Abstract:
A seal for preventing leakage of fluid from between a first member and a second member the second member is capable of moving toward and away from the first member, the seal is adapted for engaged contact with the first member and the second member so as to prevent leakage of fluid between the first member and the seal and between the second member and the seal, the seal being more easily deteriorated than the second member such that friction between the seal and the second member wears the seal faster than the second member, the seal being adapted to retain a fluid tight seal against the second member as long as the seal has not worn beyond a specified depth; and a conductor for placement about the second member, the conductor being attached to the seal at the specified depth so as to contact the second member when the seal has worn to the specified depth, such that the existence of electrical discontinuity between the conductor and the second member indicates that the seal requires replacement, the conductor is positionally associated to the seal such that wear of the seal corresponds with movement of the conductor toward the second member; and the electrical continuity indicates whether the seal requires replacement.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of my application Ser. No. 08/686,315, filed Jul. 25, 1996, and now U.S. Pat. No. 5,785,323, which is a continuation-in-part of my Ser. No. 08/114,507, filed Aug. 31, 1993, now U.S. Pat. No. 5,540,448, issued Jul. 30, 1996, entitled SEAL WITH ELECTRICAL CONDUCTOR WEAR INDICATOR, which in turn is a continuation-in-part of my Ser. No. 07/841,388, filed Feb. 25, 1992, now U.S. Pat. No. 5,246,235, issued Sep. 21, 1993, entitled SEAL WITH EMBEDDED WIRE. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to seals which are positioned against a moving surface, and more particularly to seals which prevent fluid, e.g. lubricant, leakage or passage between two surfaces. The seal includes a conductor, such as an optical or electrical conductor, for indicating that the body of the seal has undergone excessive wear or deterioration. The conductor is embedded within or attached to the body of the seal at a specified depth or location, namely the depth or extent of acceptable wear. The conductor may be an optical conductor, such as an optical fiber, or an electrical conductor, such as a wire or other means of conducting electricity. The continuity of the conductor can be checked to determine if the seal body has worn to the specified depth or been deteriorated beyond a specified extent. 
     Machinery often includes members which move with respect to each other. Bearings have long been used to facilitate such movement. Bearings are used to aid in transmitting forces from one member to another and to reduce friction. Rolling elements are often used in bearings to reduce friction, such as in ball bearings. Bearings often contain lubricant to reduce the friction created within the bearing. 
     Leakage of fluid from between mechanical parts has long been a problem. Contamination of the bearings or seals with foreign material such as dirt has also long been a problem. Both loss of fluid and contamination lead to increased friction and wear within the structure, damaging the structure and perhaps damaging the machinery. 
     Seals composed of a soft polymeric material are used with bearings to prevent lubricant leakage and contamination. The polymeric material contacts a moving surface in the bearing and provides a seal. Friction between the polymeric material and the moving surface gradually wears the surface of the polymeric material away. If the polymeric material becomes too worn, it will no longer form a tight seal against the moving surface, and fluid leakage from the bearing and contamination of the bearing again become problems. 
     In other instances metal or polymeric seals are placed between the moving parts. This arrangement is particularly useful when the movement is a reciprocal movement. Non-limiting illustrations of a reciprocating seal include a piston and cylinder structure, hatches, air locks, doors, covers, lids and caps. With regard to such seals as found in hatches, air locks, doors, covers, lids and caps, the interfitting members may be said to reciprocate with respect to each other, in the sense of opening and closing with regard to each other. However, when a seal is in fluid tight sealing relationship between such interfitting members, the seal may more properly be termed a static or stationary seal, since the interfitting members and the interposed seal are all stationary with regard to each other while the integrity of the sealing relationship is maintained. In certain types of members which are reciprocating with respect to each other, the seal may be made so that it always makes contact with the piston connecting rod and the connecting rod is electrically insulated from the piston barrel. Sealing integrity or effectiveness may also be compromised by cracking, breaking, loss of flexibility or deterioration due to such conditions as repeated flexing, bending and/or compression, or length of contact with various fluids or container contents. 
     Various methods have been developed to prevent or detect leakage past a seal. As shown in U.S. Pat. No. 4,761,023, one method involves monitoring the pressure of the fluid on the high pressure side of the seal, with a loss of pressure indicating leakage past the seal. Alternatively, as shown in U.S. Pat. No. 4,290,611, the fluid pressure on the low pressure side of the seal may be monitored, with an increase in pressure indicating fluid leakage. A third method, such as that shown in U.S. Pat. No. 4,178,133, uses colored fluid and visual monitoring of leakage past a seal. Still other methods involve manual maintenance procedures, wherein seals are inspected or replaced on a regular basis. 
