What is a Thermistor?
A thermistor is a temperature sensor whose electrical resistance changes in response to a change in body temperature. Though the initial concept of an NTC thermistor was first reported in 1833 by Michael Faraday, when he discovered the effect of temperature on silver sulfide, it wasn’t until the 1930’s when the first commercial thermistors were produced. From that time on, countless improvements have been made in thermistor technology resulting in very rugged, extremely stable, highly accurate devices.
What types of thermistors are available?
There are two types of thermistors, NTC Thermistor sensors and PTC Thermistor sensors.
NTC thermistors (Negative Temperature Coefficient thermistors) exhibit a decrease in resistance as body temperature increases. NTC thermistors are produced using powdered metal oxides and the exact composition of those oxides as well as stabilizing agents determines the electrical characteristics of the thermistor. NTC thermistor sensors have a non-linear temperature vs resistance relationship and are capable of withstanding temperatures ranging from -55°C to +300°C.
PTC thermistors (Positive Temperature Coefficient thermistors) experience an increase in resistance as body temperature increases. The two main types of PTC thermistors include the Ceramic Switching PTC, which is a non-linear
device, and the Silicon PTC, which is highly linear. The transition temperature of switching PTCs is typically between 60°C and 120°C. Silicon PTC thermistors are typically rated up to 150°C, if used above this temperature they may exhibit a negative temperature coefficient. Silicon-based PTC thermistors have a much smaller drift than an NTC thermistor. They are inherently stable devices which are hermetically sealed in an axial leaded glass encapsulated package. The Silicon PTC thermistor is extremely reliable with a very long operational life.
EI Sensor Technologies offers a wide range of NTC thermistors for temperature measurement, control and compensation applications. Thermistor elements include Glass Body, Epoxy Coated, End-Banded Surface Mount Chips and Surface Mount MELF style. We also offer Inrush Current Limiters, which are specially processed thermistors used for suppressing high inrush currents in switching mode power supplies.
Thermistor elements can be fairly fragile. To better allow them to be used in harsh environments, the sensors can be mounted into a temperature probe assembly configuration. EI Sensor has a variety of thermistor probe styles to choose from including threaded, straight, flanged and many more. Please visit our Thermistor Probes and RTD Probes section to learn more. Our design engineers are available at firstname.lastname@example.org for assistance in selecting an appropriate thermistor probe assembly for testing in your unique application.
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