Patent Application
20060249383
The present invention relates generally to a gas sensor assembly comprising a trace oxygen sensor. The gas sensor assembly may further comprise a sensor holder configured to removeably engage a connecting portion of the trace oxygen sensor.
a illustrates a cross-sectional view of a conventional oxygen sensor 5 such as, for example, a Teledyne Analytical Instruments' B-2C oxygen sensor sold by Teledyne Analytical Instruments, City of Industry, Calif. The sensor 5 may be used in a trace oxygen analyzer and capable of sensing oxygen concentrations in a range of 0-1 parts per million (ppm). As used herein, “trace oxygen analyzer” refers to an oxygen analyzer capable of measuring oxygen in concentrations from 0 to about 1,000 ppm. The sensor 5 includes a cathode 10 and an anode 15 sealed in a sensor housing 20 filled with appropriate electrolyte solution. The sensor housing 20 is designed to be received into a sensor canister 80, as discussed below in connection with
The sensor housing 20 includes a first end 25 defining a first opening 30 and a second end 35 defining a second opening 40. The first opening 30 receives an entering stream of gas to be sensed via a thin sensing membrane 45. As illustrated in
b illustrates the sensor 5 of
c illustrates the sensor 5 of
During operation, oxygen contained in the gas stream diffuses into the first opening 30 via the sensing membrane 45. Reduction of the oxygen at the cathode 10 causes a current signal to flow from the cathode 10 to the anode 15 through the sensing circuit connected to the metallic contact rings 70a-b. The magnitude of the current signal is proportional to the rate of oxygen reduction and is measured by the sensing circuit to generate an oxygen concentration output. Materials suitable for the cathode 10 and the anode 15, the composition of the electrolyte solution, and the electrochemical reactions that cause the current signal to flow are described in U.S. Pat. No. 6,524,740, which is incorporated herein it its entirety.
The use of the sensor canister 80 in conventional trace oxygen analyzers has traditionally been attributed to a need to prevent ingress of ambient oxygen through the sensor housing 20 and a need to provide thermal stability to the sensor 5 during its operation. Exposure of the sensor 5 to ambient oxygen and/or temperature fluctuations may reduce the accuracy of the oxygen concentration readings. These cited needs have typically dictated that the sensor canister 80 must entirely encapsulate the sensor 5 to prevent ingress of ambient oxygen and be of a mass sufficient for insulating the sensor 5 from temperature fluctuations. The material and labor costs necessary to fabricate a sensor canister 80 meeting these design criteria, however, is substantial and represents a considerable portion of the manufacturing cost of a conventional trace oxygen analyzer.
A conventional percent oxygen analyzer does not require a sensor canister 80 because slight ingress of ambient oxygen and temperature fluctuations do not significantly affect the accuracy of oxygen concentration readings at the percent level. Therefore, a connecting-type sensor holder is typically used in conventional percent oxygen analyzers. A connecting-type sensor holder connects with only a portion of a percent oxygen sensor and is not intended to encapsulate the sensor or provide thermal stability thereto. Thus, the connecting-type sensor holder requires substantially less material and labor to fabricate compared to that of the sensor canister 80. Despite its lower cost, the connecting-type sensor holder has heretofore not been used in trace oxygen analyzers, as it was believed to unacceptably reduce the accuracy of trace oxygen readings by increasing ambient oxygen ingress and decreasing thermal stability.
This application discloses a gas sensor assembly including a trace oxygen sensor. According to various embodiments, the sensor may include a sensor housing and a connecting portion attached to the sensor housing. The connecting portion may define a passageway for introducing a gas stream to the sensor housing.
According to other various embodiments, the sensor may include a sensor housing and a gas exposure housing encapsulating the sensor housing such that the gas exposure housing and the sensor housing define a circulation cavity therebetween. The sensor may further include a connecting portion attached to the gas exposure housing and defining a passageway for introducing a gas stream to the circulation cavity and to the sensor housing.
