Mallinckrodt NELLCOR NPB-4000, Service Manual

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Section 13: Microprocessor Computer and Control –Theory of Operation
13-4
13.3 NIBP PROCESSING
See Figure 13-2. The NIBP circuits consist of microprocessor control for
turning on and off certain signals, control logic generating the pump PWM and
valve PWM, and status signals.
Figure 13-2: NIBP Processing Circuitry Block Diagram
13.3.1 NIBP Signals Going to the A/D Converter
The NIBP circuits generate three analog signals which must be converted to a
digital code, the pressure from transducer 1, the pressure from transducer 2, and
the oscillatory signal from pressure transducer 1. The signals are connected to
the A/D converter for conversion and subsequent processing by the
microprocessor.
13.3.2 Pressures 1 and 2
The pressure transducers output 0.33 volts at 0 mm-Hg to 4 volts at 300 mmHg.
Transducer 1 is used for the main cuff pressure signal from which blood pressure
results are calculated. Transducer 2 is used as the backup cuff pressure signals
from which over-pressure warnings are obtained. These pressure voltages go to
the A/D converter and are monitored by the software.
13.3.3 Oscillatory Signal
Transducer 1’s signal is also filtered and amplified to separated cuff pressure
oscillation signals that are present on the cuff pressure signal during the deflate
portion of the measurement cycle. This signal also goes to the A/D converter
and software algorithms detect the blood pressure systolic and diastolic values.
13.3.4 Microcontroller Control and Status Signals
There are five signals that interface directly with the microcontroller and NIBP
circuits. Four of the signals are for control of the NIBP circuits from the
microcontroller software and one signal is a status signal fed back to the
software. All of the signals require 0-5 volts levels by the NIBP circuits, so each