“Remote I/O”, that term does not have quite the same meaning as it once did. For the longest time, remote I/O only referred to a system where the I/O node was located somewhere other than in the main control cabinet that housed the PLC. Alternatively, the node was remotely connected to the PLC in some type of network setting, with the PLC having the ability to read and write to I/O on the remote node.
This kind of setup solved a number of challenges in the use of PLCs, with proximity being at the top of the list. By utilizing a remote I/O approach, one could place the connection point for the sensor, switch, or relay closer to the actual devices, eliminating the need for long wires or multiple PLCs. Hardwiring the devices can be a challenging and headache-inducing, not only from a physical space limitation perspective, but also the costs associated with it.
The biggest drawback in the past with this kind of remote approach was the speed sacrificed. The main advantage to having I/O connected directly to the PLC was the speed. It was just simply a much faster setup.
Fortunately, remote I/O has evolved tremendously since its inception. Network speeds and data exchange sizes have grown… so speed is no longer a concern. Thus, the advantages started to far outweigh the costs, but the stigma seemed to remain. When machine builders heard “remote I/O” they would think of limited networks where the need was almost purely location-based.
Now, the network solution isn’t done to merely solve a proximity dilemma, but rather to streamline the interface of the PLC to the devices. In fact, it is far more appropriate to label this kind of solution as “networked I/O” as opposed to “remote I/O.”
It’s an important distinction, and one that we believe helps to change the perception and encourage more innovation on the part of the machine builders.
I penned a much more detailed piece for Control Design Magazine on this topic. If you happened to miss it, I would encourage to give it a read:
Networked I/O vs. Remote I/O.
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