Nellcor N-180, Руководство пользователя

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N-180 Pulse Oximeter Service Manual
3-4
• High saturation
• Low saturation
• High rate
• Low rate
A fifth LED flashes once per second to show the audio alarm function is
temporarily silenced or lights continuously if the alarm is disabled.
The front panel assembly includes the sensor input connector, LED Drive
PCB, LED PCB, and the front panel controls (push buttons, control knob, and
ON /STDBY switch). (This assembly is not available as a spare part but some
elements, such as the PCB
S
are included on the spares list in section 9.)
AC Power Input and Control
The AC power input and control includes the AC input receptacle, AC Power
switch, two fuses, and a filter.
Battery
The monitor takes DC power from an internal 12 volt sealed lead-acid
battery. The battery is self-contained and connects directly to the CPU PCB
at CN4. The battery charging circuit is on the CPU PCB.
CIRCUIT ANALYSIS
This portion of section three describes major functional circuit blocks in
detail. An understanding of monitor operation helps you locate and repair
malfunctions. The descriptions are organized in top-down order. Each monitor
PCB has an associated circuit analysis paragraph in this section.
Oximetry Module
The oximetry module is a self-contained assembly that provides oxygen
transducer power, conditions the resulting SAT signal, and calculates patient
oxygen saturation and pulse rate. The saturation percentage, pulse rate, and
other pertinent information are transmitted to the monitor CPU PCB for
processing.
The functional elements of the oximeter module are as follows:
• LED Drive
• Input source selection
• Input amplifier and synchronous detector
• Demodulator filters and amplifiers
• Control signals
• Analog to digital converter
• Support circuits
LED Drive Circuit
The SAT signal development scheme requires lighting the measurement site
using specific light wavelengths. Nellcor sensors have two LED sources,
infrared ( IR) and red. These LED sources are an integral part of each Nellcor
oxygen transducer. The LED s are alternately pulsed on and off by the
oximetry module microprocessor.
The LED drive bias voltages are developed by dual DAC U1 (figure 3-2).
Initially, both DAC s in U1 are directed via the DACBUS to develop
approximately 0.5 VDC on respective outputs (pins 4 and 18) coincident with
the period each LED is selected. The microprocessor alternately closes FET