Mallinckrodt NELLCOR NPB-4000, Service Manual

Page: 163 / 219

Section 14: Main Color Board Digital Theory of Operation
14-23
Figure 14-13: NIBP Hardware Block Diagram
14.15.1.2.1 Pressure Transducers
Pressure transducers PS1 and PS2 convert pneumatic pressure levels to voltages
in the range from 0.33 volts at 0 mmHg to 4 volts at 300 mmHg. Transducer
PS1 is used to sense the main cuff pressure. Transducer PS2 is used as a backup
cuff pressure sensor, from which over-pressure warning signals are obtained.
Both transducers outputs are smoothed to remove the effects of pumping
pulsation. The output of PS1 is identified as signal NIBPPRSR1, while that of
PS2 is NIBPPRSR2.
14.15.1.2.2 Filtering the Oscillatory Signal
Amplifiers U16-1 and U16-14, in combination with the lumped resistance and
capacitance values of the passive components, form a band pass filter that
separates and amplifies the oscillatory signals OSC from the deflating cuff
transducer signal NIBPRSR1. Amplifier U16-8 provides hysteresis.
14.15.1.2.3 Power Supplies
Battery power, VBATTP, connected to the board at J3, pins 13 and 14, is
regulated in U15 when that component is enabled by the NPANPWR analog
power On/Off signal input to U10-4. The regulator accepts a battery voltage of 6
to 8 volts and delivers reg5 volts to power the pressure transducers and
biasing circuitry for the operational amplifiers.
14.15.1.2.4 Over-Pressure Detector
Pump and Valve drivers are controlled by the NPPVEN pump and valve enable
signal that is generated in U16-7 level-detector amplifier circuit. One input to
that amplifier is the NIBPRSR2 signal from transducer P2. The other is a value
determined by voltage divider R68 and R64, and feedback resistor R61.
The pump and valve drivers are enabled only when cuff pressure is below
nominal 330 mmHg for adult mode, and below 165 mmHg for neonatal
measurements.