在线燃烧离子色谱仪的高精度测温电路设计

Design of High Precision Temperature Measurement Circuit for Online Combustion Ion Chromatograph

在线燃烧离子色谱仪将样品前处理和检测过程相结合,极大提高了检测效率。而燃烧温度过高会降低燃烧管的使用寿命,燃烧温度过低会使样品裂解不充分,所以设计高精度测温电路来测量燃烧温度很有必要。首先设计了RFI滤波电路,抑制高频噪声对热电偶输出热电势的影响;其次设计了双ADC自适应采集电路,实现档位的快速切换;最后设计了Pt1000测温电路来测量冷端温度,使冷端补偿误差小于0.052℃;提出了等精度最小二乘法拟合校正算法,根据测温精度在测温范围内自动划分等精度区间,提高了测温精度且降低了MCU的工作量。实验结果表明:在0~1200℃范围内,测温精度可达0.6℃。

The on-line combustion ion chromatograph combines sample pretreatment and detection process,which greatly improves the detection efficiency.However,too high combustion temperature can reduce the service life of the combustion tube,and too low combustion temperature can cause insufficient sample cracking.Therefore,it is necessary to design a high-precision temperature measurement circuit to measure the combustion temperature.Firstly,the RFI filter circuit was designed to suppress the influence of high frequency noise on the thermocouple output thermoelectric power.Secondly,a dual ADC adaptive acquisition circuit was designed to realize the fast switching of the gear.Finally,the Pt1000 temperature measurement circuit was designed to measure the temperature of the cold end,so that the compensation error of the cold end was less than 0.052℃.An equal-precision least squares fitting correction algorithm was proposed.According to the temperature measurement accuracy,the equal-precision interval was automatically divided within the temperature measurement range,which improved the temperature measurement accuracy and reduced the workload of the MCU.The experimental results show that the temperature measurement accuracy can reach 0.6℃in the range of 0~1200℃.