6.3 Explain the principle of Programmable Logic Control (PLC)

6.3 Explain the principle of Programmable Logic Control (PLC)

6.3.1 List functions of the various PLC Components

 1.  PROGRAMMING DEVICES

The PLC is programmed using a specialty programmer or software on a computer that can load and change the logic inside. Most modern PLCs are programmed using software on a PC or laptop computer. Older systems used a custom programming device

 2. POWER SUPPLY

• supply provides power for the PLC system. The power supply provides internal DC 
  current to operate the processor logic circuitry and input/output assemblies. Common 
  power levels used are 24V DC or 120

•      The power VAC.

3. PROCESSOR (CPU)

•      The processor, central processing unit, or CPU is the "brain" of the PLC. The size and type of CPU will determine things like: the programming functions available, size of the application logic available, amount of memory available, and processing speed. Understanding the CPU can be a complex subject and we will tackle that in other articles.

4.  INPUT/OUTPUT MODULE

•      INPUT           

•   CHANGE SIGNAL FROM INPUT DEVICE TO A SUITABLE SIGNAL FOR THE CPU

•      OUTPUT

•   CHANGE SIGNAL FROM THE CPU TO A SUITABLE SIGN AL FOR THE OUTPUT DEVICE

5.  INPUT/OUTPUT DEVICES

•      INPUT

–     Inputs carry signals from the process into the controller, they can be input switches, pressure sensors, operator inputs, etc. These are like the senses and sensors of the PLC.

•      OUTPUT

–     Outputs are the devices that the PLC uses to send changes out to the world. These are the actuator the PLC can change to adjust or control the process - motors, lights, relays, pumps, etc.

•      Many types of inputs and outputs can be connected to a PLC, and they can all be divided into two large groups - analog and digital. Digital inputs and outputs are those that operate due to a discrete or binary change - on/off, yes/no. Analog inputs and outputs change continuously over a variable range - pressure, temperature, potentiometer.

 

(SOURCE: http://www.plctutor.com/plc-components.html)

  

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