Implementing a reliable input/output (I/O) architecture is fundamental for any type of monitoring and control system. An increasing demand for Internet of Things (IoT) data gathering and sophisticated automation is prompting designers to find more effective I/O for connecting with sensors, motor controls and actuators. Whether onboard a small machine or distributed across a much larger-scale automation application, I/O requires the flexibility and scalability to handle scattered signal locations and be ready for future expansion.

Using a remote I/O platform for connecting with signals that are physically separated from the primary controller, which is often an industrial-grade programmable logic controller (PLC), is not a new concept. Remote I/O is an established way to avoid long wiring runs, minimize material and labor costs and provide design flexibility. However, choosing the right remote I/O platform to address a variety of applications, installation conditions and controller types requires a bit of consideration.

There are two primary hardware architectures when it comes to remote I/O—standalone and modular. Standalone remote I/O is a self-contained device, which supports fixed types and quantities of inputs and outputs. Alternatively, modular remote I/O consists of a coupler/adapter supporting varying quantities of modules (Figure 1). Stacking different cards allows the user to customize the type and quantity of I/O available at that location, ranging from just a few points to many dozens.

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Remote I/O modules are available in configurations supporting typical discrete and analog I/O signal types, in various point counts, so designers can select just what they need to accommodate the application. Modular remote I/O cards are typically available for a wider range of applications, including discrete and analog I/O, thermocouple and resistor temperature detector (RTD) and pulse output, making modular remote I/O highly configurable and extensible.

The process for selecting a remote I/O supplier should take into account the availability of these different protocol and signal types. However, there are other nice-to-have hardware features that support design, installation and maintenance. Push-in terminals provide a quick, easy and reliable connection method designed to resist loosening from vibration. A standard USB-C port facilitates local firmware updates; these are rarely needed but USB connectivity ensures the procedure can be performed.

Remote I/O applications

A few examples demonstrate how remote I/O delivers value and overcomes common pain points.

Logistics: When a large airport logistics sorting center expanded its operations to add eight new control zones, it introduced hundreds of additional I/O points linked to conveyors, sensors and actuators. These points would be added to an existing main PLC, using site-standard Profinet. With tight space constraints and minimal downtime allowed, the design team planned out 220 standalone remote I/O modules, which could be installed as each area became available during construction, reducing long wire runs and providing a compact solution within a short timeframe. Over the long term, the remote I/O installation provides flexibility to modify or expand individual control zones with minimal impact to the central control system.

Data center: In data center liquid cooling systems, continuous monitoring and control of water temperature, pressure and motor operations are paramount to ensure reliable thermal management. A cooling system manufacturer needed to connect with I/O points located throughout the facility, to provide this mission-critical functionality. Using modular remote I/O supports the current cooling system architecture and provides scalability as the data center equipment changes and expands in the future.

Manufacturing: An AI server manufacturer uses conveyors to move high-value components and assemblies through different production process stages. In this case, it added a variety of analog sensors to the conveyor system, monitoring performance and equipment conditions so it could optimize throughput and identify abnormal conditions. Modular remote I/O reduced costs associated with long wire runs, while ensuring future production line modifications can be addressed in a flexible manner.

Remote I/O—improving flexibility and reducing costs

For system designers and integrators, remote I/O reduces wiring and material costs, improves system scalability and saves control panel space. By distributing I/O hardware in the field, long cable runs between the system and central controller are reduced, minimizing both material and labor costs. Future expansion of I/O points or changes to entire control zones can be facilitated with minimal modifications to the central controller.

Reliable connectivity between PLCs, field sensors, actuators and other devices is essential for monitoring, control and IoT data collection. When designing a new system or expanding an existing one, especially where I/O points are distributed and grouped away from the central controller by any distance, designers can rely on a standardized remote I/O as the most effective way to provide the necessary flexibility and scalability.