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Industrial Automation & Network Hardware
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10 Things to Consider When Choosing a Programmable Logic Controller (PLC)

May 22, 2025

Choosing the right Programmable Logic Controller (PLC) is critical in designing an efficient, scalable, and cost-effective industrial automation system. Whether you're managing a new installation or upgrading an existing process, selecting the best PLC requires more than just price comparisons it’s about performance, reliability, flexibility, and long-term value.

This comprehensive guide will walk you through the ten key factors to consider when choosing a PLC, so you can make the best decision for your automation needs.

 Article Contents

  • What Is a PLC System?

  • Basic PLC Functions

  • What Are Some Popular PLC Brands?

  • 10 Things to Consider When Choosing the Best PLC

  • Find Your Next PLC at Industrial Automation Co.

 What Is a PLC System?

A PLC system is an industrial grade digital computer used to control machines and processes. Acting as the brain of an automation system, a PLC monitors input data from sensors, processes the data according to programmed logic, and triggers appropriate output actions.

A standard PLC system includes:

1. The PLC Unit (Controller)

Houses the CPU, memory, I/O interfaces, and communication ports. PLCs range from compact standalone units to modular, rack-mounted systems.

2. I/O Modules

These modules serve as the bridge between field devices and the PLC. Inputs gather sensor data, while outputs send control signals to actuators and machines.

3. Programming Software

Software such as Studio 5000 or RSLogix 500 is used to create the logic instructions. It enables engineers to configure input/output behavior, set conditions, and implement timers, counters, and safety logic.

 Basic PLC Functions

PLCs are essential for automating and optimizing industrial processes. Key functions include:

  • Reading Inputs: Monitoring sensors, switches, and devices

  • Executing Logic: Running ladder logic, function block, or structured text programs

  • Controlling Outputs: Triggering actuators, relays, motors, or valves

  • Data Logging: Recording system performance and faults

  • Diagnostics & Monitoring: Providing alerts, alarms, and system health info

  • Communication: Integrating with HMIs, SCADA, MES, and other controllers

 What Are Some Popular PLC Brands?

Some of the most reliable and widely used PLC brands include:

  • Allen-Bradley (Rockwell Automation): Known for CompactLogix, ControlLogix, and MicroLogix lines

  • Siemens: Offers the powerful SIMATIC S7 series, including S7-1200 and S7-1500

  • Mitsubishi Electric: Renowned for the MELSEC series with compact, modular, and high-speed control

  • Omron: Popular in machine automation and compact applications

  • Schneider Electric: Offers Modicon PLCs for flexible automation needs

 10 Things to Look for When Choosing a PLC

1. Application Requirements

Understand your process needs. How many I/O points? What voltage types? Will you require high-speed counters or motion control?

 Tip: Create a system map to define how many digital/analog inputs and outputs your process will need.

2. Scalability and Flexibility

Choose a PLC that can grow with your application. Look for modular systems or expandable I/O options.

 Ideal for growing operations that may add more stations or sensors in the future.

3. Programming Environment

Is the programming language easy to use or already familiar to your team? Popular languages include:

  • Ladder Logic

  • Structured Text

  • Function Block Diagram

Choose a PLC with intuitive software like Studio 5000, GX Works, or TIA Portal.

4. Communication Capabilities

Your PLC must connect with devices across your plant. Look for:

  • EtherNet/IP

  • Modbus TCP/RTU

  • PROFIBUS

  • DeviceNet

  • OPC UA

 Good communication = real-time control, easier integration, and less wiring complexity.

5. Reliability and Durability

Choose a rugged PLC that operates reliably in your environment dust, heat, vibration, or moisture.

 Look for IP-rated enclosures and industrial certifications (UL, CE, ATEX).

6. Performance and Processing Power

Evaluate scan times, instruction execution speed, and real-time performance. Applications like motion control or synchronized lines require faster processors.

 High-performance PLCs ensure tight control loops and fewer delays.

7. Support and Vendor Services

Pick a PLC from a manufacturer with strong support, documentation, training, and local distributors.

 Reliable support = faster troubleshooting and less downtime.

8. Integrated Safety Features

For applications involving human machine interaction, look for PLCs with integrated safety functions such as:

  • Emergency stop

  • Safe torque off

  • Safety relay integration

 Meeting SIL, ISO 13849, or IEC 61508 safety standards is a major advantage.

9. Cost and Total Lifecycle Value

While cost is a factor, don’t be lured by the lowest price. Instead, evaluate:

  • Long-term support

  • Software licensing fees

  • Expandability

  • Ease of integration

  • Training costs

 A lower-cost PLC may cost more in downtime or future upgrades.

10. Brand Reputation and Product Longevity

Stick with trusted names in industrial automation. Top-tier PLC brands offer longer product lifecycles, parts availability, and documentation archives.

 Stability matters especially when parts need replacing 5–10 years down the line.

 

For more information, contact PLG Automation:
Email: sales@plgautomation.com
Phone: 800-906-9271