Control charts with predetermined sampling intervals

Dias, J. Rodrigues; Infante, Paulo

doi:10.1108/02656710810865285

Cited by 4 publications

(1 citation statement)

References 12 publications

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“…In Rodrigues Dias (2002), a new method is proposed which addresses the problem of system failure rate. In Rodrigues Dias and Infante (2008) other results concerning this predetermined sampling intervals (PSI) method are presented.…”

Section: Introductionmentioning

confidence: 99%

Optimal economic solution for a normal sampling intervals method in quality control

Dias

2009

International Journal of Quality &Amp; Reliability Management

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PurposeThe main purpose of this paper is to present an optimal economic solution for a different adaptive sampling method that is highly intuitive in its nature: the normal sampling intervals (NSI) method.Design/methodology/approachConsidering costs associated with sampling, false alarms and imperfect operation per unit of time, the paper presents a new optimal simple solution that minimizes the expected total cost per cycle. This NSI method involves the density function of the standard normal variable, assuming that the distribution of averages is normal or approximately normal (on the basis of the central limit theorem). It depends on a single scale parameter while other methods depend on various parameters.FindingsWhen this expected total cost associated with the new NSI method is compared with the fixed (FSI) and variable sampling intervals (VSI) methods, in identical situations, it may be seen that, in general, it is lower (and may be much lower) and, also, that it is lower for a wider range of changes in terms of quality. This feature is particularly important because, in practice, the degree of change that occurs is not known, so this greater robustness in terms of performance is relevant.Practical implicationsIn the practice, the minimization of total expected costs is an important point of view in the life of companies, concerning quality and statistical process control (SPC). The paper holds that this NSI method has a great degree of potential, in particular considering that in industrial processes there is growing recourse to automated systems for the collection and analysis of samples, and thus there are no special additional costs associated with labour, management or administration.Originality/valueThe great advantages of this NSI method are its highly intuitive nature and the fact that it enables generally much better results to be achieved as compared with the use of FSI and VSI methods. An optimal economic solution for this NSI method is presented in this paper.

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Section: Introductionmentioning

confidence: 99%

Optimal economic solution for a normal sampling intervals method in quality control

Dias

2009

International Journal of Quality &Amp; Reliability Management

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Improving Shewhart control chart performance for monitoring the Weibull mean

Fernandes

Quinino

et al. 2020

Quality & Reliability Eng

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In this paper, we are interested in monitoring the stability of a Weibull process mean. We introduce a simplified variable sample size (SVSS) procedure, which consists of using alternately sample sizes nA and nB with nA>nB, to improve the performance of the traditional X¯ control chart (a fixed sample size n). Operationally, the proposal is relatively simple and its adoption yields a faster signal of an abnormal situation compared with the traditional X¯ chart in a variety of shifts. We present instructions for practitioners on how to design a control chart using the SVSS procedure. We also illustrate the proposed scheme through a numerical example.

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Cost comparisons of modifiedX̅chart for autocorrelated observations

Prajapati

2016

Int. J. Metrol. Qual. Eng.

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Abstract. This paper presents the economic design of modified X chart for autocorrelated data and comparison with the economic design of Shewhart's X chart. An attempt has been made to counter autocorrelation by designing the modified X chart; as the cost of operating a process control system is an important element in the economic design of control charts. The economic designs of both modified and Shewhart X charts for autocorrelated observations are presented; using Lorenzen-Vance [1] cost model. The modified X chart is based upon sum of chi-squares and has simplicity like Shewhart X chart but more efficient than standard chart. Two sets of parameters suggested by Montgomery [2] are used to determine the optimal sampling intervals (h) and expected costs per hour. It shows that sampling interval (h) and expected cost/hour (C) depend upon various parameters of chart, used in this model. The expected costs/hour (C) for both the charts are computed for sample sizes of 2 and 4 at the various levels of correlation and process shifts in mean. It is concluded that at each level of correlation and shift in the process mean, the expected costs/hour of the modified X chart are lower than the Shewhart chart.

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Control charts with predetermined sampling intervals

Cited by 4 publications

References 12 publications

Optimal economic solution for a normal sampling intervals method in quality control

Optimal economic solution for a normal sampling intervals method in quality control

Improving Shewhart control chart performance for monitoring the Weibull mean

Cost comparisons of modifiedX̅chart for autocorrelated observations

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