PLC Programing featured image

09 Difference between Compact PLC and Modular PLC | Block Diagram

PLC Programing featured image

When I started learning Programmable Logic Controller PLC programming, I found it very difficult to understand the actual Difference between Compact PLC and Modular PLC.

So, to make this simple for everyone, I am writing this tutorial with detail explanations.

As we all know, the programmable logic controller (PLC) has two main categories as follows.

  1. Compact PLC
  2. Modular PLC

Now, let’s compare two PLCs.

Difference between Compact PLC and Modular PLC

Sr. No. Content Compact PLC Modular PLC
01 It is also known as an Integrated PLC or Fixed PLC. It is also known as Rack-Mounted PLC.
02 Input-Output Capabilities In Compact PLC, the number of inputs and outputs are fixed.

Because I/O capabilities are decided by the manufacturer but not by the user.

In Modular PLC, the number of input and output are not fixed.

Inputs and outputs can be added to the modular PLC systems by the user.

03 Internal Module It has inputs and outputs modular fitted with CPU. In this PLC,  several components are fitted on chassis or rack or bus with different slots.
04 Repair  Compact PLC is not easily repaired. Modular PLC is easy to maintain and repair as compared to compact PLC.
05 Storage Memory It has fewer capabilities to store data/information. It has more memory and capabilities to store more data.
06 Applications It is useful for smaller applications and most suitable for domestic purposes. It is used for industrial purposes and also for future industrial expansion and growth.
07 Size It is smaller in size. It occurs in a large size with i/o connectivity, power supply, computing capabilities, etc.
08 Cost It is an economic model. It is costlier than Compact PLC.

09. Block Diagram

Compact PLC block diagram:

It includes input, output along with power supply and CPU.

Block diagram of compact plc

Modular PLC block diagram:

It consists of Power Supply, CPU and Input/Output Modules, Interface Module.

Block Diagram of Modular PLC

In the modular PLC, one rack consists of eleven slots.

Out of eleven slots,

  • the power supply connects with the slot number-one,
  •  the central processing unit (CPU) is fixed in slot number two and
  • the interface module is fixed in slot number three.

Remaining slot number four to eleven are used for the signal module, communication process, peripheral module, etc.

Hopefully, this difference between Compact PLC and Modular PLC gives you a better understanding. If you have any point to discuss, feel free to write in the comment.

If you are interested in learning PLC programming, here is PLC programming related tutorial from beginner to end.

It is simple to start with…

Happy PLC Learning!

28 thoughts on “09 Difference between Compact PLC and Modular PLC | Block Diagram”

  1. In the official site of OMRON I saw 3 categories Compact PLC, Modular PLC and Rack PLC……can u tell me whats the difference between Modular PLC and Rack PLC

    Btw thanks for sharing this !

    • The Rack PLC is the mounting base plate of the Power supply, CPU, Interface module and I/O modules. I think, there is not much difference between them.

      I didn’t get the chance to work on Rack PLC.

    • Hi, Kacung Jongos.

      Yeah,Sure! In the before tutorial ([Step-by-Step] How to Learn PLC Programming at Home for Free?), I shared the PLC software link of free basic version for practicing and learning PLC programming.

      If you are new and learning PLC, I guess using those free version of any PLC software brand is sufficient for your need.

      You can download Delta PLC software from its official website for free. Choose the version suitable based on your computer system. Install it.

      You can also download WPLSoft PLC software and install it. I am working on this PLC Software.

  2. I am a new plc learner. Loved the explanation. I wanted help from your end in the project where I am stuck. Can it be discussed further for a solution as required at present for the progress of it?


Leave a Comment