Abstract:
The present invention&#39;s efficient and economical maintenance strategy for a system of operation (such as involving various kinds of instrumentation) features a unique decision-making logic that incorporates reliability-centered maintenance principles. The initial logical inquiry filters out the non-critical cases, i.e., those instruments the failure of which does not jeopardize or compromise safety, or the environment, or an important function or operation. The logical construct proceeds as to the remaining (unfiltered) instruments in a series of logical steps wherein the satisfaction of one or more given conditions by a subject instrument directs the practitioner to the appropriate maintenance action for the subject instrument. Possible maintenance actions include the following: comparison check of the instrument with respect to the primary instrument; system operational check; repair of the instrument; replacement of the instrument; maintenance deferral until a scheduled failure finding task; system calibration procedure; individual maintenance procedure (on-site or off-site).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application No. 60/558,899, filed 2 Apr. 2004, inventors Jeffrey T. Eker, Shawn A. Egnak, Charles L. Savage, Margaret A. Connolly and Vincent L. DiFilippo, invention entitled “Installed Instrumentation Maintenance Method,” incorporated herein by reference. 

   STATEMENT OF GOVERNMENT INTEREST 
   The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to devices that require periodic maintenance such as involving calibration, more particularly to methods for systematically applying maintenance procedures to groups of such devices. 
   Four traditional maintenance strategies are “reactive” maintenance (also known as “run-to failure” maintenance), “preventive” maintenance (also known as “interval,” “cycle-based,” or “time-based” maintenance), “predictive” maintenance (also known as “condition-based” maintenance), and “proactive” maintenance. Reactive maintenance is most suitable for small or unimportant items or those that are redundant or unlikely to fail. Preventive maintenance is particularly appropriate for items that are subject to wearing out or those having a known pattern of failure. Predictive maintenance is considered to be superior to the other strategies when the item has a random pattern of failure, or is not subject to wearing out, or would be subject to failure induced by preventive maintenance were it implemented. Proactive maintenance usually involves root cause failure analysis (RCFA) or failure modes and effects analysis (FMEA). 
   In recent years a maintenance strategy known as “reliability centered” maintenance (RCM) has come into prominence. RCM seeks to optimally combine the four aforementioned strategies so as to take advantage of the respective strengths of each, thereby maximizing operability and efficiency of equipment and facilities while minimizing life-cycle costs. Essentially, RCM involves the integration of the four aforementioned strategies whereby actions are identified in order to increase cost-effectiveness and reduce probability of failure. The RCM process determines the maintenance requirements of any physical entity in the context of its operation, the overall goal basically being the provision of the required operation performance at the lowest cost. Implicit in RCM is its recognition that the various types of equipment in a typical operation will generally differ in terms of their importance as well as their failure probabilities and mechanisms. RCM analysis typically lends itself to formulation of a “decision logic tree” wherein equipment is considered with regard to (i) function, (ii) likely functional failures, (iii) likely consequences of functional failures, and (iv) action that can be taken to reduce the probability or consequences of failure, or to identify the onset of failure. 
   The U.S. Navy&#39;s customary method for conducting instrument calibration requirements analysis is pursuant to the Shipboard Instrumentation and Systems Calibration (SISCAL) program, which uses a logic tree almost identical to the “Calibration Decision Logic Tree” published in the Joint Fleet Maintenance Manual (JFFM, CINCLANTFLT/CINCPACFLTINST 4790.3) at Volume VI, Chapter 9, Appendix B-1 (formerly found at Volume IV, Chapter 12, Appendix C-1). The JFFM&#39;s Calibration Decision Logic Tree does not reflect reliability-centered maintenance (RCM) principles; in particular, it neither addresses installed instrument applications, nor considers appropriate instrument tolerances, nor considers maintenance actions alternative to calibration. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing, it is an object of the present invention to provide an improved method for evaluating components in the context of an operating system of such components, e.g., such a method for evaluating instrumentation components in the context of a shipboard operating system of such instrumentation components. 