     These various methods to prevent or detect leakage past a seal have not proven satisfactory due to a number of problems. A problem with monitoring fluid pressure is that it is only effective to detect leakage of the fluid. Often this is too late to prevent damage. It is desired that the seal be replaced before leakage has begun. Similarly, visual monitoring of fluid leakage can only indicate that leakage has begun, not that leakage is about to begin. A problem with manual inspection of a seal is that it requires an inspector who is not only trained but also diligent. Often seals are not inspected merely due to neglect or lack of diligence. Another problem with manual inspection is that it may require the machinery to be stopped during the inspection, which can be inconvenient. Scheduled seal replacement also has problems. Seals may wear more or less quickly depending on operating conditions, and scheduled seal replacement may occur too early (before the seal needs to be replaced) or too late (after the seal starts leaking). 
     An excellent solution to these problems has been provided by the inventions disclosed in my U.S. Pat. No. 5,540,448, issued Jul. 30, 1996, entitled SEAL WITH ELECTRICAL CONDUCTOR WEAR INDICATOR and in my U.S. Pat. No. 5,246,235, issued Sep. 21, 1993, entitled SEAL WITH EMBEDDED WIRE. The present invention is an improvement on my earlier disclosed seals and is particularly adapted to work with reciprocating surfaces which require a seal there between. Illustrative of such reciprocating surfaces are the piston and cylinder, hatches, air locks, doors, covers, lids, caps, etc. 
     SUMMARY OF THE INVENTION 
     The present invention provides a seal for recognizing excessive seal wear before fluid leakage occurs. The seal is placed between surfaces which may be moving or static with respect to each other and forms a seal with the moving surface or between the static surfaces to prevent fluid leakage. The seal includes a seal body and an optical or electrical conductor. The seal body is composed of a substance which allows it to make a seal with the adjacent surface. various conditions between the surface and the seal body cause gradual deterioration and/or wear of the seal body. For example, friction between a moving surface and the seal body may cause gradual wear of the seal body. Extended contact with a fluid or container contents may cause gradual deterioration or disintegration of the seal body. Aging of the seal material or repeated compression of the seal, as in continued forming and releasing of the seal, may cause gradual loss of resiliency, leading to cracking, breaking or splitting of the seal body. 
     The optical or electrical conductor may be embedded in the seal body, attached to the seal body or otherwise positioned so that deterioration of the seal body will gradually change the location of the conductor with respect to the adjacent surface or with respect to the surface of the seal body. Deterioration of the seal body to a specified depth can be detected by optical or electrical continuity of the conductor. An electrical conductor may contact the adjacent surface when deterioration of the seal body reaches a specified depth, with electrical continuity between the conductor and the adjacent surface indicating that the seal requires replacement. With an optical conductor attached to the seal, optical fibers will gradually be worn away as the seal wears. An optical sensor may be able to measure such parameters as wear, temperature or strain on the seal. Alternatively, the conductor may be positioned such that it is worn entirely through when the wear of the seal body reaches a specified depth, with loss of optical or electrical continuity through the conductor indicating that the seal requires replacement. 
     The present invention provides a simple, cost effective device and method to detect deterioration of a seal disposed between moving or reciprocating surfaces, avoiding the problems of previous devices. Because the device detects deterioration of the seal body rather than fluid leakage, the seal may be replaced prior to leakage. The problems associated with waiting until after leakage has begun before replacing the seal may be avoided. The seal may be replaced in a timely manner before leakage begins. Because the present invention is based on optical or electrical continuity, an optical or electrical signal circuit may easily be incorporated with the invention. The signal circuit may indicate to an operator when a seal needs to be replaced, and there is no problem with diligence on the part of an inspector. Because wear of the seal body may be determined without manual inspection, problems with training inspectors and with missed or failed inspections are avoided. There is also no need to stop the equipment or machinery just to check if the seal needs to be replaced. Because the present invention monitors the actual amount of deterioration on the seal body, there is no problem with early or late replacement of the seal based on a scheduled replacement program. Replacement of the seal of the present invention may be based on the actual life of the seal body in operation, not on an average seal body life. Seals may be replaced less often and cost is reduced. 
