A Guide on Choosing the Right Parts for a PLC System

Programmable Logic Controllers (PLCs) are the brain of many modern industrial systems, orchestrating tasks from basic machine functions to complex processing sequences. While programming is essential to a PLC's performance, their success is largely governed by the quality and compatibility of its supporting components. As such, this guide will cover some must-have PLC system parts and what you should consider about their selection and implementation.

The Building Blocks of a PLC System

While there are many aspects that can go into a PLC system, the most important components include the:

• Processor (CPU): The CPU executes control instructions based on the logic programmed into the PLC.
• Input/Output (I/O) Modules: These modules handle communication between external field devices and the central processing unit.
• Power Supply Units: Power supply units deliver regulated voltage and current to support all connected PLC modules.
• Communication Modules: These modules enable the PLC to interface with other systems, devices, or remote I/O configurations.
• Connector Hardware: Connector hardware ensures stable, secure wiring for reliable transmission of data and electrical power.

CPUs

One should choose a CPU with the following considerations in mind:

• System Size and Complexity: For small, stand-alone machines, compact or micro PLCs are often sufficient. However, larger or distributed systems typically require modular, rack-based controllers with higher processing capabilities.
• I/O Requirements: A controller must support the intended number and type of I/O points the system will manage, or be compatible with remote expansion modules.
• Memory and Processing Speed: Applications with complex logic, data logging, or PID control require CPUs with ample memory and high-speed processing capabilities.

I/O Modules

As the bridges between the PLC and field devices like sensors, switches, actuators, and motors, selecting the appropriate I/O modules requires a clear understanding of the types of signals field devices generate or receive.

Digital I/O Modules

• Digital Inputs detect binary signals, such as on/off or high/low, typically from devices like proximity sensors, push buttons, or limit switches
• Digital Outputs send binary signals to control devices such as relays, indicator lights, or solenoid valves

These modules are best suited for systems with straightforward logic or discrete control functions, such as machine start/stop operations, safety interlocks, or alarm triggers.

Analog I/O Modules

• Analog Inputs read continuously varying signals, such as voltage or current outputs from devices like pressure transducers, thermocouples, or flow meters
• Analog Outputs send continuous signals to operate variable equipment, such as control valves or servo motors

Analog modules are ideal for applications requiring precise measurement or gradual control, including flow rate modulation, speed regulation, or temperature control loops.

Communication Modules

Communication modules operate with specific protocols that define how data is transmitted and interpreted across a network. These protocols are not universally supported by all modules, so select a module that aligns with those already in use or slated for future integration. The following are among the most commonly utilized in industrial PLC systems:

• Ethernet/IP
• Modbus (RTU and TCP)
• PROFIBUS
• DeviceNet

Aside from confirming which protocol your system will operate on, you should also factor in:

• Network Scale and Topology: Ensure that the module can support the intended number of network nodes and is compatible with the system’s physical layout.
• Redundancy and Security: For sensitive applications, prioritize modules that support failover mechanisms, secure data encryption, and authentication protocols.
• Controller and Firmware Compatibility: Confirm that the selected module integrates with the PLC’s controller model and firmware version to avoid communication errors or configuration conflicts.

Connectors

Stable electrical connections are fundamental to maintaining signal integrity and power delivery in any PLC system, so choose connectors carefully for appropriate:

• Signal Type and Shielding: Use shielded connectors for data and signal lines to prevent electromagnetic interference (EMI), particularly in environments with variable-frequency drives or high-power equipment, as well as those using high-speed communications.
• Connector Size and Pin Configuration: Match the connector’s number of pins and layout to the intended device’s port. Also, consider their physical size to avoid creating physical strain and interference.
• Environmental Rating: Select connectors with appropriate ingress protection (IP) ratings for exposure to dust, moisture, or corrosive substances.
• Mechanical Durability: In environments subject to vibration or mechanical stress, choose connectors with locking mechanisms and rugged housings to prevent accidental disconnection. For assemblies that can expect frequent movement, strain relief features and flexible cable glands are also advisable.

Power Supply Units

Because of their integral role in converting incoming AC voltage into regulated DC power, Power Supply Units (PSUs) must match:

• Voltage Requirements: Most PLC systems operate on 24V DC, but always be sure to verify the voltage needs of each module and peripheral.
• Current Load Capacity: The PSU has to supply sufficient current to support the total draw of all connected components, including a margin for inrush current and potential system expansions.

Build a Stable PLC System in Collaboration with a Trustworthy Procurement Platform

Designing a robust and effective PLC system requires an in-depth understanding of its operational needs and matching them with the correct controller, I/O modules, communication devices, power supplies, and reliable connectors. Turning to dependable purchasing platforms ensures peace of mind in this process, and The Industrial Automation Hub has you covered with an expansive and detailed PLC system parts catalog.

As a website owned by ASAP Semiconductor, our inventory boasts all of the high-quality components your industrial operations may need, ranging from controllers like the IC697CPU771 from GE Fanuc to rugged connectors from Mencom. Moreover, we pride ourselves on offering competitive pricing, fast delivery, and comprehensive support for fulfillment needs. To see how we can specifically serve your requirements, explore our selection and connect with our expert team at your convenience.