit according to claim 34, wherein the fixture extends radially inward.

36. A conduit according to claim 34, wherein the fixture is airfoil shaped.

37. A conduit according to claim 32, wherein a first wire of the at least three wires connected to the temperature sensor comprises a sensing wire, a second wire is configured to be connected to a power supply of the flow generator or humidifier, and a third wire is configured to be a ground wire.

38. A conduit according to claim 37, wherein the first wire is between the second and third wires.

39. A conduit according to claim 32, wherein the temperature sensor comprises a thermistor.

40. A conduit according to claim 39, wherein the thermistor comprises a Negative Temperature Coefficient (NTC) material.

41. A conduit according to claim 40, wherein the tube has a diameter of about 15 mm and the thermistor has a resistance of 10,000Ω

.

42. A conduit according to claim 40, wherein the tube has a diameter of about 19 mm and the thermistor has a resistance of about 100,000Ω

.

43. A respiratory apparatus for delivering breathable gas to a patient, comprising:

a flow generator to generate a supply of breathable gas to be delivered to the patient;

a humidifier to vaporize water and to deliver water vapor to humidify the supply of breathable gas;

a first gas flow path leading from the flow generator to the humidifier;

a second gas flow path leading from the humidifier to the patient interface, at least the second gas flow path comprises a conduit according to claim 32; and

a power supply and controller configured to supply and control power to the conduit through the cuff.

44. A respiratory apparatus according to claim 43, wherein the power supply and controller comprises an over-temperature control circuit to prevent overheating of the conduit.

45. A respiratory apparatus according to claim 44, wherein the over-temperature control circuit comprises a first transistor switch that is turned on when a temperature is below a predetermined temperature and is turned off when the temperature is at or above the predetermined temperature.

46. A respiratory apparatus according to claim 45, wherein the predetermined temperature is between the range of about 30°

C. and about 45°

C.

47. A respiratory apparatus according to claims 44, wherein the over-temperature control circuit further comprises a first comparator that controls the switching of the first transistor switch by comparing a reference voltage representing the predetermined temperature to a voltage determined from a first amplifier of a sensing circuit.

48. A respiratory apparatus according to claim 47, further comprising a multiplexer to multiplex output of the first amplifier.

49. A respiratory apparatus according to claim 47, wherein the power supply and controller further comprises a heating control circuit configured to control heating to obtain a desired temperature.

50. A respiratory apparatus according to claim 49, wherein the heating control circuit is configured to switch the power supply from the power supply and controller through the tube circuit to a ground reference so that the temperature sensor of the tube circuit receives between zero volts and half the supply voltage of the power supply and controller.

51. A respiratory apparatus according to claim 50, wherein power is supplied to the tube circuit from the power supply and controller through a second transistor switch that is switched on and off to turn heating on and off, respectively, to the tube circuit.

52. A respiratory apparatus according to claim 51, wherein the second transistor switch is switched on and off with changes in a duty cycle.

53. A respiratory apparatus according to claim 51, wherein the second transistor switched is switched on to provide constant heating until the desired temperature is reached and is then switched off.

54. A respiratory apparatus according to claim 49, wherein the sensing circuit further comprises a sensing resistor.

55. A respiratory apparatus according to claim 54, wherein the power supply and controller comprises a bias generator circuit configured to provide a first source voltage to the sensing circuit so that the temperature of the tube is continuously monitored.

56. A respiratory apparatus according to claim 55, wherein when the second transistor switch is closed the source voltage and half the power supply voltage is applied to the sensing circuit and when the second transistor switch is open the source voltage is applied to the sensing circuit.

57. A respiratory apparatus according to claim 49, wherein the signal from the temperature sensor is provided to the first amplifier and the first amplifier produces a voltage that represents the temperature of the flow in the tube, and the second transistor switch is open and closed to modulate the power supplied to the tube circuit to maintain the desired temperature.

58. A respiratory apparatus according to claim 57, further comprising a multiplexer to multiplex the output of the first amplifier.

59. A respiratory apparatus according to claim 43, wherein the power supply and controller is configured to detect the internal diameter of the tube connected to the humidifier or flow generator.

60. A respiratory apparatus according to claim 59, wherein the power supply and controller detects the internal diameter of the tube based on a resistance value of the temperature sensor.

61. A respiratory apparatus according to claim 60, wherein the resistance values of the temperature sensor for differing internal diameters do not overlap within a specified operating temperature.

