Widely distributed I/O has become the de rigueur, default design for new facilities and facility expansions by all major control platform (DCS and PLC) suppliers offering some form of distributed/remote I/O as part of their system. In most cases, they use one of the available industrial Ethernet protocols to connect with the controller and remainder of the control system.
This type of architecture makes economic sense because it saves costs during construction. It reduces, and potentially eliminates, multiconductor cables—at least the traditional long and expensive home run cables from the field junction box to the interface room. The intermediate step to this architecture was using remote interface rooms throughout the facility. In most cases, these accompanied the electrical motor control center, and the fiber-optic rings to the main control center. A second economic advantage of distributed I/O is expansion. It’s easy to add more I/O to a smart junction box, but not as easy for multiplex signals on a multiconductor cable. Earlier in my career, I had more than one project that had to be canceled because we didn’t have a home run cable back to the control center.
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Distributed I/O requires power, which normally means running at least one, and preferably two, power supplies to the field cabinet. Fortunately, AC power is usually nearby. If you source from different buses, the reliability of different uninterruptible power supplies (UPS) will still be high. The market also offers field cabinet-mountable (area-classified), 24-VDC transformer/UPS systems that can provide required power for the controller and field signal-loop power (analog signals) or wetting voltage (discrete signals).
When fully implemented, Ethernet APL will combine home run and power in a one twisted pair, and take distributed I/O one step further. It will make it possible to mount an I/O cabinet adjacent to each piece of equipment with multiple signal points. Since these new sensors will be smart, they’ll likely transmit additional information about their own health via the network. This will create the future challenge of too much information, and the need to be selective about data required.
The next progression of this model is the Industrial Internet of Things (IIoT), which is the distributed I/O concept in a single device supporting one or more signals over wireless.
Though the power issue appears to be reaching resolution with reliable long-term batteries and small-footprint, alternate energy sources, IIoT is still has several hurdles to overcome including:
- Security—concerns about not only physical access, but also cybersecurity for individual devices outside the organization’s networks and potentially physical location. Zero-trust is supposed to provide cybersecurity protection to a granularity of one device or service. If properly implemented, it addresses cybersecurity concerns, but not necessarily associated mindsets of those operating a facility.
- Cloud integration—though modern SCADA systems use cloud systems. Many industries continue to have concerns about how to integrate data from outside the OT domain into the control environment. Evolving cybersecurity standards help, but since most facilities aren’t in a rush to be first, new integrations will take time.
- Protocols—though a compelling case can be made for MQTT/Sparkplug B, there isn’t an agreed-on, lightweight protocol for IIoT devices. ISO JTC1 SC41 is also developing a suite of IoT standards including architectures, reference models and others, including APIs.
The demand for data to better understand our processes and the equipment to run them continues to grow. Fortunately, technology continues to respond to the challenge with lower-cost options having both higher data density and increased capabilities at progressively lower cost, changing the relationship from one of too little data because of high costs to a situation of too much data, and managing all the associated physical and data assets. The I/O evolution saga continues.
