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A humidification system is provided for a respiratory system is provided with a controller having two processors that monitor the operation of each other and of heating elements in the respiratory system to provide CPU redundancy and heating element control. Each heating element is provided with two

A humidification system is provided for a respiratory system is provided with a controller having two processors that monitor the operation of each other and of heating elements in the respiratory system to provide CPU redundancy and heating element control. Each heating element is provided with two control paths, for example a relay and a triac connected in series with the heating element and a power supply. Each heater element has one control path connected to a first one of the processors and at least one heating element has at least one control path connected to a second one of the controllers. A hardware watchdog monitors the operation of the first processor, and can be triggered by a signal from the second processor, in response to which it can disable all heating elements.

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1. A humidifier system comprising: a heating element;a first power switch which turns on or off in response to a first control signal and a second power switch which turns on or off in response to a second control signal, the first and second power switches being in electrical series between a sourc

1. A humidifier system comprising: a heating element;a first power switch which turns on or off in response to a first control signal and a second power switch which turns on or off in response to a second control signal, the first and second power switches being in electrical series between a source of power and the heating element and both being required to be on for activation of the heating element;first and second processors, the first control signal being originated by the first processor and being provided therefrom to the first power switch along a first control path and the second control signal being originated by the second processor and being provided therefrom to the second power switch along a second control path; anda watchdog being in the first control path in electrical series between the first processor and the first power switch, the watchdog operable to normally gate the first control signal from the first processor to the first power switch and to monitor at least one of the first and second processors, and the watchdog further operable to interrupt the first control signal from the first processor to the first power switch so as to disable the heating element in response to the monitoring of the at least one of the first and second processors. 2. The system of claim 1 wherein: one of the first and second power switches comprises a relay and the other of the first and second power switches comprises a solid state switching element. 3. The system of claim 2, wherein the solid state switching element is a triac. 4. The system of claim 1 wherein: each of the first and second processors is programmed to monitor a timing signal from the other processor and to disable the heating element in response to a detected failure of one of the timing signals. 5. The system of claim 1, wherein the watchdog is operable to monitor the first processor and to disable the heating element in response to the monitoring of the first processor. 6. A respiratory system comprising a humidifier system having: a heating element;a first power switch which turns on or off in response to a first control signal and a second power switch which turns on or off in response to a second control signal, the first and second power switches being in electrical series between a source of power and the heating element and both being required to be on for activation of the heating element;first and second processors, the first processor providing the first control signal to the first power switch along a first control path and one of the processors providing the second control signal to the second power switch along a second control path; anda watchdog being in the first control path in electrical series between the first processor and the first power switch, the watchdog operable to normally gate the first control signal from the first processor to the first power switch and to monitor at least one of the processors, and the watchdog further operable to interrupt the first control signal from the first processor to the first power switch so as to disable the heating element in response to the monitoring of the at least one processor, wherein:the first and second processors include a main processor and an auxiliary processor;the heating element includes a hotplate heater; andthe respiratory system includes an inspiratory conduit and an expiratory conduit, each conduit connected to the humidification system and each having a heating element therein having a control having two control paths thereto, one responsive to a control signal from the main processor and the other responsive to a control signal from the auxiliary processor. 7. The respiratory system of claim 6 wherein: the watchdog is operable to monitor the main processor and to disable the heating elements in response to the monitoring of the main processor, the watchdog having an override responsive to the auxiliary processor and operable to disable the heating elements in response to a signal from the auxiliary processor. 8. A humidifier system controller for use in a respiratory system having a heating element, the controller comprising: a first CPU and a second CPU;a first set of switching devices comprising a first switching device responsive to a control signal from the first CPU and a second switching device responsive to a control signal from one of the first and second CPUs;conductors for connecting the heating element to a power supply through the two switching devices so as to energize the heating element in response to both of the two switching devices being in a conductive state;a hardware monitoring override operable to monitor the first CPU and to interrupt at least one of the first and second control signals, the first and second switching devices being responsive to the hardware monitoring override;a second set of switching devices comprising two switching devices;conductors for connecting a second heating element to the power supply through the two switching devices of the second set so as to energize the second heating element in response to both of the two switching devices of the second set being in a conductive state;the second CPU providing a control signal to at least one switching device of the second set; andthe first CPU providing a control signal to both of the two switching devices of the second set. 9. The humidifier system controller of claim 8 wherein: each of the two CPUs is programmed to monitor a timing signal from the other CPU over an interval, and to disable all heating elements in the respiratory system if the monitored timing signals are not as expected over the interval. 