Abstract:
A magnetic fluid rotary feedthrough has a multi-stage magnetic fluid rotary seal adapted to provide a magnetic fluid seal about a shaft for extending between a first environment and a second environment, one or more sensors integrally mounted within the magnetic fluid rotary feedthrough to sense one or more physical parameters of the multi-stage magnetic fluid rotary seal, signal processing electronics mounted to or incorporated in the magnetic fluid rotary feedthrough to receive one or more sensor output signals from the one or more sensors, to process the one or more sensor output signals and to output one or more electronic processing signals, and one or more output devices operatively connected to receive the one or more electronic processing signals from the signal processing electronics to indicate the condition of the multi-stage magnetic fluid rotary seal.

Description:
[0001]    This application claims the benefit of U.S. Provisional Pat. App. No. 61/159,458, filed Mar.12, 2009. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to the field of magnetic fluid seals. Particularly, the present invention relates to a multi-stage magnetic fluid seal assembly. More particularly, the present invention relates to magnetic fluid rotary feedthroughs. 
         [0004]    2. Description of the Prior Art 
         [0005]    Magnetic fluid feedthroughs have been developed for use in vacuum systems where they perform the function of providing a virtually hermetic rotating seal. These products rely on the entrapment of magnetic fluid and its ability to withstand a pressure differential when magnetically trapped. Vacuum feedthroughs are designed to withstand low pressures on the order of 1 to 2 atmospheres and are impervious to all gases. 
         [0006]    A conventional design of a magnetic fluid feedthrough is illustrated in  FIG. 1 . A magnetic fluid rotary feedthrough  10  typically has a housing  12  and a rotary shaft  14  that extends out of housing  12 . Shaft  14  is magnetically permeable and has two sets of stages or teeth  16 . Housing  12  is typical of a conventional feedthrough using a standard vacuum compatible flange  18  for mounting the rotary feedthrough  10  to a vacuum chamber. Shaft  14  is usually supported by a pair of bearings  20  that are disposed on either side of the magnetic fluid seal  22 . The magnetic fluid seal  22  consists of two stationary, magnetically-permeable elements  24 , which are referred to as pole-pieces. Pole-pieces  24  carry magnetic flux from a permanent magnet or magnets  26 , disposed between the pole-pieces  24 . The magnetic flux is concentrated at the shaft  14  by a series of stages or teeth  16  cut into shaft  14 . The shape of these stages or teeth  16  can be rectangular or triangular. Magnetic fluid or ferrofluid  28  is trapped within the concentrated magnetic flux and acts as “liquid o-rings” at stages  16 . Shaft  14  is rotated usually by an electric motor, which can be external or integrated into housing  12 . 
         [0007]    Magnetic fluids or ferrofluids are colloidal suspensions of magnetic particles in a continuous phase. Colloidal stability is achieved by the use of a suitable surfactant. The continuous phase is selected on the basis of the application and, for a vacuum application, this is an oil with a very low vapor pressure. The volume fraction of the magnetic particles is low, typically around 5-10%. However, owing to the surrounding surfactant layer, the effective volume fraction is significantly larger than the particle volume fraction. 
         [0008]    When magnetic fluid is trapped by magnetic forces, the liquid o-rings are able to resist an external pressure and therefore act as a seal. These seals are hermetic and, being non-contacting, do not produce contamination making them ideal for processes conducted within a vacuum chamber. The shaft is usually driven by a motor or some other means and rotary motion is transferred from the outside into the clean environment of the vacuum chamber. 
         [0009]    Such feedthroughs have been shown to successfully operate from a few revolutions per hour up to several tens of thousands of revolutions per minute. Pressure capability extends from ultra high vacuum to many tens of atmospheres. Leak rates are almost immeasurable at values of 1×10 −11  cc/sec or lower. Operating temperature vary from as low as −55° C. to +200° C. or even higher with suitable protective measures. 
         [0010]    Magnetic fluid or ferrofluid rotary feedthroughs are commonly used in vacuum systems where a hermetic, non-contaminating seal is required; systems typified by semiconductor, precision optics and solar cell manufacture. In all cases, these rotary feedthroughs are high precision components utilizing precision bearings and often including integrated motors and encoders. The systems they are typically used on are high value capital equipment and the expected uptime of the entire system can be as high as 99%. Many of these systems, particularly in the semiconductor environment, are operated under clean room conditions where entry by people is restricted. 
