Products - Automation and Controls - Automation Basics

Programmable Logic Controller (PLC):

A computer like device that is used to monitor, control, and collect data of any type of machine.

  • Ex. Allen Bradley SLC or Control Logix.

Human-Machine Interface (HMI): 

Nothing more than a computer screen to enter and display data for the operator. They can be keyboard, mouse or touch screen based.

  • Ex. Allen Bradley Panel View Plus or Versa View.
Inputs/Outputs (I/O): An input is any information coming into the PLC. Ex.  Temperatures (RTD), Push Buttons. An output any physical action that the PLC makes happen.
  • Ex. Starting a conveyor motor, Turning on a Light, An Alarm.
Digital or Discrete  I/O: Digital means nothing more than Off or ON.
  • Is that motor running? è Yes it is.
  • Turn that light on. è The light is on.
Analog I/O: Analog is a signal that varies proportional to what the device is doing or going to do.
  • Analog Output Example:
    • Make the DFR running at 50% of its max speed.
  • Analog Input:
  • The Cyclone fan is running at 77% speed. ORU tanks level is at 12 inches.

The most common types are 0-10V, 4-20mA and Resistance Temperature Devices (RTD) or Thermocouples.

  • For 0-10v, 0v is the low end (0%) and 10v being the high end (100%).
  • For 4-20 mA, 4mA being the low end (0%) and 20mA the high end (20mA).
  • RTDs change their resistance with the change in temperature.