Design and Manufacture of TDS Measurement and Control System for Water Purification in Reverse Osmosis by Classic PID with the Ability to Compensate Effects of Temperature on Measurement

Measurement and control of TDS (Total Dissolved Solids) of water has significant importance for industry, agriculture, livestock and health. The system designed and manufactured in this paper measures, displays and controls TDS of water by installing on domestic and industrial purification systems. Technology of manufacturing TDS measurement system is such that it can compensate for the adverse effect of temperature on measurement. Meanwhile, calibration of the measurement system will be explained by discussing several examinations conducted in Research Institute for Food Science and Technology. In order to control TDS, mathematical model for domestic water purification devices of reverse osmosis (RO) is obtained by running practical experiments. Then, system controller is designed by Ziegler-Nichols oscillation method with the most appropriate controller being implemented. Operation of controlling TDS is done through real time and continuous controlling of a mix valve. This valve is closed parallel with a membrane filter or RO, so one can control TDS by adding or reducing inlet water into outlet water of this filter. The system developed by this research is produced in pilot by receiving scientific approvals from relevant authorities and has found numerous applications in industry.