subject: Basic Differences Between A Thermocouple And A Thermistor [print this page] A Thermocouple and a thermistor are both temperature measurement devices used in process manufacturing. They offer different benefits, and both are widely used in the pharmaceutical industry, food industry, beverage industry, processing industry, and other industries. Understanding the difference between thermocouples and thermistors will help you know which instrument is best suited for your needs.
A thermocouple, based on the Seebeck effect, is a type of thermometer that reads the temperature by measuring the voltage created by placing one end of two different metal wires twisted together in a substance, and keeping the other ends at a constant temperature. This creates an electric voltage, and by measuring this voltage scientists in the nineteenth century were first able to accurately measure temperatures over 500 degrees Fahrenheit.
Thermocouples are excellent process temperature measurement devices, extremely well suited for harsh and high temperature environments (with some thermocouples operating perfectly well up to 4200 degrees Fahrenheit). Thermocouples are used in dozens of engineering, chemical, manufacturing, industrial, waste treatment, plastic production, energy production, and food processing facilities.
Thermocouples are made in many different types. Each type is a standardized junction of two particular metal wires (such as a junction of iron and constantan, which is known as type J). Each type of thermocouple has a certain range of temperatures that it is suited for. Types T, E, K, and J are the most common and versatile junction types for thermocouples. Other types are helpful for more extreme environments where high velocity, extreme temperatures, high pressure, corrosive temperatures, and high moisture oxidation risks are present. Thermocouples can be customized with the right coated wires and adjustments to be fire proof, explosion proof, and long lasting even in harsh environments. They are very accurate within their temperature range. Most offer very rapid response times.
Thermistors also measure temperatures, but operate differently from thermocouples. Instead of producing an electric voltage like a thermocouple, a thermistor (also known as a thermal resistor) has an electrical resistance that varies with the temperature. There are two basic types (or families) of thermistors. Positive temperature coefficient thermistors (also known as PTCs) have an electrical resistance that is in direct proportion to the temperature. Negative temperature Coefficient thermistors (also known as NTCs) have an electrical charge that changes in inverse proportion to the temperature.
Thermistors are small, rugged, and accurate, and have a fast response time. They are frequently used in laser diode applications due to their low price. They are more cumbersome and difficult to use and decipher than a thermocouple is, due to the fact of thermistors' non-linearity.