         [0011]    The maintenance of a good vacuum in the equipment is essential and the rotary vacuum feedthrough is regarded as an item of critical importance. While the reliability of these feedthroughs is excellent, there is still a need for preventative maintenance. There are circumstances such as over temperature or contamination where the integrity of the feedthrough can be compromised. 
         [0012]    In the case of solar cell manufacture where rotary vacuum feedthroughs are an integral part of the transportation mechanism and where there can be many hundred of such feedthroughs in operation on a single machine, it is often very difficult to identify one feedthrough in many where there is a problem with feedthrough integrity. This is particularly difficult in the case of an intermittent or sporadic fault. Often, the only evidence that a feedthrough is leaking is when atmospheric contamination of the product is observed rendering it unusable. Additionally, the offending rotary feedthrough needs locating and replacing, which is not a trivial exercise in a chamber that could be as much as 100 meters long with over 200 rotary feedthroughs. Once the offending feedthrough is located and replaced the chamber needs to be re-evacuated, a process that can take many days resulting in a loss of production. 
         [0013]    Therefore, what is needed is a rotary feedthrough that is more easily maintained. What is also needed is a rotary feedthrough that is more easily identified when the rotary feedthrough is about to fail. 
       SUMMARY OF THE INVENTION 
       [0014]    Magnetic fluid rotary feedthroughs are often seen as critical components in the equipment where they are used to maintain a dynamic rotary seal over extended periods of time and diverse operating conditions. Dynamic rotary vacuum sealing is a very difficult problem to solve particularly as any leak of atmospheric gases into the vacuum chamber can result in contamination of the product resulting in either loss of yield or complete ruination of the product. Consequently, magnetic fluid rotary feedthroughs have become the accepted standard and under normal operating conditions these feedthroughs are very reliable, operating successfully without servicing for many years. Indeed, it is the very reliability of these devices that leads users to assume that they will continue operating without attention indefinitely. However, it must be recognized that exposure of the magnetic fluid to a very high vacuum, particularly if the process is at a high temperature, can result in a slow and steady evaporation of the oil. The evaporation rate is mainly dependant on the level of the vacuum and the temperature, both of which tend to change over the operating life of the product. However, for high quality magnetic fluids, operating even at very high temperatures, the evaporation is at such an extremely low rate it takes place over many years. Therefore, it makes any decision of “if” and “when” to service the feedthrough particularly difficult to define. 
         [0015]    Feedthroughs, especially those operating at high speeds or high loads, are particularly demanding on the bearings. These demands are magnified as bearing lubricants that are compatible with vacuum operation are not particularly good compared to conventional bearing lubricants. Therefore, failure of the bearing within the vacuum environment is often observed while the bearing on the atmosphere side, often lubricated with a good quality conventional lubricant, remains in excellent condition. There is considerable supporting data to enable the prediction of bearing life using conventional lubricants and this enables preventative maintenance cycles to be accurately specified. There is little supporting data, however, on the demands of operating in a vacuum environment with relatively poor lubricants. The wide variation in life over diverse operating conditions coupled with the large error band on any supporting data makes the definition of a suitable maintenance schedule very difficult. 
         [0016]    For both of the above reasons, low evaporation rates and difficulty in defining bearing life, magnetic fluid feedthroughs are either replaced at unnecessarily short intervals or, alternatively, not replaced at all until they fail. Neither solution represents a satisfactory situation for a component often seen as having critical importance. It is advantageous to be able to monitor the condition of feedthroughs and signal their condition to operators or diagnostic equipment. 
         [0017]    Therefore, it is an object of the present invention to provide a rotary feedthrough that is capable of indicating the condition of the rotary feedthrough. It is another object of the present invention to provide a rotary feedthrough that is capable of indicating the condition of the rotary feedthrough to enable maintenance when required of the feedthrough at a scheduled shut down. It is a further object of the present invention to provide a rotary feedthrough with a means to easily identify a potentially failing rotary feedthrough among a plurality of rotary feedthroughs. It is still another object of the present invention to provide a rotary feedthrough that is capable of providing an advanced warning of a potential problem with the rotary feedthrough. It is yet another object of the present invention to enable identification of a problem feedthrough in a degraded condition operating amongst a plurality of feedthroughs. 
