[MUSIC] The purpose of this module is to introduce the concept of Programmable Logic Controllers, or PLCs, that coordinate the real time control functions in manufacturing operations. At the end of this module, you will be able to describe manufacturing as a process, state how automated process control benefits manufacturing, and list full components of a Programmable Logic Controller, or PLC system. This lesson will provide a basic introduction to process control. Let's start with understanding what is a process. A process is a series of tasks that take certain inputs and generates intended output. For example, manufacturing process is a process that takes input, such as operators, equipment, and material, and generate manufactured product as an output. In order to understand an important term, compliance, related to the process, let us consider an illustrative example of cruise control of a car. You use the cruise control mode in your car to set it to a speed so that you stay within the legal speed limit for a given road condition. Suddenly, the road conditions change, for example, due to ongoing construction in a segment of the road. Due to which, the legal speed limit reduces. What was legal speed before road conditions changed ceases to be legal now. In this setting, driver goes from compliant mode to non-compliant mode because of the changes in input, that is, the road conditions. Output of a process can be compliant if it meets predetermined specification, or they can be non-compliant if the output does not meet predetermined specifications. Based on whether or not a process is capable of generating a compliant output, a process can be considered to be in control if the process is capable of generating a compliant output, and out of control if a process is not capable of generating a complaint output. Processes cannot be expected to stay within control over time without any intervention. The process could start off in control, but could get out of control as time passes, if it is left alone. The main reason for processes going out of control is the change in quality of an input as time passes. In other words, in many processes, the quality of input deteriorates over time and this causes the process to get out of control. So how do we maintain the process output at a compliant level at all times, even when the process input changed? It can be done in three simple steps. Step one, obtain feedback from the actual output. Step two, measure the feedback opt in against what is acceptable, that is, predetermined specification for output. And step three, if feedback represents a current or potential variation from a specification, make changes to input, as needed. That initial is the concept of process control. Process control refers to techniques used to maintain a process within control at all times by using feedback from the output to make necessary adjustment to the process, to ensure our process remains capable of generating a compliant output at all times. In the car example, this could be human eyes looking at the changed road conditions or looking at the changed posted speed limits, and using previously acquired knowledge to realize current speed is more than the legal limit and manually intervening to apply break to reduce the speed to legal limits. This is referred to as close loop control system, which is different from open loop control system, where the feedback from the output is not necessarily used.