What is the Difference Between Eccentricity and Concentricity?

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Eccentricity and concentricity are two mathematical concepts related to the geometry of conic sections and shapes. They have significant practical applications in various scientific and engineering fields.

  • Eccentricity is a measure of the deviation of a conic section from a perfect circle. It is used to categorize conic sections, with a circle having no eccentricity (e=0). In orbital mechanics, eccentricity represents the degree of elongation of the orbit. Concepts like tube ovality and elliptical shape of rollers in machinery are also described using eccentricity.
  • Concentricity refers to two or more shapes, usually circles, sharing the same center or axis. It is a measure of alignment, and in the case of circles, it can be formulated as the ratio between the minimum difference between the radii to the maximum difference. Concentricity is important in various applications, such as ensuring the proper functioning of rollers in machinery, gear systems, fiber optic cables, and piping systems.

In summary, eccentricity is a measure of the elongation or deviation of a conic section from a perfect circle, while concentricity is a measure of alignment between two or more shapes sharing the same center or axis.

Comparative Table: Eccentricity vs Concentricity

Eccentricity and concentricity are two mathematical concepts related to the geometry of conic sections and are used in various science and engineering fields. Here is a table summarizing the differences between them:

Feature Eccentricity Concentricity
Definition Eccentricity is a measure of the deviation of a conic section from a perfect circle. Concentricity refers to two or more shapes sharing the same center, usually a system of circles.
Mathematical Description Eccentricity is a parameter used to classify conic sections and is measured by the offset with respect to the geometric center of the tube profile. Concentricity is a tolerance that controls the central derived median points of the referenced feature to a datum axis.
Applications In orbital mechanics, eccentricity gives the degree of elongation of the orbit. It is also used to measure the offset with respect to the geometric center of the tube profile in engineering. Concentricity ensures consistency in the designed system, such as in rollers of a press, gear systems, fiber optic cables, and piping systems. It is also used to control the central derived median points of a referenced feature to a datum axis in geometric dimensioning and tolerancing.
Measurement Eccentricity can be measured using a Coordinate Measuring Machine (CMM) or other metrology tools. Concentricity is considered one of the most difficult geometric tolerances to measure due to the difficulty in establishing the midpoints of the feature. Runout is often used as an indirect measure of concentricity.

In summary, eccentricity measures the deviation from a perfect circle, while concentricity ensures that two or more shapes share the same center. Eccentricity is used to classify conic sections and measure offsets in engineering applications, while concentricity is used to control the central derived median points of a referenced feature to a datum axis in geometric dimensioning and tolerancing.