In the 19th Century Baron Kelvin lectured as Professor of Theoretical Physics in Glasgow. He dealt mainly with thermodynamics. The thermal unit Kelvin is named after him. He is also the inventor of some resistance measuring instruments and the Kelvin contact. His real name was William Thomson, and he is also known as the inventor of the Thomson bridge for measuring small resistances.
Kelvin discovered a method that made it possible to measure the slightest resistance with a small measuring current. Using this method, the contact resistance of the test leads and thermocouple voltages are not included in the measurement result. By using one measurement channel, the electrical voltage across the second current is measured as the so-called „four-terminal sensing„.
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