Modular vs. Fixed Programmable Logic Controllers: What’s The Difference?

Modular vs. Fixed Programmable Logic Controllers: What’s The Difference?

Programmable Logic Controllers or PLCs are computers specifically created to run automated systems in industrial or commercial applications. These computer devices were initially developed to replace relay circuits, but now they do much more. Even though most people are not aware of their existence, PLCs are very common – whether the traffic lights in your streets or the roller coasters at a theme park, all use PLCs. They are the unseen but vital component that automates every application without even us being aware of their presence.

The two main types of PLCs are modular and fixed PLCs. It is often said that modular PLCs have many distinct and significant advantages over fixed PLCs. Fixed PLCs are also known as Compact PLCs, and Modular PLCs are known as Rack-mounted PLCs. Let us now see what the differences between modular and fixed PLCs are.

You can compare a PLC to a personal computer with a CPU and an input/output interface system. However, the PLCs handle multiple configurations and perform various control functions. The I/O systems consist of switches, sensors, or other devices that are physically linked to the primary I/O system, and the CPU controls every activity of the entire system. It is the case with both PLCs, even though they differ in application and execution. Fixed PLCs are small and typically used for essential functions.

The Differences

There are several differences between the two PLCs. They differ in size, capabilities, and cost, among others. The significant differences are:

  • The number of inputs and outputs is fixed in compact PLCs as the manufacturer decides the capacities and not the user. However, in the case of a Modular PLC, the number of input and output aren’t fixed. Users can add inputs and outputs to the modular PLC.
  • Module PLCs have inputs and outputs fitted with the CPU. However, in the case of a fixed PLC, many components are fitted on the chassis/racks or bus with various slots.
  • It is not easy to repair a fixed PLC. But Modular PLCs are easy to maintain and repair.
  • Fixed PLCs have lower memory and limited data/information storage capabilities. The modular PLC has more significant memory and storage capabilities.
  • A fixed PLC is more beneficial for smaller applications and optimal for domestic uses. A modular PLC is more suited for industrial purposes and ideal for accommodating any expansion and growth in the future.
  • Fixed PLC is smaller, whereas the modular PLC is usually large sized with greater I/O connectivity, power supply, and computing capabilities.
  • Fixed PLCs are more economical than modular PLCs.

Generally, modular PLCs are widely used in automation industries. As they are made up of different parts that plug into each other, they come with the obvious advantage of the auto-sensing option. Hence, it is easier to detect the cause of the problem and rectify it.

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