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Process Control Charts

Process Control Charts . By: Brian Murphy. Control Charts are an on-line process-monitoring technique. Used to determine if a process is capable or out of control. In control processes operate with only chance causes of variation.

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Process Control Charts

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  1. Process Control Charts By: Brian Murphy

  2. Control Charts are an on-line process-monitoring technique. • Used to determine if a process is capable or out of control. • In control processes operate with only chance causes of variation. • Out of control processes have assignable causes of variation and can be restructured when identified.

  3. Control Chart Contains • A center line (usually the arithmetic mean or the average of a collection of sample ranges) • A Lower and Upper Control Limit (LCL and UCL) • Points beyond the control limits indicate that the process is out of control.

  4. Formulas: • xave = grand average of x = (x1+x2+…+xm)/m Or R=xmax-xmin R1, R2,…,Rm: ranges of m samples Rave = (R1+R2+…+Rm)/m

  5. Control Limits for R chart: • UCL = D4*Rave • Center Line = Rave • LCL = D3*Rave • Control Limits for x chart: • UCL = xave + A2*Rave • Center Line = xave • LCL = xave –A2*Rave *See next slide for values of D3, D4 and A2

  6. *n denotes sample size

  7. Rules for determining out of control process:

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