Selecting The Right PLC

Selecting the right PLC for your application requirements can be a little intimidating. There are many reputable and capable brands available in today’s global market, but which one is right for you?



Which Brand?

First off, you need to consider the past.  Have you had any successful applications in the past with a particular brand or series of PLC?  If so, you might want to consider sticking with it, especially if you already own the licensed software associated with the programming and commissioning of the project.  Keeping a sense of consistency can really minimize the complications related to managing the upkeep of and streamlining the implementation of your all-important programs.  If there is no existing brand preference to consider, make sure to select a well-established brand with a robust and mature support network.  There are several brands available that have great reputations and have been supplying the industrial community with PLC’s for a long time  and sticking with one of these may have advantages over a smaller, less well established competitor.

Which Platform?

Once a specific brand is established as the go-to in a particular plant or organization, you need to choose the specific platform(series) to want to proceed with. Most PLC manufacturers have multiple levels of hardware and depending on the complexity or performance requirements of your particular application you will need to decide on what fits your needs most closely.  You may want to also consider the longevity of the product line(s) you are reviewing and perhaps discuss this with your PLC components supplier to make sure there are no plans to discontinue the particular platform you are considering, as no particular product line is supported forever and you don’t want to specify a soon-to-be discontinued product.

Which Parts?

After you have determined a specific platform to utilize, you will need to select the associated hardware and software. Keep in mind that oftentimes a new machine or process may have the potential to be expanded upon or modified to enable new functionality in the future so try and design in components that will allow for ease of expansion. Choose a backplane that will not only accept the number of modules associated with your immediate needs, but will leave a few slots open for that last-minute functionality the customer will undoubtedly think of at the 11th hour. You will need to select the backplane, power supply, processor, and Input/output modules that match the number and types of I/O you will be controlling. Again, leave a few open inputs and outputs and a little additional power supply capacity so that you do not find yourself in need of space or power that you don’t have available. Make sure that the processor you are selecting has enough working memory to support the programming you will need and that the processor has the appropriate communications ports to interface with your planned HMI or network connections.

What Now?

After all of your components are selected and verified, contact your preferred supplier and discuss your application and have them review your selections. An extra set of eyes may reveal some overlooked items or considerations that would save many hours of work or costly last-minute (and possible unrecovered) expenses.

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Greg Finley
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