182
Description
Oxygen Ratio Control – S-ORC
Oxygen Ratio Control – S-ORC
To prevent the setting of hypoxic gas mixtures,
Cicero EM has an O
2
ratio control system (SORC =
Sensitive Oxygen Ratio Control).
The O
2
and N
2
O flows build up control pressures for a
switching diaphragm in a flow restrictor. The pressure
ratio on the switching diaphragm controls the N
2
O flow.
N
2
O is disabled when the O
2
flow drops below approx.
200 mL/min; it is slowly re-enabled as the value rises.
When the O
2
flow reaches approx. 300 mL/min, the
proportion of N
2
O contained in the fresh gas can be
freely varied between 0 and 75 %.
Since the maximum delivery capacity of both flow tubes
is limited (but at least 9 L/min, depending on the pressure
in the gas supply), the minimum O
2
concentration
increases above approx. 2500 mL/min until both flow
tubes are completely open and the mixing ratio of
O
2
: N
2
O is approx. 50 : 50.
The principle is illustrated in the diagram:
The curves are displaced when anaesthetic vapours
(by up to 18% in the case of desflurane!) are delivered!
Concentration ratio
O
2
/ N
2
O
100 / 0
90 / 10
80 / 20
70 / 30
60 / 40
50 / 50
40 / 60
30 / 70
20 / 80
10 / 90
0 / 100
O
2
/ N
2
O
100 / 0
90 / 10
80 / 20
70 / 30
60 / 40
50 / 50
40 / 60
30 / 70
20 / 80
10 / 90
0 / 100
0
250
500
750
1 000
2 250
3 000
Minimum O
2
concentration
O
2
-Flow [mL/min]
O
2
/N
2
O ratios which can be set with the
control valves on the bank of measuring tubes
Control valves
O
2
N
2
O
O
2
N
2
O
Control
diaphragms
N
2
O-
shutoff
valve
Flow restrictors
Flow tubes
in the bank of
measuring tubes
ORC
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