CONTROL SYSTEM

CONTROL SYSTEM

INTRODUCTION       

A SYSTEM IS AN ASSEMBLAGE OF DEVICES AND COMPONENTS CONNECTED OR RELATED BY SOME FORM OF REGULAR INTERACTION OR INTERDEPENDENCE TO FORM AN ORGANIZED WHOLE AND PERFORM SPECIFIED TASKS. THE SYSTEM PRODUCES AN OUTPUT CORRESPONDING TO A GIVEN INPUT. THE THERMOMETER AND THE MASS SPRING DAMPER SYSTEM CAN BE IDENTIFIED AS SYSTEMS.

            

 A THERMOMETER HAS THE INPUT X=Q(TEMP) ANT THE OUTPUT Y= L(LENGTH OF THE MERCURY COLUMN IN THE CAPILLARY).IN THE MASS SPRING ARRANGEMENT ,THE FORCE AND THE POSITION OF THE MASS CONSTITUTE THE INPUT TO AND  OUTPUT FROM THE SYSTEM , RESPECTIVELY IN A ROTATIONAL GENERATOR OF AN ELECTRICITY, THE INPUT WOULD BE ROTATIONAL SPEED OF THE PRIME - MOVER SHAFT AND THE OUTPUT WOULD EITHER BE THE INDUCED VOLTAGE AT THE TERMINALS( WITH NO LOAD ATTACHED TO THE GENERATOR) OR THE UNIT OF ELECTRICAL POWER (WITH LOAD ATTACHED TO THE GENERATOR).

           

THE TURN CONTROL IMPLIES TO REGULATE, OR COMMAND. A CONTROL SYSTEM MAY THUS BE DEFINED AS "AN ASSEMBLAGE OF DEVICES AND COMPONENTS CONNECTED OR RELATED SO AS TO COMMAND, DIRECT OR REGULATE ITSELF OR ANOTHER SYSTEM".

            

IN A CONTROL SYSTEM, DELIBERATE GUIDANCE OR MANIPULATION IS EMPLOYED TO MAINTAIN A SYSTEM VARIABLE AT A SET POINT TO CHANGE IT ACCORDING TO PRESENT PROGRAMME.

EXAMPLE OF CONTROL SYSTEM

(1) AN ELECTRICAL SWITCH WHICH SERVES TO CONTROL THE FLOW OF ELECTRICITY IN A CIRCUIT. THE INPUT SIGNAL (COMMAND) IS THE FLIPPING OF SWITCH ON OR OFF, AND THE CORRESPONDING OUTPUT (CONTROLLED) SIGNAL IS THE FLOW OR NON FLOW OF ELECTRIC CURRENT.

(2) A THERMAL SYSTEM WHICH IT IS DESIRED TO MAINTAIN THE TEMPERATURE OF THE HOT WATER AT A PRESCRIBED VALUE .BEFORE THE OPERATOR CAN CARRY OUT HIS TASK SATISFACTORILY, THE FOLLOWING REQUIREMENT MUST BE MET:

         

(A) THE OPERATOR MUST BE TOLD WHAT TEMPERATURE IS REQUIRED FOR THE WATER. THIS TEMPERATURE, CALLED THE SET POINT OR DESIRED VALUE, CONSTITUTES THE INPUT TO THE SYSTEM.

       

(B) THE OPERATOR MUST BE PROVIDED WITH SOME MEANS OF OBSERVING THE TEMPERATURE (SENSING ELEMENT). THIS TEMPERATURE IS OUTPUT FOR THE SYSTEM AND IS CALLED THE CONTROLLED VARIABLE. THE OPERATOR WATCHES THE THERMOMETER AND COMPARES HOW THE MEASURED TEMPERATURE COMPARES WITH THE DESIRED VALUE. THIS DIFFERENCE BETWEEN THE DESIRED VALUE AND HE ACTUAL MEASUREMENT VALUE IS ERROR OR ACTUATING SIGNAL.

                                         E = R – C

WHERE R REFERS TO THE SET-POINT OR REFERENCE INPUT AND C DONATED THE CONTROLLED VARIABLE.

      
(C) THE OPERATOR MUST BE PROVIDED WITH SOME MEANS OF INFLUENCING THE TEMP AND MUST BE INSTRUCTED WHAT TO DO TO MOVE THE TEMP IN DESIRED DIRECTION.

(3) A DRIVING SYSTEM OF AN AUTOMOBILE (ACCELERATOR, CARBURETOR AND AN ENGINE VEHICLE) WHERE COMMAND SIGNAL IS TO FORCE ON THE ACCELERATION PEDAL AND THE AUTOMOBILE SPEED IS THE CONTROLLED VARIABLE. THE DESIRED CHANGE IN ENGINE SPEED CAN BE OBTAINED BY CONTROLLING PRESSURE ON THE ACCELERATOR PEDAL.

(4) AN AUTOMOBILE STEERING SYSTEM WHERE THE DRIVER IS REQUIRED TO KEEP THE AUTOMOBILE IN THE APPROPRIATE LANE OF THE ROADWAYS. THE EYES MEASURE THE OUTPUT (HEADING OF THE AUTOMOBILE), THE BRAIN AND HANDS REACT TO ANY ERROR EXISTING B/W THE INPUT (APPROPRIATE LANE) AND THE OUTPUT SIGNALS, AND ACT TO REDUCE THE ERROR TO ZERO.

(5) A BIOLOGICAL CONTROL SYSTEM WHERE A PERSON MOVES HIS FINGER TO POINT TOWARDS AN OBJECT. THE COMMAND SIGNAL IS THE POSITION OF THE OBJECT AND THE OUTPUT IS THE ACTUAL POINTED DIRECTION.

     

OTHER WELL KNOWN EXAMPLES OF THE CONTROL SYSTEMS ARE: ELECTRIC FRYING PANS, WATER PRESSURE REGULATORS, AND TOILET – TANK WATER LEVEL, ELECTRIC IRONS, REFRIGERATORS AND HOUSEHOLD FURNACES WITH THERMOSTATIC CONTROL.