Abstract:
A sensor and associated methods wherein a bolt or rod stem includes a flow path through and across the stem. A source of radiation within the stem is configured to direct radiation through the flow path and a detector subsystem in the stem is configured to detect radiation passing through the flow path. A head includes electrical conductors for the radiation source and detector subsystem resulting in a compact, inexpensive sensor.

Description:
GOVERNMENT RIGHTS 
     This invention was partially developed under U.S. Army SBIR Contract #W911 W6-06-0007-0002 “Integrated On-Line Monitor for HUMS”. The Government may have certain rights in the invention. 
    
    
     FIELD OF THE INVENTION 
     The subject invention relates, in one particular example, to infrared spectroscopy. 
     BACKGROUND OF THE INVENTION 
     Fluid used in machinery and the like (engines, compressors, hydraulic devices) can be monitored by infrared spectroscopy using known systems. In many cases, fluid is withdrawn from the machine and sent to a laboratory to determine the percentages of water, fuel, antifreeze, or the like in the fluid as a measure of machine health. 
     For in-situ systems, the fluid must be interrogated optically with at least the return radiation directed in some fashion to the infrared spectrometer. Generally, doing so involves using a waveguide (such as a fiber optic) to gather the radiation from the analysis cell, which resides within the fluid stream. See, for example, U.S. Pat. No. 5,170,056 incorporated herein by this reference. The analysis cell itself typically consists of either an attenuated total reflectance (ATR) element or a mirror coupled to the end of a fiber optic probe. Many such infrared spectroscopy systems for in-situ monitoring are complex and expensive. In place of a spectrometer-based system are systems such as in U.S. Pat. No. 8,213,006 (incorporated herein by this reference) where specific features of the fluid are desired and a filter or plurality of specially designed filters may be used to monitor such features. Such approaches may significantly decrease costs and increase optical throughput in systems where an entire infrared spectrum is not needed. 
     SUMMARY OF THE INVENTION 
     In one aspect, a compact infrared analyzer which can be screwed into a fluid bulkhead (e.g., gearbox, oil pan, or the like) is provided. Such an analyzer is designed to overcome issues associated with providing a sufficient and reproducible sampling path length of fluid as can be encountered with, for example, ATR cells. At the same time, it provides a passive, monolithic design which urges fluid into the key sampling path length. 
     Featured is a sensor comprising a bolt stem with a flow path through and across the stem. A source of radiation within the stem is configured to direct radiation through the flow path and a detector subsystem in the stem is configured to detect radiation passing through the flow path. A bolt head includes electrical conductors for the radiation source and detector subsystem. 
     In one example, the stem includes a threaded portion proximate the head. The flow path may include three spaced openings through a wall of the bolt stem. In one version, the bolt stem defines a first chamber on one side of the flow path including the source of radiation and a second chamber on an opposite side of the flow path including the detector subsystem. The first chamber can be sealed by a first window adjacent the flow path and the second chamber can be sealed by a second window adjacent the flow path. In one embodiment, the windows are zinc selenide windows. In another version, the sensor stem includes spaced prongs defining a flow path therebetween. The spaced prongs preferably define a narrower sampling gap with spaced windows on each side thereof. Further included may be optical elements positioned to direct infrared radiation from the source, through the windows, across the gap, and to the detector subsystem. 
     The infrared source is preferably a broadband infrared source with a parabolic reflector reflecting collimated radiation towards the flow path. Also, the detector subsystem preferably includes a plurality of infrared detectors such as thermopile or thermocouple devices with a tailored filter for each detector. Thus, the detector subsystem may be used to provide multiple fluid properties from a single sensor. 
     The bolt head may include a connector including pins for the electrical conductors. Further included may be an asset identification subsystem configured to provide an asset identifying signal to at least one said electrical conductor. In one example the asset identifying subsystem includes a memory. The detector subsystem may also include an electronic assembly in the stem. 
     Also featured is a sensor comprising a stem immersible in a fluid and including a gap defining a flow path, a source of radiation configured to direct radiation across the gap, and a detector subsystem configured to detect radiation passing through the gap. A head exterior to the fluid includes a connector with electrical conductors extending to the source and the detector subsystem. 
     In one example, the stem includes a first chamber within a stem wall on one side of the gap housing the source of radiation and a second chamber within the stem wall on an opposite side of the gap housing the detector subsystem. The flow path may include a plurality of circumferentially spaced openings through the stem wall. 
