Theory of Operation
Chapter 3: Theory of Operation
Isolette® Infant Incubator (Model C2000) Service Manual Page 3 - 27
3
The switches are open when the door is closed. The input is protected
with transorb diodes and is filtered to block EMI and prevent ESD
damage to the controller.
Cooling Fan
The cooling fan provides a continuous flow of air through the controller
to remove heat generated by the various components inside the
controller enclosure. The cooling fan operates whenever power is
applied to the controller. The cooling fan is equipped with a tachometer
output signal that is supplied to the microprocessor.
Ambient Temperature Sensors
The temperature sensors, located in the airflow of the cooling fan, are
NTC thermistors. The output signals of the redundant sensors feed into
the A/D converter.
Watchdogs
The first watchdog timer is internal to the microprocessor. If the
software does not update the watchdog timer within the required time
frame, the internal watchdog resets the microprocessor and all
peripherals connected to the external reset line.
The second watchdog timer circuit attaches to the microprocessor bus.
The microprocessor continuously writes the following data to the
watchdog timer:
• Data 55 hex (01010101 binary) to watchdog register #1.
• Data AA hex (10101010 binary) to watchdog register #2.
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