ABSTRACT
The control scheme was extended with feed-forward control in case measurable disturbances were present. Feed-forward control is a form of decoupling such that changes in the disturbance variable do not affect the controlled variable. In some cases it may be possible to tune certain loops much faster than others, thereby eliminating interaction to a certain extent. The relative gain matrix is a useful tool in selecting the right combination of input and output variables. The input and output combination for which the relative gain is closest to one should be selected. The decoupler signal from the reflux is added after the decoupler signal to the reflux in order to assure that a reflux change only causes a temperature change; any reflux change should not cause an additional change via the two decouplers. In the DR structure a decoupler produces an absolute value that is added to the absolute value of the controller output. It is possible to use incremental decoupling.
