Respironics BiPAP Vision Service Manual page 21

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Chapter 3: Description and Theory of Operation
Pressure Control Subsystem (PC) (Continued)
3.4.1 Microcontroller Interface
Programmable Array Logic (PAL) memory device decodes the chip selects in such a way that the program code is
retrieved from the EEPROM and data is retrieved from the RAM. An additional PAL provides the interface for the
Intermodule Communications Bus (ICB). The microprocessor monitors: oxygen and gas temperatures; Airflow
Module (AFM) and Oxygen Module (OM) detection; In-Line Flow Restrictor (ILFR), Pressure Regulation Valve
(PRV), and oxygen valve DAC control voltage; blower DAC control voltage; and power supply and reference
voltages.
3.4.2 Blower Motor Drive
The complete motor controller includes closed loop speed control via analog circuitry. When the desired speed
and actual speed are known by the processor, the speed is adjusted by increasing or decreasing the DAC converter
output to achieve proper pressure and flow.
3.4.3 Pressure Regulation Valve (PRV) and In-Line Flow Restrictor
(ILFR) Drives
The valve drives have closed loop control via the microprocessor. The microprocessor reads seven
pressure, flow, and temperature sensors through the PC hardware, and receives prescription parameters from the
MC. The microprocessor then adjusts analog DAC voltages to control the PRV and ILFR valves as required to
meet the prescription.
3.4.4 Pressure Sensors
The PC module has two dual pressure sensors (MT1 and MT2) and a single sensor (MT3). They measure patient
pressure, unit outlet pressure, and barometric pressure. These sensors are subject to calibration with their calcu-
lated slope and intercept values stored in the on-board EEPROM. MT3 is a backup outlet pressure sensor that
provides a redundant check of the primary outlet sensor located on the AFM.
NOTE: Calibration is factory programmed and field adjustment is not required.
3.4.5 Error Line Control (ELC) Circuit
The ELC circuit is designed to simply detect a failure from, or signal a failure to, the MC and Display Control (DC)
modules. If the ELC line activates, only a power On / Off of the ventilator can clear this latched circuit state.
3.4.6 Diagnostics Connector
The diagnostic connector (J3) interfaces with the microprocessor to view PC functions and system errors on units
from serial number 100500 to 105999, unless upgraded. For units greater than this, the diagnostic connector is on
the rear of the unit.
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BiPAP Vision Service Manual