62. A respiratory apparatus according to claim 60, wherein the specified operating temperature is between the range of about −

5°

C. and about 50°

C.

63. A respiratory apparatus according to claim 59, wherein the power supply and controller comprises a second comparator configured to compare the voltage across the sensing resistor sensed by the first amplifier with a reference voltage that identifies a tube having a predetermined internal diameter corresponding to a predetermined resistance of the temperature sensor.

64. A respiratory apparatus according to claim 63, wherein the power supply and controller is configured to use a different reference voltage for each predetermined internal diameter.

65. A respiratory apparatus according to claim 63, wherein the power supply and controller comprises a second amplifier configured to add gain to the sensed voltage if the temperature sensor resistance corresponds to a first predetermined internal diameter and to add no gain to the sensed voltage if the temperature sensor resistance corresponds to a second internal diameter.

66. A respiratory apparatus according to claim 65, wherein the first predetermined internal diameter is 19 mm and the second predetermined internal diameter is 15 mm.

67. A respiratory apparatus according to claim 59, wherein the power supply and controller is configured to control operation of the flow generator and/or humidifier based on the detected internal diameter of the conduit.

68. A respiratory apparatus according to claim 67, wherein the power supply and controller is configured to adjust the amplitude of the signal generated by the temperature sensor based on the detected internal diameter of the conduit.

69. A respiratory apparatus according to claim 67, wherein the power supply and controller adjusts a signal gain dependent on the detected internal diameter of the conduit to stop supplying power if the detected temperature exceeds the predetermined temperature.

70. A respiratory apparatus according to claim 43, wherein the power supply and controller is configured to detect connection of the conduit to the humidifier and/or flow generator.

71. A respiratory apparatus according to claim 70, wherein the conduit is configured to connect to the power supply and controller by rotating the second cuff relative to the humidifier and/or flow generator.

72. A respiratory apparatus according to claim 71, wherein the second cuff is configured to connect to the humidifier and/or flow generator by a bayonet connection.

73. A respiratory apparatus according to claim 70, wherein the first wire of the at least three wires that connects to the power supply and controller is grounded.

74. A respiratory apparatus according to claim 73, wherein the last wire of the at least three wires that connects to the power supply and controller is the wire connected to the temperature sensor.

75. A respiratory apparatus according to claim 74, wherein the last wire is configured to receive signal data from the temperature sensor and transmit control signals to the conduit.

76. A respiratory apparatus according to claim 75, wherein the power supply and controller further comprises a modem to modulate the control signals and demodulate the signal data.

77. A respiratory apparatus according to claim 48, wherein the power supply and controller comprises a multiplexer to multiplex the power supply.

78. A respiratory apparatus according to claim 74, wherein the power supply and controller comprises a tube fault detection circuit configured to detect a fault in the connection of the conduit to the flow generator and/or humidifier and/or a fault in the tube circuit of the conduit.

79. A respiratory apparatus according to claim 78, wherein the tube fault detection circuit comprises three resistors, a third comparator, a fourth comparator, and a second source voltage.

80. A respiratory apparatus according to claim 79, wherein the third and fourth comparators compare the voltage received from the first amplifier with threshold voltages across the three resistors.

81. A respiratory apparatus according to claim 78, wherein the fault may comprise a) a discontinuity in any of the at least three wires of the conduit, b) arcing and/or a bad connection between the conduit and the flow generator and/or humidifier and/or between the conduit and the patient interface, and/or c) low voltage.

82. A respiratory apparatus according to claims 78, wherein the power supply and controller is configured to cease supplying power in the event of a fault in the temperature sensor.

83. A PAP system for delivering breathable gas to a patient, comprising:

a flow generator to generate a supply of breathable gas to be delivered to the patient;

a humidifier including a heating plate to vaporize water and deliver water vapor to humidify the supply of breathable gas;

a heated tube configured to heat and deliver the humidified supply of breathable gas to the patient;

a power supply configured to supply power to the heating plate and the heated tube; and

a controller configured to control the power supply to prevent overheating of the heating plate and the heated tube.

84. A PAP system according to claim 83, wherein the controller prevents heating of the heating plate when a temperature of the heating plate is less than a first predetermined heating plate temperature and a sensed ambient temperature is above a minimum sensed temperature for a time less than a first predetermined maximum time.

