A control system is an arrangement of physical components connected or related in such a
manner as to command, direct, or regulate itself or another system, or is that means by which any
quantity of interest in a system is maintained or altered in accordance with a desired manner.
Any control system consists of three essential components namely input, system and output. The
input is the stimulus or excitation applied to a system from an external energy source. A system
is the arrangement of physical components and output is the actual response obtained from the
system. The control system may be one of the following type.
1) man made
2) natural and / or biological and
3) hybrid consisting of man made and natural or biological.
1) An electric switch is man made control system, controlling flow of electricity.
: flipping the switch on/off
: electric switch
: flow or no flow of current
2) Pointing a finger at an object is a biological control system.
: direction of the object with respect to some direction
: consists of eyes, arm, hand, finger and brain of a man
: actual pointed direction with respect to same direction
3) Man driving an automobile is a hybrid system.
: direction or lane
: drivers hand, eyes, brain and vehicle
: heading of the automobile.
Classification of Control Systems
Control systems are classified into two general categories based upon the control action which is
responsible to activate the system to produce the output viz.
1) Open loop control system in which the control action is independent of the out put.
2) Closed loop control system in which the control action is some how dependent upon the
output and are generally called as feedback control systems.
Open Loop System is a system in which control action is independent of output. To each
reference input there is a corresponding output which depends upon the system and its operating
conditions. The accuracy of the system depends on the calibration of the system. In the presence
of noise or disturbances open loop control will not perform satisfactorily.