arraiz
Hello, recently I have been looking at some PLC related concepts and I have some questions to make:

Whats the difference between a SCADA system and the built-in OpenPLC web dashboard ?

The web UI interface polls using ModBus like a regular SCADA so why use a SCADA (i dont care about the fancy graphics and other agregated stuff...)?

What are the limitations between OpenPLC and a regular SCADA?

Another question about Slaves, can I read a Slave directly using a Scada or is the master PLC always the entity to poll can I bypass It? 

Sorry for allll that questions...
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thiagoralves
There is a lot more to SCADA than just polling Modbus variables. SCADA is a central software used to monitor and control your entire process. This means connecting to hundreds of PLCs (not just one), keeping a database with the history of value changes, setting up alarms when things get messy, nice graphical displays showing your process with more detail, and even performing some high-level logic for things like, if PLC2 reports temperature higher than 100C open valve on PLC3.

The monitoring feature in OpenPLC is supposed to be just a little treat to help the user debug the program running. It cannot connect to other PLCs, neither keep track of changes or setup alarms, etc.

About slaves, of course you can read them directly from your SCADA software, but this is not recommended. It all depends on how you lay down your SCADA architecture. If a device is a "slave" of a certain PLC, you should let the given PLC read and control it, and then report everything back to the central SCADA software. Respecting the hierarchy of devices will keep you out of trouble most of the times.
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arraiz
Thanks Thiago, very clear explanation
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