Abstract:
A modular electrolytic sensor having the capability to be utilized with a variety of probe portions. A modular electrolytic sensor having a head assembly, a probe portion and a mounting member for removably attaching the probe portion to the head assembly.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to electrolytic sensors for determining the concentration of a constituent of a fluid stream.  
         BACKGROUND OF THE INVENTION  
         [0002]    Electrolytic sensors utilizing a solid electrolyte for measuring the concentration of a specific fluid, for example oxygen, within a sample fluid are known. Sensors may be used to measure, for example, the amount of oxygen in a furnace or other combustion chamber. It is often desirable, if not necessary, to insure that there is sufficient oxygen present within a chamber for combustion to progress. In some environments, for example, a reducing atmosphere, it may be necessary to measure and maintain the oxygen concentration in the range of parts per billion. Sensors are also used to determine the presence and/or concentration of noxious gases in enclosed environments, for example, in an underground storage tank.  
           [0003]    To ensure that a monitored sample fluid is representative of the fluid within the environment being monitored, sensors should be sufficiently elongated to avoid sampling stagnant fluid near the walls of the enclosure. Elongated probes having one or more sample fluid inlet  26  ports at the distal end of the probe have been used to ensure that a representative fluid sample is monitored.  
           [0004]    To clean and regenerate a sensor it can be removed from its service environment, disassembled and cleaned. This is a time consuming, labor intensive, and costly procedure. Additionally, a back-up sensor must be available during the period the sensor is being cleaned or there will be periods where no fluid monitoring occurs.  
           [0005]    Alternatively, methods for in-situ cleaning of contaminated surfaces of a sensor have been developed. In some environments, for example, in a combustion chamber, the sensor is subjected to a high temperature sample gas which has a low oxygen concentration. Thus, by supplying a burn-off gas to the surface of the sensor which has an oxygen concentration sufficient to support combustion, the residual film on the surface of the sensor can be ignited by the high temperature sample gas and/or sensor surfaces, and the residual film is burned off. While this burn-off procedure removes the residual film, it also requires filling the sensing area with an oxygen rich gas, and, following the burn-off procedure, the sensing area of the sensor is filled with the combustion gas produced during the burn-off procedure. Accurate monitoring of the sample gas cannot continue until the oxygen rich burn-off gas and the combustion gases produced during the burn-off procedure are removed from the sensing area.  
           [0006]    There are a wide variety of environments in which oxygen sensors must perform and survive. This necessitates a number of common configurations that are optimized for specific applications. For example, environments with temperatures in excess of 2200 F require a non-metallic outer sheath, which, in turn, necessitates a different sealing method at the probe flange. Similarly, probes that are exposed to rapidly varying temperatures must utilize components that are less susceptible to thermal shock.  
           [0007]    Traditionally, these optimized configurations have been achieved by designing an application-specific sensor from the “ground up.” For manufacturers, the utilization of several different designs leads to substantial stocks in order to meet customer demand and on-time delivery requirements. In addition, traditional oxygen sensor designs require special tools and training to assemble. This means that the manufacturer or a trained individual with special tools must perform any product refurbishment or repair.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention provides a modular electrolytic sensor having customer-replaceable components. For example, the modular approach of the present invention allows the same head assembly to be employed with any of a variety of probe portions and a variety of sensor elements included in such probe portions. The end-user may even change the probe portion or sensor elements therein using common, everyday tools. In addition, the sensors may be refurbished by the end-user simply by replacing the component needing repair or replacement (such as the internal sensor element).  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    While the specification concludes with the claims particularly pointing out and distinctly claiming the present invention, it is believed that the same will better be understood from the following description taken in conjunction with the accompanying drawings in which:  
         [0010]    [0010]FIG. 1 is a schematic, cross-sectional view of a modular sensor according to one embodiment of the present invention;  
         [0011]    [0011]FIG. 2 is a cross-sectional view of the outer sheath assembly employed in FIG. 1;  
         [0012]    [0012]FIG. 3 is a cross-sectional view of a bushing used in the modular sensor assembly of FIG. 1;  
         [0013]    [0013]FIG. 4 is an end view of the bushing of FIG. 3;  
         [0014]    [0014]FIG. 5 is a cross-sectioned view of a central mounting member used in FIG. 1;  
         [0015]    [0015]FIG. 6 is a side view of the central mounting member of FIG. 5;  
         [0016]    [0016]FIG. 7 is a schematic view depicting manipulation of pins  54 ;  
         [0017]    [0017]FIG. 8 is a schematic cross-sectional view of a modular sensor according to one embodiment of the present invention, wherein the internal sensor element and associated bushing in FIG. 1 have been replaced by an alternative sensor element and associated bushing;  
         [0018]    [0018]FIG. 9 is a cross-sectional view of a modular sensor according to one embodiment of the present invention wherein the probe portion has been replaced by another design;  
         [0019]    [0019]FIG. 10 is a schematic, cross-sectional view of the probe portion of the sensor assembly of FIG. 9.; and  
         [0020]    [0020]FIG. 11 is a side view of the connecting member used in the sensor assembly of FIG. 9.  