     The present invention provides a seal for preventing passage of a fluid between two members. The seal is in engaging contact with both members to prevent passage of fluid between the two members and the seal. The seal is adapted to retain a fluid tight seal with the members so long as the seal has not deteriorated beyond a specified degree. A conductor is placed around one of the members. The conductor serves to conduct a signal. The conductor is positioned with respect to the seal such that deterioration of the seal beyond a specified degree corresponds with signal discontinuity of the conductor. The signal discontinuity through the conductor indicates a requirement for replacement of the seal. The seal may be an electrical signal or an optical signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a cross-sectional side view of the seal in place, adjacent a bearing and around a reciprocating shaft. 
     FIG. 2 is an enlarged fragmentary side view of the seal of FIG.  1 . 
     FIG. 3 is a cross-sectional view taken along the line  3 — 3  in FIG.  2 . 
     FIG. 4 is an enlarged fragmentary side view of the seal of FIGS. 1-3, after the seal body has worn to the specified depth. 
     FIG. 5 is a cross-sectional view taken along the line  5 — 5  in FIG. 4, after the seal body has worn to the specified depth. 
     FIG. 6 shows a cross-sectional side view of an alternate embodiment of the seal in place, adjacent a bearing and around a shaft. 
     FIG. 7 is an enlarged fragmentary side view of the embodiment of the seal shown in FIG.  6 . 
     FIG. 8 is a cross-sectional side view of an alternate embodiment of the seal in place in a hatch. 
     FIG. 9 is a cross-sectional side view of an alternate embodiment of the seal in place in a door. 
     FIG. 10 is a cross-sectional side view of an alternate embodiment of the seal in place in a lid. 
     FIG. 11 is s cross-sectional side view of an embodiment of the seal in place in a piston and cylinder. 
     FIG. 12 is a perspective view of an embodiment of the seal with a PTF coating over the location of a conductor in position against a cylinder and a bearing. 
     FIG. 13 is schematic view of an embodiment of an interlocking arrangement of two sealing surfaces. 
     FIG. 14 is a perspective view of an embodiment of the seal provided with an optical fiber as an indicator of seal wear or deterioration. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows the seal  10  of the present invention in place, against a bearing  11  and around a shaft  12 . The shaft  12  may reciprocate as indicated by arrow  20 . The bearing  11  may have an inside race  13 , and outside race  14 , and a plurality of rolling elements, e.g. balls  15 . The inside race  13  may be movably engaged with the shaft  12 . In other words the shaft may reciprocate in said bearing. The outside race  14  and the seal  10  may be connected to a housing  16 . The bearing may be of spherical balls, as shown. 
     The seal  10  of the present invention includes a seal body  17  and an embedded conductor  18 . As shown in FIG. 1, the seal body  17  may press against the shaft  12 , forming a tight seal between the seal body  17  and the shaft  12 . Alternatively, the seal body  17  may press against the inside race  13 , forming a tight seal between the seal body  17  and the inside race  13 . The seal body  17  functions to prevent fluid leakage from the bearing  11 . 
     The seal body  17  may have a contact surface  19  defined as the surface which contacts the adjacent moving surface of the shaft  12  to form a tight seal. The seal body  17  may be composed of a polymeric material or other suitable substance and should be a dielectric or an electrical insulator. The material of the seal body  17  is softer than the shaft  12 , so that friction preferentially wears the seal body  17  rather than the shaft  12 . The contact surface  19  of the seal body  17  gradually wears away due to friction between the outer surface of the shaft  12  and the seal body  17 . 
     A conductor  18  may be embedded within the seal body  17  at a specified depth, as shown with reference to FIG.  2 . Alternatively, the conductor  18  may be attached to the outside of the seal body  17  at a specified depth. The seal body  17  may be initially formed such that the contact surface  19  has an interference fit with the outer surface of the shaft  12 . The portion of the seal body  17  forming the interference fit may be referred to as the wear lip. The specified depth at which the conductor  18  is embedded within or attached to the seal body  17  may be slightly less than the depth of seal wear which will cause the seal  10  to leak. For instance, the specified depth may be at 90% of the initial depth of the wear lip. In this case, if leakage of the seal  10  occurs when the wear lip is completely worn away, electrical continuity through the conductor would indicate when the seal is 90% worn toward leakage. Of course, the desired specified depth of the conductor  18  is dependant upon the particular application, and this example is not intended to limit the scope of the invention. 