This application further discloses a trace oxygen analyzer including a trace oxygen sensor and a sensing circuit. According to various embodiments, the sensor may include a sensor housing, a connecting portion attached to the sensor housing and defining a passageway for introducing a gas stream to the sensor housing, and an electrical connector adapted for communicating a current signal from the sensor to a conductor pair attached to the electrical connector.
According to other various embodiments, the sensor of the trace oxygen analyzer may include a sensor housing and a gas exposure housing encapsulating the sensor housing such that the gas exposure housing and the sensor housing define a circulation cavity therebetween. The sensor may further include a connecting portion attached to the gas exposure housing and defining a passageway for introducing a gas stream to the circulation cavity and to the sensor housing. The sensor may still further include an electrical connector adapted for communicating a current signal from the sensor to a conductor pair attached to the electrical connector.
Unless otherwise indicated, all numbers expressing a size, quantity, and so forth used in the present specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, may inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
The reader will appreciate the foregoing details and advantages of the present invention, as well as others, upon consideration of the following detailed description of embodiments of the invention. The reader also may comprehend such additional details and advantages of the present invention upon making and/or using embodiments within the present invention.
Various embodiments of the invention will be described by way of example in conjunction with the following figures, wherein:
a illustrates a cross-sectional view of a conventional oxygen sensor;
b illustrates the sensor of
c illustrates the sensor of
a and 3b illustrate cross-sectional views of a gas sensor assembly, according to various embodiments;
a and 3b illustrate cross-sectional views of a gas sensor assembly 102, according to various embodiments. The sensor assembly 102 may comprise a trace oxygen sensor 105 having features and sensing capabilities identical those of the sensor 5 described above in connection with
In one embodiment, the connecting portion 115 may be attached to and extend outward from a first surface on the rim portion 75 of the sensor housing 20 in a perpendicular fashion and be centrally positioned relative to the external wall 55 of the sensor housing 20. According to various embodiments, the connecting portion 115 may have a cylindrical geometry and comprise generally coaxial internal and external walls 120, 125, respectively. The internal wall 120 of the connecting portion 115 may define a passageway 130 axially aligned with the first opening 30 of the sensor housing 20 for introducing a gas stream received therethrough into the first opening 30 via the sensing membrane 45. The passageway 130 may have a diameter equal to that of the recessed portion 50 such that a smooth transition is provided therebetween. According to various embodiments, the connecting portion 115 may comprise a first means 135 for engaging. As described below, the sensor holder 110 may comprise a second means 175 for removably engaging the first engagement means 135 of the connecting portion 115. The first engagement means 135 of the connecting portion 115 and the second engagement means 175 of the sensor holder 110 may be any known engagement means used to form a process connection, such as for example, threaded connections, flange connections, compression connections, adhesive connections, and “quick-connect” couplings. As shown in
According to various embodiments, the gasket 140 may extend from a second surface on the rim portion 75 of the sensor housing 20 and be centrally positioned relative to the external wall 55. The gasket 140 may be, for example, an O-ring gasket sized such that the external diameter of the connecting portion 115 may be coaxially received through an internal diameter defined by the gasket 140. The gasket 140 may be fabricated from any suitably pliable material, such as, for example, an elastomer material, for providing a gas-tight seal when compressed between two opposing surfaces. The gasket 140 may be retained on the rim portion 75 by frictional contact between the internal diameter of the gasket 140 and the external wall 125 of the connecting portion 115.
The electrical connector 145 may be mounted to the circuit board 65 and be any electrical connector suitable for communicating a current signal from the contact rings 70a-b of the trace oxygen sensor 105 to a conductor pair (not shown) attached thereto. The conductor pair may be connected to a sensing circuit (not shown). According to various embodiments, for example, the electrical connector 145 may be a female RJ-type electrical connector for receiving a corresponding male end of a two-conductor shielded cable connected to the sensing circuit. Examples of other suitable types of electrical connectors include coaxial electrical connectors, terminal block/strip electrical connectors, and banana plug electrical connectors.
