Je. Schlesser et al., AUTOMATED CONTROL AND MONITORING OF THERMAL-PROCESSING USING HIGH-TEMPERATURE, SHORT-TIME PASTEURIZATION, Journal of dairy science, 80(10), 1997, pp. 2291-2296
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.