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BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the field of plant control and management
information systems, and in particular to an integrated plant monitoring
and diagnostic system for shared use by the operations, maintenance and
engineering departments of a nuclear power plant. The system collects and
monitors operating parameter data via sensors, generates prioritized
condition reports including present conditions and anticipated impending
conditions to be addressed by preventive maintenance or operational
changes, and provides users with background technical and historical data
that is ranked and cross referenced by related operational systems and
related articles of equipment.
2. Prior Art
Various management information systems are known for monitoring and
recording process parameters in connection with power generation as well
as with industrial processes generally. These systems often are reactive
in that they respond to present levels of monitored parameters, or at most
respond to present trends to control generation of alarms and the like
when a parameter exceeds preset values or threatens to do so. A typical
process control system monitors sensed parameters to ensure that they
remain within preset limits defined by the programmer of the system. Often
the present levels can be displayed graphically to highlight trends.
Another form of management information system is known in connection with
scheduling of maintenance procedures. By defining a useful life for each
article of equipment among a number of articles which are related or
inter-dependent, it is possible to schedule repair, replacement or
preventive maintenance operations more efficiently so as to minimize
downtime. The idea is to plan replacement or repair of articles of
equipment for as late as practicable before an actual failure, preferably
using intelligent scheduling procedures to minimize downtime by taking
maximum advantage of any downtime. The scheduling system prompts or warns
plant personnel to attend to each of the articles which may need attention
at or soon after the time at which the maintenance of any particular
article becomes critically important.
U.S. Pat. No. 4,908,775--Palusamy et al discloses a cyclic monitoring
system which counts down a defined useful life expected for various
structures in a nuclear power plant. This system is responsive to
operating levels in the plant, and increases the predicted aging rate of
plant structures to account for variations in usage including transient
loading. A sampling module is provided to detect the current loading of
monitored equipment periodically. Transient and steady state operating
levels are determined from the sampled data and used to generate a usage
factor. Equipment degradation due to fatigue and the like is anticipated
by integrating the usage factor over time. Whereas operating levels and
transient disturbances are taken into account in assessing the wear on
plant equipment, the system can be used to plan maintenance and
replacement activities or alternative plant operations, using a more
accurate estimation of the useful life of the plant components.
The predictive maintenance system according to Palusamy '775 incorporates
both operational data and a defined useful life data indexed to articles
of equipment. However, the system is such that it primarily serves only
maintenance functions. It would be advantageous to provide a system that
benefits operational and engineering departments as well. The present
invention is intended to accomplish this by integrating not only
information regarding usage and expected useful life, but by further
integrating design and technical specifications and historical data into a
system that monitors operational levels as well as equipment conditions.
This data is provided in a hierarchical data acquisition and processing
system providing shared access by the different departments, especially
operations, maintenance and engineering. The data is arranged and cross
referenced for presentation of meaningful reports for each of the
departments.
Nuclear reactors for generation of electric power are heavily instrumented
to enable efficient plant operation and to ensure safety. U.S. Pat. No.
4,961,898 Bogard et al discloses a system operable to record and report
neutron emission levels in and around the reactor as well as pressure and
flow parameters, for accurately assessing the accumulation of stress on
the operating structures. U.S. Pat. No. 4,935,195--Palusamy et al
similarly attempts to factor corrosion of the coolant flow path structures
for assessing the useful life of reactor components.
Typically, monitoring equipment for a nuclear power plant or similar
process is associated specifically with a particular structure or
operating system of the plant. For example, in Bogard et al the monitoring
system is specifically associated with coolant flow structures. In
Palusamy '195 the monitoring system is associated with the neutron
emissions. For the most part, monitoring systems of this type are
dedicated either to safety purposes (e.g., to detect an unsafe condition
and to shut down and/or generate alarms automatically), or to operational
control (e.g., to control the positions of valves and the like during
ongoing plant operation). Routines which accumulate a usage factor for
assessing the loading factor on a particular subsystem could use much of
the same data which is collected by safety and control instrumentation.
However, the prior art fails to provide a fully integrated system that can
take full advantage of the available instrumentation.
It would be advantageous to provide such an integrated system which not
only monitors various articles of plant equipment, but which also accounts
for the interdependence of the subsystems, makes decisions or predictions
in view of stored design criteria, and makes all this information
available generally to plant personnel. In specifying the subsystems,
design criteria and technical specifications were merged under the
assumption that the subsystems would operate under certain conditions.
