In traditional factory wiring, engineers responsible for control design and equipment commissioning have typically connected industrial PCs or PLCs directly to the control panel’s I/O terminals.
However, as more devices are added, control-panel wiring becomes increasingly complex, and longer cable runs are required as equipment is installed farther away. When issues such as electrical noise or cable failures occur, troubleshooting and recovery also become significantly more time-consuming.
As a solution, demand for remote I/O has been growing in Japan, driven by the need to reduce wiring, shorten commissioning work, and improve maintenance efficiency.
This two-part article outlines the fundamentals of remote I/O and introduces practical approaches to wiring reduction using Contec’s rugged CONPROSYS Robust I/O Series, along with key points for integrating PLC-based control systems.
Related article:
Remote I/O Basics for Reducing Factory Wiring | Next-Generation Control Enabled by Rugged Robust I/O(Part 1)
Roles and Challenges of Industrial PCs and PLCs in Remote I/O Systems
n equipment control systems, a device is required to execute control logic, determining processing steps based on input signals and controlling outputs accordingly. Industrial PCs and PLCs are typical controllers that perform this role.
PLCs have long been the standard, but in recent years, factors such as cost, scalability, and IT integration have made them less suitable in some applications.
As a result, software PLCs (PC-based PLCs), which implement PLC functions on industrial PCs, have been gaining increased attention.
PLCs vs. software PLCs: The core “brain” of machine control
A PLC (Programmable Logic Controller) is an industrial control computer designed specifically for machine control in factory and production environments.
PLCs are mainly used for sequence control, operating equipment by switching outputs—such as motors and valves—according to predefined procedures based on sensor input conditions.
For example, a washing machine progresses through steps such as Fill → Wash → Rinse → Spin. PLCs work in the same way, executing predefined sequences based on input conditions.
PLCs used in production equipment are often expected to operate continuously, 24/7, and must meet strict performance requirements to avoid unexpected downtime. As a result, PLCs are designed specifically for industrial environments and offer strong compatibility with on-site I/O devices.
On the other hand, a software PLC implements PLC control functions as software running on a general-purpose platform such as an industrial PC, rather than dedicated hardware.
Software PLCs share the same control logic concept as PLCs, switching outputs based on input conditions.
The key difference lies in how the control system is implemented. Whereas PLCs are provided as dedicated hardware, software PLCs run on flexible platforms, making it easier to modify configurations or add functions as requirements evolve.
Challenges of conventional PLCs: Cost, size, and limited IT integration
Although PLCs remain widely used in production control, they also present challenges such as rising costs, larger system configurations, and difficulty integrating with higher-level IT systems.
From a cost perspective, total expenses can increase significantly—not only for the PLC itself, but also for required I/O capacity, functions, and development tools. Key factors that commonly drive costs upward include the following:
| Item |
Cost driver |
| Number of I/O points |
As the number of inputs and outputs increases, additional modules and peripheral equipment are required. |
| CPU performance |
Higher processing speed and memory requirements may call for an upper-tier CPU model. |
| Functions and scalability |
Adding motion control or communication functions increases system complexity and cost. |
| Vendor/supplier |
Pricing can vary significantly depending on the vendor and sales structure. |
| Software licensing |
In some cases, development tool licenses are required in addition to PLC hardware. |
With conventional systems, expanding I/O capacity means adding modules directly to the PLC. This increases control-panel wiring and hardware, often adding significant installation and maintenance workload. In addition, integrating PLC-based systems with higher-level IT platforms often requires additional mechanisms for data exchange. In PLC-centered architectures, additional gateway devices or custom integration processing may be required to convert data into the formats expected by host systems and to adjust connection methods. This can increase the workload required for system expansion and operation.
However, consolidating on-site I/O through remote I/O and connecting over a network makes it much easier to address challenges related to wiring volume and cable distance.
For this reason, an increasingly effective design approach is to optimize wiring through remote I/O while expanding control and data integration through more open, flexible architectures.
Industrial Raspberry Pi + CODESYS International-Standard Software PLC: A Compact PLC Well-Suited to Remote I/O
When adopting a remote I/O system such as the Robust I/O Series, it is essential to select a suitable controller to manage and process the I/O signals.
Contec offers a compact PLC solution that combines an industrial-grade Raspberry Pi with the CODESYS internationally standardized software PLC platform. It provides key capabilities essential for industrial controllers—including RAS/RTC functionality, a watchdog timer, and hardware monitoring—ensuring high reliability and rugged performance.
