 Programmable logic controllers, or PLCs, are digital computers used in SCADA systems for automation in many different industries. PLCs utilize information received from sensors and other input devices to make decisions based on a predefined program and outputs the information to equipment. PLCs read limit switches, analog process variables like temperature and pressure, and complex positioning systems. Some PLCs can even use machine vision to carry out their program. PLCs can also operate electric motors, pneumatic or hydraulic cylinders, magnetic relays, solenoids, or other analog outputs. One of the biggest differences between the PLC and other computers is that the PLC is designed to be robust and capable of standing up to extreme conditions and environments. There are two basic types of PLCs, the integrated PLC and the modular PLC. The integrated PLC consists of several modules in a single case. As a result, the input and output capabilities are restricted based on what the manufacturer decides to put in the unit. Integrated PLCs are also known as compact PLCs. A modular PLC is built with several components that are plugged into a common rack or bus. Modular PLCs can come in different sizes and allow for a much more customizable solution based on industry needs. An individual can program PLCs to perform specific tasks using a basic programming language called ladder logic. For more information about how ladder logic came to be, check out our history of ladder logic video linked in the description below. Recently, a debate has been taking place in the mission critical community over whether ladder logic is still sufficient for PLC programming. Many individuals think that more advanced languages could be utilized to create more complex, safer programs that will serve industry better. Where do you stand? Leave your thoughts in the comments below. If you walk into any mission critical facility, you will see PLCs in action. These tiny computers do a lot to make sure that these businesses maintain operation and continue providing goods and services to individuals who need them.