A New EWMA Chart for Monitoring Process Dispersion

• Autores: Lianjie Shu, Wei Jiang
• Localización: Journal of quality technology: A quarterly journal of methods applications and related topics, ISSN 0022-4065, Vol. 40, Nº. 3, 2008, págs. 319-331
• Idioma: inglés
• Enlaces
  • Texto completo
• Resumen

  • The exponentially weighted moving average control chart (EWMA) based on the logarithmic transformation of sample variance for monitoring increases in process variability is an example of a dispersion chart that has recently received a great deal of attention. The traditional version of this chart resets the EWMA statistic to zero whenever it falls below zero. A new EWMA dispersion chart is proposed by truncating negative normalized observations to zero in the traditional EWMA statistic. Results show this new chart outperforms the traditional EWMA chart for detecting dispersion changes, especially small changes.