85. A PAP system according to claim 84, wherein the PAP system displays a first error message on a display on either the flow generator or the humidifier when the temperature of the heating plate is less than the first predetermined heating plate temperature and the sensed temperature is above the minimum sensed temperature for the time less than the first predetermined maximum time.

86. A PAP system according to claim 85, wherein the first error message is acknowledgeable by the patient or an operator through inputs on the flow generator or the humidifier.

87. A PAP system according to claim 85, wherein the controller stops the PAP system when the temperature of the heating plate is less than the first predetermined heating plate temperature and the sensed temperature is above the minimum sensed temperature for a time greater than the first predetermined maximum time.

88. A PAP system according to claim 87, wherein the PAP system displays a second error message on the display when the temperature of the heating plate is less than the first predetermined heating plate temperature and the sensed temperature is above the minimum sensed temperature for the time greater than the first predetermined maximum time.

89. A PAP system according to claim 88, wherein the second error message can not be acknowledged by the patient or operator.

90. A PAP system according to claim 84, wherein the first predetermined heating plate temperature is between about 0°

C. and 4°

C.

91. A PAP system according to claim 90, wherein the first predetermined heating plate temperature is about 2°

C.

92. A PAP system according to claim 90, wherein the minimum sensed temperature is between about 3°

C. and 8°

C.

93. A PAP system according to claim 92, wherein the minimum sensed temperature is about 5°

C.

94. A PAP system according to claim 92, wherein the first predetermined maximum time is between about 10 and 25 minutes.

95. A PAP system according to claim 94, wherein the first predetermined maximum time is about 15 minutes.

96. A PAP system according to claim 84, wherein the controller prevents heating the heating plate when the temperature of the heating plate is less than a second predetermined heating plate temperature and the sensed temperature is higher than a first maximum sensed temperature.

97. A PAP system according to claim 96, wherein the controller prevents heating the heating plate when the sensed temperature is higher than a second maximum sensed temperature that is higher than the first maximum sensed temperature.

98. A PAP system according to claim 96, wherein the controller stops the PAP system when, 1) the temperature of the heating plate is less than a second predetermined heating plate temperature and the sensed temperature is higher than the first maximum sensed temperature, or 2) the sensed temperature is higher than a second maximum sensed temperature that is higher than the first maximum sensed temperature.

99. A PAP system according to claim 96, wherein the PAP system displays a second error message when, 1) the temperature of the heating plate is less than a second predetermined heating plate temperature and the sensed temperature is higher than the first maximum sensed temperature, or 2) the sensed temperature is higher than a second maximum sensed temperature that is higher than the first maximum sensed temperature.

100. A PAP system according to claim 96, wherein the second predetermined heating plate temperature is between about 22°

C. and 30°

C.

101. A PAP system according to claim 100, wherein the second predetermined heating plate temperature is about 25°

C.

102. A PAP system according to 100, wherein the second maximum sensed temperature is between about 45°

C. and 55°

C.

103. A PAP system according to claim 102, wherein the second maximum sensed temperature is about 50°

C.

104. A PAP system according to claim 83, wherein the controller prevents heating the heated tube when a temperature of the heated tube is less than a minimum sensed temperature for a time less than a first predetermined maximum time.

105. A PAP system according to claim 104, wherein the controller displays a third error message on the display when the temperature of the heated tube is less than the minimum sensed temperature for the time less than the first predetermined maximum time.

106. A PAP system according to claim 105, wherein the third error message is acknowledgeable by the patient or operator through the inputs on the flow generator or the humidifier.

107. A PAP system according to claim 104, wherein the controller stops the PAP system when the temperature of the heated tube is less than the minimum sensed temperature for a time greater than the first predetermined maximum time.

108. A PAP system according to claim 107, wherein the PAP system displays a fourth error message when the temperature of the heated tube is less than the minimum sensed temperature for a time greater than the first predetermined maximum time.

109. A PAP system according to claim 104, wherein the controller prevents heating of the heated tube when a percentage of power supplied from the power supply to the heated tube is equal to or greater than a predetermined power percentage, the temperature of the heated tube is lower than a predetermined heated tube temperature, and an elapsed time is greater than a second predetermined maximum time that is less than the first predetermined maximum time.

110. A PAP system according to claim 109, wherein the controller stops the PAP system when the percentage of power supplied from the power supply to the heated tube is equal to or greater than the predetermined power percentage, the temperature of the heated tube is lower than the predetermined heated tube temperature, and the elapsed time is greater than the second predetermined maximum time.