     An in-situ sensing method in accordance with the invention includes immersing a stem with a source of radiation and a detector subsystem therein within fluid behind a bulkhead, allowing fluid between the source of radiation and the detection subsystem, energizing the source of radiation, and processing signals output by the detector subsystem via a connector associated with a head outside the bulkhead. 
     Also featured is a sensing method comprising fabricating a bolt stem to include a flow path through and across the stem, disposing a source of radiation within the stem oriented to direct radiation through the flow path, positioning a detector subsystem in the stem to detect radiation from the source of radiation passing through the flow path, and processing signals from the detector subsystem. 
     Further featured is a method of manufacturing a sensor wherein a stem is partitioned to include a gap defining a flow path. A source of radiation is included within the stem to direct radiation across the gap. A detector subsystem within the stem detects radiation passing through the gap. There are conductors for energizing the source of radiation and processing signals from the detector subsystem. 
     The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which: 
         FIG. 1  is a schematic three dimensional view showing an example of a sensor in accordance with the invention; 
         FIG. 2  is a schematic exploded view showing the sensor of  FIG. 1  inserted into the oil pan of a machine; 
         FIG. 3  is a schematic cross-sectional view showing the primary components associated with the sensor or  FIG. 1 ; 
         FIG. 4  is a schematic partial cross-sectional view showing another embodiment of a sensor in accordance with the invention; 
         FIG. 5  is a schematic three dimensional view showing another embodiment of a sensor in accordance with an example of the invention; 
         FIG. 6  is a schematic view showing the distal stem end of the sensor of  FIG. 5 ; 
         FIG. 7  is an end view of the distal stem end of the sensor of  FIG. 5 ; and 
         FIG. 8  is a schematic cross-sectional view showing several of the primary components associated with the sensor configured in accordance with the design of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer. 
       FIG. 1  depicts a rod like sensor  10 , in one example, with bolt head  12  including an electrical connector  14  (e.g., a box mount 12-pin connector) and bolt stem  16  with three spaced chamfered elongate openings through the stem outer wall  18 . Two openings in the outer wall are shown at  20   a  and  20   b . The openings are preferably circumferentially spaced around the wall and define a flow path for the oil in a gap as discussed below. Stem  16  houses, inter alia, an infrared source on one side of the gap and a detector subsystem on the other side of the gap. The sensor bolt may include a threaded portion  80  proximate head  12 . 
     In  FIG. 2 , sensor bolt  10  has been inserted into oil pan  30  of machine  32 , (e.g., an internal combustion engine) such that the bolt stem is immersed in the oil carried by pan  30  and bolt head connector  14  is exterior to the pan bulkhead wall  34 . A cable  36  can be used to electrically connect sensor bolt  10  to analyzer  40 . 
     Bolt stem  16 ,  FIGS. 3-4  thus provides a fluid (e.g., oil) flow path through and across the stem by virtue of one or more openings  20   a ,  20   b , and the like defining a gap between interior sections of the stem. The interior of bolt stem  16  in this particular example is divided or partitioned into two sealed chambers  50   a  and  50   b  on opposite sides of the flow path gap. Each chamber is sealed via a stem outer wall  18  and a zinc selenide, quartz, or sapphire window adjacent the flow path gap. Behind one window in chamber  50   a  is broadband infrared source  60  (e.g., a filament) optionally also provided with a band pass filter, sapphire lens, and/or parabolic reflector  62 ,  FIG. 3  for directing radiation through the gap defining the flow path to detector subsystem  64  in chamber  50   b  on an opposite side of the flow path. Another window seals chamber  50   b  with respect to the gap. 
     Electrical conductor(s) such as at  72   a  electrically interconnect infrared source  60  to connector  14  and electrical conductors as shown as  72   b  electrically interconnect detector subsystem  64  with connector  14 . Other electrical conductors are possible. 
     Analyzer  40 ,  FIG. 2  can be configured to energize the infrared source and to process signals output by the detector subsystem. In one example, both the source and the detectors are housed in TO style (e.g., TO-5) electronic packages with leads connected to conductors  72  and the like which lead to the head connector. 
