Modular and Integrated PLC : Differences, Advantages and Disadvantages

Modular and Integrated PLC - Basically, there are 2 types of PLC, modular and integrated. Each of it has advantages and disadvantages. but the function is same. Every PLC mainly consists of 3 modules which were Power supply module, CPU module, and I/O module. In some modular PLC, it also required using rack or bus.

• Power supply module

     This module function is to supply the PLC with necessary power and work by converting AC power to DC power. The power needs to converted to DC power because the CPU module and I/O module required DC power to work. Usually, the I/O and CPU module will use 24 VDC.

Power module of S7-300 (img : Parkelect)

• CPU module

     The CPU module is the main processing unit in the PLC. It is used to process all the data, accepting all the input and generate output. This module contains RAM and ROM, RAM will store the program that already written into the PLC and process all the data. While ROM store the necessary OS and application that required to make PLC work. CPU module also contains retentive memory which will save all the data if the electricity is cut and restore it when the electricity is back.

CPU module of S7-300 (img : S7automation)

• I/O module

     This module work as "terminal" for all the input and output. Sensors and actuators can be connected in here. There are 2 types of I/O modules, which were Digital module and Analog module. The Digital module will receive digital signals (ie: pulse) from the inputs and generate digital output. Analog module works with the same principle but the signal is in the form of analog ( ie: voltage, resistance). 

I/O module of S7-300 (img : alibaba)

• Rack or BUS

     Rack or BUS is usually used for modular PLC. The rack contains some slot for the modules. Modules need to arranged correctly according to the slot that the rack provided, so that the PLC can work properly. This rack also enables for putting more module so that the number of I/O can be extended, by putting the I/O module in the correct slot.

Modular and Integrated PLC

    PLC can be constructed as modular or integrated PLC, the differences between those modular and integrated PLC will be explained below :

• Integrated PLC

      Integrated PLC means "All in one" unit PLC. All those 3 main modules (Power supply module, CPU module, I/O modules) are put into one unit PLC. It is more compact in size than the modular PLC.

      There are some advantages of using Integrated PLC. First, it is less cost, most of the integrated PLC are sold with the lower cost than the modular PLC. Second, it is smaller in size, it is perfect and fit for small space. 

      There also some few disadvantages of using Integrated PLC. Because it is integrated, the number of input and output is limited. Therefore you need to adjust the input and output for your system so that it fits in the PLC. If the PLC unit is broken, it means you loss all the modules and the system is down.

integrated PLC - FX-3U 48MR (img : 999mitsubishi)

• Modular PLC

      Modular PLC comes with various size from small to large PLC. It also contains the 3 basic module with the option to add more module to the PLC. Usually, it is larger than the integrated PLC and required more space. Modular PLC is suitable for large projects that required lots of inputs and outputs.

     There are some advantages of using modular PLC. First, if the system control is getting bigger or needs more improvement that requires more inputs and outputs, we can put additional I/O modules. Second, if the plc unit is broken, we only need to replace the broken modules, not the whole PLC unit, this means less time and less cost. 

      The disadvantages of using integrated PLC is it's more costly and need more space.

Modular PLC - S7-300 (img : siemens.com)

Which one to choose? modular or integrated PLC?

      It is depend on the project or the task that the PLC will do. If it is only simple things and will not getting improvements, than the integrated PLC will fit. In the other words, modular PLC are more suitable to use in the large project or if the system control will continously growth and need more improvements.