PLC has a controller which is the "brains". Remote I/O is simpily some I/O not located in the same chassis as the controller.

Remote I/O's can be used when you don't want to put a second PLC with the I/O's. Instead, you drop an I/O chassis there, and bring the wires back.

The reasons are usually cost.

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Albert Einstein
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Can you give an example of a remote I/O as opposed to PLC.  

Centaur,

Remote I/O is typically part of a PLC or DCS. RI/O isn't an alternative to a PLC. A PLC or DCS may have remote I/O if required, but would work with only local I/O. The option to use RI/O could arise due to physical plant layout, or just sheer volume of I/O required. RI/O often occupies a different address range to local I/O, if the I/O cards are addressable as is often the case on a DCS. Analogue I/O cards take up significant chunks of the available address range, so an application with a lot of analogue I/O might be forced to use RI/O in order to accomodate the number of cards.

The RI/O doesn't have any significant processing capability, just enough to be able to run a low level communications subsystem to transmit data to and receive data from the host processor. It does not run the application software - ladder logic, analogue loops, sequence, whatever. That application runs on the host processor.

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centaur21,

A remote water pump station with a pump, pressure transmitter and valve, located somewhere out the back 40, so to speak.

"Do not worry about your problems with mathematics, I assure you mine are far greater."   
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

Hi,

ScottyUk, is absolutely 100% percent right, Remote IO means that the connections of the IO is not connected to the Controller backplane in the case of a PLC, Remote IO only gets fed back to the main controller using another protocol, typically you can hav remote IO stations that communicate to your main controller using profibus, radio, ect. There are various methods


Example
PLC IO                         Remote IO
___________                   ____________
|    |   |  |  Profibus Network | DP  |    |
|PLC|IO|DP|-------------------|SLAVE| IO |
___________                   ____________

Regards

Rheinhardt

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