   According to typical embodiments of the present invention, an inventive method is provided for evaluating maintenance requirements of individual components in the context of an operational system. The inventive method comprises, with respect to each component, the following steps, to be performed as sequentially apposite: (a) considering whether failure of the component would be unsatisfactory in at least one aspect of the operating system, the aspect or aspects being functional, safety and/or environmental; and, (b) upon a positive determination that failure of the component would be unsatisfactory, considering (e.g., deciding) what maintenance action to take concerning the component. The consideration of what maintenance action to take includes the following steps to be performed, as sequentially apposite: (i) considering whether the component is either the only component of its kind or the primary component of its kind; (ii) upon a positive determination that the component is either the only component or the primary component of its kind, considering whether the instrument is quantitatively indicative; and, (iii) upon a positive determination that the component is quantitatively indicative, considering whether maintenance of the instrument is deferrable. 
   The present invention can be embodied as computer software. In accordance with some embodiments of the present invention, a computer program product is for evaluating maintenance requirements of individual components in the context of an operational system. The computer program product is for residence in the memory of a computer and comprises a computer useable medium having computer program logic recorded thereon, the computer program logic being applicable to each component. The computer program logic includes: (a) means for enabling consideration of whether failure of the component would be unsatisfactory regarding at least one aspect of the operational system selected from the group consisting of function, safety and environment; and (b) means for enabling consideration, upon a positive determination that failure of the component would be unsatisfactory, of what maintenance action to take concerning the component, wherein the means for enabling consideration of what maintenance action to take includes: (i) means for enabling consideration of whether the component is either the only component of its kind or the primary component of its kind; (ii) means for enabling consideration, upon a positive determination that the component is either the only component or the primary component of its kind, of whether the instrument is quantitatively indicative; and, (iii) means for enabling consideration, upon a positive determination that the component is quantitatively indicative, of whether maintenance of the instrument is deferrable. 
   The present invention&#39;s methodology for evaluating maintenance requirements is founded on reliability-centered maintenance (RCM) principles. The inventors style the decision logic tree that typifies their invention an “Installed Instrumentation Maintenance Requirements and Maintenance Actions Logic” (I2MRMAL) Tree.” According to frequent inventive practice, the inventive I2MRMAL Tree is accompanied by a questionnaire referred to by the inventors as the “Installed Instrumentation (INST2) Questions.” The inventive INST2 Questions serve as a useful vehicle for facilitating practice of the inventive I2MRMAL Tree. The I2MRMAL Tree represents the present invention&#39;s logic; the INST2 Questions represent a tool for advancing the inventive process. 
   The inventive method represents an assessment mechanism that is uncomplicatedly practicable, yet complexly useful. Among the many possible applications, the present invention&#39;s assessment methodology can be used to perform engineering analysis on shipboard instrumentation in order to uniformly reduce calibration and maintenance requirements. For instance, by furthering reliability-centered maintenance goals, the present invention can potentially play an important role for the U.S. Navy in terms of providing decision-making models for maintenance of instrumentation operations. Inventive practice can thus significantly reduce the expenses (typically in millions of dollars) that the U.S. Navy incurs on instrumentation maintenance. It is noted in this regard that the present invention is the focal technical innovation of the 127-page Naval Sea Systems Command (NAVSEA) Shipboard Instrumentation and Systems Calibration (SISCAL) Transition Study Report, dated Jun. 2, 2003, incorporated herein by reference; see, e.g., the last paragraph of the Executive Summary. 
   Inventive applicability extends to foreign navies, commercial shipping, power industry, manufacturing industry, etc. By virtue of its scope and versatility and other attributes, the present invention has great potential for yielding significant cost benefits and other benefits. Reliability-centered maintenance (RCM) principles are effected by the inventive methodology. The present invention, inter alia, addresses installed instrument applications, determines appropriate instrument tolerances, and directs calibration or alternative maintenance actions. The present invention&#39;s method is applicable not only to an installed instrument but also to any other component. For instance, the U.S. Navy can apply the present invention to an installed instrument as well as to any other hull, mechanical and electrical (HM&amp;E) component. Moreover, the present invention admits of practice in various other realms, such as those involving administrative, hardware, or project-logic processes. 
