WO2009105627A1

WO2009105627A1 - Oxygen concentrator with temperature control

Info

Publication number: WO2009105627A1
Application number: PCT/US2009/034658
Authority: WO
Inventors: Michael P. Chekal; Dana G. Pelletier; Andrew M. Voto
Original assignee: Delphi Technologies, Inc.
Priority date: 2008-02-22
Filing date: 2009-02-20
Publication date: 2009-08-27

Abstract

A method of compensating for temperature changes in a portable oxygen concentrator is provided. It comprises controlling an output signal to at least one component of the portable oxygen concentrator. This is done by measuring a temperature within a housing of the portable oxygen concentrator and comparing the measured temperature with a predetermined threshold temperature. The output signal to at least one component is adjusted when the measured temperature at least exceeds the predetermined threshold temperature. In this manner, the oxygen concentrator is maintained in an operating condition below a selected temperature.

Description

OXYGEN CONCENTRATOR WITH TEMPERATURE CONTROL

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No.

61/066,664 filed February 22, 2008, the disclosure of which is incorporated by reference herein, in its entirety.

BACKGROUND OF THE INVENTION

[0002] A portable oxygen concentrating or generating system presents unique problems. It is intended to be easily moveable so that it can be easily carried about by a user, since the portability aspect of the invention improves the lifestyle of a person who requires oxygen. However, if the device is to be portable, it must be able to successfully function in significantly diverse environments, including temperature extremes. This is significantly different than typical non-portable oxygen concentrating systems, such as those used to fill oxygen tanks - where the only portable aspect is the tank itself. As such, a portable oxygen generating device must be capable of functioning in diverse environments and be relatively lightweight. A portable oxygen generating device must also be in a small package suitable for portability and it should control noise, since it will be contiguous with the patient or user of the device.

[0003] Oxygen generating systems are often used to produce an oxygen- enriched gas for a user. Oxygen generating systems typically include a gas fractionalization system configured to separate oxygen from other components, such as nitrogen, in a feed gas to produce the oxygen-enriched gas. The gas fractionalization system, for example, may include one or more sieve beds having a nitrogen-adsorption material disposed therein and configured to adsorb at least nitrogen from the feed gas. SUMMARY OF THE INVENTION

[0004] The present invention relates generally to a method of generating an oxygen-enriched gas for a user, and specifically methods to maintiain that function under diverse environmental conditions.

[0005] A method of compensating for temperature changes in a portable oxygen concentrator is provided. It comprises controlling an output signal to at least one component of the portable oxygen concentrator. This is done by measuring a temperature within a housing of the portable oxygen concentrator and comparing the measured temperature with a predetermined threshhold temperature. The output signal to at least one component is adjusted when the measured temperature at least exceeds the predetermined threshhold temperature. In this manner, the oxygen concentrator is maintained in an operating condition below a selected temperature.

[0006] An alternate method of compensating for temperature changes in a portable oxygen concentrator is also provided. It comprises providing at least one sieve bed and a compressor for pressurizing the at least one sieve bed and controlling an output signal to the compressor for driving said compressor. A target pressure is maintained in the at least one sieve bed. The method further includes measuring a temperature within a housing of the portable oxygen concentrator and comparing the measured temperature with a predetermined warning temperature. The target pressure in the sieve bed is adjusted by adjusting the output signal to reduce a drive speed of the compressor when the measured temperature at least exceeds the predetermined warning temperature.

[0007] A portable oxygen concentrator is provided. It comprises a housing, at least one sieve bed disposed within the housing and a controller disposed within the housing. At least one temperature monitoring device is also disposed within the housing and monitors a temperature within the housing of said oxygen concentrator. The temperature monitoring device produces a temperature related signal receivable by the controller. The controller uses the temperature related signal to determine a LCD contrast level, or fan speed or a compressor speed. [0008] These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

[0010] FIG. 1 is a schematic diagram of an oxygen generating system in accordance with the invention;

[0011] FIG. 2 is a block diagram showing one aspect of the invention;

[0012] FIG. 3 is a perspective view, partially in cut-away, of the oxygen concentrating device of the invention;

[0013] FIG. 4 is a block diagram showing another aspect of the invention; and

[0014] FIG. 5 is a block diagram showing yet another aspect of the invention.