         [0018]    The present invention achieves these and other objectives by providing a magnetic fluid rotary feedthrough system with a combination of one or more integral sensors, signal processing electronics and one or more output devices or devices. 
         [0019]    In one embodiment, a magnetic fluid rotary feedthrough system includes a multi-stage magnetic fluid rotary seal adapted to provide a magnetic fluid seal about a shaft which extends between a first environment and a second environment, and a combination of one or more sensors, signal processing electronics and one or more output devices operatively connected to the signal processing electronics that work together to constantly monitor and indicate the condition of the multistage magnetic fluid seal. The one or more sensors are integrally mounted within the magnetic fluid rotary feedthrough to sense one or more physical parameters of the one or more components of the multi-stage magnetic fluid rotary seal. The one or more components include the pole piece, the magnet and the shaft. The signal processing electronics are mounted to or incorporated in the magnetic fluid rotary feedthrough. The signal processing electronics receive one or more sensor output signals from the one or more sensors, process the sensor output signals and outputs one or more electronic processing signals. The output device or devices receive the electronic processing signals from the signal processing electronics to indicate the condition of the multi-stage magnetic fluid seal. 
         [0020]    In another embodiment of the present invention, the one or more sensors include, but are not limited to, pressure sensors, temperature sensors, magnetic field sensors, vibration sensors, rotational speed sensors, acoustic wave sensors, torque sensors, chemical sensors, coolant flow rate sensors, coolant temperature sensors, and humidity sensors. The sensors may be contact or noncontact sensors. 
         [0021]    In yet another embodiment of the present invention, the one or more sensors may include two or more of the same sensors located in different locations within the feedthrough for measuring differential values for pressure, temperature, magnetic field strength, vibration, and acoustics. 
         [0022]    In a further embodiment of the present invention, the signal processing electronics transmits one or more sensor signals of the one or more integral sensors. 
         [0023]    In another embodiment of the present invention, the sensor signals and/or the electronic processing signals are digital signals, analog signals, or a combination of digital and analog signals. Optionally, the sensor signals and/or the electronic processing signals may be transmitted by directly electrically coupling the transmitting and receiving components or by wirelessly coupling the components. 
         [0024]    In still another embodiment of the present invention, the signal processing electronics contains a computational circuit for determining the rate of change over time of a measured physical parameter measured by the one or more sensors. 
         [0025]    In another embodiment, a temperature sensor is adapted to sense the temperature of one or more components of the multi-stage magnetic fluid rotary seal. 
         [0026]    These components include, but are not limited to, a pole piece, a magnet or the shaft. 
         [0027]    In still another embodiment of the present invention, there is a method of determining the condition of a magnetic fluid rotary feedthrough that includes incorporating a combination of one or more sensors integrally mounted in the magnetic fluid rotary feedthrough and signal processing electronics mounted on or in the magnetic fluid rotary feedthrough. The signal processing electronics are electrically coupled to the sensors for receiving and manipulating the sensor signals from the sensors. The method also provides for one or more output devices to be electrically coupled to the signal processing electronics for receiving one or more electronic processing signals from the signal processing electronics and to monitor the output device(s) to determine the condition of the magnetic fluid seal of the rotary feedthrough. 
         [0028]    In another embodiment of the present invention, there is a method to determine the condition of a magnetic fluid rotary seal that includes monitoring the output device(s) that displays various characteristics of the magnetic fluid seal as interpreted by the signal processing electronics of the sensor output signals of the one or more different, integrally-mounted sensors. The parameters being measured are either compared to a predetermined threshold value or, if two or more similar sensors are used, the difference in the measured parameters of the two or more similar sensors are compared to a predetermined threshold value. If the measured parameters are outside of the acceptable range (i.e. the measured parameter exceeds the threshold value(s)), the output device(s) issue a warning signal related to the condition of the magnetic fluid seal. 