   Other objects, advantages and features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the present invention may be clearly understood, it will now be described, by way of example, with reference to the accompanying drawings, wherein like numbers indicate the same or similar components, and wherein: 
       FIG. 1  is a flow diagram illustrating conventional calibration methodology such as practiced of the U.S. Navy. 
       FIG. 2  is a flow diagram of an embodiment of a maintenance methodology in accordance with the present invention. 
       FIG. 3  and  FIG. 4  together constitute the flow diagram shown in  FIG. 2 , wherein  FIG. 3  is the “Maintenance Requirements Decision” section (on the lefthand side of the flow diagram shown in  FIG. 2 ) and  FIG. 4  is the “Maintenance Action Model” section (on the righthand side of the flow diagram shown in  FIG. 2 ). 
       FIG. 5  is a tabular representation of questions, in accordance with the present invention, that are associated with the inventive flow diagram shown in  FIG. 2  through  FIG. 4 . 
       FIG. 6  is an example of a chart that is completed, as to various types of instrumentation, in response to the inventive questions set forth in  FIG. 5 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to  FIG. 1 , the U.S. Navy currently implements an instrument maintenance strategy that separates calibration aspects from other maintenance-related aspects. The logic tree shown in  FIG. 1  is the aforementioned duplicate of the “Calibration Decision Logic Tree” published in the Joint Fleet Maintenance Manual (JFFM, CINCLANTFLT/CINCPACFLTINST 4790.3) at Volume VI, Chapter 9, Appendix B-1. The U.S. Navy&#39;s currently conducts instrument calibration requirements analysis through its SISCAL Program, which uses a logic tree very similar to that shown in  FIG. 1 . As previously noted herein, the JFFM&#39;s Calibration Decision Logic Tree fails to effectuate reliability-centered maintenance (RCM) principles. 
   Reference is now made to  FIG. 2  through  FIG. 6 , which are informative regarding the present invention.  FIG. 2  through  FIG. 4  illustrate the decision tree logic for a typical embodiment in accordance with the present invention.  FIG. 2  is re-represented in two parts as  FIG. 3  and  FIG. 4 .  FIG. 5  shows an embodiment of an inventive questionnaire that enhances the decision logic tree of  FIG. 2  through  FIG. 4 .  FIG. 6  depicts a sample form, a kind of inventive device that can be used pursuant to an inventive questionnaire such as shown in  FIG. 5 . The I2MRMAL Tree shown in  FIG. 2  through  FIG. 4  demonstrates the rationale of the present invention. The accompanying INST2 Questions shown in  FIG. 5  serve to facilitate the viability and comprehensibility of the inventive process. 
   The INST2 Questions shown in  FIG. 5  are clearly sequenced and formatted (and can even be paged) so as to ease response and promote understanding on the part of the person (e.g., an in-service engineering agent, or ISEA) providing such input for inventive analysis. The INST2 QUESTIONS should be arranged in a logical sequence to extract the maximum information about the subject instrument. The four sections of the INST2 Questions shown in FIG.  5 ,—viz., (A) Instrument Applicability, (B) Instrument Need and Calibration Periodicity Extension, (C) Instrument Maintenance, and (D) Instrument Criticality—foster a comprehensive understanding of the instrument in terms of application, tolerance, and appropriate calibration or alternative maintenance action. 
   For instance, if a respondent were posed an “Instrument Criticality” INST2 question (corresponding, e.g., to block A 1  or block A 2  of the I2MRMAL Tree) at the beginning of the questionnaire, rather than in “Section D” as shown in  FIG. 5 , the respondent would be less likely to answer the question meaningfully; that is, the respondent would be inclined to reply along the lines of, “Of course we need the instrument! Why do you think the manufacturer installed it? If we are not able to monitor the parameter, the equipment might cause serious harm.” Placement of the “Instrument Criticality” questions at the beginning rather than the end of the questionnaire would thus tend to impede inquiry into the true application of the instrument and its real maintenance requirements. 
