| representation of a system or element with one or more input variables and one or more output variables, symbolized primarily by a rectangle in which the functional relationship between the input and output variables is given
SEE: Figures 1 and 2.
Note 1 to entry: The functional relationship may be given by an arithmetic instruction, a transfer function, a differential or difference equation, a characteristic curve or a family of characteristic curves, or a switching function.
Note 2 to entry: This entry was numbered 351-23-02 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