DETAILED DESCRIPTION

[0015] Embodiments of the present disclosure include algorithms running on a controller and/or microprocessor for measuring temperature in an electronic device, specifically an oxygen concentrator, and utilizing temperature information to significantly improve the useability of the device.

[0016] Referring now to the drawings, where the invention will be described with reference to specific embodiments, without limiting same, and where like numerals, are use for like elements, an oxygen concentrator or oxygen system or device 10, suitable for use with embodiments of the invention, is shown in FIG. 1. Generally a nitrogen-adsorption process employed by the oxygen generating system may be a pressure swing adsorption (PSA) process or a vacuum pressure swing adsorption (VPSA) process, and such processes operate in repeating adsorption/desorption cycles.

[0017] The oxygen concentrator 10 of the present invention includes a housing 11 having an inlet 13 formed therein. The oxygen concentrator 10 is portable so that it can be easily carried about by a user. However, it will be appreciated that the present invention is suitable for any oxygen concentrator or oxygen generating device 10 , regardless of portability, where the features of the invention are useful or desired.

[0018] The inlet 13 is configured to receive a feed gas from the ambient atmosphere, the feed gas including at least oxygen and nitrogen. The oxygen concentrator also includes at least one sieve bed. In the example shown in FIG. 1 , the oxygen generating device 10 includes a first sieve bed 12 and a second sieve bed 14, each in selective fluid communication with the feed gas. In an embodiment, each of the first and second sieve beds 12, 14 are configured to selectively receive the feed gas during a predetermined supply period. The first and second sieve beds 12, 14 receives the feed gas via first and second supply conduits 16, 18, respectively.

[0019] The first and second supply conduits 16, 18 are generally operatively connected to respective first and second supply valves (or inlet valves) 20, 22. In a non- limiting example, the first and second supply valves 20, 22 are two-way valves. As provided above, the nitrogen-adsorption process employed by the oxygen generating device 10 operates via cycles, where one of the first or second sieve beds 12, 14 vents purge gas (i.e. nitrogen-enriched gas), while the other of the first or second sieve beds 12, 14 delivers oxygen-enriched gas to the user. During the next cycle, the functions of the respective sieve beds 12, 14 switch so that venting occurs from the sieve bed that previously was delivering oxygen-enriched gas, while oxygen enriched gas is delivered from the sieve bed that in the prior cycle was venting. Switching is accomplished by opening the respective feed gas supply valve 20, 22 while the other of the feed gas supply valves 20, 22 is closed. More specifically, when one of the first or second sieve beds 12, 14 is receiving the feed gas, the respective one of the first or second supply valves 20, 22 is in an open position. In this case, the feed gas is prevented from flowing to the other of the first or second sieve beds 12, 14. In an embodiment, the opening and/or closing of the first and second supply valves 20, 22 may be controlled with respect to timing of opening and/or closing and/or with respect to the sequence in which the first and second supply valves 20, 22 are opened and/or closed.

[0020] The feed gas is compressed via a compressor 24 prior to entering the first or second supply conduits 16, 18. In a non- limiting example, the compressor 24 is a scroll compressor. As shown in FIGS. 1 and 2, the compressor 24 includes a suction port 52 configured to draw in a stream of the feed gas from the inlet 13.

[0021] After receiving the compressed feed gas, the first and second sieve beds 12, 14 are each configured to separate at least most of the oxygen from the feed gas to produce the oxygen-enriched gas. In an embodiment, the first and second sieve beds 12, 14 each include the nitrogen-adsorption material (e.g., zeolite, other similar suitable materials, and/or the like) configured to adsorb at least nitrogen from the feed gas. As schematically shown in phantom in FIG. 1, the sieve beds 12, 14 are operatively disposed in the housing 11 that includes a sieve module 26.

[0022] In a non-limiting example, the oxygen-enriched gas generated via either the PSA or VPSA processes includes a gas product having an oxygen content ranging from about 70 vol% to about 100 vol% of the total gas product. In another non- limiting example, the oxygen-enriched gas has an oxygen content of at least 87 vol% of the total gas product.

[0023] A user conduit 28 having a user outlet 30 is an alternate selective fluid communication with the first and second sieve beds 12, 14. The user conduit 28 may be formed from any suitable material, e.g., at least partially from flexible plastic tubing. In an embodiment, the user conduit 28 is configured substantially in a "Y" shape. As such, the user conduit 28 may have a first conduit portion 28a and a second conduit portion 28b, which are in communication with the first sieve bed 12 and the second sieve bed 14, respectively, and merge together before reaching the user outlet 30. The user outlet 30 is an opening in the user conduit 28 configured to output the substantially oxygen-enriched gas for use by the patient. The user outlet 30 may additionally be configured with a nasal cannula, a respiratory mask, or any other suitable device (not shown), as desired.

