14.03.2014 Views

Quality and Reliability Methods - SAS

Quality and Reliability Methods - SAS

Quality and Reliability Methods - SAS

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

104 Cumulative Sum Control Charts Chapter 6<br />

Formulas for CUSUM Charts<br />

Figure 6.9 Show Parameters<br />

Formulas for CUSUM Charts<br />

Notation<br />

The following notation is used in these formulas:<br />

μ denotes the mean of the population, also referred to as the process mean or the process level.<br />

μ 0 denotes the target mean (goal) for the population. Sometimes, the symbol X 0 is used for μ 0 . See<br />

American Society for <strong>Quality</strong> Statistics Division (2004). You can provide μ 0 as the Target on the known<br />

statistics dialog.<br />

σ denotes the population st<strong>and</strong>ard deviation.<br />

σ 0 denotes a known st<strong>and</strong>ard deviation. You can provide σ o as the sigma on the known statistics dialog or<br />

through JSL.<br />

σˆ denotes an estimate of σ.<br />

n denotes the nominal sample size for the cusum scheme.<br />

δ denotes the shift in μ to be detected, expressed as a multiple of the st<strong>and</strong>ard deviation. You can provide δ<br />

as the delta on the dialog or through JSL.<br />

Δ denotes the shift in μ to be detected, expressed in data units. If the sample size n is constant across<br />

subgroups, then<br />

Δ = δσ = ( δσ) ⁄ n<br />

X<br />

Note that some authors use the symbol D instead of Δ. You can provide Δ as the Shift on the dialog or<br />

through JSL.<br />

One-Sided CUSUM Charts<br />

Positive Shifts<br />

If the shift δ to be detected is positive, the CUSUM computed for the t th subgroup is<br />

S t = max(0, S t – 1 + (z t – k))

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!