     The conductor  18  may be composed of any material which conducts electricity, such as a metal wire or a carbon filament. Preferably, the conductor  18  may be formed of an electrically conductive polymer such as a conductive epoxy known as a polymer thick film (PTF). The PTF may contain a polymer base material and a fill material to provide electrical conductivity. The fill material in the PTF may be any material which will allow the PTF to conduct electricity upon curing, such as particles of iron, aluminum, copper, silver, gold, or carbon. The PTF material may exist in a liquid or paste form prior to curing into a solid. Alternatively, the PTF material may exist in a solid solder form which converts to a liquid form upon heating. PTF materials are currently used in the surface mount of miniaturized electronic products, such as microelectronic printed circuit boards. 
     The liquid or paste state of the PTF provides ease of workability and application to the polymer material of the seal body  17 , as well as reliable adherence to the seal body  17 . The PTF may be applied to the seal body  17  by brushing or by drawing a bead of PTF out of a syringe onto the surface of the seal body  17 . Alternatively, the PTF may be applied to the seal body  17  through screen printing, masking or stenciling. 
     The cured PTF may take on similar physical properties to the polymeric material of the seal body, including that the thick film application is softer than the shaft  12  so that friction preferentially wears the PTF application rather than the shaft  12 . Accordingly, the PTF may itself form part or all of the contact surface  19  at various depths of seal wear. 
     An example of a PTF material is PTEA400 manufactured by Pinnacle Technologies, Inc. of Mattawans, Pa. The PTEA400 material is an epoxy adhesive base filled with gold particles. Upon curing, the PTEA400 material has a volume resistivity of 0.002 ohm-cm. The consistency of the PTEA400 material before curing is a smooth thixotropic paste. Curing of the PTEA400 takes place in approximately two hours at 150° C. or other similar conditions. 
     While the conductor  18  may be attached to the outside of the seal body  17  and openly exposed, it is preferable to insulate the conductor  18  by the seal body  17  or by an insulation layer of a dielectric or electrically nonconductive material. The insulation layer helps to prevent accidental or premature shorting of the conductor  18  with the shaft  12  or other exposed surfaces. The insulation layer may be provided by a material which is applied in a liquid or paste form, which dries or cures into a solid material. Using an insulating material which is applied in a liquid form has advantages similar to those discussed above for PTF. The insulation layer may have similar physical properties to the polymeric material of the seal body, and the insulation layer may itself form part or all of the contact surface  19  at various depths of seal wear. An example of a material suitable for use as the insulation layer is LIQUID ELECTRICAL TAPE manufactured by Starbright of Fort Lauderdale, Fla. 
     The conductor  18  may have a contact portion  21  together with a first post  23  and a second post  24 , as can be seen with reference to FIG.  3 . The first post  23  and the second post  24  may extend outside the seal body  17  for connection to an exterior signal-type electrical circuit, shown schematically. The electrical circuit may signal to an operator that the seal  10  requires replacement either based on the absence of electrical continuity through the contact portion  21  between the first post  23  and the second post  24 , or based on the existence of electrical continuity between the conductor  18  and the shaft  12 . 
     Illustration of the seal  10  immediately after friction between the shaft  12  and the seal body  17  has worn the seal body  17  to the specified depth can be seen with reference to FIGS. 4 and 5. At this point, the contact portion  21  of the conductor  18  has worn completely through at point  22 , so that there no longer is electrical continuity between the first post  23  and the second post  24 . A suitable mechanism may be provided in the signal-type circuit to indicate lack of electrical continuity, such as an electromagnetically driven switch which actuates a warning light. Alternatively, a suitable mechanism such as an ohmmeter may monitor electrical resistance between the first post  23  and the second post  24 , with an increase in resistance as the conductor  18  begins to wear at point  22  indicating the need for seal replacement. 
     An alternate embodiment of the seal  10  wherein the conductor  18  has only contact portion  21  and a first post  23  is depicted in FIGS. 6 and 7. The contact portion  21  of the conductor  18  does not encircle the shaft  12  but merely ends at the specified depth. When wear of the seal body  17  reaches the specified depth, the contact portion  21  contacts the shaft  12 , creating electrical continuity between the conductor  18  and the shaft  12 . As shown in this alternate embodiment, the shaft  12  may reciprocate as indicated by arrow  26 . The shaft  12  may alternatively oscillate, changing direction of rotation, or otherwise move with respect to the seal  10 . The shaft  12  may ride on a bearing surface  25  of the housing  16 . A suitable meter may be provided in the signal-type circuit to read the presence of electrical continuity, such as an ohmmeter. 
