Any change in either of the inputs will lead to change in the values of both the outputs. This phenomenon persists even when two control loops are formed as in Fig. VI.3(b). This is termed as control loop interaction. There are two types of effects of an input on an output, viz . direct and indirect. The effects are best explained by the Fig.VI.4 where blue line indicates direct effect of inputon output within its own loop, i.e. , loop 1 whereas green line indicates indirect effect of input on output that yields through loop 2.

Fig. VI.4: Direct and indirect effects of control loop interaction

The concept of this loop interaction will be used for understanding Relative Gain Array (RGA).