111. A PAP system according to claim 110, wherein the PAP system displays the fourth error message when the percentage of power supplied from the power supply to the heated tube is equal to or greater than the predetermined power percentage, the temperature of the heated tube is lower than the predetermined heated tube temperature, and the elapsed time is greater than the second predetermined maximum time.

112. A PAP system according to claim 109, wherein the predetermined power percentage is about 60%.

113. A PAP system according to claim 112, wherein the predetermined heated tube temperature is about 15°

C.

114. A PAP system according to claim 113, wherein the second predetermined maximum time is about three minutes.

115. A PAP system according to claim 83, wherein the heating plate comprises a plate formed of a heat conducting material, a heating element formed of a resistive foil provided on the plate, a thermistor formed of a resistive foil, and at least one insulating film that cover at least the heating element.

116. A PAP system according to claim 115, wherein the heating element and the thermistor are integrally formed.

117. A PAP system according to claim 115, wherein the heating element and the thermistor are separately formed.

118. A PAP system according to claim 117, wherein the heating element is formed of a first resistive material and the thermistor is formed of a second resistive material different from the first resistive material.

119. A PAP system according to claim 118, wherein at least one wire for delivering a signal to and from the thermistor is ultrasonically welded to the thermistor.

120. A PAP system according to claim 119, wherein the at least one wire is ultrasonically welded to the thermistor and the heating element.

121. A PAP system according to claim 115, wherein the at least one insulating film comprises two insulating films, a first insulating film that covers the heating element and a second insulating film that covers the thermistor.

122. A patient interface for use in a respiratory system, comprising:

an assembly configured to sealingly engage the face of a patient;

at least one circuit configured to receive a supply of power and send and receive data, a portion of the at least one circuit being removably attachable to a link from which the data and power is supplied;

at least one sensor in communication with the at least one circuit; and

at least one controller in communication with the at least one circuit.

123. A patient interface according to claim 122, wherein the at least one controller includes an active vent disposed on the assembly, the active vent being configured to regulate vent flows through the assembly.

124. A patient interface according to claim 122, wherein the link is disposed in a heated tube configured to be connected to the patient interface.

125. A patient interface according to claim 122, wherein the link is disposed in an unheated tube configured to be connected to the patient interface.

126. A patient interface according to claim 122, wherein the link comprises at least one wire for power and at least one separate wire for data.

127. The powered patient interface according to claim 122, wherein the at least one circuit further comprises an encoder/decoder to encode and decode data that is transmitted through the link.

128. The powered patient interface according to claim 122, wherein the at least one circuit further comprises a modem configured to modulate data sent to the at least one sensor and/or the at least one controller and to demodulate data from the at least one sensor.

129. The powered patient interface according to claim 122, wherein the at least one circuit further comprises a multiplexor to multiplex the power and/or data.

130. The powered patient interface according to claim 122, wherein the link includes a controller area network or a local interconnect network.

131. The powered patient interface according to claim 122, wherein the at least one sensor includes at least one of a flow sensor, a pressure sensor, a temperature sensor, a humidity sensor, an optical sensor, a voice pattern or speech recognition device, an attitude sensor, a particulate sensor, an oxygen saturation sensor, or an electrical resistance sensor and/or the at least one controller includes a humidifier to directly humidify the patient interface, an active vent, a speaker, an alarm, a noise cancellation controller, a vibration controller, an expansion foam controller, a membrane seal controller, or a light or lamp.

132. A method of controlling a heated conduit connected to a respiratory apparatus, the method comprising:

supplying power to the heated conduit;

continuously monitoring a temperature of a sensor positioned in the heated conduit; and

controlling the power supply to the heated conduit to obtain a predetermined temperature.

133. A method according to claim 132, wherein continuously monitoring the temperature of the sensor comprises continuously applying a first source voltage to a sensing resistor configured to indicate the temperature of the sensor positioned in the heated conduit.

134. A method according to claim 133, wherein controlling the power supplied to the heated conduit comprises turning on a first transistor switch when the temperature is below the predetermined temperature and turning off the first transistor switch when the temperature is at or above the predetermined temperature.

135. A method according to claim 132, wherein the predetermined temperature is between the range of about 30°

C. and about 45°

C.

136. A method according to claim 134, wherein turning the first transistor switch on and off comprises comparing a reference voltage representing the predetermined temperature to a voltage determined from a first amplifier connected to the sensing resistor.