Operational conditions such as equipment problems can change the loading
level for a given article of equipment or subsystem, and also the loading
levels of other articles and subsystems that are related to or
interdependent with the given ones. Therefore, the interrelations of the
articles or subsystems, their design specifications, their history and
their current conditions should all be taken in account when assessing
operational conditions and maintenance needs, or when evaluating
operations on an engineering level.
It is generally advisable for plant management and/or maintenance personnel
to collect any available data regarding the subsystems operating in a
plant or in an area of the plant, to coordinate maintenance and repair
activities. In this manner, a downtime for work on one or more articles or
subsystems can be used for simultaneous work on others. However, a
comprehensive calculation and analysis of relevant plant conditions can be
lengthy and costly. In a monitoring system where information on
operational conditions is only immediately available to the operators
(e.g., for safety and/or control purposes), engineers, scientists,
maintenance technicians, managers and headquarters staff must collect and
analyze much of the same information in planning their activities. Each
group tends to collect and analyze data in a manner that is best suited to
their own area of concern. Nevertheless, an integrated arrangement is
certainly more efficient and useful than one in which the various
departments operate substantially independent information systems.
The present invention is intended to integrate diagnostic and predictive
instrumentation for a number of interdependent plant systems, for taking
advantage of available synergies. Furthermore, safety and control
parameters are collected using a data network arrangement that is shared
by primary and auxiliary system control and protection groups, plant
maintenance groups, plant engineering and management. In order to
accomplish this objective, the plant computerized information system is
integrated generally with instrument data collection from a variety of
sources, and stored design criteria information. The operational
parameters are factored together in an integrated diagnostics and
monitoring system with technical specifications for condition directed
maintenance and aging management. Specific, actionable diagnostic
information on equipment condition is developed, including cross
referenced selection of background technical data, whereby operations and
maintenance decisions can be made more effectively and from a greater base
of knowledge.
The diagnostics and maintenance arrangement according to the invention puts
control and safety parameter information to use by the engineering and
maintenance departments rather than only the operations control personnel.
Conversely, the system makes maintenance and engineering information
available to operations and safety groups, thus providing various useful
lines of communication and data access availability.
SUMMARY OF THE INVENTION
It is an object of the invention to integrate operational parameter data
collection, evaluation based on stored design criteria, and plant
information reporting, in a comprehensive plant information system useful
for planning operational and maintenance decisions.
It is another object of the invention to make pertinent information readily
available for use not only by plant operators, but also generally by
engineers, scientists, maintenance technicians, managers and headquarters
staff.
It is more particularly an object to collect a wide array of information
respecting the character and operational conditions of functionally
interdependent elements of a nuclear power generation plant, including
design criteria applicable to the elements, and to process this
information using intelligent monitoring and diagnostic routines that
model operation of the plant to anticipate problems and enable efficient
planning of operations and maintenance.
It is another object of the invention to define the overall architecture
and operation of a plant information system according to these objects,
which is best suited to take advantage of technology advancements as well
as available data collection devices, processing apparatus, degradation
types and diagnostic methodologies.
These and other objects are accomplished by an integrated information
system for a plant with interactive processes running in functional
equipment subsets, such as a nuclear power generation plant. Sensors are
operatively coupled to monitor processes and equipment in the plant,
collecting sample data for assessing operational conditions and for
predicting maintenance requirements based on loading of the equipment. A
processor accesses the sample data and compares present conditions to
diagnostic specifications, technical specifications and historical data
stored in memory and indexed to equipment subsets and functional operating
groups. The processor generates prioritized reports to alert users to
potential operational and/or maintenance problems. In addition to the
prioritized reports, the processor accesses and outputs to the users
reports of the diagnostic and technical specifications applicable to the
process parameters exhibiting the potential problems. These specifications
are provided in successive levels of detail and are cross referenced
between related processes and related items of equipment. The information
system integrates operations, maintenance, engineering and management
interests in a common database of information via network-coupled data
terminals.
BRIEF DESCRIPTION OF THE DRAWINGS
There are shown in the drawings certain exemplary embodiments of the
invention as presently preferred. It should be understood that the
invention is not limited to the specific examples, and is capable of
variations within the scope of the appended claims. In the drawings,
FIG. 1 is a block diagram illustrating generally a plant information system
integrating operation, control, protection, engineering and maintenance
information according to the invention.
