Metals like platinum change resistance in a smooth, repeatable pattern as temperature changes. A resistance thermometer measures that resistance and converts it into a temperature reading using calibrated electronics. The relationship is almost a straight line over most of the useful range.
For precise work, scientists use a more exact formula called the Callendar-Van Dusen equation. Platinum resistance thermometers, often called RTDs, are popular in chemistry labs. They are very accurate, give the same reading every time, and work across a wide range of temperatures.
They outperform old-style liquid-in-glass thermometers for careful lab work, where even a tiny temperature error can throw off an experiment’s results. A common misconception is that any metal wire works equally well for this purpose. Platinum is chosen because it resists corrosion and does not react easily with air or moisture.
It also keeps its resistance-temperature relationship steady even after years of use. Cheaper metals like nickel or copper are sometimes used in less demanding applications. But they drift out of calibration faster and cover a narrower temperature range.
Resistance thermometers respond somewhat slowly compared to some other sensors. They work best in steady conditions like a water bath, rather than in a process with rapid temperature spikes.