14 definitions of common terms used in metrology 1

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1.4 DEFINITIONS OF COMMON TERMS USED IN METROLOGY 1. Accuracy – This is a measure of how close the measured value is to a true value. 2. Assembly - the connection of two or more separate parts to make a new single part. 3. Basic Dimension - The target dimension for a part. This typically has an associated tolerance. 4. Dimension - A size of a feature, either measured, or specified. 5. Dimensional Metrology - The use of instruments to determine object sizes shapes, form, etc. 6. English System Imperial; this basically refers to the standard system of measurements with British origin 7. Error - a discrepancy between expected and actual values. 8. Imperial System - An older system of measurement, still in use in some places, but generally replaced by the metric system. 9. Limits - These typically define a dimensional range that a measurement can be expected to fall within.
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10 10. Machine Tool - Generally use to refer to a machine that performs a manufacturing operation. This is sometimes confused with the actual cutting tools, such as a drill bit, that do the cutting. 11. Measurement - The determination of an unknown dimension. This requires that known standards be used directly or indirectly for comparison. 12. Measurand – this is the physical quantity or component being measured. 13. Metric System - A measurement system that has been standardized globally, and is commonly used in all modern engineering projects. 14. Metrology - The science of measurement. The purpose of this discipline it to establish means of determining physical quantities, such as dimensions, temperature, force, etc. 15. Precision - Implies a high degree of accuracy. 16. Repeatability - Imperfections in mechanical systems can mean that during a Mechanical cycle, a process does not stop at the same location, or move through the same spot each time. The variation range is referred to as repeatability. 17. Standards - a known set of dimensions, or ideals to compare others against. 18. Standard Sizes - a component, or a dimension that is chosen from a table of standard sizes/forms. 19. Tolerance - The allowable variation in a basic dimension before a part is considered unacceptable 20. Measuring is a process for ascertaining or determining the quantity of a product by application of some object of known size or capacity, or by comparison with some fixed unit. 21. Resolution is defined as the smallest increment change that gives some small but definite numerical change in the output of the measuring device. 22. Sensitivity- this is the relationship between a changes in the output reading for a given change in the input. Sensitivity is often known as scale factor of instrument magnification and an instrument with a large sensitivity (scale) factor will indicate a large movement of the indicator for small input change. 23. Repeatability- this is the ability of a measuring device to give identical indications or responses for repeated application of the same value of the measurand under stated conditions of use.
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