Profibus RS 485 connection issue

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transient

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Guys !!
I have three independent system A,B,C on the field .
50 meters from field I have the Main Control Station .

This main Control station has no connection till date with these three indpendent systems .

Now We have to do it .

From each independent system we have pulled a Profibus RS 485 cable .
So , now we have three cables .

The problem is , now on Main control Station controller we have only one PROFIBUS RS 485 interface.

Now how to connect these three cables , to this one interface ?

Please give some solution , I dont want to connect three independently systems serially , in field side , and then running one cable to the main system controller.
Because , then if i loose one of the independent system due to some failure , then other systems will also not be able to communicate with main control station .

Please see the picture for more clarity .
Transient.

IMAGE.jpg
 
131117-1143 EST

RS-485 is inherently a half-duplex system. This means that you can not transmit and receive at the same time. Thus, you can have a parallel bus system where many transmitters and receivers are connect to the same parallel bus, but only one transmitter is allowed to transmit at a time.

It also means a transmitter has to be decoupled from the transmission line when not transmitting.

Whether you have one long strung out bus or many radial buses connected in parallel makes no difference other than how these structures create undesired reflected signals based on line termination impedances and transmission line lengths.

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