What is Inside a Programmable Logic Controller (PLC)

Industrial Automation makes our machine operation very first with accuracy. We can control our machines in various ways to get our optimum output and production. Using Programmable Logic Controller (PLC) is one of the world’s most popular automation systems.

In my last post, I discussed ‘What is Programmable Logic Controller (PLC) With Application?’ So I request you before you proceed to read it first. You will know some important things that will help you understand about PLC very well.

In this post, I am going to diagnosis a Siemens S7-200 CPU 224 CN PLC hardware section and you will have a video link for observation. This PLC has 14 Digital Input (DI) and 10 Digital Output. All physical output is relay type and relay rating is 30VDC/250VAC 2A but relay coil voltage is 24VDC. All Digital Input voltage type is 24VDC 15-30V.

Related: What is a Programmable Logic Controller (PLC) With Application?

What is Inside of a Programmable Logic Controller?

This Siemens S7-200 CN PLC came with Ring Frame Machine from China and we have 73nos Ring Frame Machine in our factory. This machine made in China that’s why machine manufacture used Siemens S7-200 CN Version PLC.

But its built quality is good because I have seen several PLC with CN version is running well. But I lost 3 PLC in a single day because of the imbalance voltage problem form the national grid.

This Siemens S7-200 CN PLC has three internal PCB card. These three cards connect with each other by internal Pin. Don’t worry you can have a look at the video. The first one is the power card, second is controlling and the third is the programming card. This PLC uses 220V AC as the main operation power impute.

After converting this 220V AC power by a step-down transformer it uses different range voltage for its internal operation. This PLC has a communication port and by using this port we can add display like TD-200/400 and we have TD-400 with our machine.

This communication port also used for the Upload program form PLC and Download program to PLC. But you need a USB/PPI Cable. If you want you can collect a Siemens PLC Cable for S7-200/300/400 cable from here.

Machine manufacturer also provided us a Battery (Sorry I don’t know its real name). If you are replacing the same type, same model PLC with old one then just you need to insert this battery in PLC selected port then PLC will take the program from the battery.

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