| physical unit used for driving mechanically actuated final controlling elements Note 1 to entry: Examples of actuating drives are electric, hydraulic or pneumatic actuating drives, diaphragm systems or piston actuators. Note 2 to entry: No actuating drive is required for a final controlling element if the manipulated variable at the controller output is capable of directly influencing the mass flow or energy flow, i.e. without any mechanical intermediate variable quantity. Note 3 to entry: This entry was numbered 351-32-24 in IEC 60050-351:2006.
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