Thermistor

• From: tempsens.enquiry@gmail.com
• Posted: 08/10/2013 06:17PM
• City: Udaipur
• State: RAJASTHAN
• Phone Number: 917737308008
• Keywords: Thermistor,Thermistor
• Description:
• PRINCIPLES AND APPLICATIONS OF RESISTANCE THERMOMETERS AND THERMISTOR Resistance thermometers and Thermistor are temperature sensors, which changes there electrical resistance with temperature. The superior sensitivity and stability of these devices, in comparison to thermocouples, give them important advantages in low and intermediate temperature ranges. In addition, resistive devices often simplify control and readout electronics. Resistance thermometers are specified primarily for accuracy and stability from cryogenic levels to the melting points of metals. They are accurate over a wide temperature range and may be used to sense temperatures over a large area, and are highly standardized. The standard platinum resistance thermometer is specified by the ITS-90 (International Temperature Scale of 1990) to interpolate between fixed points in the range 13.80K (-259.35°C) to 1234.93K (961.78°C). RESISTANCE THERMOMETERS Resistance thermometers may be called as RTDs (resistance temperature detectors), PRT's (platinum resistance thermometers), or SPRT's (standard platinum resistance thermometers). These thermometers operate on the principle that, electrical resistance changes in pure metal elements, relative to temperature. The traditional sensing element of a resistance thermometer consists of a coil of small diameter wire wound to a precise resistance value. The most common material is platinum, although nickel, copper, and nickel-iron alloys compete with platinum in many applications. A relatively recent alternative to the wire-wound RTD substitutes a thin film of platinum or nickel-iron, which is deposited on a ceramic substrate and lasertrimmed to the desired resistance. Thin film elements attain high resistances with less metal, thereby lowering cost. RESISTANCE/TEMPERATURE CHARACTERISTICS Resistance thermometers exhibit the most linear signal with respect to temperature of any sensing device. Small deviations from straight-line response, however, dictate the use of interpolating polynomials to calculate resistance values between fixed temperature points. The resistance/temperature characteristic for standard platinum resistance thermometers, as defined by the ITS-90, is a complex set of equations. Platinum generally follows the modified Callendar-Van Dusen equation over the range -200 to 850°C (-328 to 1562°F):