Research On Multi-Parameter System Based On Measuring Electrical Conductivity Of Solution

The electrical conductivity of solution is a basis physical-chemical character. The salinity, TDS and pH of solution have great relation with it. To do research on multi-parameter system based on measuring electrical conductivity of solution, therefore, is very significant.In order to eliminate the influences caused by temperature, electrode-polarization and autoeciousness-capacitance, the traditional instrument has added complicated circuits so that it cause such shortcomings as big error, time-retardation and a relatively small scope.Through the problems caused by 2-probe electrode and AC current source, a new measuring circuit based on the excitation of bi-directional voltage pulse and the sensor of 4-probe electrode is proposed, using single-chip to achieve auto-temperature compensation. We can get the value of TDS and salinity by electrical conductivity.The analog circuit of the system in this thesis is composed with pre-positive circuit of 4-probe electrode sensor and temperature-measure circuit. The digital circuit regards AT89C55 single-chip as core, expanding AD, key in, display out and memory peripheral chips. Otherwise, the electrical source module is adopted to protect the system, in order to manage and analyze the data, meanwhile, a new-type USB interface is used to communicate with PC.The software design uses C51 high-level language to write the modularization programme. By dint of Matlab, the precision of system improve by software compensation. In order to avoid the blindness of temperature coefficient, meanwhile, an auto-temperature compensation way via single-chip is brought out.Testing result shows that the system has such advantages as wide scope, high accuracy and simple operation. Through further fulfilling, the system can be widely used in such fields as environmental inspection, industrial flow control, medical sanitation, science research and products'quality check...