Respironics Trilogy 02, Technical Information, Page: 45 / 424

P
AGE
4-10
T
RILOGY
S
ERVICE
& T
ECHNICAL
I
NFORMATION
1002735, V
ER
. 05
Power Supply - The system board supplies the sensor board with bulk 14VDC (J4). The bulk 14VDC is
regulated to 7VDC and 12VDC by voltage regulators U8 and U9 respectively. Precision reference (U10)
generates the 10VDC using 12VDC to power the monitor flow sensor. Linear regulator (U7) generates the
5VDC using 7VDC to power the remaining sensor board with the exception of the solenoid valve.
The precision reference voltage regulator (U5) generates a 2.5VDC output signal used by the ADC (U10) and
the instrumentation amplifier (U6). The ADCs internal reference gain amplifier generates a ratio-metric
4.096VDC reference voltage using this 2.5VDC voltage. The divide-by-two circuit generates a 2.5VDC signal.
This signal is ratio-metric voltage of 5VDC supply. It is buffered and used as an input to the ADC (U2).
Pressure Sensors - The monitor pressure signal is measured using the monitor pressure sensor (MT1). It
generates 0.2 to 4.7 VDC output for pressures range of 0 to 102 cm H20 pressure. The output of the sensor is
buffered and filtered using an anti-aliasing real pole filter with a cutoff frequency set at 222 Hz. The proximal
and control pressure signals are measured using the proximal and control pressure sensor (MT2 and MT3
respectively). They generate 0.5 to 4 VDC output for pressure range of 0 to 105 cm H20. The output of both the
sensors is buffered and filtered using an anti-aliasing real pole filter with a cutoff frequency set at 222 Hz.
Flow Sensors - The monitor flow signal is measured using the monitor flow sensor (MT4). It generates a -
25mv to +25mV output for pressures in the range of -10.5 to +10.5 cm H20. At the output of the sensor is
amplified and filtered using the instrumentation amplifier (U6). The filter used is a 2 stage passive low pass
filter with a cutoff frequency of 222Hz. The control flow signal is measured using the control flow sensor (MT5).
It generates a 0.25 to 4VDC output for differential pressures in the range of -5 to +5 cm H20. The output of the
device is a square root relationship with regard to voltage and dP. The output of the sensor is buffered and
filtered using an anti-aliasing real pole filter with a cutoff frequency set at 222 Hz.
Barometric Pressure Sensor - The atmospheric pressure is measured using the barometric pressure sensor
(MT6). The output of the sensor is scaled by a factor of .797 using a resistive divider network (R18 & R19). The
output is then buffered and filtered using an anti-aliasing real pole filter with a cutoff frequency set at 222 Hz.
Temperature Sensor - A dual element temperature sensor measures the air stream temperature. This sensor
is a negative temperature coefficient with nominal resistance of 10K @25°C. One output of the dual element
temperature sensor is buffered and fed to the 2:1 multiplexer (U4). The other input is from the on board
thermistor RT1 which has a negative temperature coefficient and a nominal resistance of 100k @ 25°C. The
output of the multiplexer is filtered by a single pole low pass passive RC circuit. Based on the input to the 2:1
multiplexer from the system board, output of one thermistor is supplied to the ADC.
Analog to Digital Converter - The analog outputs of all these sensors are converted to digital signals using
the 16 bit SAR (successive approximation register) ADC (U2). The ADC communicates with the system board
via the 4 wire SPI bus interface (J4).
Plastic Manifold – The plastic manifold provides a mechanical pneumatic connection to the sensors and
allows for mounting of the solenoid valve.
Solenoid Valve - The sensor board uses a solenoid valve to auto null/vent the control pressure sensor to
atmosphere periodically via port 1 of the plastic manifold. The solenoid valve is externally mounted on the
manifold and powered by a 29VDC nominal supply provided by the system board (J2). The N-Channel Power
MOSFET (Q2) turns the solenoid valve ON-OFF.