FIG. 2 is a block diagram of the invention showing modular elements of the
invention and the data collection and communication links between the
elements.
FIG. 3 is a plan view showing a layout for the data processing portions of
the system.
FIG. 4 is a schematic illustration of data pathways for monitoring and
control functions.
FIG. 5 is a schematic illustration of a networked installation of terminals
sharing access to commonly collected and stored information.
FIG. 6 is a tabular display of actionable directives generated by a
preferred embodiment in response to detected conditions.
FIG. 7 is a tabular display of exemplary cross referenced technical
specifications referring to certain of the directives provided in FIG. 6.
FIG. 8 is a schematic illustration of an exemplary system architecture
according to the invention, as applied to a nuclear power generation
plant.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention is applicable to a variety of industrial processes wherein
data respecting process parameters is collected and reported to enable
management decision making. A particularly apt application of the
invention is to a nuclear power generation plant. A nuclear plant is
normally highly instrumented for collecting information needed to operate
at peak efficiency, as well as to tightly monitor operation for safety
reasons. The signals developed by sensors for flow, temperature, pressure,
valve status, nuclear particle flux levels and the like are to some extent
coupled into operational circuits which are intended to effect control
operations. According to the invention, sensor signals are coupled to a
plant instrumentation control and monitoring center 20 that as shown in
FIG. 1 is further coupled to a predictive maintenance and diagnostic
center 24.
Information required for pertinent diagnostic information according to the
invention includes design criteria applicable to the plant. For example,
should a certain valve, flow element, heat transfer device or rotating
machine be specified as having an estimated useful life when operated at a
particular level of demand, pertinent diagnosis of the element requires
that the remaining useful life be decremented as a function of the demand
level. Accordingly, the predictive maintenance and diagnostic center is
coupled to a diagnostic information center which makes such information
available. In the embodiment shown in FIG. 1, the information center 20 is
shown as a separate location in data communication with the plant-located
predictive maintenance and diagnostic center 24. This is an efficient
arrangement where the utility company may have a number of plants which
share design aspects. However, the particular location of the respective
data storage and computing systems can be varied provided the information
is available to each of the processors which need the information.
Referring to FIG. 2, plant operational functions, maintenance functions and
engineering functions are all integrated to a common network of
information stored, collected and otherwise developed according to the
invention. Both operational and safety related sensing and information
collection are provided, and made available generally to operations,
maintenance and engineering stations and/or users. The system can be
physically arranged in a control center setup as shown, for example in
FIG. 3, or can be accessed from distributed terminals in various areas of
the plant or located remotely as in FIG. 4.
As shown in FIG. 2, the system preferably is based on a hierarchical system
of data paths, including interconnections that allow data access without
interfering with crucial operations. Safety related sensors 32 coupled to
the plant operational elements 34 are sampled using a protective data
acquisition system 42 and a control data acquisition system 44, which are
separate and parallel. A process protection system 46 and operation
control system 48 are coupled respectively to the protective and control
data acquisition systems 42, 44. These elements are subject to certain
inputs from the primary control and protection station(s) coupled to the
protection and control systems through an integrated control system
forming a kind of bus wherein operational and safety associated parameters
are available to both the control and protection systems. However, the
control and protection systems have a number of automatic aspects intended
to control the plant to achieve process objectives such as efficient
complementary setting of valves and the like as well as the capability of
automated shutdown without operator intervention in the event of a safety
threat.
Sensors 50 which are not directly safety related (but whose data may have
implications with respect to operations, safety and control), are coupled
to respective data processing units 54, which are coupled to data
acquisition means 56 for collecting and reducing the data. The data
processing units can collect sample data from one or a plurality of
sensors 32, 50, reject data which is impossibly out of limits, and attend
to numerical and/or graphical analyses such as average and standard
deviation, peak level identification and the like. Data collected from the
nonsafety related sensors 50 can be shared over a distributed processing
communication path 58 such as the Westinghouse WDPF distributed processing
family. In addition, the data processing units 54 are in communication
with a number of monitoring systems 62 over the WDPF data pathway 58.
Monitoring systems 62 selectively process available data in order to
effect specific functions.
