How can you choose the right industrial automation controller for your specific application?

In my experience, I have had PLCs for small scale discrete controls and DCS for large continuous process control. Where I currently work, we have various cabinets in the lubricant packaging plant with PLCs doing the discrete controls for conveyors, filling, capping and packaging machines. We don’t have a PAC or RTU because the process doesn’t require such. Also, we have a DCS unit for the lubricant and grease process plant. Assessing needs for application is crucial before a project is initiated. With the real life examples giving above, the industrial requirements/application will determine what control system architecture will be deployed.

Sometimes the customer specifically tells you what controller to use. Otherwise, you may want to look at what is common in your industry. For example, in the US, many companies use Allen-Bradley, but in Europe Siemens is more common. Also look at price. For example, Automation Direct is one of the less expensive brands. You also need to look at the IO count and any device communications needs. For example, are there 10 IO points or over 100? Will any devices communicate over Ethernet, serial, etc? This makes the difference between, say, an Allen-Bradley ControlLogix or MicroLogix PLC.

The basics are to know the application, the flow of the process, and the number of inputs and outputs involved in the process to make it automated. Then, consider the area of application or the environment where the process is happening to select the specific product, and the cost of the project is an important parameter in the selection process.

No momento de escolher o Controlador ideal para o seu projeto de Automação, é essencial a robustez da aplicação (Ambiente e periféricos) mas também considerar a robustez necessária para o Software, pois capacidade de memória, recursos de comunicação e redes e integração com outras ferramentas de Desenvolvimento. É crucial começar com este princípio em mente, pois influcienciara até na linguagem de programação escolhida para o projeto, dependendo do tamanho da aplicação no caso dos PLC's por exemplo, é mais interessante e eficiente usar uma linguagem STL ou SCL ao invés do tradicional Ladder, em projetos em que se é exigido um manuseio maior de informação.

To begin, inventory all I/O for the system. This will include everything that can change state or position. Analog inputs will include temperatures, pressures, flow rates, positions, etc. Analog outputs will include flow control valves, hydraulic proportional valves, servos. Digital IO will include everything that has only two states, on or off. Things like pushbuttons, proximity switches, solenoid valves and pressure switches are examples of digital IO.

Knowing the specifications of the site and paying attention to the peripheral equipment that are supposed to communicate with the PLC makes most of the work easier. Side modules and user interface for operation are equally important. Sometimes the employer has limitations that must be considered.

I find that programs that are well documented and easy to follow makes troubleshooting a very quick process. I relate this to wiring a control panel and not using labels. The panel may look good and functional but when something goes wrong, troubleshooting could be very difficult.

Industrial developments are designed to last for years, so selecting a brand that provides a long-term support solution is crucial. On one hand, hardware availability to prevent a lack of spares or the risk of obsolescence in the near future. On the other hand, software compatibility to allow previous work to be portable to a new platform when a new requirement arises. These two critical factors will ensure a healthy and successful life cycle of the system.

It's important to consider the signal type (Analog or Digital), its power requirement and what type of communication protocol for system interface. Compatibility with existing system, size of the controller etc.