Control System

CONTROL SYSTEM

A black box which is used to control its output in a pre-set value

OPEN LOOP CONTROL SYSTEM:

If there is no feedback device to compare the actual value with desire d one.

No control over its in put

CLOSED LOOP CONTROL SYS TEM:

If there is feedback dev ice to compare the actual value with desired one .

Elements of Closed Loop System:

The elements of closed loop control system are

Comparison U nit

Control Unit

Correction Unit

Process Unit

Measurement Device

EXAMPLES:

System of Controlling Room Temperature

Controlled Variable     : R oom temperature     

Reference Variable       : R equired Room temperature (pre-set value)    

Comparison Element   : Person compares the measured value with required value   

Error Signal        : D ifferent between the measured and required tem peratures.

Control Unit       : Person     

Correction Unit  : The switch on the fire 

Process     : H eating by the fire     

Measuring Device        : Thermometer.    

System of Controlling Water Level

Controlled variable     : Water level in the tank

Reference variable       : Initial setting of the float and lever position

Comparison Element  : The lever

Error signal                 : Difference between the actual & initial setting  of the lever

positions

Control Unit       : The pivoted lever

Correction Unit  : The flap opening or closing the water supply

Process     : The water level in the tank   

Measuring device         : The floating ball and lever    

SEQUENTIAL CONTROLLERS:

It is used to control the process that are strictly ordered in a time or sequence

DOMESTIC WASHING MACHI NE:

Pre Wash Cycle:

Pre-wash cycle may involve the following sequence of operations.

Opening of valve to fill the drum when a current is supplied

Closing the valve after recei ving the signal from a sensor when the required level of water is filled in the washing drum.

Stopping the flow of water after the current is switched off by the microproceessor. Switch on the motor to rotate for stipulated time.

Initiates the operation of pum p to empty the water from the drum. Pre-wash cycle involves was hing the clothes in the d m by cold water.

Main Wash Cycle:

Main wash cycle involves wa shing the clothes in the drum by hot water and t he sequence

of operations in main wash is as foll  ws:

Cold water is supplied after t he Pre-wash cycle is completed.

Current is supplied in large a mount to switch on the heater for heating the cold water.

Temperature sensor switche s off the current after the water is heated to required temperature.

Microprocessor or cam switc h ON the motor to rotate the drum

Microprocessor or cam switc hes on the current to a discharge pump to empty the drum.

Rinse Cycle:

Rinse cycle involves washing out the clothes with cold water a number of tim es and the sequence of operations in a Rinse cy cle are as follows:

Opening of valve to allow cold water into the drum when the microprocessor are given signals to supply current after the main wash cycle is completed.

Switches off the supply current by the signals from microprocessor Operation of motor to rotate the drum

Operation of pump to empty the drum and respect this sequence a number of times.

Spinning Cycle

Spinning cycle involves removing of water from the clothes and the sequence of operations is

Switching on the drum motor to rotate it at a higher speed than a rinsing cycle.