Design And Implementation Of Conductivity Detection Circuit For Ion Chromatograph

Ion chromatograph is a branch of liquid chromatograph,which is mainly used to detect and analyze anions and cations in solution.Since the advent of ion chromatography in the 1970 s,ion chromatography,as a standard method of ion analysis,has played a great role in environmental analysis,petrochemical industry,power industry,nuclear industry,bioengineering and other fields.The ion chromatograph consists of four parts : solution sampling system,ion separation system,conductivity detection system and data processing system.The detector is an important component of the conductivity detection system,and its performance directly affects the key parameters such as accuracy,resolution and repeatability of the instrument.At present,the detection methods of ion chromatograph detector mainly include phase sensitive detection method,double pulse excitation method and self-excited oscillation method.In this paper,a high precision,wide range and range adaptive conductance detector based on cross-correlation principle is developed.In the detection process,the measurement range is switched in real time according to the different measured conductance values,which solves the problem of undetectable and inaccurate measurement caused by the large difference in the content of ion components in the sample.At the same time,the excitation frequency of the conductance cell is changed in real time according to the range,which reduces the influence of the double-layer capacitance and the lead capacitance of the conductance cell on the circuit,and improves the accuracy and resolution of the circuit measurement.During the range switching,the hysteresis shift method is used to eliminate the problems of long shift time and shift error of the traditional ion chromatograph.The circuit system is built and its performance is tested by oscilloscope and upper computer.The test results show that the conductivity detector range of the ion chromatograph designed in this paper is 0.1-30000μS / cm;the baseline noise of the conductance detector is less than 0.3n S / cm,and the repeatability error is less than 1 %,which verifies the feasibility and correctness of the design.