Resistance Thermometry Understanding the principles of resistance thermometry as they apply to resistance thermometers and thermistors will help you achieve consistent and accurate readings from your temperature sensing instruments. A resistance thermometer consists of a metallic element whose resistance increases with temperature. Their designs range from helical-wound thermometers for laboratory use to industrial thermometers that consist of several designs which allow it to conform closely to sensed surfaces. Two key benefits of the resistance thermometer include accuracy and stability. A thermistor consists of a semiconductor material whose resistance decreases as temperature increases. Key benefits of the thermistor are high resolution measurements over limited ranges and low cost. This white paper describes resistance thermometers and thermistors in detail, and will help you accurately calibrate your temperature reading instrument by performing calculations regarding resistance/temperature characteristics and the temperature coefficient of resistance. Details are provided regarding factors that can influence the temperature/resistance ratio such as element types, leadwire resistance, electrical noise, vibration, self-heating, and exposure to temperatures at or beyond the endpoint of a specified range. Resistance Thermometers Resistance thermometers may be called RTDs (resistance temperature detectors), PRTs (platinum resistance thermometers), or SPRTs (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, which is deposited on a ceramic substrate and trimmed 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. Click Here to Download the Full PDF | 
