| functional unit that generates the manipulated variable, required to drive the final controlling element, from the output variable of the controlling element SEE: Figures 1 and 2. Note 1 to entry: If the final controlling element is mechanically actuated, it is controlled via an actuating drive. The actuator drives the actuating drive in this case. EXAMPLE: A practical example of an actuator acting directly on the final controlling element is a DC drive. The control unit takes the function of an actuator. The final controlling element is formed by the thyristor assembly that delivers a variable DC voltage as an output variable. The control unit and the thyristor assembly together form the final controlling equipment. Note 2 to entry: This entry was numbered 351-28-07 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
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