| 摘要 |
PURPOSE:To make a process value approach a set value with a high accuracy by reducing temporarily a dead zone width to the set value, in case when a deviation between the set value and the preset value of a process is larger than an allowable deviation which has been set in advance. CONSTITUTION:When a water level of a tank 1 is controlled so as to be con stant, a set value of an outflow quantity is derived by a control algorithm which has been set to a water level controller so that the water level of the tank 1 is held at a water level set value LSV3. A flow rate controller compares a flow rate present value from a flowmeter 6 with this flow rate set value, and operates an opening of a flow rate control valve 7. In this case, first of all, whether a process value is within a range of a regular dead zone W1 or not is decided, and if said value is within the range, subsequently, a deviation DELTAL to the value LSV of the process value is derived. This deviation L and the allowable deviation DELTALmax which has been set in advance are compared, and in case of DELTAL>DELTALmax, a width of the dead zone is narrowed, and a control is executed so that the process value enters a dead zone W2 (W2>W1). In this way, the process value which has stayed in the vicinity of a boundary of the dead zone W1 in the beginning is corrected and can get nearer the set value. |
