A Precision Measurement System Design for Electrical Conductivity in the Low-Concentration TOC Analysis of the Ultra-pure Water

Abstract

The concentration of total organic carbon (TOC) in water is an important key indicator of the quality of Ultra-pure water, which is useful in the semiconductor and pharmaceutical industries, among others. Therefore, as a technology to measure TOC, a technology that measures the amount of carbon dioxide (CO2) by electrical conductivity is being developed. This method uses ultraviolet light and an oxidizing agent to oxidize organic compounds to produce CO2, and measures the concentration of CO2 by measuring the electrical conductivity based on the permeable membrane of the gas, and then converts it to the concentration of TOC in the organic compound. In this study, we presented the design conditions of the alternating current control circuit applied between the two electrodes of the electrical conductivity cell, the microcurrent signal detection, voltage conversion circuit, and the amplification and noise reduction circuit for measuring the low concentration of TOC required for ultrapure water. Based on the optimal design conditions, we have fabricated a PCB for ultra-precise electrical conductivity measurement for low concentration TOC analysis using membrane conductivity, and have compared the results with a commercial product.