Enhanced Digital Interface Circuit for Three-wire Connected Resistance Thermometers

A simple digital interface circuit suitable for a three-wire resistance thermometer is reported in this article. The digitizer provides a linear transfer characteristic without dependence on the connecting wire resistances. Besides, the digital interface produces the output using two conversion cycles. The methodology of the digital interface circuit is mathematically derived and analyzed. Later, the effect of dominant error sources is also detailed. The performance of the circuit is initially verified using simulation studies as well as experimental studies. A linear output characteristic is obtained during these tests, and maximum output-nonlinearity does not exceed 0.25 %. Finally, the experimental results of the proposed circuit are compared with the theoretical and simulation results, and the prior art.