When and Why using PLC?

When and Why using PLC? - We already know a little bit about the history of PLC. The next question is why and when we need to use PLC?. Let discuss it.

Ilustration

When using PLC?

      First, we need to know the function of the system control that we want to build. Is it complex or just a simple system control?. If the system control is only needed to operate simple logic or doesn't require many inputs and produce many outputs, then it probably doesn't need to use a control device like PLC, try to consider using relays.

     Second, the cost that needed to build the system. As we already know, the old way by using relays and timers will be too costly if the system is complex. The cost that spent for the cables, railing the relays, the size, and space of the panel, that need to be considered.

Cost

     By using PLC, we can eliminate the use of other components, but the cost to buy the PLC it self and its support is also needed to be considered. If the system is more complex, then the PLC specification should be higher, enough to hold all the memories and data that required to run the system.

     To make it easier, if you wanna build a system that required 40 relays then try to find the price of each of the relays, also find the price for other components that required for your system to run. Don't forget to measure the cable length that needed to do the wiring. After that, add the cost to buy the panel. Try to combine it all and note it.

      Now, do the same things with the PLC, calculate the price of the required component (it should be less component), add with the PLC cost, also add the panel cost (it should be smaller). After that, measure the cable length that required and add it to the cost calculation. From there, you will know which that have the lower cost.

      Third, Find out which is easier to build and maintain. Of course with the PLC-based system will be a lot easier to build and maintain the system control, but if its only need a simple system that still easy to build and maintain, then the relay based system will be fine.

      From that 3 points (you can also add your own considerations), we know when we need to PLC. To summary, we better use PLC when the system is getting more complex. The more complex the system, it will harder to build and maintain, and also more costly. So if that happens, then better use PLC.

Why using PLC?

     Based on how it builds, PLC is different from another system controller. What makes it different is it is specially build to fulfill the industrial requirement. The hardware itself is robust and built with some safety standards so it will fit with the harsh environment. If the environment that the system works is a dusty environment, full of shock, PLC can fit in there.

IEC certification

     Another thing is PLC have more noise protection. In industries, there are so many motors, transformer, and other components that could produce noise such as the electromagnetic field which can disturb the system control. The protection from the PLC come from the optocoupler that put in each IO port, isolate it from any noise so it can receive the input or produce the output as good as we want it.

     PLC is also easier to program. By using simple logic or special instruction, we can program it and try it both with the simulator or directly in the system control. In PLC you just need to download the program for once and it will stay there like forever. It is not software dependent, this makes PLC different with the PC based.

See : History of PLC : Before and After PLC Exist

      Things you also need to consider is the integration process when the factory growth then maybe it will put more line in the production, so you need to integrate more system control. With the PLC, the integration process can be done. We can integrate many PLC-based system control to form a new system control. We can also form a higher level of system control like SCADA ( Supervisory Control and Data Acquisition ).

      Another option if you would not using PLC is to build a robust embedded system control that based on the microcontroller or PC. Just make sure it can withstand the environment, reliable, fast response and easy to maintain.

     From all things above you know when and why we need to use PLC. Put more considerations and thought before choosing which controller you would like to use.

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