Development Of Measuring Instrumentation For Ion Concentration

For the measurement of ion concentration, the traditional analysis method has more or less certain insufficiency, such as a low analysis speed, a high analysis cost, a bad reproduction quality and difficulties to judge the end point, but the design uses the ion selective electrode method, which is simple, fast, and the needed instrumentation equipment is simple, with a big measurable scope. The basis of this method is that the voltage of primary battery which is composed by the ion selective electrode and the reference electrode satisfies the Nernst equation with the ion concentration. The ion concentration of the measured solution can be achieved through detecting the voltage of primary battery and relevant calculation.The measuring principle of the ion concentration is detailedly studied in the paper, and many kinds of measuring methods are introduced:the multi-spot adjustment and single point adjustment methods on the measurement of pX value, and the temperature compensated and non temperature compensated methods on the measurement of F and Cl- concentration.The design of analog signal acquisition and regulating circuit is introduced in detail. The digital signal processing and display circuit based on MSP430F149 is analyzed and designed, including a 12 bit A/D converting circuit, a data processing circuit, a LED display and keyboard circuit and a RS485 communication circuit.The temperature compensation circuit based on the DS18B20 is designed, which can improve the measurement accuracy of the instrument, and basically eliminate the influence of the temperature on the measurement result. In the software module, MCU programme based on C430 and display interface programme based on VB are designed and implemented.The overall debugging of the instrument is completed, with a mass of relevant experiments done in the laboratory. The experimental data indicates that the instrument with a good performance satisfies the requirements of the system.