     
    
     DETAILED DESCRIPTION  
       [0021]    The modular sensor of the present invention allows multiple sensor functionalities to be realized with a small set of common components and a few components specific to the desired functionality, minimizing inventory needs for manufacturers. It is designed such that the sensor can be adequately serviced and rebuilt by the customer, providing a lower lifetime cost over replacement or return-to-factory refurbishment. In addition, the various sensor functionalities can be achieved by replacing only a subset of the components. This allows customers to optimize a sensor for a particular process without having to purchase an entirely new sensor. This modular design allows all of the most common optimizations to be obtained using a common core set of components with only a few that are specific to the application. Since the design is modular, a minimal stock is required to meet demand and delivery requirements.  
         [0022]    The modular design utilizes a simplified and modular parts scheme that allows the product to be assembled and disassembled with, for example, two adjustable wrenches and a flathead screwdriver. The simple nature of the design makes it possible for any minimally skilled user to repair or refurbish the product. The modular and simplified design also allows the user to modify the product so that it is optimized for a different environment than the one for which it was initially purchased. For example, if the user realizes that they now need the sensor to perform at temperatures in excess of 2200F, yet the current product they own has an alloy sheath that cannot survive at this temperature, they can simply replace the alloy sheath with a ceramic sheath. With traditional designs they would need to replace the entire product at a cost several times that of a sheath replacement.  
         [0023]    [0023]FIG. 1 is a schematic, cross-sectional view of a modular sensor  20  according to one embodiment of the present invention. Modular sensor  20  includes a head assembly  25  and a probe portion  30 . In the modular sensor assembles of the present invention, head assembly  25  may have the same configuration for a variety of types of sensors. In this manner, the same head assembly  25  may be used for a variety of sensor types.  
         [0024]    As noted in FIG. 1, head assembly  25  includes a reference air inlet through which reference air may pass and be directed into the interior of internal sensor element  33 . Head assembly  25  is also configured to have a common terminal block arrangement to which electrical leads from the probe portion may be attached. A thermocouple load assembly is also provided in head assembly  25 , as is known to those skilled in the art. In the embodiment shown, head assembly  25  has a 3-part design, however, this design is merely exemplary of one possible embodiment. In order to disassemble head assembly  25  from probe portion  30 , head assembly  25  is merely opened using common, everyday tools, since the head assembly may be assembled using, for example, threaded fasteners which may be removed using a screwdriver. Once head assembly  25  has been opened, the electrical leads from the probe portion are merely disconnected from the terminal block.  
         [0025]    As also seen in FIG. 1, the distal end of head assembly  25  includes a female threaded portion  27  which is configured to threadingly receive a male threaded portion of central mounting member  45 , as further described herein. In this manner, after the electrical leads have been disconnected from the terminal block in the head assemble, head assembly  25  may be detached from probe portion  30  using, for example, adjustable wrenches and the like.  
         [0026]    Probe portion  30  generally includes an internal sensor element  33 , an outer sheath  35 , a threaded cap  37  secured to the proximal end of outer sheath  35 , a bushing  50  secured to the proximal end of internal sensor element  33 , and a central mounting member  45  threadably attached to threaded cap  37  and configured to accommodate bushing  50  therein. In the embodiment of FIG. 1, internal sensor element  33  generally comprises a solid electrolyte, and is often referred to in the art as the “substrate.” Although not shown in FIG. 1, an internal electrode is located within the interior of internal sensor element  33 , along with a thermocouple, and a ceramic tube which accommodates the wires of the thermocouple and internal electrodes. As is known to those skilled in the art, during operation, reference air is provided to the interior of internal sensor element  33  for purposes of measuring the concentration of an analyte (such as oxygen) in a sample fluid. At its proximal end, internal sensor element  33  is secured within a central bore of a bushing element  50 , such as by means of cement or other suitable adhesive.  
