| The conductivity is an important indicator in the measure of water’s purity.Conductivity instrument is used widely in the field of environmental inspection,industrial flow control, medical sanitation, power electronics, water’s quality monitoringand science research. Measuring the conductivity of the water can monitor the quality ofwater. For a long time, how to accurately measure the water conductivity has been a greatconcern for water quality monitoring personnel and researchers. In recent years, the rapiddevelopment of integrated circuits and microprocessor technology, the electrodeconductivity measurement is gradually becoming people’s best choice.This paper studies the mechanism and the role model of solution under theconductivity electrode solution, analysis the recent conductivity measurement developmentat home and abroad and the common measurement methods, On the basis of the analysis ofthe main factors affecting the conductivity measurement accuracy, Aim at polarizationeffects, capacitive effect and narrow measurement range exist in the traditionalconductance measurement methods. In this paper, we develop an advantage method ofmeasuring the conductivity based on the dual-frequency sinusoidal signal, designed andcomplete an online conductivity measuring instrument on the basis of embedded controlsolution. The electrical conductivity on-line measurement system was designed to copletereal-time monitoring of parameter of electrical conductivity.The system measurement circuit is based on the ARM Microcontroller LPC1114corecontrolling, which on basis of the design of excitation source, conductivity impedancemeasuring circuit temperature acquisition module circuit, automatic gear switching circuitand RS485communication interface circuit and power module circuit. Two sine waves ofhigh precision are generated by AD5933under the control of LPC1114, and ARM alsocontrol multi-channel analog switch74HC4051select the feedback resistors to achievescale switching function. Analog-to-digital conversion part use ARM’s on-chip10-bit ADconverter for data acquisition and real-time acquisition of the reference voltage, the reference voltage is generated by precision voltage source ADR5040. The temperatureacquisition part use three-wire bridge circuit, Ptl00is used for temperature measurement,and software is devised to complement the error of temperature. The communication withPC is completed throw RS-485serial interface which obey industrial common transportprotocol MODBUS RTU.The system developed an integrated and intelligent conductivity measurementinstrument. Testes and the use of on-site project in different industrial environmentsindicted that it can realize aqueous resolution online real-time measurement, automaticshift, automatic temperature compensation, and software calibration. The measuringrange is rather wide from0uS/cm to10000uS/cm. The resolution is1%of full scale, thewarm-up time less than or equal to1s, and system power consumption is less than orequal to80mW. |
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