Theory of Operation
Chapter 3: Theory of Operation
Isolette® Infant Incubator (Model C2000) Service Manual Page 3 - 25
3
Audio Alarms
The audible alarm circuit incorporates an oscillator circuit to generate
the three alarm frequencies used:
• 600 Hz
• 1500 Hz
• 2500 Hz
The microprocessor, the watchdog circuit, and the power failure
detection circuitry drive the audible alarm circuit.
The audio volume is capable of three discrete sound levels. An analog
switch, incorporated in the audible alarm amplifier circuit, selects a 57
dB, 62 dB, or 65 dB output, as measured by International
Electrotechnical Commission (IEC) 601-19-2:102.3. The
microprocessor, the watchdog circuit, and the power failure detection
circuit control the analog switch.
Power Fail
The controller provides an audio output for power fail conditions. The
alarm oscillator is set for 600 Hz at 65 dB output, as measured by IEC
601-19-2:102.3. A timer circuit generates the cadence tone during
power failures.
When a Power Failure alarm is activated, the following occurs:
• The Power Fail indicator on the front panel illuminates.
• An alarm sounds.
A high energy storage capacitor powers the power failure detection
circuitry and supplies power to the audible alarm and indicator for a
minimum of 10 minutes. This capacitor charges while the unit is
operating. When power is lost to the controller and the Power switch
remains in the On position, the storage capacitor supplies power to the
power failure circuitry. The power failure circuitry incorporates a timer
circuit that periodically enables the audible alarm and Power Fail
indicator at a cadence of 520 milliseconds off and 98 milliseconds on
until one of the following occurs:
• The Power switch is turned off.
• The power is restored.
• The storage capacitor is depleted.
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