         [0029]    In yet another embodiment of the present invention, there is a method of using two or more of the same sensor integrally mounted in different locations within a rotary feedthrough to provide a differential measurement when the seal is in a degraded condition. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  is a cross-sectional view of one embodiment of a prior art magnetic fluid rotary feedthrough showing the shaft, magnet, pole pieces, support bearings and magnetic fluid disposed in a housing. 
           [0031]      FIG. 2  is a partial cross-sectional view of one embodiment of the present invention showing a magnetic fluid rotary feedthrough with pressure and temperature sensors and an Ethernet connection. 
           [0032]      FIG. 3  is a simplified, side view of one embodiment of the present invention showing a magnetic fluid rotary seal containing at least two temperature sensors positioned on the pole pieces of the seal. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0033]    The preferred embodiment of the present invention is illustrated in  FIGS. 2-3 .  FIG. 2  shows one embodiment of a magnetic fluid rotary feedthrough  100  of the present invention in a partial cross-sectional view. Rotary feedthrough  100  includes a feedthrough housing  120  and a rotary shaft  140  that extends out of feedthrough housing  120 . Shaft  140  is magnetically permeable and has two sets of stages or teeth  146 . Housing  120  includes a vacuum compatible flange  180  for mounting the rotary feedthrough  100  to a vacuum chamber. Shaft  140  is typically supported by a pair of bearings  150  that are disposed on either side of the magnetic fluid seal  160 . The magnetic fluid seal  160  includes two stationary, magnetically-permeable elements  170 , which are referred to as pole-pieces. Pole-pieces  170  carry magnetic flux from a permanent magnet or magnets  172 , disposed between pole-pieces  170 . The magnetic flux is concentrated at shaft  140  by a series of stages or teeth  146  cut into shaft  140 . The shape of stages or teeth  160  may be rectangular, triangular, trapezoidal, angular, or any other shape or combinations of the various shapes and is not critical to the present invention. Magnetic fluid or ferrofluid  164  is trapped within the concentrated magnetic flux and acts as “liquid o-rings” at stages  146 . Shaft  140  is rotated usually by an electric motor, which can be external or integrated into feedthrough housing  120 . The unique feature of the present invention is the inclusion of a combination of one or more sensors, processing electronics and output devices in rotary feedthrough  100 . In one embodiment illustrated in  FIG. 2 , the combination is a feedthrough status monitor device  200 . 
         [0034]    Feedthrough status monitor device  200  includes a monitor housing  202  connected to feedthrough housing  120 , one or more sensors  210 , one or more output devices  220 , and processing electronics (not shown). One or more housing fasteners  204  secure monitor housing  202  to feedthrough housing  120 . The signal processing electronics are preferably housed within monitor housing  202  but could also be integral to feedthrough housing  120  or encased in a separate electronics housing. Each of the one or more sensors  210  is electrically coupled to the signal processing electronics. Signal processing electronics are also electrically coupled to the one or more output devices  220 . Sensors  210  monitor various predefined measurable values that reflect the condition of rotary feedthrough  100 . 
         [0035]    One monitoring method is that of monitoring the pressure between the pole pieces  170 , that is, in the magnet space  173 . In  FIG. 2 , such a pressure sensor  210   a  is shown. This is shown as a micro-electro-mechanical system (MEMS) sensor but any suitable conventional pressure sensing device can be employed, including a simple bellows operated switch. The advantage of a MEMS device is that it can be integrated within the housing  120  of rotary feedthrough  100  and, therefore, be protected from damage. Under normal operating conditions, the pressure in the magnet space  173  is approximately that of the external atmospheric pressure, which is about 1 bar. Due to unforeseen circumstances, however, if the pressure in the magnet space  173  decreases, the drop in pressure would be indicative of failure of the integrity of the ferrofluid seal stages  160   a  adjacent to the vacuum. In the embodiment shown if  FIG. 2 , vacuum would still be maintained across the ferrofluid seal  160  and the process would not be in jeopardy as there exists a second set of seal stages  160   b  on the other side of magnet  172  to maintain the vacuum. 
