Datex-Ohmeda S/5 B-GAS, Technical Reference Manual

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S/5 Airway modules
Document No. 800 1005-1
11
Gas measuring units, ACX-200 and O
2
unit
After the zero valve, the gas passes through the ACX-200 and O
2
measuring units. In the ACX-200
measuring unit, infrared light is passed through chambers containing the main flow gas
(measurement) and a chamber containing reference gas. The measurement is made by
determining the ratio between the two light intensities.
The oxygen sensor has two inputs. One input accepts the main flow and the other draws in room air
for reference. The sensor uses a differential pressure transducer to compare the pressure gradient
produced when both gases are exposed to an oscillating magnetic field. Both gas flows exit from a
single port.
In i model, the ASX agent identification unit is installed in parallel with the oxygen sensor. The task
of the ASX unit is to identify anesthesia agents by infrared light method used also in the ACX-200
unit.
Pressure valve
The pressure valve is used to measure the pressure gradient between the O
2
measurement flow
and the O
2
reference flow. This pressure gradient reflects the condition of the D-fend water trap
filter.
Normally the pressure gradient between the O
2
measurement flow and the reference flow is
approxi8 mmHg. If the software detects the gradient to be between 0 and -5 mmHg, the
pressure valve will initiate pressure measurement of the reference flow. If the gradient is greater
than -5 mmHg, the software triggers the message ’Replace Trap’.
Flow cassettes
The internal flow rates are set using flow cassettes. These cassettes are used to set the side flow
rate and the O
2
reference flow rate, the flow rates through the measuring units and the total flow
rate of the sampling system.
Sampling pump and damping chamber
The sampling pump is a vibrating membrane pump driven by a 50 Hz/12 V/0.4 A square wave
current.
The damping chamber is used to even out the pulsating flow and silence the exhaust flow.