137. A method according to claim 136, further comprising:

multiplexing the output of the first amplifier.

138. A method according to claim 132, further comprising:

switching the power supply through a tube circuit of the heated conduit to a ground reference so that the sensor receives between zero volts and half a supply voltage of the power supply.

139. A method according to claim 138, further comprising:

supplying power to the tube circuit through a second transistor switch; and

switching the second transistor switch on and off to turn heating on and off, respectively, to the tube circuit.

140. A method according to claim 139, wherein switching the second transistor switch on and off comprises changing a duty cycle of the power supply.

141. A method according to claim 139, wherein switching the second transistor switched on and off comprises switching the second transistor switch on to provide constant heating until the predetermined temperature is reached and then switching the second transistor switch off.

142. A method according to claim 139, wherein when the second transistor switch is on the first source voltage and half the supply voltage is applied to the sensing resistor and when the second transistor switch is off the first source voltage is applied to the sensing resistor.

143. A method according to claim 139, further comprising:

providing a signal from the sensor to the first amplifier;

producing a voltage with the first amplifier that represents the temperature of the flow in the heated conduit; and

opening and closing the second transistor switch to modulate the power supply to maintain the predetermined temperature.

144. A method according to claim 143, further comprising:

multiplexing the output of the first amplifier.

145. A method according to claim 132, further comprising:

detecting an internal diameter of the heated conduit connected to the respiratory apparatus.

146. A method according to claim 145, wherein detecting the internal diameter of the heated conduit comprises detecting a resistance value of the sensor.

147. A method according to claim 146, wherein the resistance values of the sensor for differing internal diameters do not overlap within a specified operating temperature.

148. A method according to claim 147, wherein the specified operating temperature is between the range of about −

5°

C. and about 50°

C.

149. A method according to claim 133, further comprising:

comparing the voltage across the sensing resistor with a reference voltage that identifies a heated conduit having a predetermined internal diameter corresponding to a predetermined resistance of the sensor.

150. A method according to claim 149, further comprising:

adding gain to the voltage across the sensing resistor if the sensor resistance corresponds to a first predetermined internal diameter; and

adding no gain to the voltage across the sensing resistor if the sensor resistance corresponds to a second predetermined internal diameter.

151. A method according to claim 150, further comprising:

using a different reference voltage for each predetermined internal diameter.

152. A method according to claim 150, wherein the first predetermined internal diameter is 19 mm and the second predetermined internal diameter is 15 mm.

153. A method according to claim 145, further comprising:

controlling a flow generator and/or a humidifier of the respiratory apparatus based on the detected internal diameter of the conduit.

154. A method according to claim 153, further comprising:

adjusting the amplitude of a signal generated by the sensor based on the detected internal diameter of the conduit.

155. A method according to claim 154, further comprising:

adjusting a signal gain dependent on the detected internal diameter of the conduit to stop supplying power if the detected temperature exceeds the desired temperature.

156. A method according to claim 132, further comprising:

detecting a fault in the connection of the conduit to the respiratory apparatus and/or a fault in a tube circuit of the conduit.

157. A method according to claim 156, detecting a fault comprises comparing the voltage from the first amplifier with threshold voltages across at least one resistor.

158. A method according to claim 156, wherein the fault may comprise a) a discontinuity in any of at least three wires of the conduit and/or b) arcing and/or a bad connection between the conduit and a flow generator and/or a humidifier of the respiratory apparatus and/or between the conduit and a patient interface and/or c) low voltage.

159. A method according to claim 156, further comprising:

ceasing the power supply in the event of a fault in the sensor.

160. A method according to claim 132, further comprising:

receiving signal data from the sensor in the heated conduit; and

transmitting control signals to the heated conduit.

161. A method according to claim 160, further comprising:

modulating the control signals; and

demodulating the signal data.

162. A method for delivering breathable gas to a patient, comprising:

generating a supply of breathable gas;

vaporizing water using a heating plate;

delivering water vapor to humidify the supply of breathable gas;

heating and delivering the humidified supply of breathable gas to the patient using a heated tube; and

controlling a power supply to the heating plate and heated tube to prevent overheating of the heating plate and the heated tube.

163. A method according to claim 162, wherein controlling the power supply to the heating plate comprises not heating the heating plate when a temperature of the heating plate is less than a first predetermined heating plate temperature and a sensed ambient temperature is above a minimum sensed temperature for a time less than a first predetermined maximum time.

