A Novel Measurement Circuit for Four-Wire RTD Thermal Sensors Controlled by a Low-Cost Microcontroller

This work 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 with information about the sensor resistance and also the parasitic resistances involved. The signal resulting from the previous four measurements is then averaged by means of a low-pass filter to obtain a final output voltage that is independent of the parasitic resistances and also of their mismatches. The circuit features low-cost components, including OpAmps, switches, and resistors, integrated with a microcontroller for a precise measurement of the resistance of the sensor. The circuit eliminates errors arising from wire and switch resistances and their mismatches, ensuring accurate and reliable measurements. Experimental studies conducted using an OP07 Ie-based prototype demonstrate high linearity and minimal dependency on circuit parameters. The performance of the circuit is evaluated under varying RTD resistances and wire resistances, showing a maximum relative error of 0.37 %. Additionally, the power consumption of the circuit is measured as 40 m W. The results obtained from various studies indicate that the developed circuit offers a practical solution for accurate four-wire connected RTD resistance measurements, with potential applications in automotive, aerospace, and biomedical industries.