The Research And Applition Of Online Detecting Technology Of Solution Electric Conductivity By Using Voltage-controlled Oscillation Technique

In the growth and reproduction of bacterial in culture medium, some macromolecules such as carbohydrate, protein and lipid which are not easy to conductive, can be changed into small molecule conductive substances such as lactate and acetate which can raise electrical conductivity and change impedance characteristic of the culture medium. So, we can judge the growth and reproduction of bacterial in culture medium by detecting impedance of the culture medium.Based on the phenomenon, we design an online detecting system of solution electric conductivity which detects bacterial by measuring electric conductivity of nutrient solution. Applying technology of voltage-controlled oscillator, the detecting system can translate impedance signal into frequency signal and judge the bacterial by monitoring the outputted frequency signal. a voltage-controlled oscillation circuit is designed, theoretical analysis is carried out, the oscillation frequency formula of the circuit and the relations between oscillation frequency and electrical parameters of the solution is derived, combined with experimental data, PSpice simulation is carried out, the outputted frequency signal chart of culture solution and relationship chart between electrical parameters of the solution and the corresponding outputted frequency signal of oscillation circuit are obtained.The online detecting system of applies C8051F360 as microcontroller. A signal detecting and processing circuit, a motor controlling circuit, a thermostat’s temperature and door controlling circuit, a displaying circuit, a serial ports communication circuit and ferroelectric memory were designed. They ensured the practicability and reliability of the system.Testing result shows that the designed online detecting system of solution electric conductivity could quick detect the bacteria’s growth in nutrient solution and could get the same results of other similar detecting systems. It completely achieves the designed indexes and could take favorable social and economic benefits.