If you are working with automation you have probably needed to get signals from sensors and actuators back to a controller. Working with PLC I/O can be a solution but it usually means you have to pull a lot of individual wires all across the facility. This is very expensive. It is not flexible at all. It is also really hard to maintain the industrial automation system when you have to deal with all these wires. Industrial automation requires a solution, than traditional PLC I/O.
Ethernet I/O offers a smarter way: put a compact module close to the devices, connect it with a single Ethernet cable, and let the network handle the rest.
The global industrial Ethernet market is growing rapidly, with projections showing an increase from $26.63 billion in 2025 to approximately $38.5 billion by 2031, at a CAGR of 7.02% . According to HMS Networks , industrial Ethernet now accounts for 76% of new network installations . A significant portion of this growth comes from remote I/O modules, which allow engineers to place I/O where it’s needed without running hundreds of individual wires back to a central cabinet.
This guide answers five questions that come up again and again when engineers first consider Ethernet I/O—and gives you the practical answers you actually need.
1. What’s the difference between Ethernet I/O and traditional PLC I/O?
The short answer: Traditional I/O is local—modules sit in the same rack as the PLC. Ethernet I/O is remote—modules are placed near the field devices and communicate over a network.
With input/output systems every single sensor needs to have its own wire that runs all the way back, to the control cabinet. This means you have to deal with cable trays and conduit and terminations.. Let us not forget the time you have to spend trying to figure out what is going wrong. If you want to add sensors that can be a real problem. Adding just one sensor might mean you have to pull a new cable all the way across the plant.
Ethernet I/O changes the game. You mount a module right next to the machine. All the sensors connect locally with short, simple wires. Then a single Ethernet cable (or fiber, if needed) carries the data back to the PLC or control room.
The PLC doesn’t know the I/O is remote. It sees the inputs and controls the outputs exactly as if the module were in its own rack.
2. How do I connect sensors and actuators to an Ethernet I/O module?
Most Ethernet I/O modules have built-in terminals for digital inputs, digital outputs, and analog inputs. The wiring is straightforward.
Digital inputs (DI) – Use them for limit switches, push buttons, proximity sensors. Connect one side of the switch to the input terminal, the other to the common (COM) terminal. If your sensor needs power, use the module’s 24V output (if available) or an external supply.
Digital outputs (DO) – Typically relay or transistor outputs. For a relay, wire your load (e.g., a light, motor starter) between the common (COM) and normally open (NO) terminal. When the output activates, the relay closes and powers the load.
Analog inputs (AI) – For 4‑20 mA current loops or 0‑10 V signals. Connect the signal positive to the AI+ terminal, negative to AI– (or COM). Some modules accept resistance inputs like Pt100 RTDs.
Power – Most industrial modules run on 24 V DC. Connect +24 V to the power terminal, 0 V to GND. Wide-input modules (9–24 V) handle fluctuations gracefully.
The network side is even simpler: plug an Ethernet cable into the module’s RJ45 port and connect it to your switch or directly to the PLC.
3. Should I use Modbus TCP or another industrial Ethernet protocol?
Modbus TCP is what most people use for things. It is easy to understand. It is open. Every Programmable Logic Controller, Supervisory Control And Data Acquisition system and Human Machine Interface supports Modbus TCP. If you do not have a reason to use something different then Modbus TCP is a good choice. Modbus TCP is a choice because it works well and it is widely used.
| Feature | Modbus RTU | Modbus TCP |
|---|---|---|
| Physical layer | RS485 (twisted pair) | Ethernet (RJ45) |
| Max distance | 1200 meters | 100 m (per segment, extendable with switches) |
| Devices per network | 32 (without repeater) | Virtually unlimited |
| Speed | Up to 115 kbps | 10/100 Mbps |
| Typical use | Long distances, existing RS485 networks | New installations, IT integration |
Protocol characteristics: The latency of Remote Terminal Units is something we can usually predict. When we send information to a device it normally takes around 50 to 100 milliseconds to get a response. This is when we are using a speed of 9600 baud. So if we need to get information from 32 devices one after the other it can take a seconds to get all the information we need.
The good thing about using Transmission Control Protocol is that it does not have a limit on how we can send information. It also lets us send requests at the same time. This means we can get responses fast usually in, under 2 milliseconds if the network is not being used too much by other things. .
Failure modes differ significantly. RTU failures tend to be physical and obvious—CRC errors, timeouts. TCP failures can be quieter: half-open connections, elevated latency, or degraded performance that stays within timeout thresholds .
