DC motor speed control of COD sensor

• Main Author: Fang, Chen
• Other Authors: Cai Wenjian
• Format: Theses and Dissertations
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Control and instrumentation::Control engineering
• Online Access: http://hdl.handle.net/10356/18795
• Institution: Nanyang Technological University

A new COD (Chemical Oxygen Demand) sensor technology is developed in this project. It overcomes the drawbacks of existing COD sensors. The new system is proposed to be portable, fully automated, and fast in determining COD values. It can be used for on-line COD monitoring. The new COD sensor uses the dissolved O3 (ozone) obtained from ambient air as the active oxidant. The sensor’s multi-electrodes arc employed to combine the differences and the change rate of each electrode in calculating the COD up-take rats and COD values. The appropriate ratio between the dissolved O water and samples is determined by fuzzy logic strategy. The different ratios require pumps to work at different speeds for pumping proper amounts of dissolved O3 water and samples. This further requires corresponding DC motor speeds to drive pump. This dissertation describes the design and development of a digital DC motor speed control system for the COD sensor. It covers the following main contents: system hardware design, software development, system modeling, and tuning, and system simulation. For controlling the speed of the DC motor, a digital closed loop PID control method based on a one-chip microcontroller using PWM is presented. For PID tuning, two methods based on a Ziegler-Nichols tuning method and a genetic algorithm are employed and compared. The simulation results show that the digital PID control method can be implemented using only small amount of components and can be easily improved. It provides high performance with compact size and low cost.