02___Temperature - MAD 413 MAD Instrumentation &...

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MAD 413 MAD 413 by by Dr. E. Caner ORHAN Dr. E. Caner ORHAN Hacettepe University Hacettepe University Department of Mining Engineering Department of Mining Engineering Temperature Temperature
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2 Lecture Notes by Dr. E.Caner ORHAN Temperature measuring devices Methods for measuring temperature; 1. Expansion of a material to give visual indication, pressure, or dimensional change 2. Electrical resistance change 3. Semiconductor characteristic change 4. Voltage generated by dissimilar metals 5. Radiated energy
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3 Lecture Notes by Dr. E.Caner ORHAN Thermometers Mercury thermometer (-35 to 450 ° C)
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4 Lecture Notes by Dr. E.Caner ORHAN Thermometers Bimetallic strip If two strips of dissimilar metals such as brass and invar (copper-nickel alloy) are joined together along their length, they will flex to form an arc as the temperature changes. Bimetallic strips are usually configured as a spiral or helix for compactness and can then be used with a pointer to make a cheap compact rugged thermometer. Their operating range is from −180 to 430°C and can be used in applications from oven thermometers to home and industrial control thermostats.
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5 Lecture Notes by Dr. E.Caner ORHAN Thermometers Bimetallic strip
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6 Lecture Notes by Dr. E.Caner ORHAN Thermometers Bimetallic strip Relatively inaccurate Slow to respond Not normally used in analog applications to give remote indication Has hysteresis Extensively used in ON/OFF applications not requiring high accuracy.
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7 Lecture Notes by Dr. E.Caner ORHAN Resistance temperature devices (RTD) RTDs are comprised of pure metals or certain alloys that increase in resistance as temperature increases and, conversely, decrease in resistance as temperature decreases. The metals that are best suited for use as RTD sensors are pure, of uniform quality, stable within a given range of temperature, and able to give reproducible resistance- temperature readings. Only a few metals have the properties necessary for use in RTD elements.
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8 Lecture Notes by Dr. E.Caner ORHAN Resistance temperature devices RTD elements are normally constructed of platinum, copper, or nickel. These metals are best suited for RTD applications because of their linear resistance- temperature characteristics, their high coefficient of resistance, and their ability to withstand repeated temperature cycles.
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9 Lecture Notes by Dr. E.Caner ORHAN Resistance temperature devices Linear Approximation: A linear approximation means that we may develop an equation for a straight line that approximates the resistance versus temperature (R - T) curve over some specified span.
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02___Temperature - MAD 413 MAD Instrumentation &...

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