10. A humidifier system comprising: a heating element;a first power switch which turns on or off in response to a first control signal and a second power switch which turns on or off in response to a second control signal, the first and second power switches being in electrical series between a source of power and the heating element and both being required to be on for activation of the heating element;first and second processors, the first processor providing the first control signal to the first power switch along a first control path and one of the processors providing the second control signal to the second power switch along a second control path; anda watchdog being in the first control path in electrical series between the first processor and the first power switch, the watchdog operable to normally gate the first control signal from the first processor to the first power switch and to monitor at least one of the processors, and the watchdog further operable to interrupt the first control signal from the first processor to the first power switch so as to disable the heating element in response to the monitoring of the at least one processor, wherein the first processor is a main processor and the second processor is an auxiliary processor, and wherein the main processor provides the second control signal to the second power switch along the second control path, and wherein:the heating element is a first heating element; andthe system further comprises a second heating element, anda third power switch which turns on or off in response to a third control signal and a fourth power switch which turns on or off in response to a fourth control signal, the third and fourth power switches being in electrical series between a source of power and the second heating element and both being required to be on for activation of the second heating element. 11. The system of claim 10 wherein: the auxiliary processor is configured to activate the watchdog to disable the first and second heating elements. 12. The system of claim 11 wherein: the first heating element is a respiratory humidifier heater;the main processor provides the first, second, and third control signals;the watchdog gates the first, second, and third control signals;the second heating element is a respiratory conduit heater element; andthe auxiliary processor provides the fourth control signal. 13. A humidifier system comprising: a heating element;a first power switch which turns on or off in response to a first control signal and a second power switch which turns on or off in response to a second control signal, the first and second power switches being in electrical series between a source of power and the heating element and both being required to be on for activation of the heating element;first and second processors, the first processor providing the first control signal to the first power switch along a first control path and one of the processors providing the second control signal to the second power switch along a second control path; anda watchdog being in the first control path in electrical series between the first processor and the first power switch, the watchdog operable to normally gate the first control signal from the first processor to the first power switch and to monitor at least one of the processors, the watchdog further operable to interrupt the first control signal from the first processor to the first power switch so as to disable the heating element in response to the monitoring of the at least one processor, and the watchdog further operable to monitor the first processor and so disable the heating element in response to monitoring of the first processor, wherein the second control signal is not gated by the watchdog, and wherein the watchdog is further operable to interrupt the first signal and disable the heating element in response to a third control signal from the second processor to the watchdog. 14. A method of controlling a humidifier system having a heating element, first and second power switches in electrical series between a source of power and the heating element such that both switches are required to be on for activation of the heating element, first and second processors connected to, and operable to turn off, the switches upon the failure of any one of the processors, the method comprising: sending a control signal to the first switch along a control path, the control signal originating at the first processor and gated by a watchdog in the control path between the first processor and the first switch;monitoring at least one processor;interrupting the gated control signal in order to disable the heating element in response to the monitoring of the at least one processor; and sending a second control signal to the second switch along a second control path, the second control signal originating at the first processor and gated by the watchdog which is in the second control path between the first processor and the second switch. 15. A method of controlling a humidifier system having a heating element, first and second power switches in electrical series between a source of power and the heating element such that both switches are required to be on for activation of the heating element, first and second processors connected to, and operable to turn off, the switches upon the failure of any one of the processors, the method comprising: sending a control signal to the first switch along a control path, the control signal originating at the first processor and gated by a watchdog in the control path between the first processor and the first switch;monitoring at least one processor;interrupting the gated control signal in order to disable the heating element in response to the monitoring of the at least one processor; andsending a second control signal to the second switch along a second control path, the second control signal originating at the second processor. 16. The method of claim 15 further comprising: monitoring a timing signal from the first processor to the second processor;monitoring a timing signal from the second processor to the first processor; anddisabling all heating elements in response to a detected failure of one of the timing signals. 17. The method of claim 15, wherein the watchdog interrupts the gated control signal in response to receiving an override signal originating at the second processor.