Classic Control

 Classic Control 



Is a control system used remotely control the process to obtain final product with an economic and standard specification.

Classic Control system component



Digital Input



Devices that send discrete signal as a Digital signal true or false ( 0,1) using that signal to 
  • Control
  • Alarm
  • Protection

these devices called "Switch"
  • Limit switch
  • Proximity switch
  • Push button
  • Process variable switches " Pressure- Temperature- Level- Flow ..." switches
 Limit switches 



are contact switches must has physical contact with the object force them to change the switch status from NO to close or NC to open contact

 Proximity sensors 




are non-contact switches that detect the presence of an object  with a long life 


 Proximity sensors types



    using different techniques such as    

•        Inductive Proximity Sensor .

•        Capacitive Proximity Sensor.

•        Magnetic Proximity Sensor

•        Optical Proximity Sensor.

•        Ultrasonic Proximity Sensors.

 What is a proximity sensor used for?

•        Object detection

•        Counting of pieces

•        Positioning objects

•        Determine the direction of movement







Electrical Connection 
  • 2-Wires
  • 3-Wires 24VDC(Brown + , Blue - , Black "output")
  • 4-Wires 24VDC(Brown + , Blue - , Black "NO", White "NC" )






Relay




      An electromagnetic device used for remote or automatic control.

     Construction

•          Coil

•          Movable armature 

•          Set of input terminals.

 


 Timers

1- ON DELAY



Delay the operating voltage for certain adjustable time

2- OFF DELAY



Delay the cut off voltage for certain adjustable time

3-ON/OFF DELAY



 Delay the operating voltage for certain adjustable time

Delay the cut off  voltage for certain adjustable time


 Contactor 



A contactor is an electrically-controlled switch used for switching an electrical power circuit

Contactor current should be more than load current to achieve long life time and not much more for the economic side

Link between low level power (coil) and High level power                 (Motor power)

A contactor has three components:

  • Iron core
  • Main point
  • Helping point

 



Because of the starting current Contactor rating should be considered

Contactor rating

AC1 TYPE (lighting , main contacts can withstand 1.25 load current)the cheapest

AC3 type (3 phase induction motors, main contacts withstand 10 load current)

AC4 TYPE (3 phase induction motors several on/off at little time or two ways motor 12 load current) most expensive

 



Thermal Overload



Protect motor from high current as the thermal over loading or over heating of the motor may lead to insulation failure and damage of winding.

Do not protect circuit from short circuit current

Between Contactor and motor

Main poles terminal (U - V - W)    (1 - 3 -5 )   to contactor

Terminal for Motor  (T1 T2 T3  )     ( 2-4-6) TO  power circuit (Motor)

 

Circuit Breaker

Low voltage 
  • MCB  (Miniature circuit breaker)


  • Rated current up to 125A , Interrupt rating 15 kA


  • MCCB  (Molded Case Circuit Breaker)


Rated current up to 1600 A, Interrupt rating 125kA



Circuit Breaker purpose

•        Switching a circuit on and off

•        Protection against short circuit

•        Protection against Overload current



  Magnetic trip 
very small time to cut off the process "protection from Short Circuit"
Thermal Trip
 has more time to take the action " to avoid starting current time" protect from current over load

 

TRIPPING CURRENT 

Class B trip curve

Start current reaches between 3 to 5 times rated current up to 3 sec. These MCBs are suitable for cable protection OR LIGHTING .

Class C trip curve

Start current reaches between 5 to 10 times the rated current up to 10 sec. Suitable for induction motors.

Class D trip curve

Start current reaches between 10 to 20 times the rated current up to 20 sec. Suitable for inductive  motor loads with high starting currents

 


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