         [0027]    Modular sensor  20  of FIG. 1 also includes a conductive outer sheath  35  which acts as the second electrode of the sensor. A conductive tip structure  36  is located within the distal end of outer sheath  35 , and is positioned so as to contact the distal end of internal sensor element  33  for purposes of electrical conduction. Tip structure  36  may have any of a variety of configurations designed to contact the distal end of internal sensor element  33 . In particular, the tip structure described in my copending patent application titled Sensor, filed on even date herewith and incorporated herein by reference, may be employed. One or more apertures  38  are also provided at or adjacent to the distal end of outer sheath  35 , as shown. Once again, apertures  38  may have any of a variety of number and configurations, and that shown is merely exemplary of one possible embodiment. In fact, one particular configuration for apertures  38  is described in my copending provisional patent application mentioned previously. Apertures  38  allow the sample fluid to pass therethrough for purposes of sensing the desired analyte.  
         [0028]    [0028]FIG. 2 is a schematic, cross sectional view of outer sheath  35 . Since outer sheath  35  is conductive, in the embodiment of FIG. 1 it acts as the second electrode for the sensor. Typically, outer sheath  35  will be grounded via head assembly  25  in order to act as the second electrode. As also depicted in FIG. 2, the proximal end of outer sheath is welded (or otherwise affixed) within threaded cap  37 , such as in a bore provided within the distal end of threaded cap  37 . A shoulder  41  may also be provided at the upper end of this bore in order to assist in alignment and placement of threaded cap  37  on the proximal end of outer sheath  35 . Threaded cap  37  also includes a central passageway  40  through which internal sensor element  33  may extend (as shown in FIG. 1). Threaded cap  37  also includes a threaded portion  39  configured such that threaded cap  37  (and hence outer sheath  35 ) may be threadably secured to central mounting member  45 , as shown in FIG. 1.  
         [0029]    [0029]FIG. 3 is a cross-sectional view of bushing  50  employed in the modular sensor shown in FIG. 1. Bushing  50  includes a central bore  51  extending inwardly away from its distal end, as shown. A shoulder  52  is provided at the upper end of bore  51 . Bore  51  is sized and configured to receive the proximal end of internal sensor element  33 , as seen in FIG. 1. Bore  51  may, in fact, be sized and configured for a particular type of internal sensor element  33  such that the proximal end of the sensor element will be snuggly received in bore  51 . In addition, cement or other type of adhesive may be used to secure the proximal end of internal sensor element  33  within bore  51 . Although bore  51  may be tailored for any of a variety of specific internal sensor element types and structures, the external configuration of bushing  50  may be the same regardless of the type of internal sensor elements employed. In this manner, the same central mounting member  45  may be used for a variety of internal sensor element types.  
         [0030]    Bushing  50  also includes an upper bore  53  which extends inwardly away from the proximal end of bushing  50  to lower bore  51 . Bore  53  is sized and configured to accommodate, for example, a ceramic tube carrying wires from the interior of internal sensor element  33 . Reference air is also provided to the interior of sensor element  33  via upper bore  53 .  
         [0031]    A pair of pins extend away from opposite sides of bushing  50 , as seen in FIG. 3. Pins  54  may be secured to bushing  50  by any of a variety of means, such as by threads provided on the ends of pins  54  which are received in threaded bores of bushing  50 . As further described below, pins  54  assist in the assembly of the modular sensor, and particularly prevent damage to the internal sensor element during assembly. Below pins  54 , a pair of circumferential groves  55  and  56  extend around the outer circumference of bushing  50 . Groves  55  and  56  are configured to receive O-rings  57  and  58 , respectively, as seen in FIG. 1. In this manner, bushing  50  may be sealingly positioned within the interior central mounting member  45 .  
         [0032]    As also seen in FIG. 3, a cut-away portion  59  is provided in one side of bushing  50 . Cut-away portion  59  is aligned with a passageway  60  which extends downwardly away from cut-away portion  59 , as shown. Cut-away portion  59  and passageway  60  provide a fluid channel through which a burn-off gas may be supplied to the annular space between internal sensor element  33  and outer sheath  35 . The purpose of the burn-off gas is further described in U.S. Pat. No. 5,851,369, which is incorporated herein by way of reference.  
         [0033]    [0033]FIG. 5 is a cross-sectional view of central mounting member  45  of the modular sensor assembly of FIG. 1. As best seen in the side view of FIG. 6, the exterior surface of central mounting member  45  may be hexagonal in shape, or other suitable shape, in order to facilitate assembly of the modular sensor using adjustable wrenches and the like. At its lower or distal end, central mounting member  45  has a threaded recess  65  which is sized and configured to threadably receive threaded portion  39  of threaded cap  37 . A cavity  36  is located immediately above threaded recess  65 , and is sized and configured to receive bushing  50  therein. An upper bore  67  extends upwardly away from cavity  66  to the upper or proximal end of central mounting member  45 . In this manner, the ceramic tube carrying wires and the like from internal sensor element  33  may pass through bore  67  into head assembly  25 . An aperture  68  is provided on one side of central mounting member  45 , and is located such that when bushing  50  is positioned within cavity  66 , aperture  68  will be aligned with cut-away portion  59  of bushing  50 . In this manner, burn-off gas may be supplied through aperture  68 .  
