Resistance Thermometry: Principles and Applications of Resistance Thermometers and Thermistors

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.