Introduction

          The automatic control of system (or machine) is a very accurate and effective means to perform desired function by the system in which the human operator is replaced by a device there by relieving the human operator from the job thus saving physical strength. The automatic control systems are also called as self-activated systems. 

          The centrifugal actuated ball governor which controls the throttle valve to maintain the constant speed of an engine is an example of an automatically controlled system.

The automatic control systems are very fast, produces uniform and quality products. It reduces the requirement of human operators thus minimizing wage bills.

Terms used in Automatic Control of Systems

Terms used in Automatic Control of Systems

The following terms are generally used in automatic control of systems: 

1. Command:  The result of the act of adjustment, i.e. closing a valve, moving a lever, pressing buttons etc., is known as Command.
2. Response: The subsequent result of the system to the command is known as response.
3. Process control: The automatic control of variables like  change in pressure, temperature and speed etc., in machine is termed as process control.
4. Process controller: The device which controls a process is called a process control.
5. Kinetic control: The automatic control of the displacement or velocity or acceleration of a member of a machine is called as Kinetic control.
6. Regulator: The device used to keep the variables at a constant desired value is called as regulator.
7. Feed back: It is defined as measuring the output of the machine for comparison with the input to the machine.
8. Error detector: A differential device used to measure the actual controlled quantity and to compare it continuously with the desired value is called an error detector. It is also called deviation sensor.
9. Transducer: It is a device to change a signal which is in one physical form to a corresponding signal in another physical form. The example of transducer are a loudspeaker (because it converts electrical signal into a sound) and photo-electric cell (because it converts a light signal into an electric signal). Similarly, the primary elements of all the many different forms of thermometers are transducers.
10. Amplification: It is defined as increasing the amplitude of the signal without affecting its waveform. For example, an error detector itself has insufficient power output to actuate the correcting mechanism and hence the error signal has to be amplified. This is generally done by employing mechanical or hydraulic or pneumatic amplifying elements like levers, gears etc.,