Proceeding from left to right over the WDPF 58 in FIG. 2, an interface or
bridge element 64 couples the integrated safety/control system data
pathway 66 with the WDPF data pathway 58. The bridge 64 permits data to
pass between the integrated safety/control pathway 66 and the WDPF 58 in
either direction, but is arranged to allow the integrated safety/control
system bus 66 to operate regardless of the condition of the WDPF 58. For
example, a failure of an element associated with the WDPF such as a power
supply, data processing unit or even a line driver or similar element
required for operation of the WDPF, cannot affect operation of the
integrated safety/control system due to its isolation via the bridge
interfacing element 64.
An auxiliary system control unit 68 is also coupled to the WDPF 58,
enabling plant operations personnel to monitor data collected over the
WDPF and preferably to control operation of the data processing units 54
from plant operations consoles 72. The auxiliary system control unit 68 is
coupled to the data processing units 54 (and thus to the non-safety
sensors 50) relatively directly through the WDPF 58. The WDPF data pathway
is arranged for communication of data from the sensors 50, 32 to plant
operations such that individual variables can be examined. However, in
addition, the WDPF data is coupled through the intermediate processing
systems 62 to a higher level data pathway identified in FIG. 2 as
information highway 78. These intermediate processing systems 62 permit
the application of higher level long and short term analysis for
converting, e.g., a substantially database form of data collected by the
data processing units 54 into more sophisticated statistical analyses,
trend analyses and correlations that additionally use data stored in the
respective intermediate processing systems 62. The modules of the
intermediate processing systems 62 report to any and all of the plant
operations consoles, plant maintenance personnel and plant engineering
personnel. The same information highway 78 can be coupled to additional
users via known networking arrangements, telephone line modem pathways and
the like.
The intermediate modules 62 represent systems that can be arranged as
processing terminals on a data communication network or concurrently
operative routines in a larger and more sophisticated data processing
system. The function of the intermediate processing units 62 is to select
and analyze data available in a relatively less processed form on the WDPF
58, and to provide information which relies on the values and trends
identified in the individual process parameters and in selected groups of
related parameters. The output of the intermediate modules 62 is reported
to users via diagnostic packages 82 tailored to the needs of the
operations, maintenance and engineering departments, respectively. A given
department such as maintenance or operations normally at least sometimes
requires information from different ones of the intermediate modules 62,
and the departments thus share the information relating to the process
parameters.
A first intermediate processing module, identified in FIG. 2 as the beacon
module 84, is arranged to monitor and report present operating parameters.
Present operating parameter information affects not only operations
decisions, but also is pertinent to maintenance (e.g., whether a subsystem
is in use or available for mechanical work, whether a subsystem is being
stressed, etc.). The same information is useful to engineering (e.g., to
study the overall condition of the plant or interactions between process
parameters). An operator diagnostic advisory unit 86 is coupled to the
information highway for the primary purpose of collecting and usefully
analyzing, storing and reporting upon operations. The operator diagnostic
unit 86 can be arranged to run constantly, reporting information
respecting diagnostic information and recommending or suggesting
operational changes that may affect or alleviate operational problems or
potential problems which may occur.
In addition to the beacon intermediate monitoring system 84 and the
operations diagnostic unit 86, a corrosion monitoring system 88, a
generator monitoring system ("GENAID") 90 and a transient/fatigue cycle
monitoring system ("CMS") 92 operate to selectively analyze data collected
by the data processing units and made available as process parameter data
over the data highway. This information is also potentially useful in
connection with operations, maintenance and engineering decisions. The
intermediate processing units 62 are devoted to certain aspects of tasks
which affect decisions in all these departments, but are organized in a
manner that is not limited to one department. Instead, each of the
intermediate processing units serves a particular data set. The data
needed by the intermediate processing modules 62 may overlap with data
needed by others of the intermediate processing modules, and preferably is
broken down into the beacon 84 for present operational conditions,
corrosion monitoring 88 for long term deterioration due to ambient
conditions such as radiation and chemical conditions, generator analysis
(GENAID) 90 for thermodynamic and coolant flow analysis, and transient
pressure and flow variation monitoring 92, to assess fatigue.
A predictive maintenance and diagnostic unit 102 is also coupled to the
information highway 78, for diagnosing and reporting maintenance problems,
and a series of engineering diagnostic units 104 are included. The
maintenance diagnostic system 102 is preferably organized in a manner that
is most meaningful to maintenance personnel, for example referring to
individual pieces of plant equipment instead of functional aspects of the
process. However, the maintenance diagnostics are preferably arranged to
group devices whose operation has an impact on other devices according to
functional groupings as well. Preferably, the plant maintenance diagnostic
systems are grouped to provide for analysis of categories such as
mechanical devices including valves, rotating machines and the like (which
may be subject to frictional problems), and pressure/flow conduits (for
corrosion/erosion problems).
