Rabu, 10 Julai 2013

CONTROLLER PRINCIPLE

Introduction to Control Process System

Concept control system 
- To sense deviation of the output from the desired value and correct it, till the desired output is achieved 
- Desired value of the output  - reference output or set point

Controllers are the controlling element of a control loop
- element which accepts the error in some form and decided the proper corrective action 
- Their function is to maintain a process variable (pressure, temperature, level..) at some desired value


Plant 
- system or process through which a particular quantity or condition is controlled. This is also called the controlled system.
Controller - control elements are components needed to generate the appropriate control signal applied to the plant
 
Feedback elements 
- components needed to identify the functional relationship between the feedback signal and the controlled output.
 
Reference point 
- external signal applied to the summing point of the control system to cause the plant to produce a specified action. This signal represents the desired value of a controlled variable and it also called set point.

Controlled output 
- quantity or condition of the plant which is controlled. This signal represents the controlled variable.

Feedback signal 
- function of the output signal. It is send to the summing point and algebraically added to the reference input signal to obtain the actuating signal.

Actuating signal 
- the control action of he control loop and is equal to the algebraic sum of th reference input signal and feedback signal. This is also called the error signal.

Manipulated variable
- process acted upon to maintain the plant output(controlled variable) at the desired value.

Disturbance 
- undesirable input signal that upset the value of the controlled output of the plant.
 

 

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