Wireless I/O Communication in Industrial Automation; Ethernet, Wi-Fi or Radio I/O?

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Wireless I/O Communication in Industrial Automation; Ethernet, Wi-Fi or Radio I/O?

In many industrial automation projects, the problem begins when a PLC is installed in one control panel, while some sensors, actuators, or another panel are located several tens or hundreds of meters away.

The traditional solution is usually straightforward:

Run cables.

But the main question is not always: “How can we transfer these few signals?”

Sometimes the more important question is:

Do we really need to bring all these wires back to the PLC?

When the number of I/O points is small, the distance is long, the cable route is difficult, or equipment is distributed across different areas of the site, choosing the right architecture can be much more important than choosing the type of cable.

In such situations, one of the options worth considering is the use of Remote I/O and industrial wireless communication.

A Simple Example

Suppose the main PLC is located in the control room.

At a distance of 300 or 500 meters, there is a small machine or panel containing only a few signals:

• - Sensor status
  - Start/Stop command
  - Motor status
  - Valve command
  - Equipment alarm
  - Several other digital inputs

The traditional approach is to transfer all these signals by cable to the PLC panel.

At first glance, the problem seems simple.

However, in a real project, we may have to deal with:

• - Long cable routes
  - Cable trays
  - Conduits or mechanical protection
  - Difficult routing paths
  - Excavation or civil work
  - Multi-core cables
  - Terminals and accessories
  - Installation and wiring
  - Testing and troubleshooting
  - Project execution time
  - Difficulty expanding the system in the future

Therefore, the real cost and complexity is not simply the price of the cable itself.

Cable installation cost ≠ cable price

In an industrial project, the total cost of creating the communication path should be considered, not just the price of the wire.

Can I/O Be Placed Near the Equipment?

Yes.

One common approach in modern automation is to place part of the I/O close to the equipment instead of bringing all the wires back to the PLC panel.

For example:

Sensors and actuators → Remote I/O → Communication link between two points → PLC

With this architecture, there is no need to create a long cable route for every individual signal.

The Remote I/O is installed close to the equipment and transfers the I/O information to the control system through a communication link.

This communication can be implemented in several ways, including:

• - Ethernet
  - Wi-Fi
  - Industrial networks
  - Dedicated Industrial Radio I/O

However, these options are not exactly the same.

What Is the Difference Between Ethernet, Wi-Fi and Radio I/O?

These three concepts are sometimes grouped together in projects, leading to the assumption that they are simply different ways of “making the PLC wireless.”

In reality, they represent different architectures.

1. Ethernet

Ethernet is a wired network communication technology.

If a suitable network infrastructure already exists at the site and a proper cable connection can be established between the two points, Remote I/O or network equipment can be connected to the PLC or control system through Ethernet.

Advantages may include:

• - Suitable communication speed
  - Standardized technology
  - Ability to use existing network infrastructure
  - Easier troubleshooting in many projects
  - Suitability for large networked systems

However, it still requires physical network infrastructure.

If two points are several hundred meters apart and there is no existing infrastructure, creating that infrastructure becomes part of the project.

2. Wi-Fi

Wi-Fi is wireless communication based on IP networking.

In many projects, Remote I/O or an industrial device can be connected to the network through Wi-Fi.

However, industrial Wi-Fi is not simply a matter of installing an Access Point.

Factors such as the following must be considered:

• Radio coverage

• Access Point location

• Physical obstacles

• Frequency interference

• Network security

• Communication stability

• Network management

• Roaming when equipment is moving

• Dependence on existing network infrastructure

Therefore, if a factory already has a suitable industrial Wi-Fi network, using it may be a logical choice.

But if the only objective is to transfer a few I/O points between two locations, another question arises:

Do we really need a general-purpose Wi-Fi network?

3. Industrial Radio I/O

Here, the architecture is different.

The primary purpose of an Industrial Radio I/O system is not to create a general wireless network for the entire factory.

The goal is to directly connect the I/O of two or more industrial locations.

For example:

Sensors and actuators
↓
Remote I/O
↓
Radio
↓
PLC / Remote I/O

In this case, a dedicated radio link is established specifically for transferring I/O.

This approach can be attractive when:

• The distance between two points is significant

• Cable installation is difficult or expensive

• The number of I/O points is relatively small

• There is no suitable network infrastructure between the two points

• Creating a Wi-Fi network is not justified for the application

• Equipment is distributed across different locations

• Cable installation would take significant time

• Future expansion without additional cable installation is important

An important point is that Radio I/O is not necessarily a replacement for Ethernet or Wi-Fi.

Each technology is suitable for different problems.

When Does Radio I/O Make Sense?

There is no fixed distance such as 100, 300, or 500 meters that can be considered a definite boundary after which radio is always the better option.

The decision depends on the project conditions.

For example, two projects with a distance of 300 meters may be completely different.

Project 1

Two panels are located in the same industrial hall.

A cable tray already exists between them, and Ethernet infrastructure is also available at both locations.

In such a situation, using the existing infrastructure may be the simplest solution.

Project 2

Two points are 300 meters apart, but there is no suitable cable route between them.

A new cable tray must be installed, part of the route requires excavation, and an industrial cable must be installed.