[0024] In the embodiment shown in FIG. 1, the oxygen delivery device 10 also includes a sieve bed pressure sensor 37, 39 for the sieve beds 12, 14, respectively. A sieve bed temperature sensor 44 is configured to measure the temperature within housing 11 adjacent the first and second sieve beds 12, 14 during the PSA process. It will be appreciated that a single pressure sensor may also be used to measure the pressure of each of the sieve beds 12, 14. The device 10 further includes an ambient pressure sensor 45 and an ambient temperature sensor 47 to measure the pressure and temperature, respectively, of the ambient environment.

[0025] A motor 56 drives the components of the oxygen generating system 10 including the compressor 24, the sieve beds 12, 14, the controller 54, the valves 20, 22, 32, 34, 40, 42, and the sensors 37, 39, 44, 45, 47. The motor 56 is powered by a battery (not shown) located on the exterior of the housing 11. In a non-limiting example, motor 56 is a DC brushless, three-phase motor. Further, the system 10 includes a fan 58 configured to cool the compressor 24, the motor 56 and sieve beds 12, 14.

[0026] As shown in FIGS. 1 and 2, oxygen concentrator 10 further includes a liquid crystal display (LCD) panel 70, located on the exterior of housing 11. LCD display panel 70 provides basic information to the user, such as system status, flow rate, battery life and other useful information. Obviously, the LCD panel 70, may be configured to provide any information relevant to the user. An alarm 72 is also provided on housing 11. It is capable of being triggered by controller 54 to provide an audible or visual signal upon a fault condition, as will be further described below.

[0027] As shown in FIG. 1, at least the compressor 24, the motor 56, the fan

58, the LCD panel 70, the alarm 72, the first and second supply valves 20, 22, and the first and second patient (or user) delivery valves 32, 34 are controlled by the controller 54. The sieve bed pressure sensors 37, 39, the sieve bed temperature sensor 44, the ambient pressure sensor 45, and the ambient temperature sensor 47 measure parameters that are inputs to the controller 54. In a non-limiting example, the controller 54 is a microprocessor including a memory.

[0028] The first conduit portion 28a and the second conduit portion 28b may be configured with a first patient (or user) delivery valve 32 and a second patient (or user) delivery valve 34, respectively. In the embodiment shown, the first and the second user valves 32, 34 are configured as two-way valves. Thus, it is contemplated that when the oxygen-enriched gas is delivered from one of the first and second sieve beds 12, 14, to the user conduit 28, the respective one of the first or second user valves 32, 34 is open. When the respective one of the first or second user valves 32, 34 is open, the respective one of the first or second feed gas supply valves 20, 22 is closed.

[0029] The nitrogen-adsorption process selectively adsorbs at least nitrogen from the feed gas. Generally, the compressed feed gas is introduced into one of the first or the second sieve beds 12, 14, thereby pressurizing the respective first or second sieve bed 12, 14. Nitrogen and possibly other components present in the feed gas are adsorbed by the nitrogen-adsorption material disposed in the respective first or second sieve bed 12, 14 during an appropriate PSA/VPSA cycle. The pressure of respective first or second sieve beds 12, 14 is released based by opening one of valve 32 or 34 for a time to deliver a bolus mass of oxygen enriched gas to a patient or user, upon a suitable trigger. The trigger may simply be a predetermined amount of time, or detection upon reaching a predetermined target pressure, or detection of an inhalation, and/or another suitable trigger. At this point, the nitrogen-enriched gas (including any other adsorbed components) is also released from the respective first or second sieve bed 12, 14 and is vented out of the system 10 through a vent conduit for the respective first or second sieve bed 12, 14.

[0030] As shown in FIG. 1 , the nitrogen-enriched gas in the first sieve bed 12 is vented through the vent port/conduit 36 when a first vent valve 40 is open, and the nitrogen-enriched gas in the second sieve bed 14 is vented through the vent conduit 38 when a second vent valve 42 is open. It is to be understood that venting occurs after each oxygen delivery phase and after counterfilling, each described further hereinbelow. The gas not adsorbed by the nitrogen-adsorption material, the oxygen enriched gas is delivered to the patient/user through the user outlet 30.

