A control system is a device, or set of devices, that manages, commands, directs or regulates the behaviour of other devices or systems. Industrial control systems are used in industrial production for controlling equipment or machines.
There are two common classes of control systems, open loop control systems and closed loop control systems.
In open loop control systems output is generated based on inputs.
In closed loop control systems current output is taken into consideration and corrections are made based on feedback.
This is a circuit diagram of the Thomson-Houston current regulator of 1880. The diagram was reproduced in the IEE book, ‘a history of control engineering 1800-1930’, by S Bennett. The book describes the current regulator as follows;
“The Thomson-Houston regulators of 1879-1880 used an electromagnet in series with the output circuit, thus providing closed-loop control”.
The circuit diagram originally appeared in the 1886 book written by Silvanus P Thompson (no relation to Thomson from Thomson-Houston) called Dynamo-Electric Machinery from which this representation has been sourced.