Design And Research Of PT100 High-Precision Temperature Measurement Bridge Circuit System

Because of the huge volume of seawater,the great heat exchange will only cause very small temperature changes.Therefore,seawater temperature measurement is very difficult and the precision of its measurement equipment in marine scientific research and marine environment monitoring is very high.Production of measuring instruments cannot do without precision temperature measurement bridge and first-class standard platinum resistance thermometer as the temperature transfer benchmark.At present,China’s precision temperature measuring instruments are heavily dependent on imports,and domestic temperature measuring instruments generally cannot meet the accuracy requirements for calibration of marine instruments,which makes the production cost of marine instruments too high.In order to solve the practical problem,this study aims to design a low-cost temperature measuring electric bridge system for marine instrument calibration and make it implemented.This design is mainly based on the design of ultra-low input noise programmable amplifier with high input impedance and low bias current,precision reference voltage source,precision constant current source,multi-slope-integral ADC and other precision analog circuits,supplemented by the design of communication interface,host computer and human-computer interface.The measurement principle and design method of the temperature measurement bridge are introduced in detail.The project uses a Top-Down design method.First,the index requirements are proposed for the overall design according to the application background;Then according to the overall design of the system,function modules are decomposed,based on the theory of precision measurement circuit,and the index requirements of each module are elaborated.According to the requirements of the index,how to design and implement the corresponding circuit is explained,and the key modules are verified by experiments.Finally,the temperature measurement bridge is calibrated and measured in a constant temperature water bath with an accuracy of 0.000 1℃.The experimental results show that the ratio measurement accuracy of 100Ω platinum resistance thermometer can reach 1ppm at the three-phase point temperature of water(0.01℃).Compared with Fluke 1594 A super temperature measurement bridge,the temperature measurement resolution of this design can reach 0.000 01℃ and the temperature measurement accuracy can reach ±0.000 5℃in the range of 0 ～ 60℃,which meets the expected index requirements.The feasibility of this design scheme is verified,and a low-cost precision temperature measurement bridge system with complete functions is realized.