[0031 ] Since a predetermined bolus mass of gas is delivered to the user, it is contemplated that at least a portion of the oxygen enriched gas will not be delivered to the user during or after the masked time to the user outlet 30. The first and second sieve beds 12, 14 are configured to transmit that "left-over" oxygen enriched gas, if any, to the other of the first or second sieve bed 12, 14. This also occurs after each respective oxygen delivery phase. The portion of the remaining oxygen-enriched gas is transmitted via a counterfϊll flow conduit 48. The transmission of the remaining portion of the oxygen-enriched gas from one of the first or second sieve beds 12, 14 to the other first or second sieve beds 12, 14 may be referred to as "counterfϊlling."

[0032] As shown in FIG. 1, the counterfϊll flow conduit 48 is configured with a counterfϊll flow valve 50. In a non-limiting example, the counterfϊll flow valve 50 is a two- way valve. The counterfϊll flow valve 50 is opened to allow the counterfϊlling of the respective first and second sieve beds 12, 14.

[0033] As will be described in more detail below and with reference to FIGS.

2-5, the controller 54 receives a measured temperature reading from temperature sensor 44 and/or ambient temperature sensor 47 and and uses these temperature variables to execute one or more algorithms for controlling various components and/or processes used in the oxygen concentrator 10.

[0034] Referring now to FIGS. 3 and 4, oxygen concentrator 10 includes an automatic contrast control feature for the LCD panel 70, based upon temperature feedback. LCD panel 70, like all LCD panels, requires contrast adjustment when a change in temperature occurs in order to remain readable over a large temperature range.

[0035] Many LCD panels employ a voltage-control input that allows the contrast to be adjusted manually by an external contrast control input, such as a knob on the exterior of the housing. In order to perform contrast adjustment automatically, the invention utilizes empirically derived temperature correlation data that relates temperature readings from temperature sensor 44 within housing 11, or alternately ambient temperature sensor 47, with that of LCD panel 70. This correlation, in combination with proper voltage-control relation formula, allows the algorithm within controller 54, schematically shown in FIG. 4, to control a pulse width modulated output to vary the voltage to the contrast control of the LCD panel 70. Thus, LCD panel 70 maintains proper contrast voltage over substantially the entire operating range of the oxygen concentrator 10. Adjustments to the contrast can be made as frequently as desired, or as often as the temperature within housing 11 determined by sensor 44, or the ambient temperature determined by temperature sensor 47, is sampled.

[0036] In the exemplary embodiment shown in FIG. 4, the LCD panel 70 contrast control 110 works in the following manner. The LCD panel temperature is measured every 10 milliseconds, as shown in block 112 and a filtered average is saved, as shown in block 114, by controller 54. While the controller 54 is not actively busy processing a high-priority task, the voltage control algorithm, shown in block 115 and detailed below, is applied to the pulse width modulation (PWM) output, seen as block 116 and the control signal is sent to the LCD panel control 117.

[0037] The voltage is varied digitally by using Pulse- Width Modulation

(PWM) in accordance with the following equations:

PWM = MAXPWM * V/VCC

Where V is the desired voltage to the display, VCC is the system voltage and MAXPWM is the maximum value to achieve the VCC equivalent voltage

V = (0.0074T + O.2539)/(R2/(R1 + R2))

Where; T = Temperature in degrees Celsius of display

(R2/(R1 + Pv2)) = resistor divider used to set contrast (in an exemplary embodiment Rl is 3400 and R2 is 620). [0038] Controller 54 is also capable of automatically controlling fan speed, as is illustrated in FIGS. 2 and 5. Many electronic devices utilize fan speed control based on temperature to minimize audible and electronic noise produced by the system when the temperature inside the device is low enough to not require the maximum amount of available air flow. In oxygen concentrator 10, allowing temperature to increase at startup generally allows the sieve bed material, for instance zeolite, to perform more effectively. Therefore, the automatic fan control scheme 120, shown in FIG. 5, keeps the speed of fan 58 at a low setting until a reading from temperature sensor 44 within housing 11 indicates the lower threshold temperature has been reached. Fan speed may then be increased linearly using Pulse Width Modulation control until reaching its maximum speed at or above an upper threshold temperature. Rapidly warming up the device also minimizes the possibility of condensing water inside the sieve beds 12, 14, which may generally cause degradation of the zeolite or other nitrogen-adsorbing material.

