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TM 720 - Lecture 09

9/30/2012. TM 720: Statistical Process Control. 2. Assignment: . Reading:Finish Chapter 6

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TM 720 - Lecture 09

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    1. 9/30/2012 TM 720: Statistical Process Control 1 TM 720 - Lecture 09 Control Charts for Individuals

    2. 9/30/2012 TM 720: Statistical Process Control 2 Assignment: Reading: Finish Chapter 6 & 9+ 6.4 (pp. 231 – 238) 9.1 – 9.1.5 (pp. 400 – 410) 9.2 – 9.2.4 (pp. 419 – 425) 9.3 (pp. 425 – 430) End Chapter 8 Sections 8.4 – 8.8 Start Chapter 10 Sections 10 – 10.3.3 Assignments: Obtain the Chart Factors table from Materials Page Access Excel Template for P, NP, C, & U Control Charts: Download Assignment 6 for practice Use the data on the HW6 Excel sheet to do the charting, verify the control limits by hand calculations Access Excel Template for Individuals Control Charts

    3. 9/30/2012 TM 720: Statistical Process Control 3 Review Shewhart Control charts Are for sample data from an approximate Normal distribution Three lines appear on all Shewhart Control Charts UCL, CL, LCL Two charts are used: X-bar for testing for change in location R or s-chart for testing for change in spread We check the charts using 4 Western Electric rules Attributes Control charts Are for Discrete distribution data Use p- and np-charts for tracking defective units Use c- and u-charts for tracking defects on units Use p- and u-charts for variable sample sizes Use np- and c-charts with constant sample sizes

    4. 9/30/2012 TM 720: Statistical Process Control 4 Individual Measurements Sometimes repeated measures in a subsample don't make sense: inventory level accounts payable – price of an item Other reasons for using individual measurements Variation in sample only reflects measurement error, e.g., batch production of chemicals Automated inspection – every unit is analyzed Production rate very slow – inconvenient to wait for large enough sample

    5. 9/30/2012 TM 720: Statistical Process Control 5 Control Charts for Individual Measurements Notes about Individuals Charts: Sample points must be relatively frequent There is more sampling error (false alarm & insensitivity) Sample points tend to be non-normal points are not averages and central limit theorem does not apply Control Chart Types for Individuals: Shewhart x-chart and Moving Range chart (2 charts!) MA – Moving Average chart EWMA – Exponentially Weighted Moving Average chart CUSUM – Cumulative Sum chart

    6. 9/30/2012 TM 720: Statistical Process Control 6 Moving Range Control Chart MR2i = |xi – xi-1| - or - MR3i = |xi – xi-2|* Computation of the Moving Range:

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