164. A method according to claim 163, further comprising:

displaying a first error message when the temperature of the heating plate is less than the first predetermined heating plate temperature and the sensed temperature is above the minimum sensed temperature for the time less than the first predetermined maximum time.

165. A method according to claim 163, further comprising:

stopping the generating, the vaporizing, the delivering and the heating when the temperature of the heating plate is less than the first predetermined heating plate temperature and the sensed temperature is above the minimum sensed temperature for a time greater than the first predetermined maximum time.

166. A method according to claim 165, further comprising:

displaying a second error message when the temperature of the heating plate is less than the first predetermined heating plate temperature and the sensed temperature is above the minimum sensed temperature for the time greater than the first predetermined maximum time.

167. A method according to claim 163, wherein the first predetermined heating plate temperature is between about 0°

C. and 4°

C.

168. A method according to claim 167, wherein the first predetermined heating plate temperature is about about 2°

C.

169. A method according to claim 163, wherein the minimum sensed temperature is between about 3°

C. and 8°

C.

170. A method according to claim 169, wherein the minimum sensed temperature is about 5°

C.

171. A method according to claim 163, wherein the first predetermined maximum time is between about 10 minutes and 25 minutes.

172. A method according to claim 171, wherein the first predetermined maximum time is about about 15 minutes.

173. A method according to claim 163, further comprising:

not heating the heating plate when the temperature of the heating plate is less than a second predetermined heating plate temperature and the sensed temperature is higher than a first maximum sensed temperature.

174. A method according to claim 173, further comprising:

not heating the heating plate when the sensed temperature is higher than a second maximum sensed temperature that is higher than the first maximum sensed temperature.

175. A method according to claim 174, further comprising:

stopping the generating, the vaporizing, the delivering and the heating when

     1) the temperature of the heating plate is less than a second predetermined heating plate temperature and the sensed temperature is higher than the first maximum sensed temperature or

     2) the sensed temperature is higher than a second maximum sensed temperature that is higher than the first maximum sensed temperature.

176. A method according to claim 174, further comprising:

displaying a second error message when

     1) the temperature of the heating plate is less than a second predetermined heating plate temperature and the sensed temperature is higher than the first maximum sensed temperature, or

     2) the sensed temperature is higher than a second maximum sensed temperature that is higher than the first maximum sensed temperature.

177. A method according to claim 176, wherein the second predetermined heating plate temperature is about 25°

C.

178. A method according to 177, wherein the second maximum sensed temperature is about 50°

C.

179. A method according to claim 163, further comprising:

not heating the heated tube when a temperature of the heated tube is less than a minimum sensed temperature for a time less than a first predetermined maximum time.

180. A method according to claim 179, further comprising:

displaying a third error message when the temperature of the heated tube is less than the minimum sensed temperature for the time less than the first predetermined maximum time.

181. A method according to claim 179, further comprising:

stopping generating, vaporizing, delivering and heating when the temperature of the heated tube is less than the minimum sensed temperature for a time greater than the first predetermined maximum time.

182. A method according to claim 180, further comprising:

displaying a fourth error message when the temperature of the heated tube is less than the minimum sensed temperature for a time greater than the first predetermined maximum time.

183. A method according to claim 179, further comprising:

not heating the heated tube when a percentage of power supplied from the power supply to the heated tube is equal to or greater than a predetermined power percentage, the temperature of the heated tube is lower than a predetermined heated tube temperature, and an elapsed time is greater than a second predetermined maximum time that is less than the first predetermined maximum time.

184. A method according to claim 183, further comprising:

stopping the generating, vaporizing, delivering and heating when the percentage of power supplied from the power supply to the heated tube is equal to or greater than the predetermined power percentage, the temperature of the heated tube is lower than the predetermined heated tube temperature, and the elapsed time is greater than the second predetermined maximum time.

185. A method according to claim 182, further comprising:

displaying the fourth error message when the percentage of power supplied from the power supply to the heated tube is equal to or greater than the predetermined power percentage, the temperature of the heated tube is lower than the predetermined heated tube temperature, and the elapsed time is greater than the second predetermined maximum time.

186. A method according to claim 185, wherein the predetermined power percentage is about 60%.

187. A method according to claim 185, wherein the predetermined heated tube temperature is about 15°

C.

188. A method according to claim 185, wherein the second predetermined maximum time is about three minutes.