Electronic Vaporizer Subsystem (Evap) - GE Datex-Ohmeda Aisys Carestation Reference Manual

Aisys
2.10.2 Electronic
Vaporizer
subsystem (eVap)
2-30
The Aisys system uses an integrated, electronic vaporization subsystem to add agent to
the fresh gas flow. The main function of the Electronic Vaporizer subsystem is to mix the
requested amount of anesthetic agent into the fresh gas stream.
Additional functions facilitated by the Electronic Vaporizer subsystem include cassette
type detection, agent level detection, cassette overfill/overpressure handling, and
safety features. Vaporization control algorithms depend on external reported
parameters: user interface (agent setting, fresh gas composition), Mixer measured
flow, and patient airway pressure information. (Patient airway pressure measurement
is a combination of reading from gauge sensor and ambient pressure sampled at
machine startup.)
Agent is delivered from the subsystem in one of two configurations depending on
whether cassette pressure is below or above Mixer output pressure. If cassette
pressure is above Mixer output pressure, all fresh gas is routed through the
Backpressure Regulator and agent is metered out of the pressurized cassette. If
cassette pressure is below Mixer output pressure, some fresh gas is routed through the
cassette, where it picks up agent vapor. The remaining fresh gas passes through the
Backpressure Regulator. The mixed fresh gas and agent vapor from the subsystem is
sent to the CGO.
To meet the requested agent concentration, outflow from the cassette (or flow through
the cassette) is controlled with a proportional valve. This means the main subsystem
control loop is on cassette flow, not agent concentration directly. If all fresh gas flow is
through the Backpressure Regulator, the control loop depends strongly on Mixer
reported flow and the cassette flow reading. It depends weakly on reported fresh gas
composition, manifold temperature reading, and reported patient airway pressure. If
fresh gas flow is split between the cassette and the Backpressure Regulator, the control
loop depends strongly on Mixer reported flow, cassette flow reading, cassette pressure
reading, and cassette temperature reading. It depends weakly on reported fresh gas
composition, manifold temperature reading, and reported patient airway pressure.
Electrically, the subsystem interfaces to the Anesthesia Control board via the Pan
Connector board for power (10VA limited) and communications (RS422). Power and
communications to the Aladin cassette is supplied by the subsystem. While the
subsystem contains a microcontroller, the vaporization control algorithms and safety
functions run on the Anesthesia Control board. The subsystem microcontroller and
other electronics simply handle the low-level tasks of sensor data gathering and
command outputs to the actuators.
Cassette ID (type) is sensed by Hall Effect sensors that detect magnets embedded in
the cassette.
Cassette temperature is read from the cassette (Aladin
the Cassette Temperature assembly.
For Aladin DES and Aladin
Refer to section 2.11.2 for detailed description of pnuematic operation.
cassettes, agent level is read from the cassette.
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, if so equipped) or sensed with
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