Front End Interface - Mallinckrodt NELLCOR NPB-4000 Service Manual

Section 14: Main Color Board Digital Theory of Operation
14.15.1.2.5 Pump and Valve Drivers
14.15.1.2.6 NIBP Pump Control
14.15.1.3 Digital Signal Processing and Information Display

14.16 FRONT END INTERFACE

14-24
Three-way valve V1 coil is powered by VPS that is switched in series with the
coil through n-channel MOSFET Q10-6. Switching action of Q10-6 is
controlled by the input signal NP3WYV, that is gated by the enabling signal
NPPVEN at switch U23. VPS is developed from VBATTP through Q11-6 that
is also controlled by NPVEN gating transistor Q6. Diode D5 acts to suppress
voltage spikes. Resistor R101 insures that Q10-6 will be OFF in case of an open
to the input line. The valve is either fully closed, or fully open.
Control valve V2 coil is powered by VBATTP and controlled by switching n-
channel MOSFET Q10-7, in series with the coil. Q10-7 is controlled by input
signal NIBPCNTLVLV. Pulse width modulation (PWM) of a 5-volt level is
used to operate the control valve. No-voltage results in a fully closed valve. As
the duty cycle of the PWM is varied from 0 to 100%, the valve changes smoothly
from fully closed to fully open. Repetition rate for the PWM is at least 9 kHz.
Diode D4 suppresses voltage spikes, and resistor R100 assures that Q10-7 will
be OFF if the input line should open.
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 singly-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. PVENB, 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%, 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 insures that Q18 will be OFF if
the line opens. Resistor R77 and capacitor C46 suppress motor brush noise.
NPB-4000C 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.
The LNA front end multiplexes analog channels to a linear opto-coupler which is
connected to the A/D converter. The A/D converter connects to the transmit and
receive ports of the SSIO (Synchronous Serial I/O) unit in the 386EX. Control
data is passed to the A/D and the front end via the SSIO signals at the same time