Garbage In/Garbage out goes the saying regarding data, analysis and getting something worthwhile you can use in your engineering design.  And one possible culprit of the garbage in (or bad data) is the thermocouple.   As our author Dr. Cathy Biber notes,

Essentially, a thermocouple is a voltage generator that is sensitive to temperature. Two dissimilar metals generate the voltage between two junctions by the Seebeck effect. A fancy voltmeter measures the voltage and converts it to temperature if you tell it the correct metal combination (thermocouple “type”). Sounds simple enough.

The big challenge is making sure that the thermocouple junctions are at the correct temperatures: the reference junction, which you can think of as being at the voltmeter, should be at a known temperature. Usually the meter “knows” this (i.e. measures it internally) and corrects it to the standard reference of 0 °C. The other junction is the one you install on the surface of interest. The big challenge lies in making sure this junction is the same temperature as the object of interest. And the worst of it is that if you make a mistake here, you are most likely to get a reading that is lower than the real temperature – fooling you with what usually ends up being an optimistic result. There is no little alarm bell going off to alert you that there is anything wrong with the installation.

To get to the bottom of this potentially difficult to debug problem, read her full article here: “Ways to Get Bad Thermocouple Readings and Not Know It“.

We’d also like to point you two other great resources on the same topic of doing the best thermal measurement you can:

• Robert Moffat’s talk on “An Overview of the Challenges in Thermal Testing” (a one hour on-demand video)

• Dr.  Kaveh Azar on “How to Perform and Understand Temperature Measurement Within Electronic Systems” (a one hour on demand webinar)

All three of these resources will help you to have good data and not garbage in your thermal measurement.