[0039] FIG. 5 shows an example of fan speed may be automatically controlled. At initialization, the fan 58 is set to a minimum speed to both minimize noise and allow sieve bed 12, 14 temperature to rise, as seen in block 121. Before the compressor 24 is started, the temperature sensor 44 is read and fan speed is set according to the temperature control loop 130, shown indiviudally in blocks 123 -128. While compressor 24 is running, the temperature sensor 44 is checked and fan speed is adjusted about every 10 seconds to about every 20 seconds, according to the control loop 130, as seen in block 122. As seen in block 123, if temperature sensor 44 fails to communicate or indicates an error, the alarm 72 (either audible or visual or both) is generated, at block 124a, and the fan is set to maximum speed, as also seen in block 124a. If temperature sensor 44 is >= 50 degrees C, the fan 58 is set to maximum speed, as shown in block 124b. As seen in block 125, fan speed is set to minimum speed, at block 127, when the temperature is at or below 25 degrees C to its fastest speed at 49 degrees C. Block 128, in conjunction with control loop 130, shows that an adjustment is made to fan speed in linear increments of about 4 PWM counts per rise/fall in degree reading. The fan is set to off while the device 10 is sleeping or off, as shown in blocks 132 and 133, even if external power is applied. [0040] In order to allow the oxygen concentrator device 10 to keep running under extreme environmental conditions, such as high temperature, the controller 54 contemplates a scheme in which the oxygen concentrator will continue to run, but under a reduced output of oxygen to the user. The LCD panel 70 can inform the user of any reduction in output, and the controller can automatically reset the device 10 to normal output if the temperature returns to normal conditions.

[0041] As seen in FIGS. 1 and 2, controller 54 obtains a temperature value from temperature sensor 44. The controller 54 will generate an alarm at a default value of 50 degrees Celsius, if it is unable to communicate with temperature sensor 44.

[0042] Temperature sensor 44 communicates with controller 54 approximately once per minute to check for a "warning temperature" condition. The "warning-temperature" threshold is generally a calibrateable value. In one exemplary embodiment contemplated by the invention, the warning temperature is about 63 degrees Celsius. If controller 54 determine that the "warning-temperature" condition is exceeded, contoller sends a signal to the drive of motor 56, which controls the drive speed of compressor 24. This causes the drive speed of compressor 24 to decrease by a factor that will result in reducing the target pressure within at least one sieve bed, and in the embodiment shown, sieve beds 12, 14, by about 2 psi. Controller 54 may also send a signal to alarm 72 to alert the user to the warning temperature and/or may provide a visual indication of the condition at LCD panel 70. The reduction in target pressure of sieve beds 12, 14 and reduction in the drive speed of compressor results in a reduction in temperature within housing 11.

[0043] Temperarture sensor 44 continues to check temperature within housing

11 at the same one minute frequency, once the the temperature within housing 11 has exceeded the "warning-temperature". At this point, temperature sensor 44 is checking for one of two conditions, either a "good temperature" condition or a "over-temperature" condition. In one exemplary embodiment, the good temperature condition is at about 58 degrees Celsius, but it is calibrateable, depending the compressor 24 and motor 56 components used in the device 10. When the signal from temperature sensor 44 indicates to controller 54 that the "good-temperature" threshold has been met or the temperature falls below the "good-temperature" threshold, contoller 54 will increase the drive of compressor 24, through motor 56, to a normal operating state, resulting in the target pressure of sieve beds 12, 14 increasing by about 2 psi to their normal value and clearing the "warning- temperature" alarm.

[0044] If, on the other hand, an "over-temperature" condition is reached, the device 10 begins to shut down. This results in the compressor 24, motor 56, fan 58 and asssociated valves being directed by a signal from controller 54 to turn off. The "over- temperature" threshold is generally a calibrateable value and set to a value that prevents permanent damage to device 10 or its components. In one exemplary emodiment, the over temperature condition is reached when temprature sensor 44 indicates to controller 54 that the interior of housing 11 within device 10 meets or exceeds about 70 degrees Celsius. Exceeding the "over-temperature" condition can also produce an alarm signal to alarm 72 and visual indication of the over termperature status to LCD panel 70.

[0045] While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description.