     The detector subsystem may include four thermopile detectors each including custom infrared filters designed for the specific infrared sensing application. The filters may be multi-layered dielectric thin film coatings on sapphire/silicon substrates which are glued in place one in front of each of the 4 individual detectors. The result, in one embodiment, is an un-cooled four-channel broadband detector configured to analyze wavelengths from 1 to 1,000 microns in a single device to, for example, detect the presence of water and antifreeze in motor oil. The thermocouples themselves may be coated with an ultra-broadband metallic black coating absorber material, or alternatively may be coated with absorbing material which is most sensitive in the wavelength region of interest for that particular detector/filter combination. One of the 4 detectors may be used for system reference and drift compensation. As such it may gather a relatively broadband of infrared radiation. The other 3 detectors may then be “zeroed” off this reference detector. 
     An electronic circuit board or other assembly  90  can be included in chamber  50   b  for circuitry and/or electronic chip sets for signal amplification and/or digitization. 
     Also, an electronic asset identification system can be included to report an identifying signal via the electrical conductors (e.g., pins) of connector  14  and cable  36 ,  FIG. 2  to analyzer  40 . An algorithmic approach allows sampling to be uniquely identified by an asset thus tying the science/chemistry directly to the asset. This software algorithm is associated with the asset. The analyzer may include a unique library which allows classification by application rather than the chemistry of the oil. 
     In this way, a certain model or version of the sensor bolt may be specifically configured to analyze engine oil for a particular type of engine. The sensor bolt reports its configuration to the analyzer which then applies the applicable algorithms for that type of engine end oil. These algorithms are designed to calculate a set of fluid-specific properties. A sensor bolt specifically tailored for hydraulic fluid for a specific hydraulic machine would report its configuration to the analyzer which would then run a different set of algorithms for that asset/machine and report the fluid properties water, oxidation, and incorrect fluid, for example. In this way, the analyzer automatically knows which algorithms to run in order to correctly report parts per million water, percentage soot, and the like. Various technologies can be associated with circuit board  90  to output an identifying signal including a memory chip (e.g., a RAM chip) containing identifying information which is polled by the analyzer, and simple microprocessor such as a 16-bit 8051-based system which is running a real-time operating system. The microprocessor reads the memory chip state and processes the signals emerging from the detectors according to this state. In general the processing is done with a unique algorithm set for each type of fluid analyzed. The chip will point to the correct algorithm, which are stored in processor memory. Such a system serves as the core of the analyzer. 
     The result is an inexpensive and less complex on-line sensor that employs non-dispersive infrared (NDIR) technology to provide quantitatively accurate fluid analysis results. The rugged immersions sensor package allows for “crevice” sampling of the fluid without the need for extraneous optical components to define or maintain the sample interaction length. The bolt form factor provides infrared sensing technology in a smaller, more rugged and lower cost package that can be easily installed and uninstalled from standard access ports. In some examples, the device is designed to detect fuel leaks, water, and glycol. The ultra-wide bandwidth detection subsystem from approximately 1-1000 microns in wavelength is accomplished in a single device. The steel rod or bolt may include ½ inch NPT mechanical interface that can be used as screw on and screw off for the sensor at an appropriate port where it is fully immersed in the fluid analyte. The bolt can be five inches long or less. The dimensions of the sampling gap can be based on sensitivity requirements and fluid flow parameters. In one example, the gap is 0.004″ wide. As shown in  FIG. 4 , stem  16  terminates in housing  90  which can be removed from the stem in order to insert infrared source  60 . Screw button head cap  92  is also included. 
     The infrared radiation must typically be driven through only a small width gap which may inhibit oil flow therethrough. In order to eliminate the need to prewet the sensor, sensor  10 ′,  FIGS. 5-8 , in another embodiment, includes stem  16 ′ extending from head  12 ′ with spaced distal prongs  102   a  and  102   b  defining a flow path therebetween. Windows  104   a  and  104   b  protrude into this flow path to provide the requisite small width and here small area sampling gap (e.g., 0.004″ wide) but the wide area flow path elsewhere is much larger and wider as shown in  FIG. 8  to allow fluid from different directions to easily flow within the flow path and be directed within the gap. 
     Here, the IR source directs infrared radiation through window  104   a  via optic(s) including, for example, mirror  106   a , through the oil in the sampling gap g, through window  104   b , and to detector  64 ′ via optics including, for example, mirror  106   b . The gap between the windows may only be 0.004″ wide but the interior spacing between the prongs elsewhere in the flow path is much larger (e.g., 0.25″) to promote fluid to flow into the spacing between the prongs and into the sampling gap g. 
     Thus, although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. 
     In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended. 
     Other embodiments will occur to those skilled in the art and are within the following claims.