PLC Considerations: Choose Wisely

Selecting the right PLC for an application requires answers to a number of upfront questions.

With any engineering decision, it’s best to put things on paper first to see the “big picture.”

Technical experts at AutomationDirect, Cumming, GA (automationdirect.com) say the same holds true when choosing the most-effective PLC (programmable logic controller) for a specific application. An article in a recent issue of the company’s Automation Notebook pointed to several important areas of consideration in determining your PLC needs.

PROPOSED SYSTEM

Determine whether your system is new or existing. Will it be installed from scratch or are existing products already installed? The rest of your system will need to be compatible with new components.

ENVIRONMENTAL ISSUES

Consider any environmental issues that will affect your application, i.e., temperature, dust, vibration, codes specific to your facility.

DISCRETE DEVICES

Determine how many discrete devices your system will have and which types, i.e., AC, DC, are needed.

ANALOG DEVICES

Determine how many analog devices your system will have and which types, i.e., voltage, current, temperature, are needed.

SPECIALTY MODULES OR FEATURES

Determine whether your system will require any specialty features. Will your application require high-speed counting or positioning? What about data logging, a real-time clock, or other specialty features?

CPU REQUIREMENTS

Determine the type of CPU you will need. How much memory will the system require? How many devices will your system have
(determines data memory)? How large is your program, and what types of instructions will the program include (determines program memory)? What scan-time speed do you require (how fast)?

I/O LOCATIONS

Determine where your I/O will be located. Will your system require only local I/O or local and remote I/O locations?

COMMUNICATIONS

Determine the communication requirements. Will your system be communicating with other networks, systems, or field devices?

PROGRAMMING

Determine your programming requirements: Does your application require only traditional programming instructions or are special instructions necessary? Do you prefer fixed-memory addressing or tag-name-based control? To which programming language are you accustomed?

To learn more about this decision-making process, including why these areas of consideration and answers to associated upfront questions are crucial in selecting PLCs, go to library.automationdirect.com, and read the full article, “Which PLC Is for Me?” from
Issue 39–2018, of the Automation Notebook. EP

For information on a wide range of automation issues, products, and services, visit automationdirect.com.