335 research outputs found
Nonlinear data driven techniques for process monitoring
The goal of this research is to develop process monitoring technology capable of taking advantage of the large stores of data accumulating in modern chemical plants. There is demand for new techniques for the monitoring of non-linear topology and behavior, and this research presents a topological preservation method for process monitoring using Self Organizing Maps (SOM). The novel architecture presented adapts SOM to a full spectrum of process monitoring tasks including fault detection, fault identification, fault diagnosis, and soft sensing. The key innovation of the new technique is its use of multiple SOM (MSOM) in the data modeling process as well as the use of a Gaussian Mixture Model (GMM) to model the probability density function of classes of data. For comparison, a linear process monitoring technique based on Principal Component Analysis (PCA) is also used to demonstrate the improvements SOM offers. Data for the computational experiments was generated using a simulation of the Tennessee Eastman process (TEP) created in Simulink by (Ricker 1996). Previous studies focus on step changes from normal operations, but this work adds operating regimes with time dependent dynamics not previously considered with a SOM. Results show that MSOM improves upon both linear PCA as well as the standard SOM technique using one map for fault diagnosis, and also shows a superior ability to isolate which variables in the data are responsible for the faulty condition. With respect to soft sensing, SOM and MSOM modeled the compositions equally well, showing that no information was lost in dividing the map representation of process data. Future research will attempt to validate the technique on a real chemical process
Plant-Wide Diagnosis: Cause-and-Effect Analysis Using Process Connectivity and Directionality Information
Production plants used in modern process industry must produce products that meet stringent
environmental, quality and profitability constraints. In such integrated plants, non-linearity and
strong process dynamic interactions among process units complicate root-cause diagnosis of
plant-wide disturbances because disturbances may propagate to units at some distance away
from the primary source of the upset. Similarly, implemented advanced process control
strategies, backup and recovery systems, use of recycle streams and heat integration may
hamper detection and diagnostic efforts.
It is important to track down the root-cause of a plant-wide disturbance because once
corrective action is taken at the source, secondary propagated effects can be quickly eliminated
with minimum effort and reduced down time with the resultant positive impact on process
efficiency, productivity and profitability.
In order to diagnose the root-cause of disturbances that manifest plant-wide, it is crucial to
incorporate and utilize knowledge about the overall process topology or interrelated physical
structure of the plant, such as is contained in Piping and Instrumentation Diagrams (P&IDs).
Traditionally, process control engineers have intuitively referred to the physical structure of
the plant by visual inspection and manual tracing of fault propagation paths within the process
structures, such as the process drawings on printed P&IDs, in order to make logical
conclusions based on the results from data-driven analysis. This manual approach, however, is
prone to various sources of errors and can quickly become complicated in real processes.
The aim of this thesis, therefore, is to establish innovative techniques for the electronic
capture and manipulation of process schematic information from large plants such as
refineries in order to provide an automated means of diagnosing plant-wide performance
problems. This report also describes the design and implementation of a computer application
program that integrates: (i) process connectivity and directionality information from intelligent
P&IDs (ii) results from data-driven cause-and-effect analysis of process measurements and (iii)
process know-how to aid process control engineers and plant operators gain process insight.
This work explored process intelligent P&IDs, created with AVEVA® P&ID, a Computer
Aided Design (CAD) tool, and exported as an ISO 15926 compliant platform and vendor
independent text-based XML description of the plant. The XML output was processed by a
software tool developed in Microsoft® .NET environment in this research project to
computationally generate connectivity matrix that shows plant items and their connections.
The connectivity matrix produced can be exported to Excel® spreadsheet application as a basis
for other application and has served as precursor to other research work. The final version of
the developed software tool links statistical results of cause-and-effect analysis of process data
with the connectivity matrix to simplify and gain insights into the cause and effect analysis
using the connectivity information. Process knowhow and understanding is incorporated to
generate logical conclusions.
The thesis presents a case study in an atmospheric crude heating unit as an illustrative example
to drive home key concepts and also describes an industrial case study involving refinery
operations. In the industrial case study, in addition to confirming the root-cause candidate, the
developed software tool was set the task to determine the physical sequence of fault
propagation path within the plant.
This was then compared with the hypothesis about disturbance propagation sequence
generated by pure data-driven method. The results show a high degree of overlap which helps
to validate statistical data-driven technique and easily identify any spurious results from the
data-driven multivariable analysis. This significantly increase control engineers confidence in
data-driven method being used for root-cause diagnosis.
The thesis concludes with a discussion of the approach and presents ideas for further
development of the methods
Fault and Defect Tolerant Computer Architectures: Reliable Computing With Unreliable Devices
This research addresses design of a reliable computer from unreliable device technologies. A system architecture is developed for a fault and defect tolerant (FDT) computer. Trade-offs between different techniques are studied and yield and hardware cost models are developed. Fault and defect tolerant designs are created for the processor and the cache memory. Simulation results for the content-addressable memory (CAM)-based cache show 90% yield with device failure probabilities of 3 x 10(-6), three orders of magnitude better than non fault tolerant caches of the same size. The entire processor achieves 70% yield with device failure probabilities exceeding 10(-6). The required hardware redundancy is approximately 15 times that of a non-fault tolerant design. While larger than current FT designs, this architecture allows the use of devices much more likely to fail than silicon CMOS. As part of model development, an improved model is derived for NAND Multiplexing. The model is the first accurate model for small and medium amounts of redundancy. Previous models are extended to account for dependence between the inputs and produce more accurate results
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