S3.1 Overall Unit Block Diagram Analysis - Nellcor NPB-40 Service Manual

S3.1 Overall Unit Block Diagram Analysis
The following is a list of terms and definitions used in the following
paragraphs.
Analog to Digital (A/D) converter. The CPU has a 10-bit A/D converter on
board. Up to eight different analog inputs can be provided to the A/D for
measurement.
Central Processing Unit (CPU). An Intel 80C196KC 16-bit
microprocessor. The CPU sends and receives control signals to the SpO
analog section, display, and printer infrared LED.
High Speed Outputs (HSO). The 6 HSO lines control most of the timing of
the LED signal pulse and the demodulation of the received signal.
Input and Output (I/O). Digital lines that are used by the CPU to read in
data and output data.
Light Emitting Diodes (LEDs). Two LEDs are used in Nellcor Puritan
Bennett oximetry sensors. Light is transmitted through body tissue and
received by a photodetector circuit that converts it to photocurrent. The two
wavelengths, which are used for calculation of pulse rate and oxygen
saturation in blood, are transmitted at the following frequencies:
infrared (IR) light at ≈ 915 microns
•
red light at ≈ 660 microns
•
Pulse Width Modulation (PWM). The three 8-bit PWM outputs can be
software controlled; their duty cycle can be changed from 0 TO 99.6 percent of
the total pulse duration. PWM frequency is the crystal frequency of the CPU
(10 MHz) divided by 1024. The PWMs control the gains within the analog
circuit.
RCal. Sensor RCal value is a resistance value specific to an individual
sensor. This value is used by the software during oxygen saturation
computations to maximize accuracy.
Exclusive of batteries covers, keys, and external connectors, the NPB-40
consists of three main functional components: the front panel keyboard, the
CPU PCB, and the LCD PCB as follows.
• CPU PCB — contains the CPU; power supply circuitry; support
memory circuits; sensor circuits for battery voltage; a serial data port;
LCD backlight control; pulsatile beeper drive circuits; and some display
control circuits.
• LCD PCB — contains the SpO
external sensor; the power conditioning circuitry; the LCD display and
display driver circuits; the interface circuitry for the printer (which is
not used unless a printer is present); the LCD backlight; and audio
output hardware.
• Front Panel Keyboard — contains four membrane switches and a
line common to all four switches. This assembly connects to the CPU
PCB by a flex circuit.
Refer to Figure S3-1 for this NPB-40 block diagram. The CPU PCB and the
LCD PCB are each described in more detail in later paragraphs.
Technical Supplement
analog circuitry and interface to the
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