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Industrial machines have traditionally routed field-device wiring to input/output (I/O) modules and controllers housed in centralized control cabinets. As production systems become more modular, designers are increasingly placing selected I/O and control functions closer to the equipment they serve.
Traditional architectures often require long cable runs between field devices and the control cabinet, increasing installation complexity and making fault isolation more difficult. These designs can also limit flexibility when machine modules need to be added, removed, or relocated. Distributed architectures address these challenges by placing I/O closer to the equipment it services and routing communication with the control system over an industrial network.
This blog explores the key considerations for moving I/O out of the control cabinet and explains how rugged, modular I/O systems can help meet the environmental, connectivity, and reliability requirements of cabinet-free deployment.
In a traditional centralized architecture, machine components, including sensors and actuators, connect to terminal blocks and I/O modules in the control cabinet regardless of their location. This architecture works for simple plant layouts but becomes challenging as machine complexity and I/O points increase. Connecting every device to a central cabinet often results in extensive and complex wiring runs.
To reduce wiring complexity and support modular machine designs, engineers increasingly deploy distributed architectures. Distributed I/O places remote input and output modules near field devices while retaining a centralized or higher-level controller. A distributed-control architecture goes further by assigning control functions to controllers located at individual machines, stations, or production modules.
Moving I/O away from a central cabinet exposes the units to environmental conditions that the cabinet previously helped mitigate. These factors include dust and debris, moisture, vibration and mechanical shock, temperature variations, electromagnetic interference (EMI), and potential cable and connector damage. As a result, engineers need to evaluate each environmental condition when selecting hardware for the installation. Ingress protection (IP) ratings define specific levels of protection against solids and water. IP65 addresses dust ingress and water jets, while IP67 adds protection during temporary immersion under defined test conditions. The required rating depends on the application, and it applies only when the equipment is correctly assembled with the required seals, connectors, and closures.
Environmental protection is only part of the design challenge. Maintaining visibility for diagnostics and fault isolation remains critical even in distributed systems. Manufacturing environments require automation functions to be integrated without compromising safety, troubleshooting efficiency, or system availability.
Engineers must ensure that motor control hardware, I/O modules, and sensors operate together as a cohesive automation system, accounting for diagnostics to change potentially with new distributed configurations. Units need to be easily replaceable and must have clearly identifiable fault locations, preferably with wiring that does not have to be dismantled every time the electronic component is serviced.
While the flexibility to add different sensors, motors, or machines as requirements change is one of the many advantages of distributed architectures, it can easily lead to chaos if the process lacks standardization. Engineers need to work with a consistent blueprint for hardware architecture and maintenance to ensure work is verifiable and reproducible.
The shift toward distributed architectures reflects the growing demand for scalable automation and platforms that can adapt to changing production requirements. Modern manufacturing processes often consist of modular production stages that move workpieces between robotic systems, inspection stations, and packaging equipment. This modular approach benefits from keeping control and I/O functions closer to individual stations, simplifying commissioning and system integration. It also enables engineers to configure, monitor, and maintain these functions within a more unified automation environment rather than treating each station as a separate system.
At the same time, the availability of rugged, cabinet-free designs is expanding options for design engineers so they can move control functions closer to the processes they support and facilitate flexible deployment outside traditional enclosures. As these systems become more distributed, diagnostic visibility becomes increasingly important. Maintenance teams need to identify the source of a fault without tracing connections through a central control cabinet, helping limit downtime and simplify service procedures.
While distributed architecture implies a distributed I/O system first, which then connects to a central programmable logic controller (PLC), it is possible to expand that definition to also move the control to individual stations, mounted directly on the machines or situated close by. Doing so further simplifies expansion and makes reconfiguration of component modules much easier. These advantages are particularly relevant to flexible manufacturing, where equipment modules, sensors, inspection stations, and production capacity may change over the machine lifecycle. Modular architecture can reduce the scope of some upgrades and repairs, although isolating one module without stopping the line depends on the process and safety design.
A modular approach also creates opportunities to integrate standard I/O, safety, and motor-control functions into the same distributed architecture. As production requirements change, engineers can add or reconfigure individual modules without redesigning the larger automation system. Supporting this architecture requires hardware that brings operational functions closer to the equipment while allowing the system to expand as manufacturing needs change.
The SIMATIC ET 200pro from Siemens enables engineers to create an entire machine-level automation system by picking from a portfolio of modular components, including digital and analog I/O, motor starters, frequency converters, power modules, and distributed central processing units (CPUs) for integrated machine architectures. When correctly assembled, the SIMATIC ET 200pro system provides an IP65/66/67-rated design and the system can be installed directly at the machine without requiring the protection of a traditional control cabinet.
The system’s distributed I/O products, including modular I/O, safety-related components, motor control solutions, communication modules, and associated connectivity elements, align with cabinet-free automation requirements. Control can be provided through an interface module connected to a higher-level controller or through a distributed CPU that places control directly at the machine. An active backplane supports modular expansion and module replacement during operation, while tool-free connections and simplified mounting and wiring approaches help in the fast setup of modular components.
The portfolio extends distributed automation beyond standard I/O PROFIsafe-compatible modules functional support safety applications, while integrated motor starters and frequency converters add motor-control capabilities. Additionally, communication and interface options support technologies such as RFID and IO-Link, allowing additional field devices to be integrated into the same machine-level architecture. Figure 1 illustrates how these functions fit within the modular ET 200pro architecture.
Figure 1: The modular SIMATIC ET 200pro architecture combines I/O, failsafe modules, motor control, and specialized functions such as RFID and IO-Link within a machine-level automation system. (Source: Siemens)
The Siemens SIMATIC ET 200pro system also supports replacement of electronic modules without disconnecting field wiring, facilitating fast fault tracing and diagnostics. Modules can be hot-swapped while the controller remains in RUN mode, allowing affected electronics to be replaced without stopping the controller or dismantling the surrounding field wiring. This capability helps maintenance teams isolate and address problems at the machine level while minimizing disruption to the automation system.
With IP65/67 ratings for protection against dust and water ingress, the ET 200pro is designed for demanding machine-level environments where cabinet-free installation may be desirable.
Future expansion plans and the related growth of I/O points will help determine whether a distributed architecture is the right fit for an application. Regardless of the architecture selected, grounding, electromagnetic noise mitigation, and signal separation remain important design considerations. Environmental protection requirements, diagnostic visibility, maintenance efficiency, and ease of fault isolation are all factors that can make systems such as the SIMATIC ET 200pro well suited for modern, highly modular automation environments.
As manufacturing adopts increasingly flexible and modular production models, automation platforms must be scalable, rugged, and designed for efficient diagnostics, maintenance, and expansion.
Distributed architectures, whether limited to decentralized I/O placement or transferring control to individual machines, help address the wiring, scalability, and modularity challenges associated with modern automation systems. However, moving I/O and control functions beyond the control cabinet requires careful consideration of environmental protection, diagnostic visibility, maintenance efficiency, and standardization. Solutions such as the SIMATIC ET 200pro illustrate how these requirements can be addressed in machine-level automation systems. By balancing these considerations, engineers can create automation systems that are easier to maintain, expand, and adapt to changing manufacturing requirements.
Poornima Apte is an engineer turned writer with B2B specialties in robotics, AI, cybersecurity, smart technologies and digital transformation. Find her on Twitter @booksnfreshair.
Siemens focuses on industry, transport, infrastructure, and healthcare and creates technology with purpose by adding real value for customers. Combining the real and digital worlds, this company empowers engineers to transform their industries and markets.
