4- Wire RTD Formula :
The four wire resistance temperature detector (RTD) circuit diagram, principle, operation, formula and RTD questions and answers.
The current source will maintain the excitation current constantly (0.1 – 1 mA). Following the Law of Ohm, R = U / I, the resistance can be calculated.
The digital volt meter, DVM, has an input impedance of at least 10 Mohms.
Thus just an extremely small current will pass through the DVM which means that the voltage drops over the wire resistances R2 and R3 will be practically none.
Also Read : RTD Interview Questions & Answers