Similarly, the plant engineering departments use the information available
on the information highway 78, as collected by the data processing units
54 and reduced by the intermediate processors 62. A variety of engineering
and diagnostic routines 104 are preferably included, for example grouped
for residual coolant system diagnosis, transient diagnosis of pressure,
flow and/or electrical loading, generator diagnosis and chemical/nuclear
diagnosis. These diagnostic processes are related to operational
parameters (like the plant operations diagnostics) and also t specific
apparatus (like the maintenance diagnostics), and are presented in a
format which is tailored to engineering planning as opposed to operations
or maintenance procedures.
A major benefit of integrating data collection and reporting according to
the invention is that data need not be collected and analyzed redundantly.
Nevertheless, the users of the system can retain the benefit of graphic
user interfaces with which users may already using (e.g., in connection
with analysis of the operation of subsystems having dedicated monitoring
systems.). Although the data collection is common to each of the plant
departments, specialized mathematical models, xpert "intelligent" analysis
and neural networking are readily achieved.
The invention is particularly applicable to operational, maintenance and
engineering functions in a nuclear power plant. Such a plant has a variety
of apparatus which can be grouped functionally, and which affect one
another in the operational and maintenance procedures and decisions
undertaken in the plant. A key input to any decision related to life
extension of a nuclear plant is the condition of the plant systems and
components critical to the safe, reliable and economical operation of that
plant. This means not only the current condition, but the condition
predicted throughout the remainder of the plant operation. To establish
this effectively, at least two things are needed:
Data on critical parameters related to equipment condition; and,
Engineering decision making capability in terms of evaluating available
data, namely extraction, saving and use of monitored data to determine
current conditions as well as to predict future conditions and make
recommendations on actions needed to attain plant objectives.
Certain applications benefit from simply adding raw data to meet the first
requirement. However a typical nuclear plant has extensive existing
instrumentation providing abundant data. What is more lacking is an
optimal means cohesively to use that data for the second requirement,
i.e., engineering decision making. The emphasis in the data interface
packages developed for nuclear power plants has been an the needs of the
operator and his minute-by-minute needs for operations decisions.
The second requirement is met according to the invention by:
Accessing and supplementing the available plant data;
Establishing evaluation objectives (critical components, associated
measures of degradation, criteria and limits, etc.); and,
Implementing a capability to evaluate the data and make recommendations.
Of course the system of diagnostics and monitoring must be cost justified.
The relative costs of various maintenance approaches (corrective,
preventive, predictive) over the plant life are such that a factor of two
improvement in cost can be achieved by using a predictive approach to
maintenance instead of traditional approaches.
It is an aspect of the invention that the diagnostic and monitoring
functions are integrated, for example into a plant process computer and
instrumentation system architecture. In this sense, the plant process
computer can include one processor or any number of processors in data
communication, for example over the network communication paths described.
The architecture of the invention relates to the arrangements and
interconnections which link inputs to the process, the defined or required
characteristics of the process itself, and the resulting outputs from the
process. For the case of a nuclear plant diagnostics and monitoring
system, the types of data needed include process parameters, control and
response data, and preferably accumulated historical data. This
information is obtained from plant instrumentation, distributed plant
computer systems, additional sensors which may be unrelated to safety and
control systems, test and performance data (whether measured, stored from
previous measurements or specified for the equipment) and mainframe data
storage. Such data may be stored as to any appropriate frequency of
measurement, from milliseconds to years, and may be reduced into the form
of average and standard deviation over selected periods or may include raw
samples.
The type of available data and the required output define the type and
frequency of data processing steps needed to convert the available data
into meaningful presentations, and to sift through the available data to
detect conditions which should generate a diagnostic warning. One or more
processors associated with the hierarchy provide the data processing power
and data storage capabilities needed to effect timely calculations on a
real-time, automated periodic and/or on-demand basis.
