Statistics - Process Sigma


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Process sigma can be defined using following four steps:

  1. Measure opportunities,

  2. Measure defects,

  3. Calculate yield,

  4. Look-up process sigma.

Formulae Used

DPMO=Total defectTotal Opportunities×1000000

Defect(%)=Total defectTotal Opportunities×100

Yield(%)=100Defect(%)

ProcessSigma=0.8406+29.372.221×(log(DPMO))

Where −

  • Opportunities = Lowest defect noticeable by customer.

  • DPMO = Defects per Million Opportunities.

Example

Problem Statement:

In equipment organization hard plate produced is 10000 and the defects is 5. Discover the process sigma.

Solution:

Given: Opportunities = 10000 and Defects = 5. Substitute the given qualities in the recipe,

Step 1: Compute DPMO

DPMO=Total defectTotal Opportunities×1000000=(10000/5)×1000000,=500

Step 2: Compute Defect(%)

Defect(%)=Total defectTotal Opportunities×100=100005×100,=0.05

Step 3: Compute Yield(%)

Yield(%)=100Defect(%)=1000.05,=99.95

Step 3: Compute Process Sigma

ProcessSigma=0.8406+29.372.221×(log(DPMO))=0.8406+29.372.221×(log(DPMO)),=0.8406+(29.37)2.221(log(500)),=4.79