         [0034]    Slots  69  are provided on opposite sides of central mounting member  45 , and extend into cavity  66 . Slots  69  are located such that bushing  50  may be positioned within cavity  66 , with pins  54  extending through slots  69 , as shown in FIG. 1. It will be apparent that, during assembly, bushing  50  (with internal sensor element  33  secured thereto) must first be inserted into cavity  66  without pins  54  attached to bushing  50 . Once bushing  50  is in place, pins  54  may then be inserted through slots  69  and secured to bushing  50  (such as by threading into threaded bores provided on bushing  50 ). Thereafter, threaded cap  37  (with outer sheath  35  attached thereto) is threadably attached to central mounting member  45  by threadably engaging threads  39  on cap  37  within threaded recess  65  of central mounting member  45 . This completes the assembly of the probe portion of the modular sensor, and thereafter central mounting member  45  may be secured to head assembly  25 , such as by threadably engaging threads  71  within threaded portion  27  of head assembly  25 .  
         [0035]    In order to insure adequate electrical contact between internal sensor element  33  and tip structure  36  of outer sheath  35 , internal sensor element  33  may be spring biased against tip structure  36 . As shown in FIG. 1, this may be accomplished by positioning a spring  70  within cavity  66  of central mounting member  45 , immediately above bushing  50 . In this manner, spring  70  will engage the upper end of cavity  66  and the upper end surface of bushing  50 , thereby spring biasing bushing  50  and internal sensor element  33  downwardly toward tip structure  36 . Although it is possible that pins  54  and corresponding slot  69  on central mounting member  45  may be omitted and threaded cap  37  merely threaded into threaded recess  65  of central mounting member  45  in order to complete the assembly of probe portion  30 , assembling the modular sensor in this manner will cause the distal end of internal sensor element  33  to rub against tip structure  36  as the outer sheath is rotated. Such rubbing may damage the distal end of internal sensor element  33 . Therefore, pins  54  are utilized to retract internal sensor element  33  away from tip structure  36  when the outer sheath assembly is being attached to central mounting member  45 .  
         [0036]    As seen in FIGS. 5 and 6, slots  69  provided on opposite sides of central mounting member  45  each have a longitudinally-extending portion  75 . Since bushing  50  is spring biased downwardly towards tip structure  36 , pins  54  will normally be located at or near the lowermost portion of slots  69 . When pins  54  are in this position, internal sensing element  33  will be located at its lowermost position.  
         [0037]    In order to attach the outer sheath assembly (comprising outer sheath  35  and threaded cap  37 ) to the central mounting member  45 , it is desirable to retract internal sensor element  33  upwardly in order to prevent damage thereto. Therefore, pins  54  may be urged upwardly within slots  69  along longitudinally-extending portions  75 . By doing so, spring  70  will be compressed and internal sensor element  33  will be retracted upwardly. The outer sheath assembly may then be threaded into the distal end of central mounting member  45  without risk of damage to the distal end of distal end of internal sensor element  33 . Once the outer sheath assembly has been securely attached to central mounting member  45 , the pins may be slowly and carefully released, thereby causing internal sensor element  33  to be spring biased downwardly until the distal end of sensor element  33  contacts tip structure  36  (as seen in FIG. 1).  
         [0038]    In order to facilitate this assembly process, it may be desirable to provide a means for locking pins  54  in their upper (or retracted) position. Therefore, as seen in FIGS. 5 and 6, slots  69  each include a laterally-extending portion  76  which extends laterally away from longitudinally-extending portions  75 , optionally at a slight downward angle. It should also be noted from FIG. 6 that laterally-extending portions  76  located on opposite sides of central mounting member  45  extend laterally away from their respective longitudinally-extending portions  75  in the same direction. Thus, for example, when central mounting member  45  is orientated as shown in FIGS.  6 , laterally-extending portions  76  extend leftwardly away from longitudinally-extending portions  75 . In this manner, after pins  54  are retracted upwardly within longitudinally-extending portions  75  of slots  69 , pins  54  may be rotated with respect to central mounting member  45  into laterally-extending portions  76  of slot  69 . As shown in FIG. 6, pins  54  will remain within laterally-extending portions  76  due to spring  70  urging bushing  50  (and hence pins  54 ) downwardly against the lower surface of laterally-extending portions  76  of slot  69 . In this manner, pins  54 , and hence bushing  50  and internal sensor element  33 , may be locked into their retracted position in order to simplify the assembly process.  
