Whether it’s a PLC, a PAC or a PC, a controller is a fundamental piece of hardware required for an automated system to function. Controllers have been around for decades, and have faced great technological automation. Specifying controllers for a particular application has gained increased amount of complexity due to the many options available. Quality, cost, ease of use, functionality, etc. are just some of the factors that have to be taken into account before specifying a PLC.
Be True to the Requirements
Every project has its own specific requirements. When working with a controller, it’s important to know its functionalities and limitations. There’s nothing worse than selecting a particular device and then uncovering its pitfalls halfway in the project. Before you commit to a controller, its best to bench test the process.
Stay away from finalizing a controller during the start of the design phase of the project. Selection procedure should only kick in after the process automation concept has matured. If a controller is over-specified then unnecessary costs will be added to the system while if its under-specified then the design process may have to be carried out once again.
Build from the Bottom-up
If a team is to take part in the development process, then take some time to clarify the various interfaces that will be used so that everyone is at the same page. If in-house techs are being involved in the maintaining & upgrading the code, then it’s best to eliminate any “canned code”. Ensuring that your own workforce is familiar with the nomenclature & structure of the code will allow modifications & error rectifications to take place within a short period of time.
The world is slowly but surely heading towards a more integrated & network framework of devices known as IoT, Industry 4.0, Smart Factory, etc. In order to ensure that your hardware is capable of being part of this new revolution, make sure you select the right controller. Choose a PLC family that has a comprehensive portfolio of communication-supporting modules. Most PLCs today are capable of communications, however not all PLCs support every type of ethernet protocol, something that can become an issue in a multi-protocol environment. Therefore, its best to be safe than sorry; having a preemptive screening approach would go a long-way.
Key Check Points
Not all controllers or brands are the same. Consulting with people who are knowledgeable and experienced about the various hardware platforms before specifying any model or expansion card can help you save both costs & time. Whenever an upgrade is being made to a system or a replacement is required, be sure to check the controller’s major components such as power supply, I/O type, etc. Make sure that the controller has all the functions you’re looking for and is compatible with the hardware installed within the system. It would be difficult and expensive to uproot the installed peripherals than specifying another controller model.
Account the CPU Load
Be aware of the CPU load requirements that come with communication intensive applications. All programs that make heavy use of communication features of a PLC require higher processing power. Running the PLC at a maximum cyclic load results in poorer capacity and slower response times for OPC server based communications. It’s best to maintain the peak cyclic load to 65% and static cyclic load to 60% to make sure high throughput is achieved for communication.
Programmable controllers certainly bring a wave of benefits over analog devices. But at the same time, they bring them complicated problem of documentation with them. PLC code makes use of multiple function blocks, which make use of a plethora of variables. Having a technically comprehensive documentation is extremely necessary as errors are inherent in any complicated system. Even if the code is fool-proof, modifications may be required in the future from a developer who’s not aware of the semantics. Therefore, having a clean documentation is imperative for the system to be sustainable and independent.
Some automation tasks are so simple and repetitive that its clear they’ll stay the same even after years. But there are some tasks that are prone to upgrades with the passage of time as demand increases. For these, the developer & design engineer should have a futuristic mindset. Going for the cheapest controller may seem like an enticing choice but in the long-run it would be a more expensive approach. Go for hardware that has expansion capabilities and can allow upgrades even after years.
Single Control Platform
It may sound luring to have a separate controller for each industrial application, but sometimes a narrower approach in the form of single control platform can be more rewarding. Take a comprehensive survey through your requirements, selecting a platform that would remain relevant in the near-future. Having a single control platform for all your automation control needs, from robotics to numeri control to motion, etc. can greatly simplify the entire system. Concepts would overlap with each other, and less maintenance efforts would have to be made for each component. Furthermore, spare parts would be reduced as the systems would be fundamentally the same.
While all of the factors stated above hold paramount importance as part of the selection criteria for controllers. Skipping these factors may not bring considerable changes to your system, however there are a few factors that can greatly affect the outlook and performance of your controller based system. These include:
- Flexibility – the controller must be ready to take on the future requirements of at least five years. Doing so would bring down unnecessary costs and save development time.
- Support – take into account the support that’s available to you, and for how long it remains operational. If the vendor doesn’t provide support within the given timeframe, choose another controller.
- Quality – the controller based system you develop should be reliable, and thus the controller should hold a warranty.
- Cost – this factor greatly effects the choice of hardware. Every company wishes to carry out maximum tasks in the most cost-effective manner possible. Similarly, you should take into account the costs that come with a controller, from training ones to technical support ones, and only then make your decision.
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