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 Terms used in control engineering


Proportional control
Proportional band
Off-set error
2-Terms controller
Cascade control   
Ans:
i. Proportional Action of a Control System   
The action of a control element whose output signal is proportional to its input signal.
OR. Proportional Control
In this type of control system controller action is proportional to the error of the system, which is defined as the difference between measured value and the desired value of the plant’s controlled parameter.
C µ e
C = Kp e

Where ‘C’ is controller output and ‘e’ is error of the system (MV-DV), Kp is proportional constant

ii. The range of measured values of the controlled variable which operates the final actuator over its full range is known as proportional hand, PB. It is usually expressed as a percentage of the scale range. eg PB = 100 %

iii. Offset.
 Sustained deviation, which occurs when measured value stabilizes (reaches equilibrium) at some point other than the set value. It changes with change in load condition. Offset occurs in proportional control
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