     Operation of the Invention 
     Although operation of the present invention is apparent from the preceding description, it will be detailed hereinafter to provide a more complete understanding of the present invention. As the contact surface  19  of the seal body  17  wears away, the conductor  18  gradually moves closer and closer to the shaft  12 . As seal wear continues, the contact portion  21  of the conductor  18  contacts the shaft  12  and wears away along with the seal body  17 . The conductor  18  is embedded or attached at a specified depth such that the conductor  18  can wear entirely through before the seal  10  begins to leak. When the contact portion  21  of the conductor  18  is worn entirely through, as shown in FIGS. 4 and 5 at point  22 , there is no longer electrical continuity between the first post  23  and the second post  24 . This may indicate to an operator that the seal body  17  has worn to a point such that the seal  10  requires replacement. 
     ALTERNATE EMBODIMENTS 
     An alternate embodiment of the seal  110  wherein the seal is used in a hatch, such as are found, for example, in ships and airplanes can be seen in FIG.  8 . The seal  110  is disposed between the hatch lid  120   a  and the opening  120   b  defined in the hold of the ship. As has been mentioned above, the hatch lid  120   a  and the opening  120   b  may be said to reciprocate with respect to each other, in the sense of opening and closing with regard to each other. However, when a seal  110  is in fluid tight sealing relationship between the hatch lid  120   a  and the opening  120   b , the seal  110  may more properly be termed a static or stationary seal, since the hatch lid  120   a , the opening  120   b  and the interposed seal  110  remain stationary with regard to each other as long as seal integrity is maintained. 
     A conductor  118  may be embedded within the seal  110  at a specified depth. The seal  110  may be initially formed such that the contact surface  119  has an interference fit with the outer surface of the hatch lid  120   a . The portion of the seal  110  forming the interference fit may be referred to as the wear lip. The specified depth at which the conductor  118  is embedded within or attached to the seal  110  may be slightly less than the depth of seal wear which will cause the seal  110  to leak. The electrical conductor  118  may be embedded in the seal body, attached to the seal body or otherwise positioned so that wear of the seal body will gradually change the location of the conductor with respect to the adjacent surface. Wear of the seal body to a specified depth may be detected by electrical continuity of the conductor. The conductor  118  may be positioned such that it is worn entirely through when the wear of the seal body reaches a specified depth, with loss of electrical continuity through the conductor indicating that the seal requires replacement. A suitable meter may be provided in the signal-type circuit to read the presence of electrical continuity, such as an ohmmeter. 
     An alternate embodiment of the seal  210  in place in a door structure  231  is shown in the cross-sectional side view of FIG.  9 . The door structure  231  includes a door jam  232  and a pivotable door  233  such as might be used in a large commercial freezer. The seal  210  prevents movement of fluid between the door  233  and the door jam  232 . The door structure  231  is particularly useful in the environments where the room is first closed by the door, filed with a gas and then exhausted of the gas before opening the door. This is done for example in gaseous treatment of metals. The seal  210  may be mounted either on the door itself or on the sill surrounding the door. The door jam  232  and the pivotable door  233  may be said to reciprocate with respect to each other, in the sense of opening and closing with regard to each other. However, when the seal  210  is in fluid tight sealing relationship between the door jam  232  and the door  233 , the seal  210  may more properly be termed a static or stationary seal, since the door jam  232 , the door  233  and the interposed seal  210  are all stationary with regard to each other as long as the integrity of the sealing relationship is maintained. 
     A conductor  218  may be embedded within the seal  210  at a specified depth. The seal  210  may be initially formed such that the contact surface  219  has an interference fit with the outer surface of the door  220   a . The portion of the seal  210  forming the interference fit may be referred to as the wear lip. The specified depth at which the conductor  218  is embedded within or attached to the seal  210  may be slightly less than the depth of seal wear which will cause the seal  210  to leak. The electrical conductor  218  may be embedded in the seal body, attached to the seal or otherwise positioned so that wear of the seal will gradually change the location of the conductor with respect to the adjacent moving surface. Wear of the seal to a specified depth can be detected by electrical continuity of the conductor. The conductor  218  may be positioned such that it is worn entirely through when the wear of the seal body reaches a specified depth, with loss of electrical continuity through the conductor indicating that the seal requires replacement. A suitable meter may be provided in the signal-type circuit to read the presence of electrical continuity, such as an ohmmeter. 
