About Thermistors > What is a NTC Thermistor?

What is a NTC Thermistor?

The word 'thermistor' is derived from the phrase THERMally-sensitive resISTOR and “NTC” stands for Negative Temperature Coefficient. This means that NTC thermistors have an inverse relationship between their electrical resistance and body temperature. They exhibit a decrease in electrical resistance with an increase in body temperature. This resistance/temperature (R/T) characteristic is non-linear, predictable, repeatable, and can be reproduced to exacting specifications. Because the R/T characteristic is non-linear, thermistors are commonly defined by their “R/T Curve” characteristic. The resistance value of a thermistor is typically referenced at 25 °C (abbreviated to “R25”). The most common NTC Thermistors R25 values used for thermistor applications are between 100 ohms and 100 k ohms. Other R25 values as low as 50 ohms and as high as 1 megohms can be produced and resistance values at temperature points other that 25 °C can be specified. NTC thermistors are small, rugged ceramic semiconductors manufactured from compositions of the oxides of metals, such as manganese, nickel, cobalt, copper, and/or iron. Each NTC thermistor composition or mix, has a specific ratio of metal oxides which defines the thermistor’s physical dimensions, R/T curve and its resistance at 25 °C. NTC thermistors also exhibit a relatively large change in resistance vs. temperature, typically on the order of -3 % to -6 % per °C, providing a much greater sensitivity or signal response to changes in temperature when compared to other temperature sensors, such as thermocouples and RTD’s. Comparative Resistance Graph - Over the range of -50 °C to 150 °C, NTC thermistors offer a distinct advantage in sensitivity to temperature changes compared to other temperature sensors. This graph illustrates the R/T characteristics of some typical NTC thermistors and a platinum RTD. NTC thermistors can be manufactured to “interchangeable” temperature tolerances. Interchangeability describes the degree of accuracy or tolerance to which a thermistor is specified and produced, and is normally expressed as a temperature tolerance over a temperature range. For instance, a typical thermistor specification would call for interchangeability to ± 0.1 °C from 0 °C to 70 °C. This means that precision NTC thermistors can be installed into devices at the factory and/or replaced in the field without an additional calibration step, greatly reducing expensive manufacturing and field service costs. NTC thermistors are well suited for sensing temperature at remote locations using wireless technology or long, two-wire cables. High resistance, interchangeability, tight tolerances, and small size make the thermistor perfect for battery operated remote temperature modules. In non-wireless applications, the high resistance of the NTC thermistor makes the low series resistance of long lead wires insignificant. As a result of improvements in ceramic technology, Cornerstone Sensors NTC thermistors produced today offer high stability and reliability. Because of their construction, NTC thermistors typically are more rugged and better able to handle vibration, mechanical and thermal shock than other temperature sensors. NTC thermistors can be manufactured to interchangeable tolerances of ± 0.1 °C over temperature spans of 70 °C and greater, and due to their responsiveness, they are exceptional for accurately measuring small changes in temperature at multiple temperature points.

A Brief History of NTC Thermistors >>