automatic control systems

The theory of automatic control systems is an idea closely related to feedback concept. A system is a combination of components that act together and perform certain objectives. In a feedback system the output signal is fed back in order to increase or reduce the input signal.

Although the feedback concept, which is lying in the foundation of dynamic systems, has been perceived relative recently (at the end of the 19th century), it is known that the idea has been understood and applied correctly since the ancient times. In the engineering, the aim of control is to guide the system to a desired direction or kept constant at a certain value. A feedback control system is one which tends to maintain a prescribed relationship between the output and the reference input by comparing these and using the difference as the means of control. Thus, in an automatic control system, the variable to be controlled is first measured, secondly compared against a reference value and at least the difference applied to the system input, in order to influence the system in a desired manner. In the block diagram of an automatic control system, the controlled system take place in the forward path and the measuring device of the controlled variable take place in the feedback loop. A disturbance is a signal that tends to affect adversely the value of the output of a system.

To differentiate an automatic control system, realized and used unconsciously during centuries from the open loop control system, one has to check the existing system for the feedback characteristic. The oldest automatic control systems technically mindfully designed and tested for their operational merit, date back to the Hellenistic era. The oldest applications are flow rate control in water clocks.

Scientific advancement, which reached its peak in the Hellenistic age, lost its luster in the palaces of Byzantium; the Abbasid Caliphs in Baghdad once more let lit the science torch. Muhammad, Hassan and Ahmad known as Benu Musa or Sons of Musa bin Shakir of Khurasan, are very famous in the history of technology. They played an important role in the advancement of mathematical sciences during the reign of Abbasid caliph al-Ma'mun (813-833 A.D) and the succeeding caliphs. Ahmad's interest in technology might have led them to write the book titled Kitab al Hiyal (Book of Mechanical Devices) (850 A.D). The manuscript in the Ahmed III Library at Topkapi Palace is almost a complete copy (A 3474) and includes magical vessels, water jets, oil lamps, a densimeter, a bellow, and a lifting device. This science of 'ingenious devices' and 'ingenious automata' created by the use of matter, water and air is known as 'ilm al-alat al ruhaniyet': science of pneumatic devices. According to Akfani, "the science of pneumatic devices deals with the construction of various devices based on the principle of the 'horror of vacuum'. The purpose is to educate the mind while designing these systems that deal with measured cups, siphons and other elements."


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