     An alternate embodiment  310  of the seal in place in a lid structure such as a lid that is used in a vacuum pot or bottle  300  may be seen with reference to the cross-sectional side view of FIG.  10 . The lid structure  331  includes a lid  332  and a pot or bottle  333  such as might be used in a commercial laboratory. The seal  310  prevents movement of fluid between the bottle  333  and the lid  332 . The lid structure  331  is particularly useful in environments where the vacuum bottle is first closed by the lid and evacuated. Alternatively, the pot or bottle may be filled with a gas and then exhausted of the gas before opening the pot or bottle. This may be done for example in gaseous treatment of metals or chemicals. The seal  310  may be mounted either on the lid itself or on the rim surrounding the opening the bottle. The lid  332  and the bottle  333  may be said to reciprocate with respect to each other, in the sense of opening and closing with regard to each other. However, when a seal  310  is in fluid tight sealing relationship between the lid  332  and the bottle  333 , the seal  310  may more properly be termed a static or stationary seal, since the lid  332 , the bottle  333  and the interposed seal  310  are all stationary with regard to each other as long as the integrity of the sealing relationship is maintained. 
     A conductor  318  may be embedded within the seal  310  at a specified depth. The seal  310  may be initially formed such that the contact surface  319  has an interference fit with the outer surface of the bottle  320   a . The portion of the seal  310  forming the interference fit may be referred to as the wear lip. The specified depth at which the conductor  318  is embedded within or attached to the seal  310  may be slightly less than the depth of seal wear which will cause the seal  310  to leak. The electrical conductor  318  may be embedded in the seal body, attached to the seal or otherwise positioned so that wear of the seal will gradually change the location of the conductor with respect to the adjacent moving surface. Wear of the seal to a specified depth can be detected by electrical continuity of the conductor. The conductor  318  may be positioned such that it is worn entirely through when the wear of the seal body reaches a specified depth, with loss of electrical continuity through the conductor indicating that the seal requires replacement. A suitable meter may be provided in the signal-type circuit to read the presence of electrical continuity, such as an ohmmeter. 
     Another embodiment of the seal or seals  400  of this invention in place in a piston  402  and cylinder  404  is shown in the cross-sectional side view of FIG.  11 . The piston seal  400  illustrated is constructed so that the seal  400  always makes contact with the connecting rod  406  and the connecting rod  406  is insulated from the cylinder  404 . This may be done with an insulating bushing  408  on the connecting rod  406  or with an insulation seal  410  on the inner surface of the cylinder  404 . By monitoring a contact to the connecting rod  406  and one on the cylinder  404 , a closed circuit may be used to indicate piston seal  400  wear. The position of the conductor in the piston seal  400  is shown in FIG. 11, embedded within the seal  400  at a specified depth, as described above with reference to similar seals of this invention in FIGS. 1-10. FIG. 11 shows the seal  400  in place, around the piston  402  in contact with the connecting rod  406  and insulated from the cylinder  404 . The piston  402  may reciprocate as indicated by arrow  414 . The seal  400  includes a seal body  416  and an embedded conductor  409 . As shown in FIG. 14, the seal body  416  may press against the connecting rod  406  and the insulation seal  410  on the inner surface of the cylinder  404 , forming a fluid tight seal between the seal body  416 , the connecting rod  406  and the cylinder  404 . The seal body  416  functions to prevent,fluid leakage from one side of the piston  402  to the other within the cylinder  404  around the connecting rod  406 . 
     The seal body  416  may have a contact surface defined as the surface which contacts the connecting rod  406  to form a fluid tight seal. The seal body  416  may be composed of a polymeric material or other suitable substance and should be a dielectric or an electrical insulator. The material of the seal body  416  is softer than the connecting rod  406  so that friction preferentially wears the seal body  416  rather than the connecting rod  406 . The contact surface of the seal body  416  gradually wears away due to friction between the connecting rod  406  and the seal body  416 . The specified depth at which the conductor  409  is embedded within or attached to the seal  400  may be slightly less than the depth of seal wear which will cause the seal  400  to leak. The electrical conductor may be embedded in the seal body  416 , attached to the seal body  416  or otherwise positioned so that wear of the seal  400  will gradually change the location of the conductor with respect to the adjacent surface of the cylinder  404 . Wear of the seal  400  to a specified depth can be detected by electrical continuity of the conductor. The conductor may be positioned such that it is worn entirely through when the wear of the seal body  416  reaches a specified depth, exposing the conductor  409  to the cylinder  404  providing continuity from the connecting rod  406  to the cylinder  404  with electrical continuity through the conductor indicating that the seal  400  requires replacement. A suitable meter may be provided in the signal-type circuit to read the presence of electrical continuity, such as an ohmmeter. As described in detail above with reference to FIG. 2, the conductor may be composed of any material which conducts electricity, such as a metal wire or a carbon filament. Preferably, the conductor may be formed of an electrically conductive polymer, such as PTF. The process of applying PTF has been fully described above with reference to FIG.  2 . 