         [0039]    As also seen in FIG. 6, a second laterally-extending portion  77  may also be provided adjacent the lower end of longitudinally-extending portions  75  of each slot  69 . In this manner, once the probe portion  30  has been assembled and pins  54  released to their downward position against or adjacent to the bottom edge of longitudinally-extending portions  75 , pins  54  may be rotated in either direction into second laterally-extending portions  77  in order to prevent inadvertent retraction of internal sensor element  33 .  
         [0040]    One of the advantages of the modular sensor according to various embodiments of the present invention is that certain components are common to a variety of types of sensors which may be employed. For example, FIG. 8 is a schematic, cross-sectional view of a modular sensor assembly employing an alternative type of internal sensor element. In this embodiment, internal sensor element  133  is slightly narrower than internal sensor element  33  of FIG. 1 and has a slightly different tip arrangement. Nevertheless, it is not only important to insure that the tip of internal sensor element  133  makes adequate electrical contact with tip structure  36 , but also that the tip of internal sensor  133  is not damaged during assembly. However, due to the modular configuration provided by the present invention, even though a different internal sensor element  133  is employed in FIG. 8, the outer sheath assembly (outer sheath  35  and threaded cap  37 ), central mounting member  45  and head assembly  25  are identical to that shown in FIG. 1. Modular sensor  120  in FIG. 8 does employ a modified bushing  150 , as compared to bushing  50  in FIG. 1, however the only modification is the size and configuration of internal bore  151  of bushing  150 . In particular, as noted in FIG. 8, bore  151  has a slightly smaller diameter (since internal sensor element  133  is slightly smaller), and has a modified length chosen to insure that the tip of sensor element  133  will be protected during assembly, and will make sufficient electrical contact with tip structure  36  after assembly.  
         [0041]    Therefore, for example, if the end user is currently employing the modular sensor  20  of FIG. 1 and desires to change the type of internal sensor element  33 , the end user merely rotatingly disengages threaded cap  37  from central mounting member  45 , and rotatingly disengages central mounting member  45  from head assembly  25 . A different sensor element (such as internal sensor element  133 ), together with the attached bushing (such as bushing  150 ) positioned within a new central mounting member  45 , are then used to reassemble the sensor in the manner described previously. In this manner, the end user may replace the internal sensor element with a new sensor element of their choosing, or may replace any of the other modular components (such as head assembly  25  and/or the outer sheath structure).  
         [0042]    Some types of electrolyte sensors, such as oxygen sensors utilized in high temperature environments (e.g. 2200-3000 F) do not use a conductive outer sheath as the second electrode because of the high temperature environment. However, the modular sensor system of the present invention may nevertheless be used for such applications. FIG. 9 is a cross-sectional schematic view of one such sensor having an internal sensor element  233  and an outer, protective ceramic sheath  235 . The second electrode may be provided, for example, by layers of painted platinum located within protective sheath  235 . In addition, one or more apertures (not shown) are provided in outer sheath  235  for passage of a fluid sample therethrough. It should be pointed out that the internal configuration of sensor element  233  and the related electrodes are well-known to those skilled in the art.  
         [0043]    As best seen in FIGS. 10 and 11, the upper end of ceramic sheath  235  is secured to a connection member  237 . By way of example, connection member  237  has a central bore into which the upper or proximal end of ceramic sheath  235  is inserted and cemented into place. An aperture  240  may be provided on connection member  237  such that cement (or other suitable adhesive) may be injected through aperture  240  in order to secure ceramic sheath  235  to connection member  237 .  
         [0044]    At its upper end, connection member  237  includes a threaded portion  239  which is configured for securing connection member  237 , and hence probe portion  230 , to a central mounting member  245  (see FIG. 9). As best seen in FIG. 9, central mounting member  245  includes a female threaded portion configured to receive threaded portion  239  of connection member  237  therein. At its proximal end, central mounting member  245  includes a threaded portion which is sized and configured to be threadingly received within threaded portion  27  of head assembly  25 . Since head assembly  25  includes a common terminal block arrangement suitable for a variety of types of sensors, as well as a commonly-configured reference air supply arrangement, probe portion  230  of the high-temperature variety may be employed with the same head assembly  25  as the previous sensor embodiments. Therefore, the end user may once again modify the sensor system, as desired, in order to provide the most suitable sensor arrangement for the particular application. In the past, such modifications could generally not be made and therefore the end user would be required to either purchase an entirely new sensor assembly or return the sensor to the manufacturer for appropriate modifications.