About NTC Thermistors
NTC thermistors are the most sensitive temperature sensing devices in general use for temperature measurement control, indication and compensation for the temperature range of -50 °C to +150 °C.
A thermistor is composed of a semiconducting material that acts like a thermally sensitive resistor. The primary function of a thermistor is to exhibit a change in resistance with a change in body temperature whether caused by a change in ambient temperature or current-induced self-heating. By measuring the resistance of a thermistor in a non-self heat mode, we can accurately determine it's temperature and its surrounding medium. In some measurement applications, thermistors are deliberately self-heated by an electrical current under controlled conditions. In this case, a self-heated thermistor may be used to measure the flow of gases or liquids.
NTC thermistors (Negative Temperature Coefficient) decrease in electrical resistance as body temperature increases while PTC thermistors (Positive Temperature Coefficient) increase in electrical resistance with increasing body temperature. North Star Sensors specializes in manufacturing precision NTC thermistors from basic raw materials to finished products. Each production step is closely monitored and controlled.
The thermally sensitive, semiconductor material in an NTC thermistor is composed of tightly packed and sintered grains of metal oxides such as manganese oxide, nickel oxide, iron oxide, and copper oxide. These solid structures are semi-conductive to electricity and, as temperature increases, electrons have a higher chance of being in the conductive energy band of the material. This is why electrical conductivity increases with an increase in body temperature and electrical resistance decreases. Conversely, a decrease in body temperature results in an increase in electrical resistance.
This resistance/temperature (R/T) characteristic of an NTC thermistor is non-linear, predictable, repeatable, and can be reproduced to exacting specifications. Because the R/T characteristic is non-linear, NTC thermistors are commonly defined by their “R/T curve” characteristic. The resistance value of an NTC thermistor is typically referenced at 25 °C (abbreviated to “R25”). The most common R25 values used for NTC thermistor applications are between 100 ohms and 100,000 ohms. R25 values as low as 50 ohms and as high as 1 Megohms can be produced. Custom NTC thermistors with resistance values point-matched at temperature points other than 25 °C can be specified.
Each NTC thermistor composition or mix, has a specific ratio of metal oxides which defines the thermistor’s physical dimensions, R/T curve characteristics and its resistance at 25 °C. They 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.
NTC thermistors are considered to be one of the most versatile temperature sensor product lines in the industry because they are available in a variety of physical configurations; leadless NTC thermistors, leaded NTC thermistors, and temperature probe assemblies.
Leadless NTC thermistors may be soldered or epoxied to hybrid circuits.
Leaded NTC thermistors may be PC board-mounted or have extension leads attached.
NTC thermistor probes and assemblies are designed to protect the NTC thermistor from the environment while placing in optimal sensing locations. For fast response applications, micro NTC thermistors can fit into a stainless steel 22 gauge needle.
Besides standard NTC thermistor probe/assembly configurations, North Star Sensors can build custom NTC thermistor products to meet unique application requirements. When desired, North Star Sensors can also incorporate other sensor technology into a probe design. Custom RTD and thermocouple assembly services are offered as well.