Redundant power control for respiratory system heaters

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;
• and
• a 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;
• and
• the 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.

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;
• and
• the first CPU providing a control signal to both of the two switching devices of the second set.

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;
• and
• a 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;
• and
• the system further comprises
• a second heating element, and
• a 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.

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;
• and
• a 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.

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.

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 second processor.