A project has been developed and implemented in which the temperature and salinity are controlled in a small volume of water which is circulated using a small pump. A conductivity sensor measures salinity, and a Resistance Temperature Device (RTD) monitors temperature, providing data to a BASIC Stamp controller. Two relays are used to operate solenoid valves that release either fresh or salty water into the system, and a third relay is used to activate a heating element used to control temperature. A cascaded switching arrangement utilizing transistors allows the BASIC Stamp to drive these high-current devices. A DC motor-driven pump continuously circulates water through a fluid loop into which the conductivity sensor is integrated. Students fabricate an inline conductivity sensor (using a 555 timer), the RTD (using photolithography), a heating element (using a high-wattage resistor) and a wooden platform to which all of the components are mounted. The students develop programs to accomplish closed-loop control of the system, as well as provide a user interface where key system parameters are displayed. As part of our integrated freshman curriculum, this project provides hands-on experience to accompany traditional approaches to teaching science and engineering fundamentals including conservation of mass and energy, basic salt-water chemistry and electric circuitry. Assessment of the skills imparted through this project is provided using before and after survey data measuring student confidence in designing, fabricating and testing a working electro-mechanically controlled system.
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