What is Modular PLC?

What is a PLC?

A programmable logic controller is a small computer that can accept data and deliver operational instructions through its inputs and outputs. A PLC’s primary duty is to control the functions of a system using the underlying logic that has been programmed into it. PLCs are used by businesses all over the world to automate their most critical procedures.

Types of PLC

PLCs are mainly classified into two. They are

  • Fixed/Integrated/Compact PLC
  • Modular PLC

Click here to know the different types of plc

In this article, we are going to discuss Modular PLC

What is modular PLC?

The modular PLC is a form of PLC that allows for multiple expansions of the PLC system by the use of modules, hence the name “modular.”

Modules provide extra functionality to the programmable logic controller, such as an expanded number of I/O units, and they are typically easier to operate because each component is independent of the others.

The power supply, communications module, and input/output module are all independent of the microcontroller, so you must manually connect them to form your PLC control system.

Rack-mounted or rack-mount PLCs are a type of modular PLC. The communications module of a rack mount PLC is housed in the rack itself, thus all connections are consolidated.

Difference between Modular PLC & Compact PLC

Advantages and Disadvantages of Modular PLC

Advantages of Modular PLC

  • Expanded Memory
  • Higher Number of I/Os
  • Expansion available
  • Easy to troubleshoot and less downtime


Fixed PLCs can only store a certain amount of data. This is due to the fact that all of the necessary components are housed in a single entity. Furthermore, there isn’t much opportunity for extending information beyond the very fundamental functions required. Modular PLCs have significantly more memory and can store a greater volume of data.

Number of I/Os

The fixed PLC has a restricted number of I/O modules, restricting its performance. The modular PLC can do more complex procedures, making it more advantageous.

Expansion available

When the need to expand your operation emerges, the fixed PLC will be unable to keep up. Modular PLCs were created for this reason, to expand and tailor processes to allow for continuous expansion.

Easy to troubleshoot and less downtime

Downtime is expensive, and no one wants a system that drains profits. Problems are not detected by fixed PLCs. As a result, when they crash, troubleshooting takes a long time. However, modular PLCs can readily troubleshoot difficulties while keeping some processes operating. While fixed PLCs may be less expensive at first, the modular PLC provides more long-term economic assurance.

Disadvantages of Modular PLC

  • Cost is high
  • Complex structure

Expanding an Existing PLC System

A small or fixed PLC is less expensive than a modular PLC and is utilised for standalone duties.

If we want to expand an existing process, we must replace a fixed component. A modular PLC does not need to be replaced because it can be expanded.

Modular PLCs or Rack type refers to a form of PLC that connects its power supply, CPU unit, and I/O system via a backbone called Rack.

A small PLC system that is delivered fully assembled and cannot be modified or upgraded. A modular PLC system is made up of pieces that may be swapped out, upgraded separately, deleted, or replaced with new ones.

Compact PLCs contain fewer input and output modules than modular PLCs, but more memory. They are commonly employed in industries.

Modular PLCs have significantly more capacity and can store a greater volume of information, whereas compact PLCs have restricted input-output modules, restricting their performance.