Osss Greenbelt Training Demo

Accuracy and Precision TM

Accurate but not precise On average, the shots are in the center of the target but there is a lot of variability

OSSS LSS Green Belt v9.0 - Measure Phase

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Precise but not accurate The average is not on the center, but the variability is small

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MSA Uses TM

MSA can be used to: Compare internal inspection standards with the standards of your customer. Highlight areas where calibration training is required. Provide a method to evaluate inspector training effectiveness as well as serves as an excellent training tool. Provide a great way to: –Compare existing measurement equipment. –Qualify new inspection equipment.

OSSS LSS Green Belt v9.0 - Measure Phase

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Bias TM

Bias is defined as the deviation of the measured value from the actual value. Calibration procedures can minimize and control bias within acceptable limits. Ideally, Bias can never be eliminated due to material wear and tear! Bias

OSSS LSS Green Belt v9.0 - Measure Phase

Bias

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Stability TM

Stability of a gauge is defined as error (measured in terms of Standard Deviation) as a function of time. Environmental conditions such as cleanliness, noise, vibration, lighting, chemical, wear and tear or other factors usually influence gauge instability. Ideally, gages can be maintained to give a high degree of stability but can never be eliminated unlike reproducibility. Gage stability studies would be the first exercise past calibration procedures. Control Charts are commonly used to track the stability of a measurement system over time. Drift Stability is Bias characterized as a function of time!

OSSS LSS Green Belt v9.0 - Measure Phase

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Linearity TM

Linearity is defined as the difference in Bias values throughout the measurement range in which the gauge is intended to be used. This tells you how accurate your measurements are through the expected range of the measurements. It answers the question, "Does my gage have the same accuracy for all sizes of objects being measured?"

B i a s (y)

Linearity = |Slope| * Process Variation +e % Linearity = |Slope| * 100

-e

0.00

Low

Nominal

*

*

High

*

Reference Value (x) y = a + b.x y: Bias, x: Ref. Value a: Slope, b: Intercept

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Types of MSA’s TM

MSA’s fall into two categories: – Attribute – Variable Attribute – – – – –

Variable

Pass/Fail Go/No Go Document Preparation Surface imperfections Customer Service Response

– – – – –

Continuous scale Discrete scale Critical dimensions Pull strength Warp

Transactional projects typically have attribute based measurement systems. Manufacturing projects generally use variable studies more often, but do use attribute studies to a lesser degree. OSSS LSS Green Belt v9.0 - Measure Phase

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