Datex-Ohmeda Anesthesia Delivery Unit S/5, Technical Reference Manual

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Technical description A-FGC1
Document No. 8502854
B-11
The liquid prevention valve (14) prevents liquid from the cassette to enter the fresh gas line in a failure
situation. The valve is a polypropylene ball located in the vaporizer valve block beside the outflow
channel. The liquid will lift the ball up and seal it to the valve seat.
The cassette pressure relief valve (8) opens the channel to the scavenging line, if a high pressure is
detected in the cassette or the liquid level measurement device detects overfilling.
The scavenging chamber (16) is used as a buffer for a possible release of anaesthetic liquid from the
Aladin cassette. This is in order to prevent the tubing to be filled with liquid if the scavenging valve has
opened due to an overfilled Aladin cassette.
Agent concentration control
The green LED on the front panel beside the agent wheel is used to indicate that the vaporizer is on.
The A-FGC1 CPU switches on the agent LED when the anaesthetic concentration is set above zero.
The agent concentration is set by turning the agent wheel. The agent wheel operates a digital
potentiometer that gives signal pulses to the A-FGC1 CPU. There are two inputs to the CPU I/O ports.
The rotation direction is detected from the phase of these two signals. The amount of pulses is
calculated and converted to set concentration.
Software sets the agent concentration according to the number of output pulses from the agent
wheel.
By measuring the pressure and the temperature in the cassette, thereby knowing the agent
concentration, the correct cassette flow can be calculated to achieve the set concentration.
•
Anaesthetic agent identification
Anaesthetic agent type is detected by a cassette identification sensor board (11) The cassette
identification sensor is located at the top, inside the cassette slot. It consists of five HALL sensors,
one for each Aladin cassette magnet position. The configuration of two magnets in five possible
positions, identifies agent type.
•
Liquid temperature
The temperature is measured by two curve-fitted NTC thermistor sensors. The resistors are mounted
into a conical gold plated copper piston that makes a thermal connection with the Aladin
temperature measurement rod (10). The resistors are connected so that a short circuit, ground
connection or cross connection between the sensors is detected by the A-FGC1 software. If the
temperature measurement is defective, an alarm is displayed and vaporizing is continued, using a
default value of 45° Celsius. The sensors are calibrated. The procedure is described in the calibration
section.
A fan (13) is mounted inside the fresh gas control unit underneath the Aladin housing and is required
to heat the cassette when using high concentrations as vaporizing cools the cassette. In practise only
needed when Desflurane is vaporized.
The fan operates when the cassette temperature is below 17
o
C and stops when the temperature is
above 20
o
C
•
Cassette Pressure
The cassette pressure (6) is measuring the pressure in the cassette outflow channel. If the pressure is
above 1200 mmHg (1.6 bar), the scavenging valve is opened.
Desflurane liquid level measurement
The Desflurane Aladin Cassette has a built in electronic liquid level measuring device (12). If the
cassette is overfilled, the scavenging valve (8) is opened and the O
2
test flow is used to flush the extra
agent liquid out of the cassette through the valve. Agent delivery will be cut off and has to be
restarted.