Nellcor Oximax NPB-40, Service Manual

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Technical Discussion
NPB-40 81
LCD
The liquid crystal display (LCD) is driven by the CPU. The LCD displays the
patient’s %SpO
2
and pulse rate. The LCD also displays icons indicating the status
and functions of the NPB-40. Refer to the NPB-40 Operator’s manual for a
description of the icons.
IrDA
The IrDA (Infrared Data Association) is an industry standard for infrared
communications. The IrDA receives information from the CPU, converts it, and
sends it to an external printer. The external printer communicates with the IrDA.
Refer to the printer manual for more information.
Power Supply
The user interface PCB power supply receives power from the SpO
2
PCB power
supply. The power supply provides a regulated 3.0 volts DC to the CPU.
Power Supply Monitoring
The power supply outputs are monitored by the power monitoring function to
ensure stability. The power supply monitoring circuit sends a reset signal to the
watchdog circuits to shut down the NPB-40 when voltages are out of tolerance.
The power supply monitoring circuit monitors the battery output voltage and shuts
down the NPB-40 when the battery voltage is critically low. The circuit provides
the low battery signal.