Development of an Algal Optical Density Sensor
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Algae, which are high in lipids productivity and photosynthesis rate, have the potential to be one of the major sources for large scale biodiesel production due to the lack of the fossil fuel. Optical density (OD) which is directly related to algal density in culture media is a key parameter for the automation of production systems. In order to save labor, cost, and realize a fully automatic algal production system, an OD sensor was developed. To evaluate its performance, current to voltage amplifiers, LED drivers and the system power were designed and built to drive the LEDs in the sensor and process the signal. Also, a program was created for the data-acquisition system used with the sensor to record and plot the output data. The sensor was calibrated and tested under both lab and raceway environments. During the tests, more issues were discovered, such as temperature drift, unstable output signal, and noise problems during the tests. In order to achieve a more robust and repeatable output, a new sensor was developed based on the original sensor. First, the sensor housing was redesigned to accommodate a new optical measurement configuration. Second, a constant current LED driver circuit was built to stabilize the LEDs illumination output. Third, a feedback temperature control mechanism was built to control the temperature of LEDs in order to reduce output temperature drift. Finally, a logarithmic IC chip was used for processing of raw outputs from photodiodes. All the parts were assembled and enclosed in a specially modified box. Then, the new sensor was calibrated and tested in the lab and raceway production environments. The results showed that the performance of the sensor was improved.
Yao, Yao (2013). Development of an Algal Optical Density Sensor. Master's thesis, Texas A & M University. Available electronically from