         [0036]    The signal from pressure sensor  210   a  would indicate that there has been a partial failure of the vacuum integrity and replacement of the feedthrough  100  at the next maintenance cycle is advisable. Although a signal has been activated, it is required to process this signal and alert operators or diagnostic equipment of the problem. The output device  220  can be visual such as, for example, a flashing LED  220   a  that alerts the operator. By having the signal in an electrical form, however, means that more sophisticated communication methods can be employed. Before detailing output devices it is necessary to highlight the options available as input devices or sensors  210 . 
         [0037]    Using of inter-pole-piece or magnet-space pressure sensor  210   a  has been discussed above. However, it can be appreciated that the measurement of pressure can be achieved at any position along the stages  160  such as between each stage or a collection of stages. In addition to the measurement of a simple pressure change, the rate of change of pressure can also be monitored. Whereas the straightforward monitoring of pressure gives a “yes” or “no” signal, rate of change of pressure provides an indication of the severity of the leak and the rate at which it is progressing. Such information, suitably processed, enables alerts to be ranked in terms of urgency. A rapid change of pressure rate would imply an urgent problem that requires immediate attention whereas a slow rate of change would indicate a less urgent problem. 
         [0038]    Another indicator of a potential problem is temperature. This can be measured on static elements, such as the pole pieces, with any of the range of temperature measurement sensors available, such as thermocouples, resistance thermometers or thermistors. A resistance thermometer  210   b  is shown in  FIG. 2  although the type and nature of the sensor is not important to the invention. What is important is the ability to measure conditions within a feedthrough, interpret those conditions and communicate that information. 
         [0039]    As with pressure measurements, the rate of change of temperature can also be monitored. Temperature measurements can also be made of either or both bearings  150 . 
         [0040]    Turning now to  FIG. 3 , there is illustrated a partial view of a rotary seal.  FIG. 3  is an example of one embodiment for measuring temperature differential using two temperature sensors. A shaft  140  is magnetically permeable and has two sets of circumferential stages or teeth  146  disposed around shaft  140 . Shaft  140  is typically supported by a pair of bearings  150  (not shown) that are disposed on either side of the magnetic fluid seal  160 . The magnetic fluid seal  160  includes two stationary, magnetically-permeable pole pieces  170 . Pole pieces  170  have a bore through which shaft  140  is disposed and typically include elastomeric O-rings  190  between the external surface of pole pieces  170  and the internal surface of a housing (not shown) containing the magnetic fluid seal. The size of the bore in pole pieces  170  is such that it creates a relatively small gap or space G between the circumferential stages  146  and the inside surface of the bore of pole pieces  170 . Pole-pieces  170  carry magnetic flux from a permanent magnet or magnets  172 , disposed between pole-pieces  170 . The magnetic flux is concentrated at shaft  140  by the series of stages or teeth  146  cut into shaft  140 . The shape of stages or teeth  160  may be rectangular, triangular, trapezoidal, angular, or any other shape or combinations of the various shapes and is not critical to the present invention. Magnetic fluid  164  is trapped within the concentrated magnetic flux and acts as “liquid o-rings” at stages  146 . A temperature sensor  310  is positioned on each pole piece  170 . 
         [0041]    Using two temperature sensors  310  provides a means for measuring the difference in temperature between each of the pole pieces  170 . This measurement of temperature differential between pole pieces  170  provides a better indicator of magnetic seal condition than a single temperature measurement of the magnetic seal. There are several advantages of using temperature differential measurements over single temperature measurements of a magnetic fluid seal. Using temperature differential measurements tends to null out external influences that can affect the interpretation of a temperature reading performed using a single temperature sensor. A magnetic fluid seal may experience evaporative losses of the magnetic fluid&#39;s base oil, lost stages caused by various factors including, but not limited to, stage blowouts, particulate contamination of the magnetic fluid, chemical contamination of the magnetic fluid, and the like. Any of these conditions degrades a pole piece sealing structure, which includes the pole piece, stage geometry and the magnetic fluid. Measuring the temperature difference between the pole pieces  170  magnifies these degradations since the rate of degradation is not instantaneous across the entire seal but progresses through the magnetic fluid seal over time. This is especially so since the magnetic fluid seal has one side exposed to the atmosphere and the other side exposed to the process environment. This means that as some stages degrade, the temperature of the pole piece aligned with the plurality of stages having the degraded stage(s) will change in operating temperature relative to the pole piece that does not have any degraded stages. The difference between the pole piece with the degraded stage(s) and the next pole piece without any degraded stages indicates the condition of the entire seal. 
