The Complete Handbook of Automation Control Components

Chapter 1: Understanding Automation Control Components

Automation control components are the parts of a machine or process that make it run according to a desired sequence without a human standing at a control panel flipping switches for every single step. They range from something as simple as a mechanical limit switch on a packaging press to as complex as a programmable logic controller (PLC) coordinating a dozen servo axes on a CNC machining center. If it turns electricity into motion, reads a physical condition, or makes a decision based on a signal, it is likely an automation control component.

The easiest way to understand how these components behave is to see them as three distinct functional groups. First, there are the input devices. These are the sensors and switches that tell the controller what is happening. A photo-eye detecting a bottle on a conveyor, a thermocouple reading the temperature inside a plastic injection mold, or a pressure transducer on a hydraulic press are all input devices. Second, there is the logic or decision-making layer. This is usually a PLC, a programmable automation controller (PAC), or a dedicated safety relay. Its job is to read the input signals and, based on a stored program, decide what the machine should do next. Third, there are the output devices. These are the ones that act on that decision: contactors that energize a motor, solenoid valves that allow air to drive a cylinder, or analog drives that set the speed of a variable-speed blower.