A thermocouple is a temperature sensing element that operates on the principle that when two dissimilar metals are junctioned and the junction is heated, they produce a low voltage (millivoltage) which is proportional to the temperature. Thermocouples have a predictable and repeatable relationship between temperature and voltage. They are used widely in higher temperature applications because they can withstand greater temperatures than resistance temperature detectors (RTDs), and are less expensive in most cases.
The practical life of a thermocouple is limited by the environment it is exposed to and also by aging. The thermoelectric coefficients of the wires in a thermocouple change with time and the measurement voltage accordingly drops. As thermocouples age within a process, their conductors can also lose homogeneity due to chemical and metallurgical changes caused by extreme or prolonged exposure to high temperatures. One of the disadvantages of using thermocouples is the loss of accuracy when the thermocouple is cycled. For example, when the temperature is raised and lowered significantly over a period of time, this will cause the thermocouple to “drift”, thus creating errors in the reading.
Overview of the features and benefits of our thermocouples
T-PAK® thermocouples are mineral insulated, metal sheathed probes that can be exposed to most environments without further protection as they are very accurate and sensitive to changes in temperature. The outer sheath of stainless steel or other alloys, coupled with tightly compacted magnesia (MgO), ensures relatively long life by protecting the thermocouple from oxidizing, reducing, or other corrosive atmospheres.
At Thermo-Kinetics, we standardize on special limit grade wire in many instances to ensure that our thermocouples are the most reliable and accurate they can be.
We also custom make base metal and noble metal elements as well as high temperature Platinum (noble metal) elements to our customers’ specifications. These come in many different configurations including metal protection tubes, ceramic protection tubes to name a few, but can be tailored to suit the customers’ application.
We can also provide thermocouples that are CSA approved for hazardous locations in Class 1, Div. 1, Groups B, C and D environments.
Our in-house calibration service is ISO 17025 accredited and we are able to calibrate temperature sensors from -196° C to 1250° C.
Below is a table of different thermocouple types: