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Showing 1 to 20 of 37 for “"Shewhart"”.
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Variable sampling in multiparameter Shewhart charts
This dissertation deals with the use of Shewhart control charts, modified to have variable sampling intervals, to simultaneously monitor a set of parameters. Fixed sampling interval control charts are modified to utilize sampling intervals that vary depending on what is being observed from the …
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A robust Shewhart control chart adjustment strategy
The standard Shewhart control chart for monitoring process stability is generalized by selecting a point in time at which the distance between the control limits is reduced. Three cost models are developed to describe the total cost per unit time of monitoring the mean of a process using both the …
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A comparison of alternative methods to the shewhart-type control chart
A control chart that simultaneously tracks the mean and variance of a normally distributed variable with no compensation effect is defined in this work. This joint control chart is compared to five other charts: an Χ chart, an s² chart, a Reynolds and Ghosh chart, a Repko process capability plot, …
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An economic evaluation of variable sampling interval Shewhart control charts for means
A model is developed to describe the total expected cost per unit time of monitoring the mean of a production process with a Variable Sampling Interval control chart. This chart has the feature that the time delay between successive samples is not constant but depends on the result of the most …
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Determining the most appropiate [sic] sampling interval for a Shewhart X-chart
… charts. This thesis examines this problem for Shewhart X̅ charts. Duncan's economic model (1956) is used to develop a relationship between the most appropriate sampling interval and the present rate of"disturbances,” where a disturbance is a shift to an out of control state. A procedure is …
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Monitoreo y control estadístico de atributos en procesos con alta tasa de producción y bajo número de defectos: aplicación a un caso real de planta
… a través de los gráficos tradicionales de Shewhart (3-sigma), basados en la aproximación normal. Pero este tipo de gráfico no es exacto cuando la tasa de defectos p es muy pequeña. En la presente tesis se realiza una comparación entre los gráficos tradicionales de Shewhart con otros tipos …
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Cumulative sum quality control charts design and applications
… in terms of GM( I, I) model will be merged into Shewhart and CU SUM two-sided version control charts and establish Grey Predictive Shewhart Control chart and Grey Predictive CUSUM control chart. On the other hand the GM(2, I) model is briefly checked its of how accurate it could be as compared to …
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Monitoring for a Shift in a Process Covariance Matrix Using the Generalized Variance
… matrix Σ. In particular, we will study the Shewhart V and U charts supplemented with runs rules. Also, we examine the methods that are useful in studying the run length properties of the cumulative sum (CUSUM) U charts. Further, we will study the effect that estimating Σ₀ has on the …
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Variable sampling interval control charts
… are developed for the variable sampling interval Shewhart and cusum charts. A Markov chain is utilized to approximate the average time to signal and the corresponding variance for the cusum charts. Properties of the variable sampling interval Shewhart chart are investigated through Renewal Theory …
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Efficient Sampling Plans for Control Charts When Monitoring an Autocorrelated Process
… process plus a random error. Combinations of two Shewhart control charts and combinations of two exponentially weighted moving average (EWMA) control charts based on both the original observations and on the process residuals are considered. Three types of sampling plans are investigated: samples …
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Adaptive Threshold Method for Monitoring Rates in Public Health Surveillance
… these methods correctly signal an outbreak using Shewhart and exponentially weighted moving average (EWMA) charts. Our results indicate the adaptive threshold method gives more consistent statistical performance across different parameter sets and amounts of baseline historical data used for …
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The development of performance measures and diagnostic procedures for X(bar) and S(2) charts
… statistical process control methods, such as Shewhart charts, are responsible for the observation, evaluation, and diagnosis of processes to aid in the decision and implementation of corrective action.
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Anomaly detection methods for detecting cyber attacks in industrial control systems
… a baseline detection method, the multivariate Shewhart control chart, and four extensions to the Shewhart chart which use machine learning or optimization methods to improve detection performance. Two of these methods, stationary subspace analysis and maximized ratio divergence analysis, are …
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A statistical process control approach for network intrusion detection
… we developed the Modified Batch Mean Shewhart chart, the Modified Batch Mean Cusum chart, and the Modified Batch Mean EWMA chart and analyzed the performances of each one on simulated data. The simulation studies showed that the MBM charts perform especially well with large signals …
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Control chart procedures based on cumulative gauging scores
… the quality characteristic more quickly than the Shewhart type X-chart. The efficiency of the cusum type gauging score chart is close to the regular CUSUM chart. The random walk type gauging score chart is more robust than the Shewhart and CUSUM charts to observations which have heavy a tailed …
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Nonparametric procedures for process control when the control value is not specified
… values. Examples of the control charts are the Shewhart chart and the cumulative sum control chart (CUSUM chart). In designing a control chart, the exact distribution of the observations, e.g. normal distribution, is usually assumed to be known. But, when there is not sufficient information in …
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SIMULTANEOUS APPLICATION OF MULTIPLE PROCESS CONTROL RULES
… and the various combinations of these rules with Shewhart rule (or WECO rule 1) to SPC charts. As more rules are added to a process control scheme with Rule 1, there is a trade-off: a higher false out-of-control signal rate but an increase in sensitivity, that is the ability of a specified process …
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Monitoring the Process Mean of Autocorrelated Data
… parameters of the model. The performance of the Shewhart X chart and CUSUM X chart are compared. This includes determining the number of unobserved values between samples for the charts to perform as they would be expected if the samples were independent. Some recommendations are given.
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Control of a semiconductor dry etch process using variation and correlation analyses
… not have been detected using traditional x-bar Shewhart charts are detected by monitoring non-uniformity. Finally, cost analysis suggests that implementing SPC would be a modest investment relative to the potential savings.
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Statistical control and experimental design for edge bead reduction in laminating process
… process capability was calculated. After that, Shewhart control charts were employed to identify the assignable causes and to bring the process to in-control state. Then, a designed experiment was conducted to find the optimal operating conditions. It was found that line speed, screw speed, …
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