Module 2C

Module 2C - IE 361 Module 2 Basic Concerns of Metrology and...

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Unformatted text preview: IE 361 Module 2 Basic Concerns of Metrology and Some Simple Applications of Elementary Probability and Statistics to Metrology Reading: Section 2.2 Statistical Quality Assurance for Engineers (Sections 2.1-2.2.1 of Revised SQAME ) Prof. Steve Vardeman and Prof. Max Morris Iowa State University Vardeman and Morris (Iowa State University) IE 361 Module 2 1 / 26 Formulating Appropriate Measures of Process Performance In a quality assurance/process improvement context, measures of process performance should be customer-oriented . A nice example of this point is an early attempt by one of the "Big 3" US auto makers to track initial customer satisfaction. This company &rst tried using corporate warranty costs (charged to the company by dealers doing in-warranty service) as its measure of satisfaction. That was clearly not anything a customer cares about. A more appropriate measure that was later adopted was "per vehicle visits to a dealer for warranty service." Huge modern marketing eorts are aimed at &nding out what is important to customers. In successful organizations, these help de&ne what measures of process performance are employed and monitored by the organizations. Vardeman and Morris (Iowa State University) IE 361 Module 2 2 / 26 Formulating Appropriate Measures of Process Performance In any data collection context (including a process improvement e/ort) direct measures of a quantity are always preferable to relatively indirect ones. If one wants to know about y , it is better to try to measure y than to measure w that is presumed to be related to y . If, for example, one is designing a controller for a clothes dryer, somehow measuring weight loss as water is removed from a load is preferable to measuring air temperature of the dryer&s exhaust, even if it is easier to do the latter than to gure out how to do the former. In the above auto initial customer satisfaction context, some direct inquiries to customers about satisfaction is probably preferable to reliance on only the per vehicle service calls measure. The matter of measuring process performance brings us naturally to the general topic of measurement, or the science of "metrology." Vardeman and Morris (Iowa State University) IE 361 Module 2 3 26 Basic Terminology and Concerns of Metrology A quantity for which one hopes to establish a true or correct value is called a measurand . (A measurand can be anything from the surface roughness of a machined metal part, to the torque delivered by a pneumatic torque gun, to the color of a printed carton.) "The problem" is that in the real world, a measurand can rarely (if ever) be known perfectly. That is, there is almost always some measurement error associated with attempts to evaluate a measurand. A measurement y never perfectly re&ects a measurand x . This is illustrated in cartoon form in the next gure. (We are here going to use the generic term "device" to describe a particular combination of equipment, people, procedures, etc. used to produce a measurement.) Vardeman and Morris (Iowa State University) IE 361 Module 2 4 / 26 Basic Terminology and Concerns of Metrology...
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Module 2C - IE 361 Module 2 Basic Concerns of Metrology and...

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