Selecting/Developing Test Procedures
Selecting/Developing Test Procedures: Many appropriate procedures are available for assessing measurement systems. The choice of which procedure to use depends on many factors, most of which need to be determined on a case-by-case basis for each measurement system to be assessed. In some cases, preliminary testing may be required to determine if a procedure is appropriate for a particular measurement system or not.
General issues to consider when selecting or developing an assessment procedure include:
Should standards, such as those traceable to NIST, be used in the testing and, if so, what level of standard is appropriate? Standards are frequently essential for assessing the accuracy of a measurement system. If standards are not used, the variability of the measurement system can still be assessed, but it may not be possible to assess its accuracy with reasonable credibility. Lack of such credibility may be an issue, for instance, if attempting to resolve an apparent difference between a producer’s measurement system and a customer’s measurement system.
For the ongoing testing in Phase 2, the use of blind measurements may be considered. Blind measurements are measurements obtained in the actual measurement environment by an operator who does not know that an assessment of the measurement system is being conducted. Properly administered, tests based on blind measurements are usually not contaminated by the well-known Hawthorne effect.
The cost of testing.
The time required for the testing.
Any term for which there is no commonly accepted definition should be operationally defined. Examples of such terms include accuracy, precision, repeatability, reproducibility, etc.
Will the measurements made by the measurement system be compared with measurements made by another system? If so, one should consider using test procedures that rely on the use of standards such as those discussed in Phase 1 above. If standards are not used, it may still be possible to determine whether or not the two measurement systems are working well together. However, if the systems are not working well together, then it may not be possible, without the use of standards, to determine which system needs improvement.
How often should Phase 2 testing be performed? This decision may be based on the statistical properties of the individual measurement system and the consequence to the facility, and the facility’s customers of a manufacturing process that, in effect, is not monitored due to a measurement system not performing properly.
In addition to these general issues, other issues that are specific to the particular measurement system being tested may also be important Finding the specific issues that are important to a particular measurement system is one of the two objectives of the Phase 1 testing.
source of Selecting/Developing Test Procedures : Analysis of measurement systems
