Nellcor N-180, Руководство пользователя

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N-180 Pulse Oximeter Service Manual
3-2
The functional elements of the oximetry module are:
• LED driver
• Input amplifier and synchronous detector
• Input source selection
• Demodulator filters and amplifiers
• Analog to digital converter
• Support circuits
Support
Circuits
LED
Driver
A:D
Converter
Input Amplifier
and
Synchronous
Detector
Filters
Input Source
Selection
W -1
2
3
4
5
JP2
Data and Control
Power Option
Selector
Host Power and
Communications
JP4
Host Comm Lines
Power
Configuration
Jumpers
Red_ADC
IR_ADC
IR
Red
Saturation Signal
External
Pre-amp
Connector
JP3
JP1
Sensor
Connector
JP5
Figure 3-1: Oximetry Module Block Diagram
The patient signal ( SAT for saturation), is conditioned and used to derive sat-
uration percentage and pulse rate values. This same patient information is
serial coupled to the CPU PCB and processed for display and for output
through the serial communication port.
Section 2, Principles of Pulse Oximetry, explains how Nellcor sensors operate.
An oxygen saturation signal is obtained from a Nellcor oxygen transducer at
the selected patient measurement site such as a finger, nose or toe. Sensor
LED s generate alternate infrared and red light pulses at this site. A photodi-
ode in the transducer responds to the modulated light energy transmitted
through the measurement site. The photodiode SAT signal is coupled into the
oximetry module via the monitor front-panel sensor connector.
LED Driver
The LED drive circuits control the current to, and the timing of, the sensor
LED s. The current is controlled to maintain an optimal signal to noise ratio.
Input Amplifier and Synchronous Detector
The SAT signal is conditioned by the input amplifier and the synchronous
detector to provide signal gain and reduce or eliminate the effects of ambient
interference (such things as ambient light and spurious electrical noise). The
final analog conditioning of the SAT signal is accomplished by circuits in the
filter block.
Input Source Selection
There are two possible inputs to the oximetry module. These inputs are
controlled via the LEMO signal. Only one input is used in the model N-180,