| Ion selective electrode is an electrochemical sensor, since the invention of the first pH glass electrode in 1906, there have been more than 100 years of development. Nowadays, we can produce a variety of commercial electrodes. Ion selective electrode used for measuring ion concentration has a lot of advantages, such as it is little affected by color, turbidity and suspended solids of the solution, operating simply and fast, easy to achieve automatic measurement. With the widly application of computer technology, ion selective electrode technology has become a very important means of automatic analysis for laboratory analysis, industrial and agricultural production, health and environment testing and so on.We deisgned the online water hardness measurement which was used for industrial boiler water detecting. And this system is based on ion selective electrode technology and a high-performance mixed-signal MCU(C8051F020) control as core. The main contents include reading electrode signal, calculationing and displaying water hardness. As the characteristic impedance of the ion selective electrode is usually at 109Ω, it makes the measurement of the potential of electrode as the key and difficult issue of analog circuit design. The paper has chose the high input impedance OPAMP CA3140 and a dual high resistance impedance converting circuit solves this problem, to ensure reading the electrode signal accurately. In control part, MCU collects the electrode signal and detects the temperature in a real-time mode. Then auto-complete the data processing, choose the calculation method by temperature, and finally obtains the current water hardness value, that was greatly simplified the operation process.The experimental results show that this equipment is easy operation, high accuracy and high speed. It basically adapted to the various actual requirements, and it is suitable for promotion to the industrial boiler water practice as a product.
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