Security considerations: Modbus has no built-in authentication. On a serial bus, physical access is required. On Ethernet, devices reachable from a corporate network will respond to commands from anyone—a consideration for network architecture .
Other protocols like PROFINET, EtherNet/IP, or EtherCAT are common in specific ecosystems (Siemens, Rockwell, Beckhoff). If your plant already uses one of those, you may need a module that supports it directly—or you can use a gateway.
What about Modbus RTU? Some Ethernet I/O modules, like the Valtoris 4CH-IO-ETH and 8CH-IO-ETH, include an RS485 port in addition to Ethernet. They can act as a bridge between Modbus TCP and Modbus RTU networks, letting you mix old and new equipment seamlessly .
4. How many I/O points do I need, and what about analog signals?
Start by counting. Walk through your machine or process and list every sensor, switch, and actuator. Digital devices (on/off) go to DI or DO. Continuous measurements (temperature, pressure, level) go to AI.
| Application | Typical DI | Typical DO | Typical AI |
|---|---|---|---|
| Conveyor monitoring | 4–8 limit switches | 2–4 motor starters | – |
| Pump station | 4–6 float switches | 1–2 pump relays | 2 pressure transmitters |
| HVAC unit | 8–12 status sensors | 4–6 fan/valve controls | 4 temperature sensors |
| Packaging machine | 16–24 photo-eyes | 8–12 solenoid valves | – |
Source: Industry standard engineering practices
When you are planning you should think about what you will need in the future. So you should add 10 to 20 percent for expansion. If you have 6 inputs now an 8-channel module is a good idea because it gives you room to grow. If you have 14 inputs you should consider getting two 8-channel modules or a single 16-channel unit. This is because it is an idea to have some extra space. People in the industry think it is an idea to have 10 to 20 percent extra for normal systems. For important systems like those used in chemical processing you should have 20 to 30 percent extra. This is because chemical processing systems are very important and need to be reliable. So future expansion and extra space are important, for chemical processing systems.
Analog inputs come in different flavors: current (4-20 mA), voltage (0-10 V), or resistance (Pt100, 0-10 kΩ). Make sure the module supports the type you need. Many Valtoris modules allow you to specify the input range at the time of order.
If you need a mix of digital and analog, look for modules that combine them. The Valtoris 8CH-IO-ETH, for example, gives you 8 DI, 8 DO, and 8 AI in one compact unit.
5. What about power, mounting, and environmental ratings?
Industrial environments are hard on electronics. Here’s what to check before you install.
(Environmental requirements checklist)
Power: Industrial panels almost always have 24 V DC. Modules that accept a wide voltage range (9-36 V) are more forgiving during brownouts and can be powered directly from plant 24V supplies without additional regulation .
Temperature: Consumer-grade electronics fail above 50°C. For factories, outdoors, or unheated spaces, you need modules rated -40°C to +70°C or wider. Leading industrial manufacturers offer extended temperature ranges of -40°C to +70°C for extreme environments .
Isolation: If you have sensors in different buildings or powered from different phases, ground loops can corrupt data and damage equipment. Look for modules with optical isolation between field wiring and network. According to IEC 61000‑4‑2/‑4‑4 standards, industrial equipment should withstand ±15kV ESD and 4kV fast transients.
Putting It All Together: A Quick Selection Guide
Still not sure? Here’s a simple matrix based on your needs.
| Your situation | Recommended Valtoris model |
|---|---|
| Small machine, 4‑8 I/O points, need Ethernet | 4CH-IO-ETH |
| Medium machine, 8‑16 I/O points, analog too | 8CH-IO-ETH |
| Adding I/O to existing RS485 network | 4CH-IO-RS232/485 |
| Can’t run Ethernet cable (but have WiFi) | 8CH-IO-WF |
| Completely remote site with cell coverage | 8CH-IO-LTE |
All Valtoris Ethernet I/O modules share the same industrial DNA: -40°C to 85°C operation, 9–24 V DC power, DIN rail mounting, and rock‑solid reliability.
One Last Thing
Ethernet I/O is not a trend it is the standard, for modern automation. When you put I/O where the sensorsre you save on wiring. This also makes maintenance simpler.. Your systems can easily grow.
To find the solution start with these five questions. This will help you match your needs to the module. Then you will have a solution that lasts for years.
Note: Valtoris offers a full range of Ethernet I/O modules. Visit our product pages for detailed specs, manuals, and ordering information. Need help choosing? Contact our engineering support—we’re glad to help.
