How do we physically measure temperature? “We all know we can measure temperature using a thermometer. This is a very simple design used for hundreds of years. It’s simply a sealed glass tube which is partly filled with some liquid like Mercury or Alcohol. As heat is applied, the liquid expands and rises up the column.
Thermocouple“The oldest way to accurate digital temperature measurements is to use a Thermocouple. If you have a hand held temperature probe or even a multimeter which can take temperature readings, it’s probably going to come with one of these. They are also built into solid cases a much more rugged design which is typically used for industrial installations. “With a Thermocouple we connect two different metals together at one end, and the other ends connect into a terminal block. Then we use a voltmeter to read the voltage difference between the two metals. The voltage here will be very tiny.
How does this work?“If we held a metal rod in our hand and place the other end into a flame, we know the rod will heat up and this heat will travel along the length of the rod to our hand. What’s happening here is the heat is exciting the atoms and molecules which form the materials structure. “The heat causes the molecules and the atoms to vibrate. This vibration is so tiny you can’t feel it in your hand. The excited atoms will allow their free electrons to move more easily and they will move towards the cooler end of the rod.
Resistance temperature detector or RTD.
Which type of temperature sensor is better?“They all have different pro’s and cons. There is no perfect fit, it depends what you need to use it for. “Consider that these are used for everything from water, steam ,air, gas, refrigerants, oil and they are used everywhere from engines, air conditioning systems, air compressors, heating systems, hydraulics, production lines etc. “But I’ve put together a rule of thumb table to compare the different types. You can see they each have different ranges, accuracies and robustness which is going to be reflected in the price.”