Mallinckrodt NELLCOR NPB-4000, Service Manual

Page: 113 / 219

Section 12: NIBP - Theory of Operation
12-5
12.3.6 NIBP Pump Control
Note: The following description is duplicated in the Power Supply section.
Reference designations for the two paragraphs that follow are found in
power supply schematic drawing, Figure 17-3and Figure 17-4.
The power supply mechanical assembly holds the blood pressure pump and
shield. The power supply contains circuitry that allows logic level control of the
pump power from the processor board. For single-point fault protection, the
pump requires two signals (PUMPON and PVENB to activate the pump.
PUMPON (when high) turns on FET Q18 that pulls the bottom lead of the motor
to ground. The PVENB
signal through level translator Q19, turns on FET Q17
that pulls the top motor lead to VBATT.
When no voltage is present at Q18, the pump is fully off. As the duty cycle
increases from 0 to 100 percent, the pump power changes smoothly from full
OFF to fully ON. This control technique minimizes overshoot of the targeted
pressure. Diode D32 suppresses voltage spikes, while R78 ensures that Q18 will
be OFF if the line opens. Resistor R77 and capacitor C46 suppress motor brush
noise.
12.3.7 Digital Signal Processing and Information Display
NPB-4000/C software, resident in the microprocessor controller and memory
peripherals, include the algorithms needed to process the digitized outputs of the
digital hardware just described. It also includes the system software that
responds to the commands for desired modes of NIBP measurements, display of
NIBP values of systolic, diastolic and mean arterial pressure, storing trend data,
and for recording/printing of such data, and for initiation and silencing alarms.
Details of these functions are contained in the theory of operation of the
microprocessor and control circuitry.