| self-acting artificial system the behaviour of which is governed either in a stepwise manner by given decision rules or continuously in time by defined relationships, while the output variables of which are created from its input and state variables|
Note 1 to entry: An essential characteristic of a program controlled automaton is the existence of at least one branching in the program, offering different alternatives of control actions between which a decision is made based on external inputs or inner states. Deactivation, too, is an alternative branch of the program. The program sequence is triggered or controlled by an external stimulus which is part of an external input or the input itself.
EXAMPLE 1: In a vending machine the program is started by inserting a coin. The program can respond in two ways: either accept the coin and release the article or return the coin with the article output remaining blocked. The decision is made based on the result of the check of the inserted coin and the article stock.
EXAMPLE 2: A machine tool which automatically executes operations under program control is an automaton. Examples: automatic lathe, milling machine.
Note 2 to entry: A controller, governed by the defined relationships in a control loop is an automaton.
EXAMPLE 3: In a temperature controller a reference variable is set, which will be compared with the feedback variable. Based on the result of the comparison the controller drives the final controlling equipment. In other words, based on the difference between the reference variable and the feedback variable (representing the temperature as controlled variable) the controller and the final controlling equipment influence the temperature via the manipulated variable (output variable).
Note 3 to entry: This entry was numbered 351-21-42 in IEC 60050-351:2006.