How PLCs Work

         A programmable logic controller is a special computer that controls machines and processes. It therefore shares a common ground with PCs like central processing unit, memory, software, and communications. Unlike PCs the PLC is designed to survive in harsher industrial environments and are very flexible in its interfacing with inputs and outputs.

PLCs are typically have the following components: 

·         Power supply and rack

·         Central processing unit

·         Input/Output System 

PLC-en

PLCs come in many different shapes and sizes. Some can fit into your pocket, while larger control systems require large PLC racks. 

·         Power Supply and Rack

o    The rack holds everything together. It can be designed to hold multiple modules. It holds the cards to communicate with the CPU. The power supply regulates the DC power to each of the modules on the rack.

·         CPU

o    This is the brains behind the PLC. The CPU is typically behind the power supply. The CPU consist of a microprocessor, memory chip, and other logic circuits for monitoring and communication. This is where the logic program is implemented and executes the program and operates the process.

·         Input/Output System

o    This is where the physical connections between equipment and the PLC meet. A terminal strip is used for the I/O cards for the device connections. 

        The input/output system works in tandem with the CPU. Where the input devices record and measure the data received by the monitoring components and provides information for the CPU to determine what the machine or process should do with it. The output system relays the execution of the program from the CPU into the operating machines and processes. Usually the PLC executes a single type of execution for a specific task or process. This allows the system to automate the task based on the PLCs feedback sensors. 

What Industries Use PLCs 

        With PLC design and development reaching new heights every year, the potential industrial applications continue to grow. Here are a few of the industries that use PLCs and the applications for them. 

Snack Food Industry

·         Oven Control Systems

·         Batching Systems

·         Cooker Systems

·         Extrusion and Cutting Systems

·         Slurry Mixing and Distribution 

Material Conveying

·         Material Handling

·         Variable Speed Drives and Systems

·         Motor Control Center Systems

·         Valve Sequencing Control Systems

·         Plugged Line Countermeasure Controls 

Building Products

·         Kiln Control Systems

·         Cutting Control Systems

·         Forming Systems

·         Gypsum Mixing and Distribution 

Pharmaceuticals

·         Autoclave Control Systems

·         Vial Capper Machines

·         Validation Reports

·         R&D Operations

·         Vial Washing

·         Vial Labeling 

Steel Industry

·         Machine Control

·         Furnace Control Systems 

Packaging and Labeling

·         Material Positioning

·         Inventory Control Systems

·         Product Conveying Systems 

F-35-Empennage-line-at-Samlesbury

PLCs Right for Your Industry?

1.      Are PLCs needed for your manufacturing?

         Its basic, but understanding application requirements will help determine if PLCs are best for your automation system. Typical factory automation applications, which PLCs were designed for, involve the manufacturing/assembling of specific items. These applications involve one or more machines and a large amount of material movement. Typically these types of processes are monitored by an operator that watches the progression through the manufacturing line. These processes are highly logic controller and require high-speed requirements. This is often controlled by PLCs and Human Machine Interface (HMI) combination. 

2.      Product value versus downtime cost

        If product value is relatively low, and/or downtime results in lost production, but with little additional cost or damage to the process, the PLC is a good choice. For on-demand product manufacturing, where manufacturing is non-continuous, which a company is allowed proper shutdowns for maintenance, troubleshooting, or upgrades having little impact on production screams the PLC application. 

3.      What does a successful operator needs?

        Typically in a PLC environment the operator primarily handles exceptions. Status information and alarming aids the operator in staying aware of what the process is doing. This is essential the definition of “Lights Out Manufacturing”. If an operator is needed only to supervise then a PLC system might be for you. 

4.      What is the desired manufacturing performance?

        PLCs are designed for high-speed applications that require high scan rates involving motion control, high-speed interlocking, or control of motors and drives. Fast scan rates are necessary to be fully effective in controlling these devices. Which make them great for the on-demand product market. 

5.      Is there a need for customization?

PLCs were designed as the customizable king. The development of customized routines and functions is required to satisfy unique application needs. A systems integrator can switch from one type of manufacturing machine today and switch over to using it in a completely different system tomorrow. This is the power of programmable logic controls and their ability to switch from one application to another by rewriting the code. 

6.      Engineering Expectations?

Factory industrial automation engineers want customizable platforms where individual components can be reprogrammed to accomplish the desired task. Integrators and engineers breakout the PLCs and begin programming based on what they need. The tools provided by PLCs typically support a “bottoms-up” approach to engineering, which works wonders for smaller applications.