Overview of Type A and Type B Evaluation of
The analysis of a measurement system involves
understanding the uncertainties associated with
taking a particular measurement and then, where
possible, quantifying those uncertainties.
Evaluation of measurement uncertainties are
classified into Type A and Type B.
Type A Uncertainties
can be quantified by
statistical means. Type A Uncertainties include
- Implementation and use of a solid Calibration
Program helps address accuracy issues.
- Looks at the accuracy of
measurements over the full range of the device and can be evaluated using statistical methods.
- Stability studies evaluate a measurement
device performs over time.
Studies of repeatability and reproducibility
are called Gage Repeatability and
Reproducibility studies or GR&R for short.
The variation from the test equipment is
called Repeatability. A good way to think about
repeatability is that it is the variation we get
when we measure the same part a number of times
with the same measuring device.
Reproducibility variation is the uncertainty,
or variation, we get between people who are
measuring the same parts with the same gage.
Many times this is the largest source of
measurement system variation.
There are other uncertainties associated with
measurement systems that cannot be evaluated as
readily by statistical methods. These are called
Type B Uncertainties.
- Errors in part form
- Fixture variations
- Conditioning requirements