     In order to prevent arching or sparking through a bearing, thus ruining the bearing, it is necessary to continually ground or short a seal of the present invention. Such arching or sparking can occur in bearings, such as on generators and motors. As illustrated with reference to FIG. 12, this potential condition can be remedied according to the present invention by coating the entire sealing surface  528  of the seal  526  with an electrically conductive polymer, such as PTF. FIG. 12 shows a rod  520  supporting a hub  522 , a bearing  524  and a seal  526 , according to the present invention. The seal  526  forms an interference fit between the bearing  524  and an adjacent sealing surface (not shown). As seen in FIG. 12, the entire sealing surface  528  of the seal  526  which contacts the rod  520  may be coated with a layer of PTF. The process of applying PTF has been fully described above with reference to FIG.  2 . 
     An embodiment of the seal of this invention, which may be of particular value with regard to static seals, is described with reference to FIG.  13 . As described above, in seals such as found in interfitting members of hatches, air locks, doors, covers, lids, caps, and the like, when a seal is in fluid tight sealing relationship between such interfitting members, the seal may be termed a static or stationary seal, since the interfitting members and the interposed seal are all stationary with regard to each other while the integrity of the sealing relationship is maintained. The present static seal may be formed, for example, between a hatch door  610  and the structure  620  defining the hatch opening. The hatch door  610  includes a set of intermeshing and interlocking members  630 . The structure  620  includes a corresponding set of intermeshing and interlocking members  632 . As illustrated in FIG. 13, a sealing relationship according to this invention may be effected by interengaging the first and second sets of intermeshing and interlocking members  630 ,  632 , each of which may comprise plurality of such intermeshing, interlocking members  630 ,  632 , respectively. Members  630  may be embedded with or have applied thereto a first portion of a conductive circuit. Members  632  may be embedded with or have applied thereto a second portion of a conductive circuit. Interengaging members  630  and  632  may then operate to complete a conductive circuit throughout the sealing relationship, according to this invention. As illustrated in FIG. 13, the plurality of members  630  and  632 , respectively, are mirror images of each other, although other arrangements may operate equally as well, as long as they can effectively interengage to complete a conductive circuit. Thus, seal body  610  may be formed with a first set of members  430 , while the adjacent sealing surface  620  may be formed with a second set of members  432 , such that members  430  and  432  interengage each other is effecting a sealing relationship. Interengagement of members  630  and  632  thus ensures a secure fluid tight seal, while also providing a means of detecting that the sealing relationship is complete between the seal body  610  and the adjacent sealing surface  620 . Electrical conductivity throughout the sealing relationship indicates that all members  630  and  632  are securely interengaged, while an absence of such electrical conductivity indicates that a lack of seal integrity. This may indicate either that the seal needs to be more firmly engaged or that either the seal body or hatch  610  or the adjacent sealing surface  620  of the opening need to be replaced. As described above, a PTF circuit may be applied on the two sealing faces  630   a ,  632   a  in such a way that one side contacts the other as the faces  630   a ,  632   a  interengage. The design may be similar to a zipper, as shown in FIG. 13, although other interengaging configurations may work equally as well. 
     According to another embodiment of the present invention, an optical conductor, such as an optical fiber, may be embedded in or applied to a seal. Optical sensor technology may then be used in measurement of temperature, strain and wear of seals of this invention provided with optical fibers. 
