Selection of Temperature Sensors in Aerospace and Automotive Industries

For this entry we would like to share a contribution prepared by Laura Oviedo from GTS Mexico. If you have interesting information related to heat treat that you want to share, do not hesitate to contact us. We will be happy to publish every value added article with the heat treat community.

A thermocouple is a sensing device that consists of two conductors of dissimilar electro thermal characteristics. The conductors are joined together at one end (hot junction), where the junction is placed in contact with the item whose temperature is to be measured. At the other end, cold junction, a voltmeter  is used to measure the  voltage that is produced by the difference in temperature between the two junctions.

There are different types of sensors for thermocouples and their classification is as follows.
  • Base Metal Thermocouple: Thermocouple whose thermo elements are composed primarily of base metals and their alloys. Examples include K, E, N, J and T.
  • Noble Metal Thermocouple: Thermocouple whose thermo elements are composed primarily of noble metals (example: platinum/platinum-rhodium) and their alloys. Examples include types R, S and B.

Each thermocouple has special applications which it can be used for depending on its thermo-element compositions. This defines wether or not it is useful for measuring temperature in a specific process. Applications for thermocouples can go from vacuum furnaces, to oxidizing or reducing atmospheres.
So, when selecting the right sensor for your application, the following considerations should be taken into matter:
  1. What are the temperatures the sensor will be exposed to?
  2. What are the process specifications and allowable tolerances for error?
  3. How long is the measurement process expected to run?
  4. Are there any cost limits?
  5. Are the users experienced in proper sensor management?

Getting the right thermocouple in our industry can be a stressful task (and risky). That is why we have summarized the basic considerations in the following  guideline that can be used when purchasing new thermocouples. Hoping you find it valuable!

Victor Zacarias

Heat treat management expertise: CQI-9, AMS2750

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