A Feedback System for Control of an Unstable Process

Apparatus for investigating boiling phenomena in a fibrous porous medium

“…Water level in the cell is controlled simply by interfacing a capacitive proximity switch with a normallyopen solenoid valve to meter flow of heated make-up water, and does not interact with the other components of the control system.The Surface Temnerature Control SystemThe temperature of the boiling surface of the copper heating block is one of the controlled variables for the boiling experiment. Since minimal instabilities are encountered in this boiling study, adequate control is maintained throughout the experiment with a standard PID controller, rather than the complex systems needed for control of classical pool boiling studies that utilize surface temperature as the control variable[12][13][14][15].As previously mentioned, the temperature of the heater surface is calculated from the readings of three thermocouples positioned within the heater block in proximity to the boiling surface. To facilitate control of surface temperature, the control software interfaces with the data A schematic of the interface between the data acquisition and process control systems.acquisition system and the temperature controller.…”