         [0042]    Other options contemplated by the present invention to enhance the thermal differential include using different magnetic materials for magnet  172  having a lower thermal conductivity. The lower the thermal conductivity, the greater the differential in temperature between pole pieces  170 . For example, ferrite or ceramic ferrite at 2.9 W/mC would provide advantageous characteristics to the enhancing the thermal differential. Still another option contemplated by the present invention is the use of different magnetic fluids on either pole piece or using the same magnetic fluid but having different magnetization saturation for each pole piece or on some of the stages within the same pole piece. Yet another option contemplated by the present invention is the inclusion of relatively thin (&lt;1.0 mm thick) insulating shim or an insulating layer between the pole piece  170  and the magnet  172 . The shim and/or layer acts as a thermal break and reduces the heat transfer between the magnet  172  and pole piece  170  and again increasing the temperature differential. 
         [0043]    The magnets  172  used in feedthroughs  100  are of the Alnico type. However, there is more and more use of the so called rare earth magnets, which allow savings in space and cost. Unfortunately, such magnets have a lower maximum operating temperature and can be irreversibly de-magnetized if they are over heated. Therefore, some form of magnetic sensor, such as a Hall effect device, will allow monitoring of the magnets. 
         [0044]    It is in the nature of a magnetic fluid feedthrough  100 , especially at high speeds, that the heat generated in the sheared magnetic fluid  164  is transferred to either the stationary pole-piece  170  or the rotating shaft  140 . While it is relatively straightforward to remove the heat from pole-piece  170  by using liquid cooling (water is usually employed), removing heat from the rotating shaft  140  is not so simple. Accordingly, shaft  140  is often left un-cooled. A consequence of not cooling shaft  140  is that shaft  140  is often at a considerably higher temperature than pole-piece  170 . Where the process of shearing the fluid  164  is the source of the generated heat, temperature measurements of shaft  140  provide a much better approximation of the fluid temperature than measurements of pole-piece  170 . Ideally, measuring the magnetic fluid temperature within the gap between the rotating shaft and the stationary pole-piece is preferred. However, as this gap is quite small, typically 50-150 microns, this presents difficulties and therefore shaft temperature measurements are a viable alternative. The simplest way to measure the temperature of the rotating shaft  140  is to use an infra red detector. Again, as with measurements of the pole-piece temperature, measuring and monitoring rate of change of temperature may also be performed. 
         [0045]    As noted above, there are issues with the bearing lubricants used in vacuum processes. The degradation of this lubricant, which leads to premature bearing failure, is a potential problem. Condition monitoring of bearings  150  is a viable approach to indicate emerging potential problems. Bearing monitoring can be carried out readily in two possible ways: (1) monitoring the vibration spectrum of the bearings  150  using accelerometers and noting changes; and (2) acoustically using, for example, piezoelectric sensors mounted to the structure to monitor acoustic waves. All methods can be used to generate appropriate signals, suitably amplified, filtered and processed to signify changes in bearing condition. 
         [0046]    Most problems associated with deterioration in the condition of feedthrough  100  will manifest themselves in an increase in the torque required to rotate feedthrough  100 . As noted above, the surfactant layer means that magnetic fluids tend to be operated at a point on the “volume fraction versus viscosity” curve where small changes in volume fraction will result in significant increases in viscosity. Therefore, long term changes due to evaporation of oil in ferrofluid  164  leads to an increase in volume fraction and an increase in viscosity. This manifests itself as either a change in running torque and/or an increase in temperature of magnetic fluid  164 . These can be quite significant. Although less common, it is possible that liquid contamination, often from cleaning solvents used to prepare the vacuum chamber, can reduce the volume fraction resulting in a decrease in viscosity and reduction in torque. 