According to various embodiments, the sensor holder 110 may have an open-ended cylindrical geometry and comprise generally coaxial internal and external walls 150, 155, respectively, and generally parallel internal and external bottom surfaces 160, 165, respectively. The sensor holder 110 may be fabricated from materials such as, for example, thermoplastic materials or metal, such as stainless steel. The internal wall 150 of the sensor holder 110 may define a cylindrically-shaped receiving portion 170 centrally positioned relative to the external wall 155. The sensor holder 110 may comprise a second means 175 for removably engaging the corresponding first engagement means 135 of the connecting portion 115 such that such the connecting portion 115 is received into the receiving portion 170. As noted above, the second engagement means 175 of the sensor holder 110 and the first engagement means 135 of the connecting portion 115 may be any known engagement means used for establishing a process connection, but may, as shown in
The sensor holder 110 may further comprise a gas supply inlet 185 for receiving a gas stream to be sensed into the sensor holder 110 and for introducing the received gas stream into the passageway 130 of the connecting portion 115 via the receiving portion 170. The sensor holder 110 may further comprise a gas supply outlet 190 for receiving the sensed gas stream from the passageway 130 of the connecting portion 115 via the receiving portion 170 and for exhausting the sensed gas stream out of the sensor holder 110. According to various embodiments, the gas supply inlet 185 and the gas supply outlet 190 may comprise passageways 195, 200, respectively, that connect corresponding apertures in the external wall 155 of the sensor holder 110 to the receiving portion 170. The passageways 195, 200 may be positioned between the internal and external bottom surfaces 160, 165 of the sensor holder 110 and connect to the receiving portion 170 through a common aperture 205 defined by the internal bottom surface 160.
As can be seen in the embodiments of
The gas exposure housing 215 may be attached to the sensor housing 20 of the trace oxygen sensor 210 and be of a size and geometry suitable for encapsulating the sensor housing 20 such that the gas exposure housing 215 and the sensor housing 20 define a circulation cavity 235 therebetween. According to various embodiments, the gas exposure housing 215 may have a geometry similar to, but larger than, that defined by the sensor housing 20 and positioned such that the circulation cavity 235 is symmetrically defined throughout. The gas exposure housing 215 may be fabricated from any resilient insulating material such as, for example, a thermoplastic material.
According to various embodiments, the gas exposure housing 215 may comprise an insulation jacket 237 for insulating the trace oxygen sensor 210 from external temperature fluctuations. As shown in
According to various embodiments, the connecting portion 220 may be identical to connecting portion 115 of the sensor 5 described above in terms of geometry, size, and features. For example, the connecting portion 220 may have a cylindrical geometry and comprise generally coaxial internal and external walls 240, 245, respectively. The connecting portion 220 may be centrally positioned on an external surface of the gas exposure housing 215 adjacent to the first end 25 and extend outward in a perpendicular fashion therefrom. The internal wall 240 of the connecting portion 220 may define a passageway 250 axially aligned with the first opening 30 and connected to the first opening 30 and circulation cavity 235 via an aperture 255 defined by the gas exposure housing 215. The connecting portion 220 may comprise a first engagement means 260 for removably engaging a second engagement means 175 of the sensor holder 110. The first and second engagement means 260, 175 may be any known engagement means that may be used to form a process connection. According to various embodiments, for example, the first engagement means 260 may be similar to that described above with respect to connecting portion 115.
