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From the History of Automatic Control Theory
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- A closed- loop control system
- An open-loop system
| From the History of Automatic Control Theory
The concept of control and the use of control devices were known long ago. Simple control systems with an input signal controlling an output element have been used by people for a long time. In recorded history it is found that the Romans invented a water-level control device 2000 years ago. The mathematical foundations for control theory have been laid by J. Fourier and P. Laplace. Research work in analytical dynamics was carried out by A. Routh. A. Lyapunov was the first to develop the theory of stability of automatic control systems. Real development of automatic control theory began in 1920s. World War I brought a tremendous impetus for the advancement of control. Such problems as the automatic bombing and control systems for anti-aircraft guns required fundamental theory and complex equipment. To meet these requirements investigations in the field of automation were accelerated. Nowadays automatic control systems play an important role in the development of civilization. There has been an enormous growth in the application of controllers, in technologies and everyday life. Domestically, automatic controls in heating and air conditioning systems regulate the temperature and humidity. Industrially, they are employed in quality control of manufactured products, power stations, etc. In space technology and weapon systems they appear in the form of guidance systems, fire control systems, etc. It is automation that ensures speed, accuracy, reliability, high quality and economy of technological processes. Automation control is irreplaceable where it is necessary to maintain various physical properties at a desired level. Among many physical properties that can be controlled there temperatures and pressures in chemical industry, moisture content in textile industry, thickness of insulation around wires in electrical engineering. 11. Write down the translation of these two texts and entitle them: Text A As it is known control systems are classified according to the degree of their automation. A control system is called automatic if the basic functions of control are performed without the participation of man, that is automatically. Completely automated control systems are defined as closed-loop systems. Partially automated control systems are termed open-loop ones. A closed- loop control system or feedback system automatically controls and modifies its own operation by responding to data generated by the system itself. The example of a closed-loop control system is a switch of a high-speed printer, used in computer systems. The switch finds if there is paper in the printer. If the paper runs out, the switch signals the system to stop operation. An open-loop system does not provide for its own control or modification. It must be controlled by people. The example is the operation of a printer having no switch. In this case a human operator must notice when the paper runs out and signal the system to stop printing. The former system is automatically controlled by self-regulation, the latter one being controlled by man. This difference determines their application. Open systems are used for stabilization and program control. Closed systems replace man in hard and dangerous work. Text B Today forms and applications of electric relay are numerous and varied. Having improved relays scientists received a more reliable form of control. As it is known there is a large range of electric relays which are utilized to operate switchgear, totalisator, road traffic signals and certain types of automatic telephone equipment. Sometimes it is necessary to operate a circuit by reversing a current in the actuating circuit. This is done by using a polarized relay. The special feature of this relay is the employment of a permanent magnet. Giving the armature a definite polarity, the permanent magnet makes it possible to control the direction of the armature movement when a current passes through the relay coils. This permanent magnet is necessary to maintain the same polarity at each end of the armature. When energized with the poles directed to the north and south, the relay attracts one end of the armature and repels the other one.
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