PURPOSE: To decrease the overshooting of hot water temperature at the time of starting the burning when the load is low by causing the PID computation to be carried out after once clearing the burning rate for the previous hot water discharge if the load, i.e., the required calorific value to bring the hot water temperature up to the set temperature is low, and causing the PID computation to be carried out with the previous burning rate retained if the load is high.
CONSTITUTION: The level of load computed by the FF computation is determined by a sequence control means 9c, and, if the load is determined to be low, the result of the PID computation formula Tc = Kc . (TER + Ti . ΣTER + Td . ΔTER), where TER is the deviation, Kc the proportional constant, Ti the integration constant, and Td the differential constant, i.e., the value of the integration term employed at the time of the burning control from the previous PID control is retained in a memory means 9d. When beginning the PID computation the PID computation means 9a, the PID computation is carried out without applying the value of the previous integration term to the formula, and, based on the computed load level, the opening of the proportioning valve 5 is controlled by the sequence control means 9c to regulate the burning rate at the burning section 2. On the other hand, if the load is great, the previous PID computation result is not cleared but is applied to the formula as is to begin the PID computation for burning control.
SHINO YOSHIFUMI
SHIRE TAKASHI