According to various embodiments, the gasket 225 may be identical to the gasket 140 of the sensor 5 described above in terms of geometry, size, and features. The gasket 225 may be, for example, an O-ring gasket sized such that the external diameter of the connecting portion 220 may be coaxially received through an internal diameter defined by the gasket 225. The gasket 225 may be retained on an external surface of the gas exposure housing 215 adjacent to the first end 25 of the sensor housing 20 by frictional contact between the internal diameter of the gasket 225 and the external wall 245 of the connecting portion 220. The threaded portions 175, 260 may be sized such that their continual engagement causes the gasket 225 to be compressed between the external surface of the gas exposure housing 215 and the opposing rim portion 180 of the sensor holder 110 in a manner similar to that described in connection with
According to various embodiments, the electrical connector 230 may be any electrical connector suitable for communicating a current signal from the contact rings 70a-b of the trace oxygen sensor 210 to a conductor pair (not shown) attached thereto. For example, the electrical connector 230 may be a female RJ-type electrical connector for receiving a corresponding male end of a two-conductor shielded cable connected to a sensing circuit. Examples of other suitable types of electrical connectors include coaxial electrical connectors, terminal block/strip electrical connectors, and banana plug electrical connectors. The electrical connector 230 may be mounted on the external surface of the gas exposure housing 215 adjacent to the second end 35 thereof and electrically connected to the contact rings 70a-b via corresponding leads (not shown) that sealably enter the gas exposure housing 215.
During operation, a gas stream received into the sensor holder 110 through the gas supply inlet 185 may be introduced into the passageway 250 of the connecting portion 220 via aperture 255 and the receiving portion 170. From the passageway 250, a portion of the gas stream may be introduced into the first opening 30 via the sensing membrane 45. The remaining portion of the gas stream may be introduced into the circulation cavity 235 and circulated therethrough. Both portions of the gas stream may then be received into the gas supply outlet 190 via the passageway 250, and the receiving portion 170, and the aperture 255, whereupon the portions are exhausted from the sensor holder 110.
The insulative properties of the gas exposure housing 215 and the circulation of a portion of the gas stream through the circulation cavity 235 enhance the thermal stability of the trace oxygen sensor 210 and decrease the adverse effects of external temperature fluctuations upon its operation. Additionally, in the event that caustic electrolyte solution contained in the trace oxygen sensor 210 is leaked through the sensor housing 20 during handling or operation, the gas exposure housing 210 may serve to contain the leaked solution, thus reducing the risk of injury to personnel or damage to equipment.
As discussed above, the sensor assembly 102 may generate a current signal used to derive the concentration of oxygen contained in a sensed gas stream. The current signal may be communicated from the electrical connector 145 of the sensor assembly 102 to the sensing circuit 270 via the conductor pair 275. The conductor pair 275 may be, for example, a shielded conductor pair having an end configured for mating with the electrical connector 145.
The sensing circuit 270 may be any known sensing circuit typically used in trace oxygen analyzers for converting the current signal received from the sensor assembly 102 into an oxygen concentration output. According to various embodiments, the sensing circuit 270 may include one or more microprocessors, signal processors, power supplies, data input devices, and display devices for implementing the conversion and for outputting the corresponding result. Additionally, the sensing circuit 270 may include one or more outputs for controlling one or more solenoid-operated flow control valves. The flow control valves may be operated such that the sensed gas stream and zero and span calibration gas streams are introduced to the sensor assembly 102 in the appropriate manner.
The enclosure 280 may be any type of known enclosure suitable for housing the sensor assembly 102, sensing circuit 270, and cable 275 and for accommodating process lines and control valves necessary for the delivery and exhaust of the sensed and calibration gas streams. Although the sensor assembly 102 is shown in
As shown in
The above-described results obtained using the sensor assembly 102 in a trace oxygen analyzer are unexpected given the prevailing view among those skilled in the art that a sensor canister 80 is necessary in order to realize acceptable levels of thermal stability and ambient oxygen ingress in a trace oxygen analyzer comprising a conventional trace oxygen sensor.
Whereas particular embodiments of the invention have been described herein for the purpose of illustrating the invention and not for the purpose of limiting the same, it will be appreciated by those of ordinary skill in the art that numerous variations of the details, materials, configurations and arrangement of components may be made within the principle and scope of the invention without departing from the spirit of the invention. The preceding description, therefore, is not meant to limit the scope of the invention.
