Choosing the right controller for your automation task

In whichever form they come, PLCs, PACs, PCs or a mixture of the three, controllers are at the heart of all automated systems and vital to their operation. The capabilities and functions of different controllers are hugely varied. This means you can select a controller which perfectly suits the dimensions of your project. But this selection process must be a careful one. Consulting with DualTEC’s team of experts, who will hold information on the specificities of hardware platforms, will help you to make these decisions and ensure the controller selected performs to your purpose and expectations.

Look ahead

Think carefully about which controller will provide the least complicated solution for your system. Opting for a PC-based system when you need no more than advance I/O control will run up costs unnecessarily. However, looking to the simplest option does not necessarily mean the cheapest. Simplicity must be combined with forward thinking. Planning for five years’ worth of changes in your system will help you to choose a PLC that is long-lasting and cost-effective. Consider the increasing integration, peer-to-peer networking and data exchange of controllers which will inevitably take place.

Selecting a controller that can field all your current and near-future needs will be more valuable than one that is overly customised. Working with a single control platform across all motion, robotics, numerical control, C program and sequence control requirements will allow you to lean into further integration and reduce maintenance needs. Overall, ensuring your controller allows for flexibility into the future will keep costs low in the long term.

Pay attention to detail

Controller selection shouldn’t take place at too early a stage of system design. Choosing a controller specified to an original conception of the project, which later changes, will add to the project’s costs. Controller selection should instead take place after the machine’s initial conceptual design is confirmed. From time to time, systems also require an upgrade. During this process it is important to ensure you check the new controller’s power supply, memory, I/O type, size, availability within the panel and model number, against its required purpose.

 

Confirming that the controller holds the basic features you require, which might include online bypass and programming, alarm management and closed loop control, will further confirm that your choice is suited to your system’s needs. For PLC-based controls, it is vital to confirm the communication abilities of your preferred controller. Despite ODVA reducing the need to consider communication, this can still cause concerns for systems operating with advanced sensors and peripherals. Whilst most PLCs are able to communicate via device buses, many do not hold communication modules for all types of Ethernet. Ensuring your PLC is compatible with your all device types will save time and redesign issues later.

If communication handling is important to your system, you must pay attention to the controller’s CPU load. Controllers should not run at maximum cyclic load which reduces capacity and response times. Instead, in all conditions peak cyclic load should not exceed 65%, and static cyclic load kept below 60%. For systems with high communication throughput, cyclic loads between 30-40% are recommended.

As always, keeping costs in mind is important. But make sure to look beyond hardware and software costs, and towards other ancillary costs such as software licensing and technical support fees and training costs.

Always have a Plan B

Programmable controllers offer new opportunities for systems that would previously have run on analog devices. However, in case of disaster recovery events it is important to keep track of the programmable parameters outlined in the software configuration control document. To avoid re-writing code when introducing the HMI, it is also recommended that this element is programmed first.

Make sure your vendor is transparent about the warranty of their products, to ensure your system’s security is guaranteed. Those vendors that offer lengthy warranties are also those most confident in their product. Researching product warranty is therefore also a great way of ensuring you purchase a high-quality controller.

Ask yourself questions

Reflecting on the end goals for your project can help you to map the route which will best help you to get there. Is your focus on increasing productivity, repeatability, or consistent accuracy?

You can then apply this thinking to the elements incorporated into your system. For example, what motor should be used? Servomotors, for example, provide high acceleration but stepper motors hold positions reliably. What controller type would be the best fit? PLCs are a great fit for basic material and conveyor control, but if more complex motion, product registration and electronic gearing are required, a dedicated motion controller will be required.

Finally, think to the details of your chosen controller to consider if it will perform all the functions required of it. Always overestimate on the number of axes you will need the controller to control. Fast processors will be able to keep up with large control demands but also be sure to check that the processing power accommodates for all potential needs, and that it holds sufficient user memory.

How can DualTEC help you?

Whichever route you decide to go down for your project, you can be sure that DualTEC’s team will guide and assist you throughout so that the outcome matches your expectations.

Please call us on 01535 609314 or email info@dualtec.co.uk for further information, or if you have a project you would like to start.

 

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