AUTOMATED CONTROL AND MONITORING OF THERMAL-PROCESSING USING HIGH-TEMPERATURE, SHORT-TIME PASTEURIZATION

High temperature, short time pasteurization was used to evaluate a com puter-based system for controlling the pasteurization process, acquiri ng data, and monitoring records. Software was used for the control of hot water temperature, flow rate through the centrifugal timing pump, and diversion of under-processed product. Three types of control strat egies were conducted: single loop, cascade, and multivariable. The sin gle loop control strategy showed the most rapid responses to temperatu re changes, but the temperature response curve was slowest to return t o its set point. The cascade control strategy showed slower recoveries to temperature changes, but the temperature response curve was smooth er. The multivariable control strategy responded slightly faster than the cascade control strategy, and the temperature response curve was s lightly smoother than the cascade control strategy. The multivariable control strategy was able to control the flow diversion valve by the u se of a lethality controller. The data acquisition system, used to mon itor the data obtained from the high temperature, short-time pasteuriz ation system, was within +/- 0.1 degrees C of the temperature recorded by the safety thermal limit recorder. Reliability was determined by e xamining the changes in the position of the flow diversion valve to id entify process deviations and by comparing the changes to the event ma rker on circular charts. The data acquisition system was an effective alternative for monitoring the completeness of data.