Question

MECH641- Process Instrumentation and Control (Assignment 3) Answer the following: (Each Question carries 5 marks) 1. List the difference between open loop and closed loop control system with suitable example. 2. Draw the block diagram representation of a heating system. 3. Explain in detail the ratio control with suitable example. Rubrics Rubrics for descriptive questions: 5 marks: complete correct answer. 4 marks: correct answer with minor mistakes. 1-3 marks: partially correct answer (Deduction Method applies) 0 marks: incorrect answer.

Answer 1

Ans 1) Comparison between Open Loop and closed loop control Sytem

the control system open top control system (Non feedback systems) An open loop control system to the one eof in which control action is independent of the desired output The actuating signal depends only on the input comment & output has no control over it Reference input. Controller Actualing signal compelled Plocess Controlled variable control : speed control of is no is close or open loop. systems fore, the automobile in open loop system there way ensure that the actual • speed mot to the desired speed automatically Closed loop control Byslem (feed back control system) en closed loop system control action is somehow dependent on the output. In this case the controlled output is fed back through a feedback eten element and compared with the reference input. Thus the actuating signals is the difference of desired output & reference input. helps comparison of the output with the input of the systesss so that Feedback is the property which CamScanner

appropriate control action may be performed Error detector | Reference input load Torque Output controller Engine + feedback system Closed loop idle speed control I system open loop closed loop 1) less accurate 1) More accurate 2) Generelly build easily (2) Generelly complicated & Costly 3) Control edjustment 3) The control ajustment depends on human judge depends on output & feedback element 11 Automatic washing machine 6) siquid level control system (2) Io affe signal system ment & estimate Lex. 2) Electric switch Scanned with Ca B) Automatic toaster

Ans2) Block diagram representation of heating system

vent Exhaust gases Brunes chamber Son z water in Water Hotwater at ADOM AMDIATOR plot flame Detectos THERMOCOUPLE main flame Natteral gas VALVESTOR K THERMOSTATI Temperature controller fon/ off) & Transmetter External temp. o Deured furnace t Controller (C) Temper- ature feedback CS stanned with CamScanne Block DIAGRARY OF A KEANG By Shery

Ans 3) The function of ratio controller or ratio control is to control the other flow so as to maintain the desired ratio between the two flows. The flow controlled by the ratio controller is called the controlled flow. There many examples of ratio control .

For example, treatment of drinking water with chlorine, where we want the controlled flow of chlorine in the wild flow of water.

Another example is ratio control used in the production of paint, where a base liquid must be mixed with one or more pigments to achieve a desired consistency and color.