Patent ID: 6240324
Filing Date: 2001-05-29
Classification: G05B

Abstract:
In a process controller where an output signal of a first controller is used as an input signal to a second controller where input to the second controller has a maximum limit (MAXLIMIT) and a minimum limit (MINLIMIT), an improved method for cascade control, comprising the steps of:inputting a measured variable to the first controller;determining whether the measured variable has a first predetermined relationship with the MINLIMIT and if so, lowering the value of the MINLIMIT;determining whether the measured variable cannot reach the MINLIMIT with the controller output ON full and if so, raising the value of the MINLIMIT;determining whether the measured variable cannot reach the MAXLIMIT with the controller output OFF and if so, lowering the value of the MAXLIMIT; anddetermining whether the measured variable has second predetermined relationship with the MAXLIMIT and if so, raising the value of the MAXLIMIT, wherein the first controller and the second controller cooperate so that the second controller produces an output signal in a range limited by MAXLIMIT and MINLIMIT values that are continuously recalculated.