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 : Room temperature
Reference Variable : Required Room temperature (pre-set value)
Comparison Element : Person compares the measured value with required value
Error Signal : Different between the measured and required temperatures.
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 receiving 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 pump to empty the water from the drum. Pre-wash cycle involves washing the clothes in the d m by cold water.
Main Wash Cycle:
Main wash cycle involves washing the clothes in the drum by hot water and t he sequence
of operations in main wash is as follws:
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 switches off the current after the water is heated to required temperature.
Microprocessor or cam switch ON the motor to rotate the drum
Microprocessor or cam switches 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 times and the sequence of operations in a Rinse cycle 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.
