Lecture 9 - Measurement Flashcards
Define Resolution
The smallest change in the input that the measuring tool can observe. Verier calipers have a resolution of 0.001”
Accuracy Vs Precision
Accuracy is a comparison: the true condition compared with the measured value. “quality of conformity”
Precision reports the dispersion of results or degree of repeatability. “the quality of refinement”
Range vs Span of a measurement tool
Range: the limit of the tool’s input
Span: Max range minus Min range
Caliper has a range of 0-6” and a span of 6”
Define Error
Error is the difference between the result of the measurement and the true value of the quantity being measured.
Error = measured value - true value
What is the “Rule of 10”?
The measuring device must be 10 times more precise than the specified tolerance.
What’s the difference between measured and gauged inspection?
product dimensions that are gauged to see if they meet tolerances. think “go/ no go gauge”
product dimensions that are measured give a numerical value.
What are gauge blocks made from? and which is better?
Gauge blocks are usually made from steel or ceramics. Ceramics are better but more expensive
What 3 things hold gauge blocks together?
Vacuum - applies pressure between the blocks because the air is squeezed out of the joint.
Surface Tension - from oil and water vapor that is present between the blocks.
Molecular attraction - when 2 very flat surfaces are brought into contact.
What are the types of measuring Instruments and gauges?
1) Precision gauge blocks
2) Measuring instruments for linear dimensions (Ex. vernier)
3) Comparative instruments (Dial indicators)
4) Fixed gauges (feeler gauges, go/no-go gauge)
5) Angular measuring instruments (vernier protractor)
What are the types of Surface roughness measurement tools?
1) Subjective comparison - Chart with different surface finishes
2) Stylus Instruments - electronic device using a Dimond cone traversed across surface
3) Optical Techniques - light reflectance, light scatter or diffusion, and laser technology
What is a Coordinate Measuring Machine(CCM)? what are some advantages?
Consists of contact probe that moves in 3 dimensions relative to a surface and feature of a workpart. Locations are computer generated and recorded for high accuracy.
Advantages: Higher Productivity, Greater inherent accuracy and precision, reduced human error and computer generated documentation, analysis and reports.
