Theory of Operation
Chapter 3: Theory of Operation
Page 3 - 26 Isolette® Infant Incubator (Model C2000) Service Manual
The Power Failure alarm silence is hardware-controlled. Pressing the
Alarm Silence key during power failure silences the alarm for the
duration of the power failure. The Power Fail indicator flashes until one
of the following occurs:
• The storage capacitor is depleted.
• The Power switch is turned off.
• The power is restored.
The System Failure alarm is unaffected by the Alarm Silence key.
Interfacing
An interface port enables an RS-232 serial communication link. The
serial port is fully isolated from the remaining controller circuitry. The
power to the serial port interface circuitry derives from an isolated
winding on the power supply transformer. The RS-232 interface
connector is a female DB-9, mounted on the rear of the controller. An
RS-232 transceiver converts the RS-232 to logic voltage levels and vice
versa. Optocouplers provide the isolation barrier and interface the RS-
232 transceiver to the PC16550 UART. The UART interfaces the serial
port to the microprocessor bus. All lines connected to the RS-232
connector are filtered to block EMI. The RS-232 transceiver
incorporates electrostatic discharge (ESD) protection.
An interface enables communication between the controller module and
the sensor module. The sensor module interface connector is a female
DB-9, mounted on the rear of the controller and comprised of a bi-
directional data line, a clock output line, and a reset output line. The
data lines are fully isolated and optocoupled to the microprocessor. The
controller provides isolated power to the sensor module.
Door Switches
The controller connects to the two door switches that are wired in
parallel. The controller performs the following:
• Provides no more than 5 milliamperes (mA) of current to the
switches
• Provides less than 6V of power to the switches
• Monitors the return current to determine if either door is open
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