PLCs emerged as a reliable alternative to the relay logic. Earlier, the highly distributed and hardwired process control systems in a factory used relays, timers and electrical loop controllers. As you can imagine, monitoring these systems was very time consuming. All day, the technicians needed to walk around the factory because of the difficult fault finding system. Considering a high value business, a downtime of a few hours may cause a loss of millions of dollars. Thus emerged the demand for an integrated control resulted the discovery of PLCs.
First PLC
PLCs made a huge impact. It needed large amount of cables to wire field devices, remotely. First PLCs were very big that it needed central control rooms to install. Even though the initial expenses are more, it made the business more profitable. Safety improved, downtime reduced, faults became easier to find. Thus goes the benefits of PLC.
Advancement with IIOT
As the technology progressed, advanced PLCs came which are capable of operating in harsher environment. They were compact structured having reasonable cost. Thus achieved great opportunities to increase the level of control. With advanced communication methods, it became possible to connect all machines together, in multiple factories, in any part of the world. Internet of things (IIot) has become popular nowadays. Whatever things are changing with the advancement of IIoT, PLCs Still remains at the heart of the industrial control.
IIoT refers to the billions of industrial devices connected to wireless networks, gathering and sharing data. These data are collected and analysed which enables faster and better decision making. This make it possible for the machines to run a master program fed from a smaller central controller to individual PLCs. Certain low-cost AC drives comes with onboard PLC at no extra cost. In short, a simple PLC can remove the need for complex and costly electromechanical options. This make the business processes more efficient.
Centralized and Decentralized System
Industrial automation can be applied to an assembly line with centralized or decentralized control technology. Assembly lines are structures consist of modules for the different manufacturing stages. It includes pick-and-place units, robots, welding stations and a logistics unit that transports individual parts between modules and controls the supply of assembly parts. With IIoT, the question arises is about to choose a centralized or a decentralized control as a best option to adopt in an industrial control system.
Benefits of using a Decentralized PLC
An option is to remove the central controller is to spread the work across smaller PLCs. Because large PLCs are expensive. AC drive with onboard PLC reduces the cost further.
Extra coding might requires when upgrading or making a change to an existing system. Considering a centralized control system, this may need shutting down a whole production line. Or else we can use an isolated local controller to make the rest of the line to keep going.
In rare cases, processes may run too fast for a central controller to respond immediately. Decentralized controller can possibly reduce lag which benefits in more uptime.
If the unit is local to the operator, it is easy to connect for capabilities such as trending analysis, alarming, batching or printing.
As there is very less information to analyse, distributed control software is easier to maintain. When it comes to troubleshooting faults using one large system, as opposed to working on smaller ones, is a difficult task.
If the central controller goes into fault, the entire process may fail, which may interrupt process. That’s why field-based distributed controllers do not wholly rely on the central controller. A decentralized system partitioning is easy. For example, zoned interlocks or light guards provides better safety.
Why Centralized PLC?
There are reasons why many people still use centralized systems despite the benefits of a decentralized system. Changing an existing system would be expensive and counterproductive and may cost downtime. Considering an industry where airborne particles or high temperatures cause malfunction. Here, a simple setup with a conditioned centralized PLC is the better option. Also, decentralization might add extra complexity to a new equipment that is not needed. Size, communication and software standards all have an impact on our choices. The possibilities of IIoT are about to be realized, offering more intelligent products that increase uptime.