Vyaire VELA, Руководство по обслуживанию

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2-4
Chapter 2: Theory of Operation
33373-001 Version A
2.4.2 Power System
The Power System conditions and controls electrical energy from the AC line input and the internal
batteries. The Power System supplies 24VDC, 8VDC, and 5VDC to the Main System PCB. When
energy is available from the AC line, the ventilator operates from this source, and also recharges
the internal batteries. When AC line power is not available, the power system draws energy from
the internal batteries. The power system uses energy efficient DC-to-DC converter technology to
convert energy from the AC line or batteries to appropriate voltages and currents to supply power to
ventilator components and systems.
2.4.3 Main System PCB
The Main System PCB is comprised of three pressure transducers, an analog-to-digital converter,
two digital-to-analog converters, solenoid valves, and the Watchdog and Hardware Fault Monitors.
One of the pressure transducers measures the patient circuit pressure. This pressure is an input to
the control system. A differential pressure transducer measures the pressure across the turbine.
This pressure is also an input to the control system. A second differential pressure transducer is
used to measure the flow at the outlet of the exhalation valve. This pressure is also an input to the
control system.
Analog to digital converters are used to change the analog pressure signals into measured binary
numeric values for use by the microprocessor.
Digital to Analog converters are used to change the binary numeric commands generated by the
microprocessor in the control system into analog signals which drive the turbine and exhalation
valve.
The microprocessor also performs several repetitive tasks such as generating the refresh signals
for the display system, cycling the A-to-D converters through a pattern of measurements from the
multiple signal sources, and scanning the control panel for pressed buttons.
Solenoid Valves and Valve Drivers (including the Auto Zero valves) are employed on the Circuit
Pressure transducer and on the Turbine Differential Pressure Transducer. These valves allow the
control systems software to compensate for long term drift and temperature induced zero shift in the
pressure transducers by periodically rechecking the zero pressure readings. Similar solenoid valves
are employed in the Oxygen Blending System. The valve drivers for the Auto Zero and Blender
valves are similar.
The Main System PCB controls all ventilator functions. All user settings for alarms, controls,
ventilation mode, waveform, and monitoried data are stored here and are combined with measured
pressure, flow, and speed data to cause the ventilator to function. The algorithms, formulae, and
control functions which define ventilator behavior are contained in the software program executed
by the microprocessor.
2.4.4 The Watchdog Circuit and Hardware Fault
The Watchdog circuit requires the microprocessor to periodically send a signal. If the signal is not
received by the Watchdog Circuit then the ventilator will be shut down. When the Watchdog shuts
down the CPU it forces the ventilator hardware to a safe state. The Hardware Fault Monitors check
the status of the power supplies to the ventilator electornics. If any is out of the safe operationg
range, the ventilator will shut down and cannot be made to operate until the fault is corrected.