SEE: Figures 1 and 2.

Note 1 to entry: The final controlled variable is a variable stemming from the control task. It has to be connected functionally with the controlled variable but needs not to be part of the control loop. In contrast to this the controlled variable always belongs to the control loop. In case of warranties it may be helpful to differentiate beween controlled variable and final controlled variable.

Controlling the composition of a mixture by the final controlled variable, the mixture proportion may not be measured directly. It is depicted by a mixture proportion dependent property (for example density, clouding, electrical or thermal conductivity) which is used as the controlled variable.

Note 2 to entry: This entry was numbered 351-27-10 in IEC 60050-351:2006.

Figure 1 – Functional diagram indicating typical elements of an elementary open-loop control system

Figure 2 – Functional diagram indicating typical elements of an elementary closed-loop control system