A METHODOLOGY FOR RANKING OF ALARMS IN CONTROL CHARTS
Keywords:
Control chart, statistical process control (SPC), graded SPC, and decision making using zonesAbstract
Control charts are main tools used to detect whether variation in the quality characteristic
is because of chance or assignable cause. Traditional control chart is separated into
definite zones and engineers use them as a criterion to either continue or stop the process
depending upon the position of the newly observed points in the zones. Since the control
charts are defined using zones, points that are in the same zone are viewed as having the
same risk of being out of control. This paper discusses the limitations of the traditional
zoning of control charts and problems faced by engineers in taking corrective actions
based on the results of the charts. A new methodology is proposed in this paper for
estimating the risk of the points lying on a control chart. A severity number is then
assigned to the points to show the degree of severity of each point. The propose d severity
number will be useful for engineers in generating different action plans. Engineers will
actually place different approach or rigorousness in investigat ing for any assignable
causes based on the different ranking of the severity number. Later, a simulation is used to
show how the proposed method is used in ranking the out of control points.
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