Design, Implementation, and Experimental Evaluation of an Accurate Analog Front-End Circuit for Four-Wire Resistive Sensors

This paper presents the design, implementation, and experimental evaluation of a novel measurement circuit for four-wire resistive sensors, such as RTD thermal sensors. The proposed circuit sequentially measures four resistances, providing information on both the sensor resistance and the associated parasitic resistances. The signals from these four measurements are then averaged using a low-pass filter to generate an output voltage that is independent of the parasitic resistances and their mismatches. The circuit utilizes low-cost components, including operational amplifiers (OpAmps), switches, and resistors, eliminating errors caused by wire and switch resistances, as well as their mismatches, to ensure accurate and reliable measurements. Additionally, the methodology for implementing the circuit topology using a low-cost microcontroller is demonstrated. Experiments are conducted with both the analog and microcontroller-based designs, demonstrating high linearity and minimal dependence on circuit parameters. The analog design is evaluated with varying RTD and wire resistances, showing a maximum nonlinearity of 0.011 % and a relative error of 0.08 %. A detailed comparison with conventional and existing techniques demonstrates the superiority of the proposed method. The findings indicate that the developed circuit provides a practical solution for accurate four-wire RTD resistance measurements, with potential applications in the automotive, aerospace, and biomedical industries.