A Multi-Sensor Chip for Monitoring the Quality of Drinking Water

• Main Author: Purrington, Heidi M
• Format: Dissertation
• Language: English
• Published: Ann Arbor ProQuest Dissertations & Theses 2010
• Subjects: Electrical engineering; Environmental engineering
• ISBN: 9781124332468; 1124332464

Drinking water should meet quality standards for the safety and satisfaction of the consumer. Quality parameters of interest include turbidity, total dissolved solids (TDS), and temperature. It is desirable to monitor these parameters in typically good sources of water to indicate if and when the water becomes unacceptable for drinking. The Environmental Protection Agency recommends that turbidity levels in drinking water remain under 5 NTU and that TDS levels remain under 500 mg/L.
A MEMS based multi-sensor chip has been developed for the purpose of monitoring turbidity, TDS, and temperature in a sample of drinking water. The benefits of MEMS technology over conventional sensors include compact size, low power consumption, integration capability, and low cost bulk manufacturing. Two revisions of the multi-sensor silicon chip were designed, fabricated, and tested. The layout of the chip and the fabrication process were redesigned in the second spin to provide more robust and sensitive responses.
The sensor structures include photodiodes, temperature diodes, interdigitated electrodes in direct contact with the sample, and capacitive interdigitated fingers. The sensors were characterized with the use of commercially available thermometers, turbidity standard solutions, and TDS standard solutions. Signal conditioning circuitry was implemented to convert each sensor output to a DC level between 0 and 1 V. The sensors were shown to be responsive to temperature, turbidity, and TDS in the ranges applicable to drinking water, although obstacles relating to reliability and signal conditioning still remain.