As we approach the end of the semester, many things may come to mind. Some think of the holiday season or of their inevitable hell week where all of their professors have seemingly conspired to make everything due at the very same moment (as per usual), while others think of how the Hoboken wind chill will be reminiscent of Dante’s ninth circle. Now what common item binds all of these together for me? The answer is the thermometer. Holiday meals are not complete without certain meats hitting the correct internal temperature, I happen to be a TA for D1 where the DHT sensors have been giving all of us headaches, and I squirm in bed when I check the real feel each morning.
Speaking of D1, despite its frequent troubleshooting frustrations, it has been one of my most dependable sources of joy this semester. I have always loved teaching, which many could have seen coming given both my parents, my maternal grandparents, and paternal grandfather all having been teachers at some points in their lives. I have TAed plenty of courses during my time here at Stevens, but I have found that D1 brings a certain blend of nostalgia and full circle satisfaction. Although it’s been a little over four years since I was sitting masked and gloved up in Babbio talking Professor Joo’s ear off with questions, I hear my students having some of the conversations, comments, and jokes I made with my friends and peers all that time ago. But I also get to witness them come up with concepts and ideas I scarcely would have thought of back then. For any of my students reading, I am so incredibly proud and impressed with all the work you have done, and could not be more happy to be passing the torch to you all as the next generation of Stevens engineers. 🙂
Now onto the technical talk.Thermometers have been around for quite some time and today their functionality varies in underlying mechanisms. Keeping in spirit with D1, I am going to discuss thermistors. Thermistor is a portmanteau of the words thermal and resistor. As the name suggests, thermistors are semiconductors whose resistance depends upon their temperature. Without getting too much into the weeds, semiconductors have some nonlinear properties when it comes to the relationship between voltage, current, and resistance. That is to say, you cannot simply state that voltage is the product of current and resistance like with simple circuit components. However, for the sake of explanation, this is a good enough approximation. If Ohm’s Law holds true, then that means resistance is equal to the voltage divided by the current passing through the thermistor.
If we use a source, like an arduino board, to supply a constant current, the only way that the measured voltage across the thermistor would change is if the resistance changes. As mentioned, the resistance of the thermistor changes as temperature changes. If we check the resistance at a couple of known temperatures, we can determine a relationship between the measured voltage and the temperature. To sum up, put a current across a thermistor, check the voltage, use a predetermined formula from testing, et voila, you know your current temperature. For any digital thermometer, it’s just a matter of getting a signal and interpreting what it means. This basic idea even applies to us as humans. While not as precise, certain nerves near our skin’s surface are attuned to certain temperatures and fire off electrical impulses to our brains to help us feel temperature. I know I stated before that just about everything is a vibration, but taken another way, everything is a signal. Whether it be your final project or just the day you’re having may your external signals not throw an error!