This section explains how PLC functionality can be implemented using Raspberry Pi and CODESYS, and highlights the advantages of adopting the CPI Series.
How Raspberry Pi and CODESYS can function as a PLC
Raspberry Pi is a compact and highly versatile single-board computer. With broad hardware and software options, it can also be applied to industrial control usage scenarios.
CODESYS is a software PLC platform compliant with the international standard IEC 61131-3. Control programs can be developed using languages such as ladder logic (a PLC language for assembling operations like relay circuits) and executed on the CODESYS runtime to provide full PLC functionality.
Contec’s CPI Series is a compact PLC designed for industrial applications, combining Raspberry Pi 4 compatibility through the Computer Module 4 (CM4) with integrated RAS expansion hardware and the CODESYS runtime environment.
Executing control programs on the CPI and reading/writing remote I/O signals over the network makes it possible to control on-site sensors and actuators.
Related article:Raspberry Pi 4-based small embedded all-in-one PLC | Contec
Advantages of adopting the CPI Series
When implementing control systems in panels and integrating with existing equipment, it is important to consider not only wiring minimization and operability but also development efficiency and connectivity with higher-level systems.
This section summarizes the five key advantages to help illustrate the impact of adopting the CPI Series.
- 1. Minimized wiring with a space-saving design
- 2. Cost optimization by focusing on only the necessary functions
- 3. Improved productivity through internationally standardized control development
- 4. System connectivity supporting IT and IoT utilization
- 5. Distributed I/O architecture that pairs well with Robust I/O
1. Easy balance of minimized wiring and a space-saving design
The CPI Series supports compact configurations, making it easier to optimize control-panel space and simplify cable routing.
It also provides greater flexibility in mounting and layout, helping reduce installation and maintenance workload. When combined with remote I/O, it becomes easier to consolidate on-site I/O while reducing control-panel wiring at the same time.
2. Easy incremental adoption while controlling costs
In conventional control architectures, increasing I/O capacity or adding functions often leads to more modules and peripherals, driving up costs.
The CPI Series allows systems to be built according to application needs, making it easier to start with only what is required and expand step by step. This helps prevent systems from becoming overbuilt and is well-suited for situations where initial investment and expansion workload must be kept low.
3. Improving productivity through standardized development with CODESYS
CODESYS supports not only PLC programming but also HMI screen creation, device communication setup, and interface configuration for transferring data to host systems—all within a unified development environment.
This reduces the need to switch between multiple tools and minimizes variation between engineers, enabling more consistent workflows from design and commissioning through maintenance.
This makes handovers and change management smoother, improving productivity in both development and operations.
4. Easy extension to IT/IoT-ready system integration
The PC-based architecture of the CPI Series makes it easier to build in mechanisms for data visualization and analysis from the design stage.
For example, systems can be designed to transfer on-site data to host platforms over a network, and monitoring or logging targets can be added later through gradual expansion.
5. Seamless compatibility with Robust I/O
In remote I/O architectures, on-site I/O is consolidated locally, while control logic and system coordination is executed by the controller.
The CPI Series integrates smoothly into this architecture, enabling efficient controller implementation while maximizing the benefits of distributed deployment and minimized wiring.
When paired with the Robust I/O Series, it becomes even easier to balance rugged on-site I/O operation with flexible, scalable controller-side system design.
Conclusion
In traditional factory wiring architectures using I/O cards, I/O is centralized within the control panel. As the number of points increases, wiring and hardware expand, often increasing the workload required for retrofits and troubleshooting.
One effective way to reduce this workload is to use remote I/O, distributing I/O devices closer to equipment and connecting them via network communication.
However, factories and outdoor installations are more susceptible to temperature variation, electrical noise, and wiring errors, making it essential to choose equipment with environmental robustness capable of handling the installation conditions.
The CONPROSYS Robust I/O Series provides wide-temperature operation, high noise immunity, and overvoltage/overcurrent protection, making it a practical choice for deploying remote I/O in harsh environments.
In addition, leveraging remote I/O effectively also requires selecting an appropriate control controller. In addition to conventional PLCs, compact solutions such as Contec’s CPI Series—combining Raspberry Pi with the IEC 61131-3-compliant CODESYS software PLC—are also viable options.
For anyone looking to optimize on-site wiring and control-panel space while preparing for future data utilization and system integration, a configuration combining rugged remote I/O with a compact PLC is definitely worth considering.
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