Computerized feedback control of an environmental chamber

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Virginia Tech

Most existing environmental chambers cannot simulate dynamically changing environmental conditions. Hence there is a need for a dynamically controlled artificial environment for plant studies. This project demonstrates the control of temperature, humidity and SO₂ concentration in a Continuous Stirred Tank Reactor (CSTR) system using feedback control through a computer.

An IBM-PC was connected to the measuring instrumentation and control equipment through a data acquisition and control system. Temperature and humidity were controlled by an ON-OFF control scheme. Sulfur dioxide concentration was controlled by means of a modified proportional derivative control algorithm.

The system is capable of achieving a wide range of temperatures (7°C to 40°C), humidities (30% to 97%), and SO₂ concentrations. Temperature is maintained within ±0.5°C of the desired value and humidity is controlled within ±4% of the desired value. Sulfur dioxide concentration is kept within ±10% of the desired concentration.

It was found that as humidity increases, the supply rate of SO₂ must be increased to maintain a given concentration. Software response time is slow. This causes time lags in the modification of the controlled parameters to achieve desired values. The heating and cooling characteristics of the system can be improved by better insulation of the chamber walls. The system demonstrates that computerized feedback control is practical for application to controlling environmental parameters in a fumigation chamber.