In this situation, a radio architecture may deserve serious consideration.

Therefore, the right question is not:

“Is radio better than cable?”

The right question is:

“For this number of I/O points, this distance, and these site conditions, what is the most appropriate architecture?”

What Is the Real Cost of Cable Installation?

Comparing solutions based only on cable price can be misleading.

For a long cable route, the following costs may also be involved:

Direct Costs

• Cable

• Cable tray

• Conduit and protection

• Cable glands

• Connectors

• Terminals

• Junction boxes

• Installation accessories

Execution Costs

• Cable installation

• Panel wiring

• Equipment installation

• Testing

• Troubleshooting

• Commissioning

Project Costs

• Excavation

• Civil work

• Production downtime or restrictions

• Project execution time

• Difficult access to the route

And there is another important issue:

Future expansion.

If we have only four signals today but need 12 signals next year, how easily does the selected architecture allow the system to expand?

Radio I/O Also Has a Cost

Of course, using radio does not mean eliminating all costs.

An industrial radio system may include:

• I/O modules

• Radio units

• Antennas

• Installation accessories

• Power supply

• Configuration

• Link testing

• Commissioning

Therefore, a proper comparison should be based on the total cost of the solution, not simply:

“Cable price versus radio price.”

Several Real-World Scenarios

Scenario 1: Two Panels with Several Signals

• One PLC panel is located in the control room.

• Another panel is 400 meters away and has only 6 inputs and 4 outputs.

Three main solutions can be considered:

• Solution 1: Direct I/O cabling

• Solution 2: Remote I/O + Ethernet

• Solution 3: Remote I/O + Industrial Radio

The final choice depends on existing infrastructure, cable routing, environmental conditions, installation cost, and project requirements.

Scenario 2: Adding a New Machine

Suppose an existing production line has its PLC in the main panel.

Now a new machine is installed at a remote location.

If we have to bring a large number of cables from the new machine back to the main panel, the project can become complicated.

Instead, a Remote I/O can be installed near the machine and only the communication link between the two locations needs to be established.

The system architecture can then be simplified:

Machine → Local I/O → Communication Link → PLC

Scenario 3: Distributed Equipment

In some factories, equipment is distributed across different areas of the site:

• Pumps

• Valves

• Sensors

• Local panels

• Machines

• Measurement equipment

If multiple cables have to be routed from every location back to the control room, the infrastructure gradually becomes larger and more complex.

In such projects, a Distributed I/O architecture can be considered.

If establishing a wired connection is difficult, Wireless I/O can also be one of the possible options.

Reliability; Radio Is Not Only About Distance

In an industrial project, simply knowing that a radio link can operate over a certain distance is not enough.

The actual site conditions must be evaluated.

Factors such as:

• Obstacles

• Metal structures

• Antenna position

• Frequency interference

• Environmental conditions

• Power supply

• Installation quality

• Fail-Safe behavior

• System behavior during communication loss

are all important.

Therefore, Radio I/O should be designed like any other part of an automation system, based on the actual project conditions.

What Applications Are Suitable for Radio I/O?

This technology can be considered for applications such as:

• Digital I/O transfer between two panels

• Controlling equipment located away from the main panel

• Transmitting sensor status

• Valve control

• Equipment Start/Stop

• Alarm transmission

• Distributed machines

• Large production lines

• Pumps and outdoor equipment

• Projects where cable installation is difficult

However, the appropriate architecture should be evaluated separately for each project.

ESP-Rline; A Solution for Wireless I/O Communication

For such applications, ESP has developed the ESP-Rline product family.

ESP-Rline is a solution for wireless I/O communication between different points of an industrial system.

For example, a simple architecture can be:

Field Devices
↓
ESP-Rline I/O
↓
Wireless Radio Link
↓
ESP-Rline I/O
↓
PLC / Control System

In this architecture, the I/O is placed close to the equipment, while the communication between the two locations is established wirelessly.

This architecture can be considered for projects where long cable installation or creating network infrastructure for a limited number of I/O points is not practical.

An Important Point When Choosing a Solution

The purpose of Wireless I/O is not to eliminate all wired communication.

In a factory, all three technologies may be used together:

Ethernet for the main network

Wi-Fi for applications requiring wireless networking

Industrial Radio I/O for direct connections between certain remote locations

And alongside them:

Cable for many local devices.

Good engineering means choosing the appropriate technology for each part of the system.

Conclusion

When a piece of equipment is located far from the PLC, the first solution that usually comes to mind is to run cables.

But before making the final decision, it is worth asking:

• How many I/O points actually need to be transferred?

• How far apart are the two locations?

• What does the cable route look like?

• Is Ethernet infrastructure already available?

• Is suitable Wi-Fi available at the site?

• What is the actual cost of cable installation?

• Is future system expansion important?

• Could a dedicated radio link provide a simpler architecture?

• What are the environmental conditions and reliability requirements?

Ultimately, the issue is not simply “cable or radio.”

The real issue is choosing the appropriate architecture for transferring information between different points of an automation system.

Sometimes, instead of bringing the wires to the PLC, it makes more sense to bring the I/O closer to the equipment.