         [0047]    Similarly, any deterioration of the bearing  150 , either mechanical or lubricant deterioration, will result in a change in running torque and heat being generated. Consequently, integrated measurement of torque is a useful diagnostic tool especially combined with temperature measurements. The preferred sensors are contactless torque transducers that use surface acoustic wave technology, optical or strain gauge technology. Although the use of traditional torque measuring devices can be used, they require an element to be stationary making dynamic torque measurement a complex and expensive process. Finally, it is also noted that rotational speed sensors may also be integrated into feedthrough  100 . The data from these sensors can be used to derive the power taken to rotate feedthrough  100 . Another derived variable to assess the condition of feedthrough  100  is the rate of change of torque and/or power. 
         [0048]    Many feedthroughs used at high speed and/or high temperature are often cooled, usually using water. Therefore, one can use such derived variables as water flow rate, temperature, temperature rise, and rate of change of these variables as diagnostic tools. 
         [0049]    Water cooled feedthroughs  100  use static o-rings (not shown) on the pole-pieces  170  to seal against water. The pole pieces  170  are required to be magnetically permeable and the commonly used stainless steels, while reasonable against corrosion, do suffer more than the nonmagnetic ones. Therefore, by providing a moisture sensor, any water leaking across the o-rings can be detected. 
         [0050]    Not all magnetic fluid feedthroughs  100  are used in vacuum applications. Some are used in pressure applications where a gas or chemical needs to be hermetically contained as any leakage of the gas or chemical could have serious consequences. Typical applications are (1) sterilisers where there is an explosion risk or (2) drug processing equipment where there is a potentially fatal risk to operators should any of the drug escape. Embedding suitable sensors within the feedthrough  100  and linking them to the communication devices allows potentially dangerous leaks to be detected before there is a leak to the environment. 
         [0051]    Having identified the possible variables that can be measured within the feedthrough  100 , it becomes possible to incorporate suitable electronics to process these variables and derive much useful data. From speed measurements, the total number of revolutions can be evaluated. By integrating a timer, elapsed time and total running time can be evaluated. As noted above, from speed and torque, power can be calculated. 
         [0052]    Having derived these variables and processed them, it is necessary to communicate these externally. Three situations will be defined: 
         [0053]    1. Local, meaning any indicator that is local to the feedthrough  100 . Such indicators could be visual, e.g. LED&#39;s, shown as reference number  220   a  in  FIG. 2 , gauges, or audible devices such as sounders, buzzers or sirens. 
         [0054]    2. Remote, where the signal is transmitted, either in digital or analog form, away from the feedthrough  100  but remaining within the machine&#39;s or its operator&#39;s environment, its operating equipment or operating computer. 
         [0055]    3. Global, meaning where the signal is transmitted, either in digital or analog form, away from the feedthrough  100  and outside the immediate machine environment. Typically, this is envisaged as a network or field bus. Ethernet-based systems may incorporate a web server and other network services, including “phone-home” systems, e-mail systems and simple network management protocol systems. Field bus systems would contain a transceiver required for the relevant bus system. 
         [0056]    Remote or global signal transmission systems can also be effected by use of appropriate telemetry or wireless communication systems. Such systems are also contemplated by the present invention. 
         [0057]    When there is a need to power the integrated electronics, various sources may be used including either integral energy sources such as batteries, power generation either from the rotation or from heat using thermo-electric modules, or by systems that supply power as well as data connectivity for example the Power Over Ethernet (POE) system and other Power Derived from Signal Bus (“Parasitically Powered”) systems. 
         [0058]    There are many advantages of the present invention. These advantages include, but are not limited to, remote monitoring of the feedthrough, early warning of the condition of the rotary feedthrough to enable maintenance of the feedthrough at a scheduled shut down, advanced warning of a potential problem with a rotary feedthrough or identification of its location in a system with a plurality of feedthroughs, more cost effective maintenance of feedthroughs, and improved reliability of the processes that use feedthroughs. 
         [0059]    Although the preferred embodiments of the present invention have been described herein, the above description is merely illustrative. Further modification of the invention herein disclosed will occur to those skilled in the respective arts and all such modifications are deemed to be within the scope of the invention as defined by the appended claims.