   With reference to  FIG. 2  through  FIG. 4 , the “A” series of blocks (blocks A 1  through A 6 ) of the I2MRMAL Tree set forth the various criteria in an initial inquiry toward an initial decision of whether or not any maintenance action at all is required; if any one of these factors obtains, maintenance action of some nature is required. If no maintenance action is required, the logic proceeds to block M 1  of the “M” series of blocks. Block M 1  urges consideration of the possibility of instrument removal from the operating system. If any action whatsoever is required, the logic proceeds to the “B” series of blocks (blocks B 1  through B 10 ), which directs toward the appropriate course of action (e.g., the minimum required maintenance action) selected from among blocks M 2  through M 8  in the “M” series of blocks. Blocks B 1  through B 10  guide or decipher toward the minimum required maintenance action. Blocks M 2  through M 8  each describe an individual maintenance action to be taken. 
   The “M” series action options include, for instance, performance of a comparison check to the primary monitor (block M 2 ), or performance of an SCP (system calibration procedure) (block M 6 ), or performance of an MRC (maintenance requirements card) (block M 8 ). An MRC can be associated, for instance, with a PMS (planned maintenance system), a condition-based plural maintenance system, such an association being termed a PMS MRC (planned maintenance system maintenance requirements card). Generally, an MRC involves performing needed action with respect to a single instrument, whereas a PMS involves a more systematic mode of action, with respect to plural instruments. 
   While rendering the maintenance requirements decision depicted in  FIG. 3 , the inventive practitioner may encounter situations analogous to the following examples pertaining to blocks A 1  through A 6 . If a gage on a high pressure air tank were not providing the proper indication, the tank might be over-pressured and perhaps rupture, thus causing death or serious injury (block A 1 ). It is noted that the notion of safety in block A 1  broadly encompasses the possibility of any kind of risk, danger, hazard, injury or unhealthful situation. If a gage on a fuel oil transfer line were not providing the proper indication, the line might rupture, resulting in a hazardous oil spill (block A 2 ). If a chilled water flow switch unnecessarily shut down an air conditioning plant, the loss of chilled water cooling to combat systems equipment might cause a mission degradation (block A 3 ). If a lube oil pump auto start switch did not function properly, the equipment would shut down (block A 4 ). A gage measuring the pressure drop across a lube oil filter is used to determine/plan the maintenance to replace the filter (block A 5 ). PMS requires the recording of the CPS (collective protection system) zone pressure gage readings on a monthly basis (block A 6 ). It is noted that the notion of safety in block A 1  broadly encompasses any injury or danger or risk to health of any kind. 
   Regarding block M 1 , when two types of instruments measure the same parameter, a question may arise as to whether to retain both types of instruments. For instance, two types of gages (local gages and remote gages) may have come as part of an original equipment manufacturer (OEM) package. It may be efficient to remove the unnecessary instrument, since its operation is extraneous or redundant. It may be of no consequence to leave the unnecessary instrument, since it would cause no harm and would not be maintained anyway. It may be “more trouble than it&#39;s worth” to uninstall the unnecessary component than to keep it. 
   In the maintenance action model section shown in  FIG. 4 , block B 1  represents an affirmation that the instrument must be maintained. As an example of plural, duplicative means that monitor the same parameter, a parameter may have readout on a control panel and also on a local gage (block B 2 ). Regarding block B 3 , one may ask which readout or readouts is or are most important; for instance, where the watch stander takes readings may be worthy of consideration in this regard. Blocks A 1  through A 6  determine that the instrument must be maintained; in contrast, block B 3  presupposes that the instrument must be maintained, and delineates the significance of such maintenance. Block B 3  directs performance of a comparison check (block M 2 ) if the instrument is not the primary monitor, and directs further inquiry (beginning with block B 4 ) if the instrument is the primary monitor. 
