667 research outputs found
Multivariate control charts based on Bayesian state space models
This paper develops a new multivariate control charting method for vector
autocorrelated and serially correlated processes. The main idea is to propose a
Bayesian multivariate local level model, which is a generalization of the
Shewhart-Deming model for autocorrelated processes, in order to provide the
predictive error distribution of the process and then to apply a univariate
modified EWMA control chart to the logarithm of the Bayes' factors of the
predictive error density versus the target error density. The resulting chart
is proposed as capable to deal with both the non-normality and the
autocorrelation structure of the log Bayes' factors. The new control charting
scheme is general in application and it has the advantage to control
simultaneously not only the process mean vector and the dispersion covariance
matrix, but also the entire target distribution of the process. Two examples of
London metal exchange data and of production time series data illustrate the
capabilities of the new control chart.Comment: 19 pages, 6 figure
Multivariate Statistical Process Control Charts: An Overview
In this paper we discuss the basic procedures for the implementation of multivariate statistical process control via control charting. Furthermore, we review multivariate extensions for all kinds of univariate control charts, such as multivariate Shewhart-type control charts, multivariate CUSUM control charts and multivariate EWMA control charts. In addition, we review unique procedures for the construction of multivariate control charts, based on multivariate statistical techniques such as principal components analysis (PCA) and partial lest squares (PLS). Finally, we describe the most significant methods for the interpretation of an out-of-control signal.quality control, process control, multivariate statistical process control, Hotelling's T-square, CUSUM, EWMA, PCA, PLS
A Time Truncated Moving Average Chart for the Weibull Distribution
A control chart of monitoring the number of failures is proposed with a moving average scheme, when the life of an item follows a Weibull distribution. A specified number of items are put on a time truncated life test and the number of failures is observed. The proposed control chart has been evaluated by the average run lengths (ARLs) under different parameter settings. The control constant and the test time multiplier are to be determined by considering the in-control ARL. It is observed that the proposed control chart is more efficient in detecting a shift in the process as compared with the existing time truncated control chart. ? 2013 IEEE.11Ysciescopu
Monitoring of the BTA Deep Hole Drilling Process Using Residual Control Charts
Deep hole drilling methods are used for producing holes with a high lengthto- diameter ratio, good surface finish and straightness. The process is subject to dynamic disturbances usually classified as either chatter vibration or spiralling. In this work, we propose to monitor the BTA drilling process using control charts to detect chatter as early as possible and to secure production with high quality. These control charts use the residuals obtained from a model which describes the variation in the amplitude of the relevant frequencies of the process. The results showed that chatter is detected and some alarm signals are related to changing physical conditions of the process. --
Quantitative infrared thermography resolved leakage current problem in cathodic protection system
Leakage current problem can happen in Cathodic Protection
(CP) system installation. It could affect the performance of
underground facilities such as piping, building structure, and
earthing system. Worse can happen is rapid corrosion where
disturbance to plant operation plus expensive maintenance
cost. Occasionally, if it seems, tracing its root cause could be
tedious. The traditional method called line current
measurement is still valid effective. It involves isolating one
by one of the affected underground structures. The recent
methods are Close Interval Potential Survey and Pipeline
Current Mapper were better and faster. On top of the
mentioned method, there is a need to enhance further by
synthesizing with the latest visual methods. Therefore, this
paper describes research works on Infrared Thermography
Quantitative (IRTQ) method as resolution of leakage current
problem in CP system. The scope of study merely focuses on
tracing the root cause of leakage current occurring at the CP
system lube base oil plant. The results of experiment
adherence to the hypothesis drawn. Consequently, res
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