The calculations undertaken by the processor(s) are of the type used in
monitoring subsystems for the respective plant components; however,
according to the invention the calculations are not limited to input based
upon current parameter values in an isolated subsystem. Accordingly,
diagnostic routines applicable to a subsystem, as undertaken by the
integrated diagnostic and monitoring system, are affected by the
conditions in related subsystems. The specific calculations can be
mathematical algorithms, logical rule based (as in fuzzy logic) or neural
network processes involving a multidimensional chain of calculations and
decisions. The calculations can also include statistical analyses and
database management type processes.
Output data is to be used to alert operators to conditions which may become
critical shortly or not for a long time, and preferably also enable
general monitoring as to what is going on in the plant. Accordingly, the
output is preferably generated in forms including on-screen graphic and
tabular data displays, storage of data on disk, tape or hardcopy, as well
as audio and/or video signalling. In addition to selection of data from
the inputs or from first or second level information generated from the
inputs, the output data includes diagnostic information for monitored
devices and subsystems, recommendations for action which are selected
based on the diagnostic information and plant conditions, and additional
backup information about the devices and subsystems (such as their
physical characteristics, ratings and the like), from which the operators
can discern the basis of the diagnosis and recommendations.
The users of the output generated by the system include most types of plant
personnel. General categories of users include the operations support
staff, maintenance, engineering and scientific staff, and plant
management. Outside of the plant, headquarters engineering and management
staff preferably have access to the data, and it is even possible to allow
vendors access in order to enable them to assess the conditions under
which requested equipment is to operate, or to assess the present
conditions applicable to equipment already supplied. Under such conditions
the vendors may be aware of an aspect of the equipment that should be made
known for diagnostic purposes.
Insofar as users remote from the processor generating the output data may
be coupled to the processor, various high speed and low speed data
communications links can be employed. Such users may be on-site or
off-site, and are coupled in data communication with the processor by
hardwire, modem, radio or fiber optic links, as required in view of the
data capacity needed.
For output and display, utility personnel need specific diagnoses of
critical aspects of plant condition. According to the invention, such
critical aspects are ranked and prioritized in a tabular display 110 from
which the user can select further information on the diagnosis, the
recommended corrected action, and background information on the affected
structural elements and/or plant subsystems. The current status of the
plant must always be available and easily accessible. A sample of a
tabular display of diagnostic considerations in summary form appears in
FIG. 5.
In the example shown, there are a number of conditions 114 rated by
priorities 116. The list includes conditions which represent reactor
status or operational information, and some suggesting a need for
maintenance. Based on preprogrammed relationships between components of
the plant, operations and maintenance personnel can react as appropriate.
FIGS. 6 and 7 are examples of backup information respecting the items
mentioned in the diagnostic summary. In the example, a valve identified as
8701A is described as having an incorrect stem packing tightness. Based
only on the information on the summary, the implications of incorrect stem
packing tightness in the particular valve may be unclear. However, the
diagnostics summary 110 is a gateway to additional information describing
the valve, and in fact also includes reactor operational information which
likewise identifies the valve as an element in need of attention.
Item 2 on the diagnostics summary states that thermal stratification in the
residual heat removal (RHR) system exceeds level 1 limits, level 1 being a
minimum warning threshold. By selecting item 2, the operator is provided
with background information 120 on RHR thermal stratification conditions.
The backup information as shown in FIG. 6, includes a longer explanation
124 of the problem, a description 126 of the consequences of inaction, and
recommendations 128 for activities which may fix the problem. In the
example, the explanation identifies valve 8701A as the likely culprit,
suggesting that the valve may be leaking. In conjunction with the
diagnostics summary, the user is led immediately to the cause of the
problem and can readily assess the severity thereof.
The residual heat removal system is an operating subset of the reactor, and
preferably a series of tabular, graphic and text screens can be selected
by paging through the respective levels of diagnosis. FIG. 7 illustrates
further informational screens 130 under the groupings of RHR
Stratification Status, and also Valve Monitoring Status, which are
alternative cross referenced paths leading to a resolution of the problem
shown in the summary 110. The screens applicable to RHR Stratification
include the subject valve, and the screens relating to valve monitoring
mention the function of the subject valve. By proceeding through the
screens and selecting cross referenced information it is possible to
obtain a full picture of the situation.
Preferably, the diagnostic system includes means 132 for the user to
acknowledge receipt of the recommendation. In this manner the system
ensures that appropriate attention is paid by those people who can act on
the recommendation, and one person does not assume that another is taking
responsibility for attending to the recommendation. Acknowledgement, as
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