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2. Measurement Process Characterization


Statistical control of a measurement process

The purpose of this section is to outline the steps that can be taken to exercise statistical control over the measurement process and demonstrate the validity of the uncertainty statement. Measurement processes can change both with respect to bias and variability. A change in instrument precision may be readily noted as measurements are being recorded, but changes in bias or long-term variability are difficult to catch when the process is looking at a multitude of artifacts over time.

What are the issues for control of a measurement process?

  1. Purpose
  2. Assumptions
  3. Role of the check standard

How are bias and long-term variability controlled?

  1. Shewhart control chart
  2. Exponentially weighted moving average control chart
  3. Data collection and analysis
  4. Control procedure
  5. Remedial actions & strategies

How is short-term variability controlled?

  1. Control chart for standard deviations
  2. Data collection and analysis
  3. Control procedure
  4. Remedial actions and strategies
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