PI CONTROLLER SWITCHING SYSTEM

PURPOSE:To execute a shockless switching by controlling a set value by a deviation controlling means so that a deviation between the set value from a setting device and a detected value from a controlled system is eliminated, when a PI controller is switched to present use from stand-by use. CONSTITUTION:A set value by an electrically-driven setting device 22 in a PI controller 2 and a detected value by a control variable detector 23 are inputted to a deviation operator 31 in an automatic follow-up device 3, and a deviation operation between both of them is executed. As a result, a generated control deviation is inputted to a pulse generator 32, and the generator 32 sends a decrease or increase command to the setting device 22 in accordance with the polarity of the deviation so that said deviation is eliminated. This operator 31 is an operator having no direct relation to control of a controlled system, therefore, its gain can be taken high enough irrespective of a characteristic of the controlled system, and accordingly, an offset error can be reduced. As a result, the set value of the setting device 22 is made to follow a set value by an electrically-driven setting device 12 in a PI controller 1, and can be made to coincide with it.