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# Ch.5 SPC

### DS 412 TEST 1

Question | Answer |
---|---|

X-bar | Average, use past if offered bc already in control |

R-bar | Range, use past if offered bc already in control (less accurate as sample size gets larger) |

UCLx | (X-bar2) + A2*R-bar (for x-bar chart) |

LCLx | (X-bar2) - A2*R-bar (for x-bar chart) |

UCLR | D4*R-bar (for R-bar chart) |

LCLR | D3*R-bar (for R-bar chart) |

A2 | on table dependent on sample, used in X-bar & R-bar chart |

n | sample *do not confuse with sample size larger then 10 |

D3 & D4 | used with R-bar chart, on table |

Out of Control/Causal | past UCL/LCL, run, extreme jump/drop |

σ | standard deviation |

σx | σ/√n |

Z | normal deviate (# of standard dev from average) or tolerance; closer to 6 (six sigma) more accurate. 2 if not really important, 3-life threatening/small difference is important |

UCLx using σx | x-bar2 + Z*σx |

LCLx using σx | x-bar2 - Z*σx |

σp | √ p-bar (1-Pbar)/n |

P-bar | # defects/#observations |

UCLp | P-bar + Z*σp |

LCLp | P-bar - Z*σp |

Process Capability Index (Cpk) | use when target & x-bar not close MIN of [x-bar-Lower spec/3σ,Upper-x-bar/3σ |

Process Capability Ratio (Cp) | Upp-Low Spec/6σ |

Capable? | if not below 1.33 |

Variable | MEASURED/quantitative (weight, length, volume, time)*not used if specifications are complex/costly/difficult/unnecessary |

Attribute | COUNTED/Qualitative (Yes/No) color,taste,smell,surface texture |

Non-destructive sampling | 100% sampling,if easy/not expensive ie software test comp speed |

Destructive Sampling | costly, can't be reused |

In Control (random) | 1. No sample points outside limits 2. Most pts near process avg 3. Approx equal # pts above&below center 4. Randomly distributed around center 5. No extreme jumps 6. Cannot detect trend |

Average σ = Average R (when...) | n=2 |

Type I error | Probability of searching for a cause when none exists |

Type II error | Probability of concluding that nothing has changed |

Errors controlled by... | Choice of control limits |

+/- 1σ | 68.26% normal distribution |

+/- 2σ | 95.44% normal distribution |

+/- 3σ | 99.97% normal distribution |

Created by:
victoriaoharra