PLC Hardware

PLC Hardware

Instructor: Shahpour Shapournia

There is something very cool about automating Christmas lights that flash to the beat of a particular song – especially if you are the one that can do that.
We’ve all seen them, those videos showing the house that has more lights on it than the Vegas strip, all flashing in unison to the latest pop singers rendition of Grandma Got Runover By A Reindeer. We’ve all secretly wanted to be “that house”, the one that everyone drives by to ooooh and ahhhh at your latest creation.
Control systems are used in a variety of industrial applications such as Culinary Water and Waste-water treatment, steel, gas and oil refining, manufacturing, etc. They may also be used for the control of non-industrial processes such as home security and/or automation, and synchronized Christmas lighting. If you are interested in the automation arena, knowing the basics of the control system is one of the first steps on that journey.

Be warned: extensive knowledge of these systems may just land you a job with the title of “Automation or Controls Engineer”. Or you could opt for the “Awesome Christmas Light and Music Synchronizing Engineer” or “Home Anti-Theft, Lighting, Sound, and Entertainment System Operations Specialist” job titles, whatever tickles your fancy.

1) The Rack

The Rack is the foundation of the control system. Each control component will be mounted on the Rack. In a small system, you may have only one rack while in a larger system; you may have many additional racks which are referred to as expansion racks.

2) The Slots

The Rack has divisional lines that are not seen, just assumed. These divisions are called Slots. A Slot is simply a position in which you will place a module. Though Slots are not seen, they are definitely used in the programming software. Each module that is fitted in a Slot has a callout within the software.

3) The Power

The Rack must have a Power Supply to power all of the control components. The Power Supply should be selected based on the power usage of the components that will be placed on the Rack. The Power Supply always occupies the first Slot in the Rack.

4) The Brains

The Brains of the control is a component called a CPU. Yes, the same CPU, central processing unit. This Brain is also called a PLC or Programmable Logic Controller. In the CPU, code resides that will control the entire control system associated with the Rack. The CPU is always placed in the second Slot in the Rack.

5) The Modules

Along with the Power Supply and CPU modules, I/O or Input/Output modules also reside within the Rack. Discrete I/O modules take care of items in the field that are in (input) or want to be controlled (output) in one of two states, either on or off. Analog I/O modules are responsible for reading (input) or controlling (output) items that are of a variable state such as a heater that is controlled by thermostat. The I/O modules reside in the Rack slots after the CPU.

6) The Specialists

There are occasions when a special module is needed for different types of control processing. These special control modules are called Function Modules or FM’s. These modules handle signals outside of the CPU and are not typical. When using FM’s, they should be placed in Slots after standard I/O modules.

7) The Communicator

The CPU is typically equipped with a single or multiple communication protocol port. It may be necessary, in a particular installation, for additional communications ports. When they are required, use of a Communications Module or CM may be employed. The placement of this module should follow the standard I/O or after an FM is used.

Understanding the components, their use, and proper placement of them within the control system is essential to a smooth startup. As you become more familiar with the control system hardware, this knowledge will become second nature.

PLC Hardware