Surgery – Respiratory method or device – Means for supplying respiratory gas under positive pressure
Reexamination Certificate
1999-08-20
2004-02-10
Lo, Weilun (Department: 3761)
Surgery
Respiratory method or device
Means for supplying respiratory gas under positive pressure
C128S204290, C128S205110
Reexamination Certificate
active
06688308
ABSTRACT:
DESCRIPTION OF INVENTION
This invention relates to a method of testing the performance of a oxygen supply system in an aircraft, and additionally optionally re-calibrating the system if required.
Known oxygen supply systems comprises an oxygen concentrating device which separates air into oxygen enriched product gas and oxygen depleted gas and provides the, product gas to a breathing regulator which regulates the pressure at which that gas may be breathed.
A sample of the product gas fed to a monitoring means which monitors the oxygen concentration or partial pressure within the product gas. A control means responds to the monitoring means to provide control signals to the oxygen concentrating device so that the concentration or partial pressure of oxygen in the product gas can be controlled. The control means may also receive control data signals indicative of for example, the altitude of an aircraft, so that the concentration or partial pressure of oxygen in the product gas can appropriately be adjusted for breathing at that particular altitude.
Of course, when such an oxygen supply system is manufactured, the system is calibrated so that appropriate control signals are provided from the control means to the oxygen concentrating device, to result in the maintenance of, or a desired increase or decrease of, oxygen concentration or partial pressure in the product gas. However, in use, the performance of the oxygen concentrating device and/or the oxygen monitoring means may change. For example, the ability of the oxygen concentrating device to produce product gas with high oxygen concentrations or partial pressure may degrade with use, brought about, perhaps due to contamination of the oxygen concentrating device. Hence a particular control signal from the control means to the oxygen concentrating device may not bring about an expected oxygen concentration or partial pressure in the product gas.
In U.S. Pat. No. 4,516,424 there is described an apparatus for monitoring the performance of an oxygen monitoring means. Gas from an external source, with a known oxygen concentration or partial pressure such as ambient air is provided to a monitoring means, to test that the oxygen concentration material is that of the known concentration. In U.S. 4,516,424, the system is a breathing system for medical use and there is a complex series of valves whereby ambient air can be fed to the monitoring means for testing purposes.
Another approach is to provide external monitoring of the oxygen concentration or partial pressure in the product gas which may involve duplication of components.
These prior proposals have disadvantages in that where it is required to provide an external source of gas or external testing apparatus, if testing is regularly to be carried out it is necessary to provide an external source of oxygen, additional valves and the like, and/or external testing equipment which, particularly where the system is applicable to an aircraft, undesirably adds weight.
According to a first aspect of the invention we provide a method of testing the performance of an oxygen supply system in an aircraft comprising an oxygen supply device adapted to supply oxygen in varying concentrations within a product gas in accordance with demand, in response to control signals, a monitoring means to monitor the concentration or partial pressure of oxygen in the product gas, and a control means responsive to the monitoring means to provide the control signals to the oxygen supply device, the method being characterised in that the control means provides a predetermined control signal to the oxygen supply device which is expected to respond to supply a known concentration or partial pressure of oxygen in the product gas, and monitoring the concentration of oxygen supplied.
Thus by utilising the method of the invention, performance of the oxygen supply system in response to the control signal can be tested without requiring any substantial extra apparatus or components and thus weight. Simply, the control means can be modified to provide the predetermined control signal to the oxygen supply device when testing of the system is required.
Although the invention is applicable to an oxygen supply system in which the oxygen supply device actually generates oxygen, e.g. a ceramic type oxygen generator, the oxygen supply device preferably comprises an oxygen concentrator adapted, in response to control signals, to separate from a gas stream e.g. ambient air, oxygen and thus to increase the concentration or partial pressure of the oxygen in the product gas stream.
The control means may be adapted in normal use of the system, to provide a control signal to the oxygen supply device in response to the monitoring means and in response to control data, the control signal being determined by the control means to cause the oxygen supply device to supply oxygen at a concentration or partial pressure in the product gas appropriate to a demand for the oxygen indicated by the control data.
Thus for example only, the control data may contain information concerning the altitude of the aircraft as well as the demand for the oxygen determined by a breathing regulator which supplies breathing gas to an air crew member. However the control data may contain other information pertinent to the demand for the oxygen.
The predetermined control signal provided to the oxygen supply device during testing may be such that the oxygen supply device is expected to supply a maximum or minimum concentration or partial pressure of oxygen in the product gas which the oxygen supply device is capable of supplying.
Thus, the oxygen concentrating device may be arranged simply to allow ambient air to pass through the device without separating out oxygen so that the concentration of oxygen in the product gas would be that naturally occurring in the air, i.e. about 21%. Alternatively, the predetermined control signal be that which is expected to result in the oxygen concentrating device providing product gas containing the maximum possible concentration or partial pressure of oxygen, which in a zeolite based pressure swing system would typically be about 95% oxygen.
The method may include first providing a control signal so as to achieve a minimum concentration of oxygen in the product gas, and then providing a control signal to the oxygen supply device which is expected to achieve a maximum concentration of oxygen in the product gas.
Of course the invention is also applicable to other oxygen concentrating devices such as, for examples other pressure swing systems, or thermal swing systems, or electrolytic systems.
In the event that the concentration or partial pressure of oxygen in the product gas in response to the predetermined control signal is found not to be as expected, the control means may be arranged either simply to provide an error signal to an indicating means such as an alarm or monitoring gauge, or alternatively the control means may be arranged to recalibrate the system such that in subsequent normal use the oxygen supply device supplies in the product gas stream a desired concentration or partial pressure of oxygen in response to control data indicating oxygen demand.
The method of testing in accordance with the invention may be carried out at any desired time on the oxygen supply system but particularly, may be carried out at intervals during normal operation of the system and/or upon start-up of the system and/or upon shut down and/or by manual initiation.
Preferably the method is carried out before the aircraft takes off, or at least before the oxygen supply system is required to operate.
According to a second aspect of the invention we provide an oxygen supply system for an aircraft comprising an oxygen supply device adapted to supply oxygen in varying concentrations within a product gas stream in response to control signals, a monitoring means to monitor the concentration or partial pressure of oxygen in the product gas, and a control means responsive to the monitoring means to provide the control signals to the oxygen supply devi
Noonan Christopher Michael
Phillips Robert John
Lo Weilun
Marshall & Gerstein & Borun LLP
Normalair-Garrett (Holdings) Limited
Weiss, Jr. Joseph F.
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