VIASYS Bear Cub 750PSV, Service Manual, Page: 28 / 98

28
Bear Cub 750PSV
The Display circuit board is the user interface for the ventilator electronics. Ventilator
controls and alarms are set by the clinician, and Monitors feed current ventilator
status back to the display.
The Control circuit board includes the Monitor MCU and Control MCU. The Control
board drives the system solenoids which control breath phase, flow, and pressure.
This is achieved using front-panel settings from the display board, as well as
incorporating its own real-time pressure and flow readings. The Control board also
enables bidirectional (digital) communication to the optional Graphic Display in order
to chart ventilator data. Also, analog outputs proportional to pressure and flow, plus
a breath phase signal are provided to the back panel. The electronics to drive and
read the flow sensor are also contained on the Control PCB.
Power Supply
The Power Supply converts the AC line voltage to DC voltages for the electrical
system. AC line voltages of 100, 120, 230, and 240 volts (at frequencies from 50 to
60 Hertz) can be used as input power. Five DC voltages are used in the ventilator
electronics: 5, 7, 10, -10 and 22 VDC. All power levels that are high enough to pose
an ignition hazard in the presence of oxygen concentrations greater than 21% are
housed in a separate enclosure from the rest of the system. If input power fails, a 12
volt rechargeable, sealed, lead-acid battery is included to provide a minimum of 30
minutes of ventilator operation. A two-level battery charger circuit is contained on
the Power Supply PCB in order to keep the battery on continuous charge whenever
the ventilator is plugged into an AC outlet.
Ventilator Software
The BEAR CUB™ 750PSV Infant Ventilator is a shared processor system,
incorporating two Motorola 68HC11 microcontroller units (MCU), the Monitor and the
Controller. Each processor, and thereby its software, have specific and duplicated
tasks. Each processor is based on a 2.5 m-sec timer interrupt, referred to as a ‘tick.’
The Controller directs basic control of the ventilator based on operational settings
communicated from the Monitor MCU, as well as on pressure transducer, and flow
sensor data read on its own 8 bit Analog to Digital (A/D) converter. The Monitor has
the following functions: (1) reads the front panel switches, back panel switches, and
potentiometers, (2) monitors ventilator performance as well as the performance of
the Controller MCU, (3) transmits front panel status to the Controller, (4) receives
performance data back from the Controller, and (5) transmits display data and
annunciator status to the front panel.
During power-up, both processors perform RAM (Random Access Memory), and
ROM (Read Only Memory) tests to verify integrity of these two memory systems.
Solenoid and Control Potentiometer continuity are also tested during power-up by
the Control and Monitor processors respectively. Continuous communication checks
between the two processors are used to verify functionality of each sub-system. If
an error is detected, either processor has the ability to shutdown the ventilator while
enabling the audible and visual Failed to Cycle alarms. These systems, among
others, are provided to reduce the possibility of a software/hardware error leading to
an undetected hazardous condition.
L2346 Revision B June 2004