Question

Draw the labeled block diagram of process control system and explain each block.

Answer 1

Explanation - Process control system consists of process or plant, sensor, error detector, automatic Controller, actuator or control element. 1) Process or plant- process means some manufacturing sequence. It has one variable or multivariable output. Plant or process is an important element of process control system in which variable of process is to be controlled. 2) Sensor measuring elements – It is the device that converts the output variable into another suitable variable which can acceptable by error detector Sensor is present in f/b path of close loop system. 3) Error detector – Error detector is he subtracting summing points whose output is an error signal i.e. e(t)=r(t) b(t) to controller for comparison & for the corrective action. Error detector compares between actual signal & reference i/p i.e. set point. 4) Automatic controller- Controller detects the actuating error signal, which is usually at a very low power level, and amplifies it to a sufficiently high level .i.e. means automatic controller comprises an error detector and amplifier. 5) Actuator or control element – Actuator is nothing but pneumatic motor or valve, a hydraulic motor or an electric motor, which produces an input to the plant according to the control signal getting from controller.

OR

Explanation : The block diagram of process control system consists of the following blocks:- 1) Measuring element: It measures or senses the actual value of controlled variable “c” and converts it into proportional feedback variable b. 2) Error detector: It receives two inputs: set point “r” and controlled variable “p”. The output of the error detector is given by e= r-b. “e” is applied to the controller. 3) Controller: It generates the correct signal which is then applied to the final control element. Controller output is denoted by “p”. 4) Final control element: It accepts the input from the controller which is then transformed into some proportional action performed by the process. Output of control element is denoted by “u”. 5) Process: Output of control element is given to the process which changes the process variable. Output of this block is denoted by “u”.