     Optical sensors are available which cover the entire range of the spectrum, including both visible and invisible light, such as infrared (IR). Non-contact temperature measurement and control may be effected by coupling optical fibers to IR detectors and signal processing electronics. As well known in the industry, fibers used in IR transmission may be made of glass or other suitable materials selected to transmit radiation of the spectral region of interest. If optical fibers expand thermally or become physically strained, this can easily be determined by appropriate optical sensors. With multiplexing, a number of sensors on different light wavelengths may be able to input to a single signal processor, and a number of parameters or variables may be monitored simultaneously. Signal processing may correlate strain or thermal expansion with wavelength shift. These properties of optical fibers are applied to the sealing relationship of the present invention. 
     An optical conductor, such as an optical fiber  740 , may be embedded in or applied onto the sealing surface  742  of a seal body  744  of the present invention, as illustrated with reference to FIG. 14, in the same manner as has been described herein above with regard to the electrical conductor. The optical fiber  740  may be embedded within the seal body  744  at a specified depth. Alternatively, the optical fiber  740  may be attached to the outside of the seal body  744  at a specified depth. FIG. 14, shows a rod  746  supporting a hub  748 , a bearing  750  and a seal  752  provided with an optical fiber  740 , according to the present invention. The seal  752  forms an interference fit between the bearing  750  and an adjacent sealing surface (not shown). The portion of the seal body  744  forming the interference fit may be referred to as the wear lip. The specified depth at which the optical fiber  740  is embedded within or attached to the seal body  744  may be slightly less than the depth of seal wear which will cause the seal  752  to leak. For instance, the specified depth may be at a certain percentage of the initial depth of the wear lip, such as, for example, 90%. In this case, if leakage of the seal  752  occurs when the wear lip is completely worn away, optical continuity through the optical fiber  440  would indicate when the seal  752  is 90% worn toward leakage. Of course, the desired specified depth of the optical fiber  440  is dependant upon the particular application, and this example is not intended to limit the scope of the invention. Similarly, a seal in association with an optical fiber according to this invention need not be limited to the specific type of seal or sealing relationship illustrated in FIG.  14 . Thus, a seal associated with an optical fiber may also be suitable for use in connection with other types of moving, sliding or reciprocating seals or with other types of stationary or static seals as described herein. 
     The optical fiber  740  may be attached to the seal  752 . As the layers of slightly denser fiber  740  are worn away, the exact rate of wear of the seal  752  may be monitored. If the fiber  740  expands thermally or becomes strained, the resultant change in optical activity may be measured. Signal processing may measure wear, temperature and strain. Suitable optical sensors for measuring changes in the optical fibers due to changes in temperature, strains and wear are commercially available. By measurement of changes in such parameters, the optimum time for replacement of seals can be readily determined. 
     According to another embodiment of this invention, polymer thin films, carrying embedded indicators sensitive to the presence of a certain chemical of interest, may be coated on a seal, to indicate exposure of the seal to that chemical. The embedded indicator may change to a distinct identifying color upon contact with the chemical of interest. Such a coating of indicator-embedded polymer thin films on a seal of this invention may be used to indicate not only exposure of the seal to a certain chemical, but also any possible deterioration or weakening of the seal due to such exposure. The polymer thin films which may be used for this purpose are commercially available. Suitable embedded indicators for this application are Polymer thin films with chemical sensitive embedded indicators admixed therein are available from Geo-Centers Inc., Newton Centre, Mass. Such seals may be useful, for example, in static seals as described above and with the seals described with regard to FIGS. 8-10. By shining an appropriate querying light on the seal coated with the indicator embedded polymer thin film, the color of the indicator may be used to measure exposure of the seal to the chemical, leaking of the chemical and wear or deterioration of the seal due to the action of the chemical. In a suitable querying light, the color of the embedded indicator may be transmitted by an optical fiber back to a signal processor. Such a querying light may use at least two light sources, one where the indicator shows the most change and one where it shows the least. Such a querying light is available from Geo-Centers Inc., Newton Centre, Mass., under the trade name “Optrode.”. Another suitable querying light may be a flashlight which illuminates using a light-emitting diode (LED) of a proper wave length, rather than an incandescent bulb. Such LED flashlights are available from LEDtronics, Inc., 4009 Pacific Coast Hwy., Torrance, Calif. 90505. Strain and temperature may also be measured in this manner. Temperature may be remotely measured using an IR thermometer. Target emissivity error may be eliminated by matching the emissivity of the embedded indicator in the polymer thin film and minimum, maximum or average temperatures may be measured. Suitable IR thermometers are the OS520 series handheld IR thermometers available from OMEGA Engineering. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be make in form and detail without departing from the spirit and scope of the invention.