A lubricant is an organic or synthetic substance (it can occur in any physical state: liquid, solid, gaseous and even semi-solid or viscous) which has the property of reducing the friction between surfaces in contact under any operating condition, dissipating the heat generated during the relative movement between the surfaces, maintaining its chemical stability, protecting…

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A gear (or cogwheel) it is the main element in a transmission system, in which teeth are cut around cylindrical or cone shaped surfaces with equal spacing; or in the case of a cogwheel, inserted teeth (called cogs). By meshing a pair of these elements, they are used to transmit rotations and forces from the…

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A semiconductor is a substance with an electrical conductivity between that of a conductor and an insulator — the conductivity of a semiconductor increases as temperature increases. Adding appropriate impurities also increases conductivity. Amorphous semiconductor An amorphous semiconductor also called “thin film” is a non-crystalline semiconductor material that has no long-range order. Although easier and…

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An electric circuit is an unbroken loop of conductive material that allows electrons to flow through continuously without beginning or end. If a circuit is broken, that means it’s conductive elements no longer form a complete path, and continuous electron flow cannot occur in it. The location of a break in a circuit is irrelevant…

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Humidity is the amount of water vapor in the air, measured as mass of water per unit volume or mass of air, or as a percentage of the maximum amount the air would support without condensation, or indirectly via the dew point. Saturation of the air occurs when the water vapor pressure reaches the vapor pressure…

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Dynamic electricity, or electric current, is the uniform motion of electrons through a conductor. Static electricity is an unmoving, accumulated charge formed by either an excess or deficiency of electrons in an object. Although it is electrons which are the mobile charge carriers which are responsible for electric current in conductors, it has long been…

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The length, quantitatively and objectively, identifies a material body according to a single main or prevalent dimension of the body itself. The measure of length leads to the knowledge of the geometry of bodies, that is to their “dimensions.” Many length measurements are also based on many (indirect) measurements of other physical quantities. Length measurements…

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The MEMS technology (acronym of Micro Electro Mechanical Systems) is a manufacturing technology of microelectronic devices which, combining the principles of electronic technology based on silicon with micromachining, allows the creation of “intelligent” devices with high integration between electronic circuits and optomechanics devices, on the same chip. It merges at the nano-scale into nanoelectromechanical systems…

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A linear variable differential transformer (LVDT) is one of the most popular electromechanical devices used to convert small mechanical displacements (of the order of a few millimeters or fractions of a millimeter) into amplified electrical signals. An LVDT provides an alternating current (AC) voltage output proportional to the relative displacement of a transformer core with…

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An accelerometer is a measuring instrument able of detecting and/or measuring acceleration (or the gravitational force), calculating the force measured with respect to the mass of the object (force per unit of mass). Therefore the operating principle of an accelerometer is based on the detection of the inertia of a mass when it is subjected…

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The International System of Units universally abbreviated SI (from the French Le Système International d’Unités), is the modern metric system of measurement, used prevalently in science and international commerce. How to write unit symbols and names, expressing the values of quantities Unit symbols are printed in roman (upright) type regardless of the type used in the surrounding text. They…

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In Metrology the term measurement is closely associated with all the activities about scientific, industrial, commercial, and human aspects. It is defined as the assignment of a number to a characteristic of an object or event, which can be compared with other objects or events. The knowledge of the reality that surrounds us is based on the…

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A device used for the measurement of a certain physical quantity is called a measuring instrument. The instruments indicate the value of these quantities, based on which we get some understanding and also take appropriate actions and decisions. There are two main types of measuring instruments: analog and digital. The analog instruments indicate the magnitude…

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In Metrology, tolerance means the limit or acceptable limits of the variations of a physical dimension, a physical property of a manufactured object, of a system, or other measured values such as temperature, humidity or time. In other words, it is the maximum allowable error in the measurement is specified in terms of some value.…

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In Metrology, dead space or threshold is a static characteristic of an instrument defined as the range of different input values over which there is no change in output value. If the instrument input is increased very gradually from zero there will be some minimum value below which no output change can be detected. This minimum value defines the threshold…

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Hysteresis is a delay of the effect when the forces acting upon a body are changed (as if from viscosity or internal friction), or lagging in the values of resulting magnetization in a magnetic material (as iron) due to a changing magnetizing force. Hysteresis error The hysteresis error of a measuring instrument is defined as…

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