High precision Pt-resistance temperature measurement system

Interfered by factors such as short and long term drifts of a constant current source and the thermal electromotive force of a wire, the measurement accuracy of conventional 4-wire Pt-resistance temperature measurement system is hard to achieve the order of 0.1°C. After analyzing the principle error of an enhanced 4-wire Pt-resistance temperature measurement method, a high precision Pt-resistance temperature measurement system was designed. By using a reference resistance with small temperature coefficient and high stability as the Pt-resistance measurement datum, the temperature measurement error caused by the long term drift of a constant current source was eliminated. At the same time, the short-term drift of the constant current source was suppressed by temperature control using a Thermoelectric Cooler(TEC). For wire thermal electromotive force, it was a great advantage to be short-term invariable. Measured under the positive and negative current conditions, the two voltages on Pt-resistance were subtracted. In this way, the effect of wire thermal electromotive force was eliminated. To realize high precision voltage measurement for Pt-resistance and reference resistance, a time-sharing voltage acquisition unit with high precision and quick step response was also designed. Experimental results show that the high precision Pt-resistance temperature measurement system can achieve the stability of 0.005 °C/10 day, the resolution of 0.005 °C and the accuracy of 0.02 °C(k=2). It meets the requirements of high accuracy temperature measurement in ultra-precision laser interferometers.