   An example of an instrument indicating a quantitative value is a switch that starts a lube oil pump at a particular pressure, e.g., 10 psi (block B 4 ). An example of non-evident failure of a quantitatively indicative instrument is where the lube oil pressure never drops below a particular pressure, e.g., 10 psi; under these circumstances, one would not know whether the switch would start the pump (block B 5 ). As an example of a case of non-evident failure, lube oil pressure can be induced in order to perform an operational check of a switch (block M 3 ). As for a case of evident failure, the instrument can be either fixed or replaced, whichever is more practical or otherwise preferable (block M 4 ). 
   If, for instance, maintenance is appropriately based on evidence of deterioration or failure, the answer to the maintenance deferral question in block B 6  (Can maintenance be deferred?) is affirmative, leading to block B 7 . If, on the other hand, for instance, historical experience shows that the instrument fails after a certain period of time (e.g., 3000 hours), the answer to the maintenance deferral question in block B 6  (Can maintenance be deferred?) is negative, leading to block B 8 . Typically, if a plant is routinely shut down (e.g., at selected intervals) to observe the operation of a switch (e.g., to observe a resultant fall in lube oil pressure), the answer is affirmative to the question posed in block B 7 , and action is deferred (block M 5 ) to the scheduled failure-finding task unless other action is necessitated in the interim so as to perform only the minimum required maintenance. However, if failure of the switch would be catastrophic, or if loss of readiness or mission would result from a scheduled failure-finding task, the answer is negative to the question posed in block B 7 ; under either of these circumstances, waiting until a scheduled failure finding task would not be justified. 
   Block B 8  commences what may generally be described as encompassing a more traditional concept of maintenance actions. As an example of an instrument that is part of a measurement chain (block B 9 ), the sensor in a tank that measures liquid level is part of an instrument chain that may have local readouts as well as readouts on a control panel. According to block M 6 , rather than perform maintenance on each instrument in an instrument chain, it is much more efficient to maintain the entire chain using a system calibration procedure (SCP). However, if the instrument cannot be isolated for maintenance, it might be necessary to remove the instrument in order to perform maintenance (block B 10 ). Normally, instruments that must be removed for maintenance are sent to a lab (block M 7 ). Per block M 8 , performing a planned maintenance system maintenance requirement card (PMS MRC) action on an installed instrument on site (e.g., in place) is not only efficient but also eliminates the possible introduction of errors and damage inherent in instrument removal procedures for maintenance purposes. 
   In the course of negotiating the “B” series of the present invention&#39;s I2MRMAL Tree, there is variation in the level of intricacy of the questioning that leads to some form of maintenance action. A negative response to block B 3  directs one to a quick comparison check (block M 2 ). Block B 4  leads, in the alternative based on evidence of failure, to a operational check (block M 3 ) or to a fix or replacement of the instrument (block M 4 ). The operational check of block M 3  is slightly or somewhat more time-consuming than is the comparison check of block M 2 . Block B 6  commences the addressing of the concept of maintenance deferral. The present invention integrates maintenance deferral in the inventive process for good reason, since the maintenance concepts beginning at block B 8  (which include traditional maintenance concepts) are the most labor-intensive and resource-intensive. Note that, generally as one progresses through the “B” blocks, the application and significance of the instrument require more comprehensive maintenance actions. 
   The present invention is not to be limited by the embodiments described or illustrated herein, which are given by way of example and not of limitation. Nor is the present invention to be limited in applicability to devices aboard marine vessels, as the present invention admits of practice relating to maintenance in association with multifarious devices in multifarious contexts. Other embodiments of the present invention will be apparent to those skilled in the art from a consideration of this disclosure or from practice of the present invention disclosed herein. Various omissions, modifications and changes to the principles disclosed herein may be made by one skilled in the art without departing from the true scope and spirit of the present invention, which is indicated by the following claims.