Dimensional metrology

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Dimensional Metrology is the science of calibrating and using physical measurement equipment to quantify the physical size of or distance from any given object. Inspection is a critical step in product development and quality control. Dimensional Metrology requires the use of a variety of physical scales to determine dimension, with the most accurate of these being holographic etalons or laser interferometers. The realization of dimension using these accurate scale technologies is the end goal of dimensional metrologists.

Early Mesopotamian and Egyptian metrologists created a set of measurement standards based on body measures such as fingers, palms, hands, feet, Cubits, and paces and agricultural measures such as feet, yards, paces, fathoms, rods, cords, perch, stadia, miles and degrees of the Earth's circumference. Early Egyptian rulers based on units of fingers, palms and feet based on inscription grids that incorporated standards of measure as canons of proportion were made commensurate with Mesopotamian standards based on fingers, hands and feet so that four palms or three hands equaled one foot and ten hands equaled one meter. These standards which were used to measure and define property such as buildings and fields were adopted by the Greeks, Romans and Persians as legal standards and became the basis of European standards of measure. They were also used to relate length to area with units such as the khet, setat and aroura, area to volume with units such as the artaba and space to time with units such as the Egyptian minute of march, the itrw which recorded an hours travel on a river, and the days sail. Specialized units for carpenters, masons and other craftsmen such as the remen were worked into a system of unit fractions that allowed calculations utilizing analytic geometry. Carpenters and surveyors were some of the first dimensional inspectors.

Modern measurement equipment include hand tools, CMMs (Coordinate-Measurement Machine), machine vision systems, laser trackers, and optical comparators. For hand tools, see Caliper and micrometer. A CMM is based on CNC technology to automate measurement of Cartesian coordinates using a touch probe, contact scanning probe, or non-contact sensor. Optical comparators are used when physically touching the part is undesirable. Optical comparators can now build 3D models of a scanned part and internal passages using x-ray technology. Furthermore, optical 3D (laser) scanners are becoming more and common. By using a light sensitive detector (e.g. digital camera) and a light source (laser, line projector) the triangulation principle is employed to generate 3D data, which is evaluated in order to compare the measures against nominal geometries.

Data is collected in or compared to a print. A print is a blueprint illustrating crucial features. Prints can be hand drawn or automatically generated by a CAD model.

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Industrial Metrology for manufacturing quality and for Standards room/calibration activities are called as first principle method of deriving the actual value of measurement. the field of in process gauging, incycle gauging and post process gauging are excluded from this topic

Equipment generally used for manufacturing quality depends on industry, but broadly around mechanical engineering and in particular automotive aerospace, machine tool, any other precision parts suitable for instrumentation. This is broadly listed below:

1. Basic hand held instruments like Vernier Caliper, digital caliper, micrometer etc.

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