Measurement Of The Conductivity Of Water Based On AD5933

Conductivity is an important indicator of water purity. According to measuring the conductivity of water, the water quality can be monitored. Electrode conductivity general use AC excitation to avoid electrode polarization effect. AC is the quasi-steady analysis method. It will not cause serious instantaneous change of the concentration and surface if the signal frequency is high enough and the time that each half of the week continuing is short enough. In addition, the alternating current appears alternately process of anode and cathode on the one electrode. Even if the measurement signal acted on the conductivity cell for a long time, it will not lead to the accumulation of polarization. It eliminates the effect of electrode polarization.Based on AD5933 which is impedance converter, the electrode conductivity method is presented. The frequency generator by the on-board DDS which is to a maximum frequency of 100 kHz allows an external complex impedance to be excited with a known frequency. The response signal from the impedance is sampled by on-board ADC and a discrete Fourier transform is processed by an on-board DSP engine. The DFT algorithm returns a real and imaginary data-word at each output frequency. The magnitude of the impedance and relative phase of the impedance at each frequency point along the sweep is obtained.Discussion a conductivity of water method based on AD5933. The controlling command and acquired data are transmitted by serial port communication between the Micro-Computer Unit (MCU) STC12C5410 and the PC. Some issues about circuit designing are to extend measurement frequency downward, to choose the measurement frequency, to eliminate the DC component reducing polarization effect, to design driver reducing the influence of incentive-impedance. Data processing method involves the calibration of the phase error and gain factor.Through multiple measurements of calibration resistor, two-end-points method calibrate phase angle and gain factor. The effect on different excitation frequency and excitation voltage on conductivity of water is analyzed. The conductivity measuring device eliminates the polarization and capacitance effects. The experimental results show this design is simple, accurate and have a highly integrated, and the performance is stable.