A COMPUTERISED METHOD FOR CONTROLLING THE TEMPERATURE OF A PHARMACEUTICAL CREAM DURING PILOT-SCALE MANUFACTURE

AbstractA microcomputer—based system has been developed to control the rate of cooling of a cream in a commercial pilot-scale turboemulsifier. Control is achieved by opening a valve in the cooling circuit for a calculated time during any control period, allowing water to circulate in the vessel jacket. The length of time for which the valve is open is calculated from the discrete form of the Proportional-Integral-Derivative (PID) control equation. This equation contains three constants which must be optimised for any given system. These will depend on factors such as the temperature and flow-rate of the cooling water, the heat input from the homogeniser and the heat transfer characteristics of the processing vessel.The theory behind PID control is discussed briefly. The development of the system, including methods for obtaining the control constants is also discussed. Control of the temperature of a cream to within ± 1°C of a target temperature profile has been achieved routinely with the present system.