An RTD sensor is a “passive” electrical component in which a small current is passed through the RTD while in use. The voltage across the RTD is regulated by the varying resistance of the RTD and the voltage drop across the RTD is measured and converted into temperature. To minimize self-heating, it is best to limit the current flowing through the RTD to 1mA maximum. In two-wire RTDs, extra care should also be taken to compensate for the extension lead wire resistance if necessary. Platinum RTDs have a nearly linear resistance vs. temperature relationship, a key characteristic for precisely measuring temperature over an extended operating temperature range.