Claims

CLAIMSHaving thus described the invention, it is claimed:

1. A method of compensating for temperature changes in a portable oxygen concentrator comprising:

controlling an output signal to at least one component of said portable oxygen concentrator;

measuring a temperature within a housing of said portable oxygen concentrator;

comparing said measured temperature with a predetermined threshhold temperature;

adjusting said output signal to said at least one component of when said measured temperature at least exceeds said predetermined threshhold temperature; and

maintaining said oxygen concentrator in an operating condition below a selected temperature.

2. The method of claim 1, including adjusting said output signal to said at least one component when said measured temperature is less than said predetermined threshhold temperature.

3. The method of claim 1, wherein said adjusting said output signal to said at least one component includes adjusting a voltage supplied to said at least one component.

4. The method of claim 3, wherein said adjusting the voltage supplied to said at least one component is accomplished with pulse width modulation control.

5. The method of claim 4, including adjusting said pulse width modulation output in four pulse width modulation step increments in a selected temperature range.

6. The method of claim 5, wherein said selected temperarture range is between about 25 degrees Celsius and about 50 degrees Celsius.

7. The method of claim 1, wherein adjusting said output signal to said at least one component includes reducing a target pressure within at least one sieve bed within said housing.

8. The method of claim 7, wherein said at least one component includes a gas compressor for pressurizing gas within said at least one sieve bed.

9. The method of claim 7, wherein said target pressure is reduced by about 2 psi.

10. The method of claim 1, wherein said at least one component is at least one of a cooling fan, a liquid crystal display panel or a compressor.

11. The method of claim 1 , including producing an alarm if said measured temperature at least exceeds said predetermined threshhold temperature.

12. The method of claim 1, including comparing said measured temperature with said predetermined threshhold temperature at predetermined time intervals.

13. The method of claim 1, wherein said at least one component is a liquid crystal display panel on said housing and adjusting said output signal to said liquid crystal display (LCD) panel by pulse width modulation (PWM) according to the formula PWM = MAXPWM( V/VCC) where V is the desired voltage to said LCD panel, VCC is the oxygen concentrator system voltage and MAXPWM is the maximum vlaue to achieve the VCC equivalent voltage.

14. A method of compensating for temperature changes in a portable oxygen concentrator comprising:

providing at least one sieve bed and a compressor for pressurizing said at least one sieve bed;

controlling an output signal to said compressor for driving said compressor; maintaining a target pressure in said at least one sieve bed;

measuring a temperature within a housing of said portable oxygen concentrator;

comparing said measured temperature with a predetermined warning temperature; and

adjusting said target pressure in said sieve bed by adjusting said output signal to said compressor to reduce a drive speed of said compressor when said measured temperature at least exceeds said predetermined warning temperature.

15. The method of claim 14, including producing an alarm when said measure temperature exceeds said predetermined warning temperature.

16. The method of claim 14, including measuring said temperature within said housing at predetermined time intervals.

17. The method of claim 16, including adjusting said target pressure in said sieve bed by adjusting said output signal to increase said drive speed of said compressor when said measured temperature is less than said predetermined warning temperature.

18. The method of claim 14, including comparing said measured temperature with a predetermined over temperature threshold and shutting down said portable_oxygen concentrator when said over temperature threshold is exeeded.

19. A portable oxygen concentrator comprising:

a housing;

at least one sieve bed disposed within said housing;

a controller operatively disposed within the housing; at least one temperature monitoring device disposed within the housing and configured to monitor a temperature within said housing of said oxygen concentrator and produce a temperature related signal receivable by said controller; and

at least one LCD display operatively disposed on the housing, wherein the controller uses said temperature related signal to determine a preferred LCD contrast level, and said controller adjusts a LCD contrast level to cause said preferred LCD contrast level to be displayed.

20. A portable oxygen concentrator comprising:

a housing;

at least one heat generating component disposed within said housing;

at least one sieve bed disposed within said housing;

at least one gas compressor disposed within said housing and operatively connected to said at least one sieve bed;

at least one fan configured to move cooling air around said at least one heat generating component of said portable oxygen concentrator;

a controller disposed within said housing; and

at least one temperature monitoring device disposed within said housing and configured to monitor a temperature of said portable oxygen concentrator and produce a temperature related signal receivable by said controller, said controller controlling a speed of said fan to maintain the temperature within said housing within a desired range of temperatures and the controller increasing said speed of said fan when said temperature exceeds said desired range of temperatures.