Thermocouples for Dummies

How thermocouples work

Some of the strangest "science" our staffers run across is published courtesy of the Leaf Group website Sciencing.com, which is little more than a repository for articles from the former eHow.com that seem to be of a scientific nature. Given that many of them were written by the scientifically illiterate, the website is a fertile hunting ground or DotD candidates, especially those who picked up degrees in journalism and English literature. With that in mind, meet J-school grad Jordan Whitehouse and his vain attempt to answer the rather strange question, "How Do I Check Millivolts on a Thermocouple?"

Whitehouse was right about one thing: you use a multimeter. He was, unfortunately, wrong about pretty much everything else he said. Here's a partial list:

• "A thermocouples [sic] uses a sensor to measure the temperature of current passing through an object." – No, Jordan, the thermocouple is the sensor, and it measures the temperature of its environment, not of a current.
• "...thermocouples use millivolts to determine the temperature..." – No, thermocouples generate a current in the millivolt range that varies with temperature.
• "Plug the red wire on the thermocouple to the red port on the multimeter. " – Ummm, Jordan? You're cribbing the general directions for measuring voltage with a multimeter; so that should read "the red probe" or something like that.
• "Plug in the multimeter and turn it on." – Few, if any, multimeters require an external power source.

• "Turn the multimeter's dial to 'Celsius' or 'Fahrenheit' -- the reading will be taken in the temperature units you choose." – We know of no multimeters that measure temperature. We're surprised to learn that a few high-end models do, though they require a probe with – naturally – a thermocouple...
• "Consult the appropriate thermocouple-millivolt conversion table... to convert the temperature reading to millivolts. " – Dumbass, a multimeter reads voltage directly. No "conversion" is necessary!

With stupid friends like Whitehouse, it's for darned sure that no one working with thermocouples needs an enemy. Regardless, we'd like to call Jordan up to the stage to receive his Dumbass of the Day award, scientifically illiterate journalism graduate division.

SI - PHYSICS