GE Datex-Ohmeda Aisys Carestation Reference Manual page 57

RS422 Serial
Interface Driver
Regulator
12.5
VDC
Valve
Oxygen Valve
Drive
Drive
Alternate
O2
O2
Air
Balance
Gas
N2O
Figure 2-20 • Electronic Gas Mixer block diagram
M1046983 04/08
Desired gas flows are sent from the Anesthesia Control board to the Gas Mixer.
Gas Mixer operation is controlled through a microcontroller which:
• Sends requests for the Anesthesia Control board to open and close selector valves for
O , N O and Air.
2 2
• Regulates flow control valves for O
Closed-loop flow control is accomplished through a hot-wire anemometer in concert
with the flow control valves. Gas flow, based on a calibration table, is on target when
the reference measurement equals the flow measurement.
Pressure measurements across each of the flow sensor channels are used as checks
on the flow measurement for hazard mitigation, ambient pressure compensation, and
compensation for back pressure downstream of the Mixer.
In case of certain failures or errors, Alternate O
delivers O and agent through an alternate pneumatic path to the patient circuit.
2
Alternate O can be activated manually through a front panel control. Agent delivery
2
cannot be activated in case of certain Gas Mixer failures
FAN Hi/Lo
Regulator
3.3 VDC
130 ma max.
5.5 VDC
Regulator for
Flow Sensors
Balance Gas
Valve Drive
350 ma max.
Flow Sensor
Assembly
Press.
T
T1
Press.
T
T2
and balance gas (N
2
2
Atmel AVR Mega128L
Processor with
Fan
128K Flash,
300ma
4K RAM,
max.
4K EEPROM
A/D
VDD
Port
I2C
SPI Port
Port
12 Bit A/D
Signal
Conditioning
F1
F2
2 Theory of Operation
O or Air).
2
control activates automatically to
Watchdog
JTAG Emulator
Interface
Analog
References
8 Channel Analog
Mutiplexer
(BIT Signals)
Press.
Vaporizer
CODE
CPU
RCV
XMIT
VLV1
VLV2
FAIL
Diagnostic
Indicators
2-25