Thermocouples Assemblies are the most common and versatile sensors used to measure temperature. They can be designed to work in any application where a temperature measurement is required ranging from minus 300 oF to over 4000 oF.

Thermocouples operate on the principle of thermal emf (Electromotive Force). Thomas Seebeck observed in 1821 that two dissimilar metal wires, if joined at both ends, produce a current when the junctions are at different temperatures. The current produced is a function of the junction temperature and the type of metals used. This relationship between thermal emf and temperature is now known as the Seebeck effect.

The thermal emf can be measured by breaking the thermocouple loop at any point and measuring the open circuit voltage. For example, a thermocouple, made of Chromel/Alumel metals (Type K) generates about 40 microvolts per degree Celsius.

The voltage/temperature relationship varies depending on the metals used. The metal combinations used depend on the output voltage required and the temperature range monitored. ANSI Thermocouples are tested and graded against the American National Standards Institute standards and are available in Standard and Special Limits grades. The Special Limits grade has only half the error of the Standard grade and is recommended for high temperature applications.

Thermocouples are considered to be “tip sensitive” because they measures temperature at the junction, which is located at the end or tip of the sensor. Care should be given when considering the best assembly to fit an application. To acquire accurate temperature readings careful consideration should be given to the design and sensor location in the process.

GIC Thermodynamics’ sales and engineering staff will assist you with designing the best thermocouple sensor style to fit your process and application. Selecting the proper sensor style is very important, as each application or process has its own specific inherit problems that require careful consideration in order to determine the sensors life, accuracy, and dependability. When choosing a sensor it is important to consider its location, temperature range, accuracy required, how rapidly the temperature cycles, heat conduction, process environment, vibration, and ease of installation. If you need additional assistance with the selection of a sensor for your application, please feel free to contact our sales and engineering staff.