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How To Measure Temperature with a Soldering Iron

Forget those expensive temperature sensors. Now you can use an ordinary heating element like a soldering iron to measure temperature. Daniel Maliks's upgraded soldering iron will be a great addition to your workbench. In Circuit Cellar 191, Malik writes:

There are many applications that involve the conversion of electric current into heat by means of a heating element with some degree of temperature control. Hot water boilers, kettles, and irons are typical examples. In this article, I'll explain how you can eliminate the need for a temperature sensor by using the heating element itself to accurately measure temperature.

I appreciate that electronics enthusiasts don't necessarily want to read about cooking and ironing. So, I'll describe a device you might be more comfortable thinking about: a soldering iron. All of the aforementioned appliances and tools have one important thing in common that makes them different from, say, a hair dryer. Any thoughts?

The important common factor is that the thermal resistance between the heating element and the heated medium is much lower than the thermal resistance between the medium and the ambient world. Thus, if electric current stops flowing through the heating element, the temperatures of the element and the medium will equalize long before the medium loses much of its temperature via heat radiation and conduction. Because the resistance of all the conductors used for constructing heating elements has some temperature coefficient, you can measure the temperature of the heating element by measuring its resistance and comparing it to its resistance at, say, 25°C. This brings us neatly to the basic idea behind this project. Continue Reading & Download

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Circuit Cellar #299

June 2015

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Circuit Cellar is a media company that serves the international embedded design community with its products and services. As a reliable content provider for professional engineers and programmers, Circuit Cellar publishes Circuit Cellar magazine, engineering/programming-related books, a website, and a newsletter. Circuit Cellar also manages international design challenges relating to embedded design and programming.